Mostly Open Ocean

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Mostly I write about the biology and evolution of life in the sea.

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  • May 9, 2013
  • 08:17 AM
  • 33 views

Living fossils are evolving.

by Mostly Open Ocean in Mostly Open Ocean

Charles Darwin coined the term living fossil in On the Origin of Species. He didn’t use it the same way that it has come to be used. He suggested that living fossils are modern species that can be used to link to groups in the same way that fossils can. One of the examples he gave was the platypus, which lactates and lays eggs, which is evidence that mammals and reptiles share a common ancestor. I don't think he meant it to mean an unchanged relict, as some people interpret his words.Today, a living fossil is a species that retains many features of their fossil ancestor so that it is recognisably closely related. There are some stunning examples of this, such as orb-weaving spiders. In 2011 a 165 million year old spider fossil was described by Seldon et al., which shared so many features with modern Nephila spiders that it was placed within the same genus. Interestingly, I have never heard of web building spiders being referred to as living fossils despite there being amazing conservation of traits in many groups.The orb-weaving spiders Nephila clavipes (left) and N. jurassica (right) are separated by 165 million years, but placed within the same genus (image of N. clavipes from Wikipedia and N. jurassica from Seldon et al. 2011).Unfortunately, living fossil has become synonymous with a species, or group of species, displaying no evolutionary change or very slow change. This is completely wrong. Although the conservation of morphology in Nephila is remarkable, there are more than 150 known species in the genus. Clearly there has been evolutionary diversification within the group. Indeed, whenever living fossils are examined in more than superficial detail it becomes difficult to see them as organisms that evolution forgot.Horseshoe crabs are one of the most iconic living fossils. There are four living species in three genera. They are placed within the subphylum chelicerata, which makes them more closely related to spiders and scorpions than they are to true crabs, which are placed within the subphylum crustacea. Although there are fewer species of horseshoe crabs than Nephila, that fact that there are four species that are all different from fossil species is a strong indication that evolution hasn't stopped for them.The Atlantic horseshoe crab, Limulus polyphemus, mating (photo Wikipedia) The general shape of modern horseshoe crabs is strikingly similar to the fossils that date from about 450 million years ago. Close examination, though, shows that parts of their shape, their legs in particular, have changed over time. Briggs et al. 2012 looked at a fossil horseshoe crab from 425 million years ago, which is relatively early in their evolution. They found that modern horseshoe crabs are missing an entire set of limbs that were present in their ancestors.All modern chelicerates, including living horseshoe crabs, have unbranched limbs; each limb is a single series of segments. Most crustaceans have limbs that branch at the base into two series of segments. Branched limbs, like those in crustaceans, are the ancestral condition and unbranched limbs are thought to have evolved several times among the arthropods. Indeed, Briggs et al. found that the fossil horseshoe crab had branched limbs, which have been lost in their descendents. Like horseshoe crabs, tadpole shrimp have a broad semi-circular carapace protecting their heads and are considered living fossils. There are 11 recognised species in two genera, Lepidurus and Triops. The two genera probably diverged about 180 million years ago, but there are fossil tadpole shrimp dating from about 250 million years ago. That's not as long as the really iconic living fossils, like horseshoe crabs and the coelacanths, but it is still an impressive amount of time to retain enough features to be easily recognised as related.The tadpole shrimp, Lepidurus apus (photo Wikipedia)The problem with relying on features that preserve in the fossil record is that it underestimates the actual amount of evolutionary change because generally only hard parts are preserved. A recent study of tadpole shrimp highlights this point. Mathers et al. 2013 used genetic analyses to construct the evolutionary relationships among the 11 species of tadpole shrimp. They found that there are actually 38 species and that these species arose relatively recently. This shows that rather than evolutionary stasis, there is likely to be high species turnover in the group.There are many reasons why some features may be conserved over long periods of time. None of these have to do with natural selection taking a break. In fact, if natural selection did cease we should expect to see features wander under random genetic drift, as has been hypothesised for eyes in cave dwelling animals. Conserved features are much more likely to be the result of developmental constraints or stabilising selection. ... Read more »

Briggs, D., Siveter, D., Siveter, D., Sutton, M., Garwood, R., & Legg, D. (2012) Silurian horseshoe crab illuminates the evolution of arthropod limbs. Proceedings of the National Academy of Sciences, 109(39), 15702-15705. DOI: 10.1073/pnas.1205875109  

Mathers, T., Hammond, R., Jenner, R., Hänfling, B., & Gómez, A. (2013) Multiple global radiations in tadpole shrimps challenge the concept of ‘living fossils’. PeerJ. DOI: 10.7717/peerj.62  

Selden, P., Shih, C., & Ren, D. (2011) A golden orb-weaver spider (Araneae: Nephilidae: Nephila) from the Middle Jurassic of China. Biology Letters, 7(5), 775-778. DOI: 10.1098/rsbl.2011.0228  

  • April 14, 2013
  • 08:26 PM
  • 60 views

The resilience of coral reefs

by Mostly Open Ocean in Mostly Open Ocean

Many people are justifiably concerned with the potential impacts of climate change and ocean acidification on coral reefs. But, coral reefs have been declining for at least the last 25 years and probably much longer, overwhelmingly due to threats that are unrelated to climate change. If we do not address these impacts we will continue to lose coral cover and reefs will be more vulnerable to climate change and ocean acidification.A coral outcrop on the Great Barrier Reef (photo Wikipedia)A new paper serves as an illustration of how resilient coral reefs are to climate impacts when they are isolated from other anthropogenic impacts, such as overfishing and agricultural runoff. James Gilmour and other researchers from the Australian Institute of Marine Science and some from the Centre of Excellence for Coral Reef Studies followed the recovery of the Scott Reef system after a catastrophic bleaching event in 1998 that reduced coral cover from 50% to 10%. There was great concern for the reef system because it was isolated from other reefs that could supply coral larvae to fuel recovery.The Scott Reef system. The crescent shaped reef at the bottom is Scott Reef South, the small reef above the left arm of the crescent is Scott Reef and the pear shaped reef is Scott Reef North (photo Wikipedia).It turns out that, on balance, the isolation was a good thing. The supply of coral larvae reaching the reef was less than 6% of what it was prior to the bleaching event for six years. But, the reef was also isolated from chronic anthropogenic pressures, particularly overfishing. The number of herbivorous fish was already high at the time of the bleaching and jumped afterwards. As coral cover increased the numbers of herbivorous fish declined back to what they were prior to the bleaching.The daisy parrotfish, Chlorurus sordidus, is an important herbivore on coral reefs (photo Dennis Polack, EOL).The herbivorous fish kept seaweed and other organisms that compete with coral from taking over. Remnant corals that survived the bleaching were able to grow quickly and the small numbers of coral larvae reaching the reef had unexpectedly high survival. The fast growth of existing coral drove the initial recovery of the reef. Once young corals became established and began reproducing the supply of larvae increased and the recovery of coral cover accelerated.Ten years after the bleaching event the supply of coral larvae had returned to the levels seen before the bleaching. Two years later the amount of coral cover and community structure on the reef had largely been restored. The rate of recovery is made more remarkable by the occurrence of a second more moderate bleaching event, two cyclones and a disease outbreak.The study highlights just how resilient coral reefs can be to the effects of climate change and other disturbances if chronic anthropogenic stress is low. Overfishing, sedimentation and pollution are causing severe declines in coral cover right now. If we can control these threats, coral reefs might be able to survive in a warmer, more acidic ocean. Reference:Gilmour, J., Smith, L., Heyward, A., Baird, A., & Pratchett, M. (2013). Recovery of an Isolated Coral Reef System Following Severe Disturbance Science, 340 (6128), 69-71 DOI: 10.1126/science.1232310... Read more »

Gilmour, J., Smith, L., Heyward, A., Baird, A., & Pratchett, M. (2013) Recovery of an Isolated Coral Reef System Following Severe Disturbance. Science, 340(6128), 69-71. DOI: 10.1126/science.1232310  

  • April 11, 2013
  • 10:53 PM
  • 88 views

In the cave of the blind, the no-eyed crab is king

by Mostly Open Ocean in Mostly Open Ocean

Cave dwelling creatures are often blind. The prevailing view is that, in such species, mutations in the visual system have little or no effect on fitness and vision is lost as these mutations gradually accumulate. There are several other types of characters that we can be reasonably confident are adaptations to life in caves, such as elaboration of structures for touch or smell. However, it is often hard identify which population cave adapted species are descended from and, therefore, how long ago they invaded caves. Without this information it has been hard to test ideas about the evolution of traits associated with life in the dark.A cave form of the fish, Astyanax mexicanus, which is eyeless and unpigmented, traits typical in caves. It is a commonly used model species in studies of adaptation to cave environments (photo Wikimedia Commons).Sebastian Klaus and colleagues from the National University of Singapore and Goethe University examined five species of freshwater crab in the genus Sundathelphusa, which occur on Bohol Island in the Philippines. Four species are only found in caves and the other has established several populations in caves. The repeated invasion of caves by the crabs has led to varying degrees of adaptation to life in the dark within the group. Freshwater crabs in the genus Sundathelphusa from Bohol Island. Thy are arranged from least cave adapted (top) to most cave adapted (bottom). From top to bottom the species are Sundathelphusa boex, S. vedeniki, S. urichi, S. sottoae and S. cavernicola (from Klaus et al. 2013).The team used genetic data to estimate the time at which each species and population last shared a common ancestor. They then compared several features of cave-adapted crabs with their closest terrestrial relatives. Reductions in the visual system were just as pronounced as changes in cave-adapted features, indicating that evolution occurs at similar rates. The authors argue that this is a clear sign that eye loss is under directional selection because changes should appear more slowly if they are a result of selectively neutral mutations. They don’t speculate at all about what might favour eye-loss in the Bohol crabs, but hint in the introduction that it could be due to trade-offs between vision and other sensory systems. Trade-offs occur where increasing one aspect of fitness necessarily requires the reduction of fitness in another. If eyes are energetically costly to build and maintain then retaining functional eyes might prevent greater investment in other senses. Trade-offs are ubiquitous in biology and have been implicated in the loss of eyes in other cave dwelling species. While I was doing research on this study I came across several creationist websites that argue cave adapted creatures are strong evidence that evolution is false because a trait is lost. According to them this shows evolution progressing in the wrong direction to what is predicted. They argue that evolution should progress towards more information and greater complexity. This is incorrect and shows, yet again, that creationists typically have a poor understanding of evolutionary theory. The 'logic' of this argument is similar to the idea of a "Great Chain of Being", which pervaded early thinking about biology. This type of thinking is where we get several antiquated, but persistent terms, such as "missing link" and "highly evolved". It continues to dog evolution in the way that evolutionary information is often presented, such as the placement of org... Read more »

Klaus, S., Mendoza, J., Liew, J., Plath, M., Meier, R., & Yeo, D. (2013) Rapid evolution of troglomorphic characters suggests selection rather than neutral mutation as a driver of eye reduction in cave crabs. Biology Letters, 9(2), 20121098-20121098. DOI: 10.1098/rsbl.2012.1098  

  • March 27, 2013
  • 09:25 PM
  • 130 views

Are there really plenty of fish in the sea?

by Mostly Open Ocean in Mostly Open Ocean

We started trying to manage fisheries using science-based principles more than 150 years ago. Today, despite great improvements, we are still struggling to manage fisheries well. Perhaps the greatest missing piece in our understanding is an ability to accurately link the number of spawning adult fish with the number of their offspring that survive to replenish the population. Recognition that individual differences play a role in the dynamics of natural populations promises to greatly improve fisheries management.A classic example of our inability to effectively manage harvested fish populations is the collapse of the northwest Atlantic cod fishery. Despite being managed using best practices, in 1992 the number of cod had collapsed to less than 1% of the number present in 1977. A moratorium was declared to allow the fishery to recover. It was predicted to rebound within a decade, but twenty years on and cod stocks are still at less than 5% of their previous levels and some authorities suggest the fishery may never fully recover.An Atlantic cod, Gadus morhua (photo Wikipedia).Most fishes are highly fecund, releasing tens to hundreds of thousands or even millions of eggs. Mortality during the early life of fish is incredibly high, often with fewer than one in a thousand surviving the first few days. But, because of the shear number of offspring, small changes in the mortality rate can lead to enormous differences in the number of fish that survive to replenish the population. The great difficulty has been to determine which factors contribute to changes in mortality rate.Predation and starvation are the two greatest sources of mortality for fish eggs and larvae. Neither of these is random. Bigger, better provisioned eggs are more likely to produce larvae that survive the larval period and replenish the adult population. There are also characteristics of the parents that effect the survival of their offspring, such as when and where they choose to spawn, and how big or old they are.Predators of fish eggs and larvae are numerous. Jellyfish, like Aurelia aurita, are among them (photo Wikipedia).Early hypotheses about what regulated survival in the larval period focused on starvation. Hjort's 'critical period' hypothesis (1914) proposed that food resources must be present when larval fish were switching from using their yolk reserves to feeding. Cushing's 'match-mismatch' hypothesis (1975, 1990) recognised that as larvae grow they need progressively larger prey and timing of prey requirement needs to be a match with the timing of prey availability.Good evidence to support these hypotheses has only emerged recently, with the arrival of technology that can provide long-term measurements over large spatial scales. Platt et al. (2003) combined data from remote-sensing satellites with long-term population surveys of haddock, Melanogrammus aeglefinus. Their data showed that when the peak of spawning occurred after the peak in the spring plankton bloom, survival of larval haddock was much higher.A haddock, Melanogrammus aeglefinus (photo Wikipedia).Beaugrand et al. (2003) used data from continuous plankton sampling devices that are opportunistically attached to merchant ships. The devices gave them not only plankton abundance data, but allowed them to measure the size of prey species. Data on cod, Gadus morhua, were obtained from two largely overlapping population surveys. Like Platt et al., they found that the timing of the plankton bloom was important for larval survival, but they also found that the abundance and average size of prey species were important too.Predation was recognised early on as an important factor influencing the survival of fish larvae. However, research into its effects on fish populations didn't begin in earnest until the 1970's. The research showed that bigger, faster growing larvae were more likely to survive that larval period. Several, subtly different mechanisms were proposed to explain this pattern and are often combined into the 'growth-predation' hypothesis. Testing the growth-predation hypothesis in the wild has proved tricky. But, fish have structures in their ears called otoliths that lay down growth rings a bit like the growth rings in a tree. Because the growth rings in otoliths are laid down daily in many fish species they can be used as proxy measurements of size and growth. Several studies have used otoliths to calculate size and growth rates and have universally supported the growth-predation hypothesis (e.g. Hare & Cowen 1997, Meekan et al. 2006).The otolith of a black rockfish, Sebastes melanops, showing the light and dark bands of yearly growth incre... Read more »

Beaugrand, G., Brander, K., Alistair Lindley, J., Souissi, S., & Reid, P. (2003) Plankton effect on cod recruitment in the North Sea. Nature, 426(6967), 661-664. DOI: 10.1038/nature02164  

Beldade, R., Holbrook, S., Schmitt, R., Planes, S., Malone, D., & Bernardi, G. (2012) Larger female fish contribute disproportionately more to self-replenishment. Proceedings of the Royal Society B: Biological Sciences, 279(1736), 2116-2121. DOI: 10.1098/rspb.2011.2433  

Cushing, D. (1969) The Regularity of the Spawning Season of Some Fishes. ICES Journal of Marine Science, 33(1), 81-92. DOI: 10.1093/icesjms/33.1.81  

Cushing, D. H. (1990) Plankton production and year-class strength in fish populations - an update of the match mismatch hypothesis. Advances in Marine Biology, 249-293. DOI: 10.1016/S0065-2881(08)60202-3  

Platt, T., Fuentes-Yaco, C., & Frank, K. (2003) Spring algal bloom and larval fish survival. Nature, 423(6938), 398-399. DOI: 10.1038/423398b  

Hare, J., & Cowen, R. (1997) Size, Growth, Development, and Survival of the Planktonic Larvae of Pomatomus saltatrix (Pisces: Pomatomidae). Ecology, 78(8), 2415. DOI: 10.2307/2265903  

Hedgecock, D., Launey, S., Pudovkin, A., Naciri, Y., Lapègue, S., & Bonhomme, F. (2006) Small effective number of parents (N b ) inferred for a naturally spawned cohort of juvenile European flat oysters Ostrea edulis. Marine Biology, 150(6), 1173-1182. DOI: 10.1007/s00227-006-0441-y  

Hjort, J. (1914) Fluctuations in the great fisheries of northern Europe viewed in the light of biological research. Reun. Cons. Int. Explor. Mer, 1-228. info:/

Marshall, D., Heppell, S., Munch, S., & Warner, R. (2010) The relationship between maternal phenotype and offspring quality: Do older mothers really produce the best offspring?. Ecology, 91(10), 2862-2873. DOI: 10.1890/09-0156.1  

Meekan, M., Vigliola, L., Hansen, A., Doherty, P., Halford, A., & Carleton, J. (2006) Bigger is better: size-selective mortality throughout the life history of a fast-growing clupeid, Spratelloides gracilis. Marine Ecology Progress Series, 237-244. DOI: 10.3354/meps317237  

  • March 21, 2013
  • 12:36 AM
  • 81 views

Giant squid have a giant distribution

by Mostly Open Ocean in Mostly Open Ocean

As many as twenty one species of giant squid have been identified, but most of these were controversial. The general consensus was that there could be one with three subspecies or up to eight distinct species. Now, research shows that there is only one species with no subspecies. This is remarkable given that giant squid are found in nearly every part of the deep sea and their populations are probably large.Winkelmann et al. (2013) sequenced the mitochondrial genome of 43 giant squid that covered individuals from all of the most widely accepted of the proposed species. They found extremely low genetic diversity and almost no genetic structure between squid from different locations. Only basking sharks, which have long generation times, small population sizes and are recovering from a recently small population size, have lower genetic diversity.The most likely explanation for the low genetic diversity is that sometime during the last ice-age the population of giant squid declined to a very small size. Small populations are associated with low genetic diversity because random genetic drift affects gene frequency more strongly than it does in large populations. What caused the decline in the first place can only be speculated at, but changes in populations of predators or competitors are reasonable suggestions.The lack of genetic structure is interesting. It suggests that giant squid are incredibly mobile. It is unlikely to be the adults that are moving long distances as other studies show that they stay in relatively contained patches of the deep sea. That argues for long distance dispersal in the eggs and larvae of the giant squid. It is common for marine species to have larvae that disperse long distances, but dispersal distance in the giant squid is extreme. Winkelmann, I., Campos, P., Strugnell, J., Cherel, Y., Smith, P., Kubodera, T., Allcock, L., Kampmann, M., Schroeder, H., Guerra, A., Norman, M., Finn, J., Ingrao, D., Clarke, M., & Gilbert, M. (2013). Mitochondrial genome diversity and population structure of the giant squid Architeuthis: genetics sheds new light on one of the most enigmatic marine species Proceedings of the Royal Society B: Biological Sciences, 280 (1759), 20130273-20130273 DOI: 10.1098/rspb.2013.0273... Read more »

Winkelmann, I., Campos, P., Strugnell, J., Cherel, Y., Smith, P., Kubodera, T., Allcock, L., Kampmann, M., Schroeder, H., Guerra, A.... (2013) Mitochondrial genome diversity and population structure of the giant squid Architeuthis: genetics sheds new light on one of the most enigmatic marine species. Proceedings of the Royal Society B: Biological Sciences, 280(1759), 20130273-20130273. DOI: 10.1098/rspb.2013.0273  

  • March 8, 2013
  • 08:01 PM
  • 191 views

It's allometric, my dear Watson

by Mostly Open Ocean in Mostly Open Ocean

Giant and colossal squid have the largest eyes of any living animals. Eyes are expensive organs to build and maintain, which led some researchers to suggest that there must be a strong evolutionary advantage for large eyes in giant squid. Using a mathematical model they found that giant squid eyes were best suited for detecting large dimly lit objects. They argued that the only stimulus that was both large enough and important enough for giant and colossal squid to detect was the light produced by bioluminescent organisms disturbed by hunting sperm whales.A giant squid, Architeuthis dux (top), and a colossal squid, Mesonychoteuthis hamiltoni (bottom), being hauled up from the depths (images from National Geographic here and here respectively).When I wrote about the paper, one of the criticisms I had was that the authors had failed to consider allometric scaling. Although the authors made comparisons of eye size with fish and extinct marine reptiles of similar size, they had not looked at eye size in other squid. Giant and colossal squid are the largest of all squid and their eyes could simply be large because they scaled up with their body size. I did a very crude analysis by conducting a literature search for papers that reported both eye size and body size in squid. From that I concluded that eye size was not disproportionately large relative to body size in giant and colossal squid.Now, fortunately, nobody needs to rely on my poor-man's analysis. Schmitz et al. have published in BMC Evolutionary Biology that examines data from 87 different squid species and concludes that when allometric scaling is taken into account eye size in giant and colossal squids is not exceptional. In fact, it's pretty much exactly what you would expect if you scaled up another squid species to the same size. Indeed, there were a couple of groups, such as the bobtail squid, that had larger eyes relative to body size than the giant squid.A regression of eye diameter on mantle length for 87 species of squid. Points for individual measurements in giant (yellow) and colossal (red) squid are shown for comparison (taken from Schmitz et al. 2013).Further, Schmitz et al. also argue that many of the parameter values used in the original study are inappropriate. The original study based all of their optical performance calculations on the largest recorded giant squid eye diameter of 27 centimeters. But, this is problematic because the optical ability of such a large eye is likely to apply mainly to very large old squid, who are likely to have already reproduced. Eyes that only provide an advantage late in life are unlikely to contribute much to individual fitness. The original paper also probably set the values for the density and amount of light emitted from bioluminescent organisms in the deep sea too high. When Schmitz et al. used more realistic values in the model they found that there was no unique advantage of large eyes for detecting large luminous objects, such as foraging sperm whales. Pupil sizes ranging from 2 centimeters up to the 15 centimeters used in the original model performed roughly equally well at detecting point sources and large luminous objects. Moreover, as eye size increased there was a slightly greater advantage for detecting point sources of light rather than large luminous objects. Thus, with more realistic parameter values, the conclusions of the original paper are essentially reversed.References... Read more »

Schmitz, L., Motani, R., Oufiero, C., Martin, C., McGee, M., Gamarra, A., Lee, J., & Wainwright, P. (2013) Allometry indicates giant eyes of giant squid are not exceptional. BMC Evolutionary Biology, 13(1), 45. DOI: 10.1186/1471-2148-13-45  

Nilsson, D., Warrant, E., Johnsen, S., Hanlon, R., & Shashar, N. (2012) A Unique Advantage for Giant Eyes in Giant Squid. Current Biology, 22(8), 683-688. DOI: 10.1016/j.cub.2012.02.031  

  • February 26, 2013
  • 06:27 AM
  • 190 views

Fish get wasted on wastewater

by Mostly Open Ocean in Mostly Open Ocean

In most cities sewage is treated to remove most of the things that we don't want going into the environment. But, some things get through and out to sea. The Western Treatment Plant in Melbourne, which treats over 50% of Melbourne's wastewater (including my contribution), releases large amounts of nitrogen into Port Phillip Bay. Indeed, a 1996 report from the Commonwealth Scientific and Industrial Research Organisation recommended that nitrogen released from the Western Treatment Plant be reduced by 1000 tonnes per year. Nearly 20 years later they've achieved half that amount.The Western Treatment Plant. Covering 10,500 hectares it treats about 50% of Melbourne's wastewater.Nitrogen pollution is significant issue. It, along with other types of nutrient pollution, has been linked to coral and seagrass declines, and jellyfish blooms. Other things that cause problems in the ocean also slip through sewage treatments plants. From the relatively large things, like plastic fibers from clothing, to the very small, like the drugs we take.Not all drugs remain active after they've done their job in the human body, but many do. One of the best known and most researched drugs to escape sewage treatment is ethinyl oestradiol, the active ingredient in birth control pills. Decades of research has shown that ethinyl oestradiol has negative impacts on fish and other aquatic organisms. Even very small doses can lead to male fish that produce eggs in their testes, leading to reduced fertility and potentially to population collapse (Kidd et al. 2007). Sections through the testis of two male fish showing developing eggs, which are the large circular cells surrounded by purple staining tissue. The smaller purple staining flecks are the sperm cells. Many recreational drugs also make it through wastewater treatment, such as illicit  amphetamines (Kasprzyk-Hordern et al. 2009). To my knowledge, it has not been shown that these arrive in the environment at high enough doses to cause any negative effects. Caffeine, my favorite recreational drug, is detected in seawater at concentrations high enough concentrations to produce measurable, but probably minor effects in mussels (del Rey et al. 2011, 2012).Exposure to the concentrations of caffeine that are normally found in the environment probably have little or no effect on fish. Unlike caffeine, some drugs can build up in the body tissues of fish, making chronic exposure to even low concentrations a risk. Recently a study found that the concentration of a common anti-anxiety medication, oxazepam, was six times higher in the muscle of redfin perch (Perca fluviatilis) than it was in the surrounding river water (Brodin et al. 2013).A redfin perch, Perca fluviatilis, in an aquarium (photo Wikipedia)Interestingly, Brodin et al. went on to test what effects oxazepam had on the redfin perch. Annoyingly, they used concentrations of the drug that were three times higher than they recorded in the river and higher than other studies have documented. But, their treatments produced levels of the drug in the muscle tissue of the fish that were comparable to the fish in the river, indicating their results are probably biologically relevant. They found that the fish exposed to the drug exhibited increased activity, reduced sociality, and higher feeding rate relative to control fish.Although they scuffed their experiment a little with their choice of concentrations, they did do something that few other ecotoxicology studies do. They looked at behavioural traits that are important for the survival of fish in the wild. Too slowly are excotoxicologists moving away from testing the lethal effects of pollutants, often requiring doses that never occur in the wild. Hopefully, the publication of the Brodin et al. paper in the prestigious journal Science will encourage more researchers to examine the effects of pollutants at the levels which they typically occur and on a greater range biologically interesting traits.References:Kidd, K., Blanchfield, P., Mills, K., Palace, V., Evans, R., Lazorchak, J., & Flick, R. (2007). Collapse of a fish population after exposure to a synthetic estrogen Proceedings of the National Academy of Sciences, 104 (21), 8897-8901 DOI: 10.1073/pnas.0609568104 ... Read more »

Kidd, K., Blanchfield, P., Mills, K., Palace, V., Evans, R., Lazorchak, J., & Flick, R. (2007) Collapse of a fish population after exposure to a synthetic estrogen. Proceedings of the National Academy of Sciences, 104(21), 8897-8901. DOI: 10.1073/pnas.0609568104  

Kasprzyk-Hordern, B., Dinsdale, R., & Guwy, A. (2009) The removal of pharmaceuticals, personal care products, endocrine disruptors and illicit drugs during wastewater treatment and its impact on the quality of receiving waters. Water Research, 43(2), 363-380. DOI: 10.1016/j.watres.2008.10.047  

Rey, Z., Granek, E., & Buckley, B. (2011) Expression of HSP70 in Mytilus californianus following exposure to caffeine. Ecotoxicology, 20(4), 855-861. DOI: 10.1007/s10646-011-0649-6  

Rodriguez del Rey, Z., Granek, E., & Sylvester, S. (2012) Occurrence and concentration of caffeine in Oregon coastal waters. Marine Pollution Bulletin, 64(7), 1417-1424. DOI: 10.1016/j.marpolbul.2012.04.015  

Brodin, T., Fick, J., Jonsson, M., & Klaminder, J. (2013) Dilute Concentrations of a Psychiatric Drug Alter Behavior of Fish from Natural Populations. Science, 339(6121), 814-815. DOI: 10.1126/science.1226850  

  • February 16, 2013
  • 10:38 PM
  • 264 views

Flying squid really fly

by Mostly Open Ocean in Mostly Open Ocean

Many pelagic squid are able to launch themselves into the air using jets of water expelled through a funnel beneath their head. There are a number of photos online that show squid out of the water and holding their fins and tentacles in a gliding position. But it has been unclear whether the squid where using simple gliding, like a paper plane, or actively controlling the flight.The neon flying squid, Ommastrephes bartramii, holding its fins and tentacles for flight (photo Geoff Jones).Now researchers have taken photographic sequences for two schools of the neon flying squid, Ommastrephes bartramii, in flight. The sequences captured the entire flight process, from exiting the water to reentry. Their analysis of the photographs provides the first compelling evidence that flying squid are performing true biomechanical flight.Neon flying squid in flight with a red footed booby looking on (photo from Muramatsu et al. 2013)The researchers identified four phases of the flight; launching, jetting, gliding and diving. During the launch phase the squid's fins and tentacles are held in a streamlined position and the squid propels itself out of the water. The squid then spreads its fins and tentacles jetting through the air. Once the water within the mantle cavity is expended the squid continues to glide. Finally, the squid folds its fins and tentacles back into a streamlined position, changes is pitch and dives into the water with barely a splash.The phases of squid flight; a) launching, b) jetting, c) gliding and d) diving (from Muramatsu et al. 2013)Using birds within some images the researchers were able to estimate the length of the airborne squid and therefore their speed and distance covered. During the jetting phase the squid travelled at between 8.8 and 11.2 meters per second, which is about human sprinting speed. The squid covered up to 33.5 meters in flight, substantially less than a flying fish (~400 meters), but better than previous estimates for flying squid (~10 meters).Muramatsu, K., Yamamoto, J., Abe, T., Sekiguchi, K., Hoshi, N., & Sakurai, Y. (2013). Oceanic squid do fly Marine Biology DOI: 10.1007/s00227-013-2169-9... Read more »

Muramatsu, K., Yamamoto, J., Abe, T., Sekiguchi, K., Hoshi, N., & Sakurai, Y. (2013) Oceanic squid do fly. Marine Biology. DOI: 10.1007/s00227-013-2169-9  

  • February 16, 2013
  • 03:00 AM
  • 233 views

A stepping stone of rotting wood

by Mostly Open Ocean in Mostly Open Ocean

Many of the animals living at hydrothermal vents and cold seeps carry chemosynthetic bacterial symbionts in their body, which convert methane or hydrogen sulfide into food. Some have lost the ability to feed on anything other than what the bacteria living inside their tissues provide them. Almost all cannot survive without a sufficient supply of methane or hydrogen sulfide. One hypothesis is that decomposing organic matter that has sunk from the surface, like whale carcasses, seaweed, and wood could serve as a food source, providing stepping stones between vents or seeps.A field of mussels at a cold seep (photo Wikipedia)Animals more typically found at vents and seeps are known to colonise the remains of whales in the deep sea. Smith et al. (1989), were the first to report vent animals colonising whale skeletons. They also provided a conservative estimate of the distribution of whale carcasses on the ocean floor and suggested that they would provide a persistent and abundant habitat for cold seep and hydrothermal vent animals. Adding sunken wood and seaweed to the list only increases the amount of available habitat.A whale skeleton in the deep sea with patrolling hagfish (photo Wikipedia)A gap in our understanding, though, is how enough methane or hydrogen sulfide is produced to support populations of chemosynthetic animals by decaying wood. The deep sea is a cold place, which is not conducive to the rapid breakdown of organic material. A large amount of wood would be required to provide the surface area necessary to produce enough gas. One hypothesis though, is that the surface area of wood might be increased by larger organisms, such as wood-boring bivalves, breaking it up first.Researchers tested this idea by depositing wood logs on the Eastern Mediterranean seafloor at 1700 meters down and returned a year later to examine the animals and bacteria the had colonised the wood. They also measured the chemicals in the water released by the bacteria breaking down the wood. Using underwater robots, they observed that wood-boring bivalves had indeed broken the wood into smaller pieces, which were further broken down by other organisms. The activity of the organisms digesting the wood reduced the amount of dissolved oxygen, resulting in anoxic conditions that allowed sulfate-reducing bacteria to move in and produce hydrogen sulfide. The hydrogen sulfide then attracted a species of mussel, which usually found at cold seeps where it gains energy from symbiotic chemosynthetic bacteria. The mussels seemed to preferentially colonise cavities under the bark of the wood, presumably because sulfide levels were higher there.The chemosynthetic mussel Idas modiolaeformis was found in the sunken wood piles (photo from Bienhold et al. 2013)So it appears that wood boring organisms are able to pave the way for chemosynthetic organisms to colonise sunken wood in the deep sea. Their burrows, feces and the chips of wood that they produce all increase the surface area of material available for hydrogen sulfide producing bacteria to digest. Moreover, their activity and the activity of other organisms produce the anoxic conditions required for sulfate reduction, which is necessary to support chemosynthetic life.... Read more »

SMITH, C., KUKERT, H., WHEATCROFT, R., JUMARS, P., & DEMING, J. (1989) Vent fauna on whale remains. Nature, 341(6237), 27-28. DOI: 10.1038/341027a0  

Bienhold, C., Pop Ristova, P., Wenzhöfer, F., Dittmar, T., & Boetius, A. (2013) How Deep-Sea Wood Falls Sustain Chemosynthetic Life. PLoS ONE, 8(1). DOI: 10.1371/journal.pone.0053590  

  • February 2, 2013
  • 07:34 AM
  • 198 views

Attack of the jellyfish swarm

by Mostly Open Ocean in Mostly Open Ocean

Jellyfish are not as charismatic as some marine species and consequently they have not received much research attention. Recently though, there has been increasing interest in them because their numbers appear to be on the rise worldwide. There are a few hypotheses about why this might be the case floating around in the literature.The beautiful and under appreciated jellyfish, Cyanea capillata. Perhaps the World's biggest (photo Wikipedia).Corals, which are in the same phylum (Cnidaria) as jellyfish, have been on the decline in northern Australia and other parts of the world. Two major hypotheses have been proposed to explain this; overfishing reducing herbivorous fish numbers leading to algal overgrowth and agricultural runoff decreasing water clarity through sedimentation and by promoting phytoplankton growth. These same pressures are thought to have a positive effect on jellyfish populations.Overfishing is argued to increase jellyfish numbers by reducing predation and competition for food, particularly of young jellyfish. While agricultural runoff stimulates phytoplankton blooms that directly or indirectly provide increased amounts of food to jellyfish. Some others argue that changes to marine communities that are occurring as a result of climate change are tipping the ecological balance in favour of jellyfish. But there isn't much agreement, even among experts, about whether jellyfish have actually increased globally.Nomura jellyfish, Nemopilema nomurai, causing problems for Japanese fishermen (Photo Shin-ichi Uye)Recently, a collaboration of scientists from around the world have conducted one of the most comprehensive and rigorous analyses of the available data on jellyfish numbers. Condon et al. found that jellyfish numbers go through cyclical population booms roughly every 20 years. Their data suggest that increasing jellyfish numbers in the last few years are simply a part of this 20-year population oscillation. But, there is a hint in the data that since 1970 jellyfish numbers have be increasing.During the last population minimum, which occurred in 1993, jellyfish numbers were higher relative to previous population minimums. This resulted in a weak, but statistically significant trend towards increasing jellyfish abundance in the last 40 years. The authors caution that the trend is too weak, given the limitations of the data set, to conclude that jellyfish populations really are on the increase. Data collected in the next few years should be able to determine, with confidence, whether the upwards trend is real.Although they found no strong evidence that jellyfish numbers are increasing worldwide, there was good evidence that numbers are increasing in some regions. These regions included the Sea of Japan, North Atlantic shelf regions, the Barents Sea, and parts of the Mediterranean Sea. All of these regions exhibited the 20 year oscillation, but local factors seem to have acted in concert with the global population fluctuations. Notably, fishing is heavy in many, if not all, of those regions.... Read more »

Condon, R., Duarte, C., Pitt, K., Robinson, K., Lucas, C., Sutherland, K., Mianzan, H., Bogeberg, M., Purcell, J., Decker, M.... (2013) Recurrent jellyfish blooms are a consequence of global oscillations. Proceedings of the National Academy of Sciences, 110(3), 1000-1005. DOI: 10.1073/pnas.1210920110  

  • January 30, 2013
  • 10:54 PM
  • 171 views

Evolution, climate change and coral

by Mostly Open Ocean in Mostly Open Ocean

Increased carbon dioxide in the atmosphere poses several problems for organisms living in the marine environment. Increases in temperature and ocean acidification are the two best known and most worrying. In order to predict how climate change and ocean acidification will affect marine species, we need to know how they respond to these conditions. The effect of climate change on corals has attracted a lot of attention because of their importance for biodiversity.We can't just expose corals to predicted conditions because corals of the future won't be naive to these environments and are likely to have evolved. We know that evolution can be extremely rapid, often within decades. Ignoring the potential for evolution to influence the effects of climate change on marine organisms could lead to inaccurate projections of the effects of climate change on extinction risk. Yet many authors are ignoring the effects of evolution and acclimation in making their predictions. The three-spine stickleback, Gasterosteus aculeatus has been documented adapting to freshwater conditions from saltwater ancestors in just 13 generations (photo Wikipedia)In their 2007 paper, Hoegh-Guldberg, et al. dismiss the importance of evolution because "reef-building corals have relatively long generation times and low genetic diversity, making for slow rates of adaptation". But, long generation times are not present in all coral species and the response of corals to climate change is going to depend partly on their algal symbionts, which have short generation times. Unfortunately, the rates of evolution in corals and their symbionts are extremely poorly known. In terrestrial systems though, genetic variation for traits related to thermal performance is common and evolutionary responses to changing climate are typical. For instance, changes in allele frequencies consistent with responses to global warming have been documented in a number of insects, such as fruit flies and mosquitoes (e.g. Bradshaw & Holzapfel 2001, Umina et al. 2005). Acclimation, or phenotypic plasticity, will also affect the way that corals respond to climate change. Plastic responses to the environment can occur within generations and across them. For instance, Donelson et al. (2011) looked at the tropical damselfish, Acanthochromis polyacanthus, and found that their offspring could completely compensate for the negative effects of higher temperatures. But, this only occurred when both they and their parents where reared at the same temperature.The tropical damselfish, Acanthochromis polycanthus (photo Wikipedia)There are indications that some acclimation is occurring in corals too. Under stress, corals expel their algal symbionts, which gives them the appearance of having been bleached. Coral reefs that experience greater variability in sea surface temperature and those that have recently been subjected to bleaching are less susceptible to bleaching. This greater resilience suggests that some acclimation to climate change is possible within short time-frames. A bleached coral in the foreground with an unbleached coral of the same species behind (photo Wikipedia)We need a better understanding of how evolution and acclimation may influence the response of corals to climate change so that our predictions are accurate. But, we already know which direction things are probably going to go. John Pandolfi's work has shown that under historical climate change, diversity on corals reefs has declined and populations have moved to higher latitudes (e.g. Pandolfi et al. 2011, Kiessling et al 2012). Climate change is currently more rapid than previous episodes and this will limit the amount of adaptation that can occur. Corals are also already under significant pressure from other anthropogenic sources of stress that have resulted in substantial declines and changes in population composition. These pressures, too, will decrease the ability of corals to cope with the effects of climate change. By removing these pressures, we will give corals the best chance possible to adapt to a warmer and more acidic ocean.Hoegh-Guldberg, O., Mumby, P., Hooten, A., Steneck, R., Greenfield, P., Gomez, E., Harvell, C., Sale, P., Edwards, A., Caldeira, K., Knowlton, N., Eakin, C., Iglesias-Prieto, R., M... Read more »

Hoegh-Guldberg, O., Mumby, P., Hooten, A., Steneck, R., Greenfield, P., Gomez, E., Harvell, C., Sale, P., Edwards, A., Caldeira, K.... (2007) Coral Reefs Under Rapid Climate Change and Ocean Acidification. Science, 318(5857), 1737-1742. DOI: 10.1126/science.1152509  

Bradshaw, W., & Holzapfel, C. (2001) Genetic shift in photoperiodic response correlated with global warming. Proceedings of the National Academy of Sciences, 98(25), 14509-14511. DOI: 10.1073/pnas.241391498  

Umina, P., Weeks, A. R., Kearney, M. R., McKechnie, S. W., & Hoffmann, A. A. (2005) A Rapid Shift in a Classic Clinal Pattern in Drosophila Reflecting Climate Change. Science, 308(5722), 691-693. DOI: 10.1126/science.1109523  

Donelson, J., Munday, P., McCormick, M., & Nilsson, G. (2011) Acclimation to predicted ocean warming through developmental plasticity in a tropical reef fish. Global Change Biology, 17(4), 1712-1719. DOI: 10.1111/j.1365-2486.2010.02339.x  

Pandolfi, J., Connolly, S., Marshall, D., & Cohen, A. (2011) Projecting Coral Reef Futures Under Global Warming and Ocean Acidification. Science, 333(6041), 418-422. DOI: 10.1126/science.1204794  

Kiessling, W., Simpson, C., Beck, B., Mewis, H., & Pandolfi, J. (2012) Equatorial decline of reef corals during the last Pleistocene interglacial. Proceedings of the National Academy of Sciences, 109(52), 21378-21383. DOI: 10.1073/pnas.1214037110  

  • January 14, 2013
  • 05:58 AM
  • 136 views

A wrinkly hypothesis

by Mostly Open Ocean in Mostly Open Ocean

The aquatic ape hypothesis was first proposed 70 years ago by German pathologist Max Westenhöfer. The hypothesis has more recently championed by Elaine Morgan, most notably in her book The Aquatic Ape. But the hypothesis has not drawn a lot of attention in the literature and has been dismantled in various places (here's one that's pretty good). Essentially the hypothesis interprets certain features, such as human hairlessness, as adaptations to an aquatic environment.In 2011 Changizi et al. published a paper arguing that water-wrinkled fingers are an adaptation to life in aquatic environments. A new paper, just published, purports to test this hypothesis. Kareklas et al. had test subjects soak their hands in 40°C water for 30 minutes. Then they got the subjects to move marbles from a source container that was either filled with water or dry. The performance of the wrinkly handed participants was compared to a control group that performed the same task without soaking their hands.Their results showed that the wrinkly finger group completed the marble moving task 12% faster when the source container was filled with water. There was no difference between the two groups when it was dry. They argue that their study shows a clear advantage to having wrinkly fingers when manipulating submerged items. But, I find the experiment completely underwhelming as support for wrinkly fingers as adaptations.Most obviously, participants had to soak their hands in 40°C water for 30 minutes in order to obtain the small advantage. If wrinkled fingers are important for manipulating submerged objects, it seems to take an inordinately long time for fingers to wrinkle. Moreover, prior research has shown that lower temperatures, which are more likely to be encountered by our ancestors, result in slower and less exaggerated finger wrinkling (reviewed in Wilder-Smith 2004).Marbles are also particularly small and slippery when compared with almost all conceivable objects that a paleolithic primate would be interested in picking up. It would be far more compelling if they had shown that the performance advantage remained when other objects were manipulated underwater. Given the very small advantage for marbles, I strongly suspect that the advantage would disappear for a vast array of other items.The proponents of the aquatic ape hypothesis will probably incorporate the new study into their lists of evidence for a close association with with water in our ancestors. But, like most of their evidence, it is little better than plausible speculation dressed up as a compelling theory that deserves attention. It's a great way to get your ideas attention in the popular press, it's a horrible way to do science. The inoculation for such adaptationist nonsense is, as always, Gould and Lewontin 1979.  Kareklas, K., Nettle, D., & Smulders, T. (2013). Water-induced finger wrinkles improve handling of wet objects Biology Letters, 9 (2), 20120999-20120999 DOI: 10.1098/rsbl.2012.0999 Changizi, M., Weber, R., Kotecha, R., & Palazzo, J. (2011). Are Wet-Induced Wrinkled Fingers Primate Rain Treads? Brain, Behavior and Evolution, 77 (4), 286-290 DOI: 10.1159/000328223... Read more »

Kareklas, K., Nettle, D., & Smulders, T. (2013) Water-induced finger wrinkles improve handling of wet objects. Biology Letters, 9(2), 20120999-20120999. DOI: 10.1098/rsbl.2012.0999  

Changizi, M., Weber, R., Kotecha, R., & Palazzo, J. (2011) Are Wet-Induced Wrinkled Fingers Primate Rain Treads?. Brain, Behavior and Evolution, 77(4), 286-290. DOI: 10.1159/000328223  

Wilder-Smith, E. (2004) Water immersion wrinkling. Clinical Autonomic Research, 14(2), 125-131. DOI: 10.1007/s10286-004-0172-4  

  • January 7, 2013
  • 01:26 AM
  • 147 views

Waterfall climbing fish

by Mostly Open Ocean in Mostly Open Ocean

Diadromous fish are those that live part of their lives at sea and part of their lives if freshwater. Some of these fish reproduce in the upper parts of rivers above barriers like waterfalls, which they must scale in order to make it to the breeding sites. A newly published paper looks at how the Nopili goby, Sicyopterus stimpsoni, manages to climb waterfalls. The researchers found that the way the goby feeds and the way it climbs are very similar.The Nopili goby, Sicyopterus stimpsoni (photo Takashi Maie)During feeding the Nopili goby extends its upper jaw out much further and its lower jaw much less than other gobies. In climbing the basic motion is the same except the upper jaw maintains closer contact with the rock. Climbing is also assisted by pelvic fins fused into a sucker, a feature of all gobies. Because no other goby feeds in the same way, it's unclear whether the feeding or climbing movements evolved first.The climbing galaxias, Galaxias brevipinnis (photo Robert McCormack)There are many other fish that have a diadromous life-history, eels and salmon being the classic examples. There are fewer fish that climb waterfalls. However, in southern Australia and New Zealand there is a fish close to my heart that has a very similar life-history to the Nopili goby, but it climbs waterfalls in a different way. The climbing galaxias, Galaxias brevipinnis, climbs using its broad pectoral and pelvic fins and wiggling upwards.Cullen J. A., Maie T., Schoenfuss H. L., & Blob R. W. (2013). Evolutionary Novelty versus Exaptation: Oral Kinematics in Feeding versus Climbing in the Waterfall-Climbing Hawaiian Goby Sicyopterus stimpsoni PLOS One, 8 (1) DOI: 10.1371/journal.pone.0053274... Read more »

Cullen J. A., Maie T., Schoenfuss H. L., & Blob R. W. (2013) Evolutionary Novelty versus Exaptation: Oral Kinematics in Feeding versus Climbing in the Waterfall-Climbing Hawaiian Goby Sicyopterus stimpsoni. PLOS One, 8(1). info:/10.1371/journal.pone.0053274

  • December 17, 2012
  • 04:44 AM
  • 184 views

Shifting baselines in coral cover

by Mostly Open Ocean in Mostly Open Ocean

A great problem for conserving marine ecosystems is that we rarely have a good data on what things were like before human impacts started. In my last post, I wrote about a study that showed that coral cover had declined on the Great Barrier Reef by 50.7% since 1985. At the start of the study coral cover was at 28%, but pristine coral reefs can have over 70% coral cover. This suggests that impacts on the Great Barrier Reef predate the time monitoring started by many years.A coral outcrop on the Great Barrier Reef (photo Wikipedia)John Pandolfi at the University of Queensland has been trying to establish the past state of the Great Barrier Reef in numerous ways. One way is to take sediment cores from coral reef and compare the historical diversity and abundance of corals on the reef to the modern community composition. A new study lead by Pandolfi has reconstructed the past coral communities on reefs around Pelorus Island in the Palm Island group. They took cores containing coral remains dating back as far as the mid-third century. They found that there was a pronounced transition in the coral species on the islands reefs between 1920 and 1955. The transition strongly correlated with a 5 to 10 fold increase in the amount of sediment found in the cores beginning in 1870, but showing several large peaks between the 1920s and 1970s. White settlement and land clearing of the area began in about 1870, the same time that high sediment loads were found in the cores. Prior to that, there was remarkable stability in the coral communities and the amount of sediment reaching the reef. The new study highlights that reefs in 1985 that were thought to be relatively pristine probably had not been for 50 or 60 years. Therefore attempts to conserve reefs as they were in 1985 is inadequate because these reefs are likely to be already severely impacted by human activities. If we a serious about returning coral reefs to a pristine state, we should be restoring them to what they were like prior to white settlement, not what they were like now after a century of mistreatment.Roff, G., Clark, T., Reymond, C., Zhao, J., Feng, Y., McCook, L., Done, T., & Pandolfi, J. (2012). Palaeoecological evidence of a historical collapse of corals at Pelorus Island, inshore Great Barrier Reef, following European settlement Proceedings of the Royal Society B: Biological Sciences, 280 (1750), 20122100-20122100 DOI: 10.1098/rspb.2012.2100... Read more »

Roff, G., Clark, T., Reymond, C., Zhao, J., Feng, Y., McCook, L., Done, T., & Pandolfi, J. (2012) Palaeoecological evidence of a historical collapse of corals at Pelorus Island, inshore Great Barrier Reef, following European settlement. Proceedings of the Royal Society B: Biological Sciences, 280(1750), 20122100-20122100. DOI: 10.1098/rspb.2012.2100  

  • December 2, 2012
  • 07:55 PM
  • 200 views

Conservation priorities on the Great Barrier Reef

by Mostly Open Ocean in Mostly Open Ocean

A recently published paper on the decline of coral cover on the Great Barrier Reef serves to illustrate an important point; even without climate change we are doing a great deal of damage to some ecosystems. The study by De'ath et al. and published in the Proceedings of the National Academy of Science, finds that coral cover has declined by 50.7% since 1985. They partitioned the losses into 48% tropical cyclones, 42% predation by crown of thorns starfish and 10% to coral bleaching.The crown of thorns starfish, Acanthaster planci (image Wikipedia)The declines were not uniform across the reef. Most of the declines were in the southern part of the reef and near to shore, where more people live. Partly this may be due to more frequent storms in the southern part of the reef, but storm frequency has declined in the last 100 years or so. Mostly it's probably because outbreaks of crown of thorns starfish are linked to human activities, such as agriculture and fishing. And these same human activities leave coral less resilient to other impacts and make it more difficult for them to recover from disturbances.Pollution, sedimentation and overfishing can all change the dynamics of coral reef communities by impairing the ability of corals to recover from other disturbances. Human activities can also increase the mortality of adult coral and reduce the number larvae that survive to become coral. Shifts from coral-dominated communities to seaweed-dominated communities due to these impacts are well documented. Overfishing, particularly of herbivorous fish, has been strongly linked to shifts in community composition. In direct competition corals lose out to seaweed, which overgrows coral and in some cases uses toxins to kill the coral. Herbivorous fish though, eat the seaweed tipping the balance in favour of the corals. So important are herbivorous fish to corals that some have formed mutualistic relationships with fish, which they signal for help when seaweeds encroach on their space. Overfishing has also been suggested to reduce predation on larvae of the crown of thorns starfish, allowing it to reach plague proportions when fish would normally control their numbers. A second hypothesis is that nutrient inputs from farms and cities provides the crown of thorns larvae with large amounts of food, increasing their survival. Neither hypothesis is well supported, but there is growing evidence that both mechanisms are playing a role in crown of thorns outbreaks. For corals, like seagrasses, access to light is critical for their survival. Coral derive as much as 90% of their energy from symbiotic algae growing in their tissues. Nutrient inputs and sedimentation reduce the light available to their algal symbionts, which reduces the energy available to them. This can decrease the resilience of corals to other stressors, such as natural disturbance events. The main sources of sedimentation on the Great Barrier Reef are from human activities, such as agricultural run-off and dredging.  De'ath et al. conclude that there is an urgent need to control crown of thorns outbreaks, especially through improvements to water quality. In the absence of disturbances, the data showed that reefs were able to increase in cover by nearly 3% per year. This is likely to be higher when the full impact of human activities are taken into account. Moreover, their data only go back to 1985, but human impacts on the reef date back to about 100 years before that. The true decline of coral cover on the Great Barrier Reef is, therefore, likely to be far greater than that measured in their study.De'ath et al. also highlight the impending effects of climate change and ocean acidification. Many people are focused on human emissions of carbon dioxide as the sole problem we need to fix to save the reef. But, it's clear that even without the threats of climate change and ocean acidification the Great Barrier Reef is in great deal of trouble. In order to conserve the reef we need to address the source of these issues now.De'ath, G., Fabricius, K., Sweatman, H., & Puotinen, M. (2012). The 27-year decline of coral cover on the Great Barrier Reef and its causes Proceedings of the National Academy of Sciences, 109 (44), 17995-17999 DOI: 10.1073/pnas.1208909109... Read more »

De'ath, G., Fabricius, K., Sweatman, H., & Puotinen, M. (2012) The 27-year decline of coral cover on the Great Barrier Reef and its causes. Proceedings of the National Academy of Sciences, 109(44), 17995-17999. DOI: 10.1073/pnas.1208909109  

  • October 15, 2012
  • 04:03 AM
  • 259 views

It's Yoda, but not as you know him

by Mostly Open Ocean in Mostly Open Ocean

A new species of acorn worm has been named after Jedi Master Yoda, the best character in the Star Wars trilogy*. Acorn worms are not true worms. They are more closely related to echinoderms (starfish, sea urchins, sea cucumbers, etc.) than they are to worms. They were once placed as a subphylum of the chordata (i.e. our own phylum), but are now placed within their own phylum, the hemichordata.Yoda purpurata, the newly described species of acorn wormThe paper described three new species of deep-sea acorn worms in the family Torquaratoridae. Two of which, Allapasus isidis and Tergivelum cinnabarinum, were from previously known genera. But, Yoda purpurata is a new genus and species. It's named after Yoda because the appendages at the head end of the animal are reminiscent of Yoda's ears. All three species were found at about 2.5 kilometers deep on the mid-Atlantic ridge. *To count as a true Star Wars film, it can't just carry the name. You also have to be able to sit through it without wanting to punch George Lucas. This caveat leaves just three films that can be considered part of the Star Wars canon. And these three films are the originals, not the remakes. Priede, I G, Osborn, K J, Gebruk, A V, Jones, D, Shale, D, Rogacheva, A, & Holland, N D (2012). Observations on torquaratorid acorn worms (Hemichordata, Enteropneusta) from the North Atlantic with descriptions of a new genus and three new species Invertebrate Biology, 131 (3), 244-257 DOI: 10.1111/j.1744-7410.2012.00266.x... Read more »

Priede, I G, Osborn, K J, Gebruk, A V, Jones, D, Shale, D, Rogacheva, A, & Holland, N D. (2012) Observations on torquaratorid acorn worms (Hemichordata, Enteropneusta) from the North Atlantic with descriptions of a new genus and three new species. Invertebrate Biology, 131(3), 244-257. DOI: 10.1111/j.1744-7410.2012.00266.x  

  • October 13, 2012
  • 09:14 AM
  • 586 views

Human-induced evolution

by Mostly Open Ocean in Mostly Open Ocean

Human activities have influenced that evolution of many species and not just through artificial selection. Our impacts on ecosystems, use of drugs and pesticides and our harvesting of wild populations is all having an effect on the rate and direction of evolution in many organisms. In fact, many of the frequently cited examples of 'evolution in action' are also examples of evolution human-induced evolution, such as mosquito resistance to DDT and drug resistant bacteria.The detailed studies on the peppered moth, Biston betularia, provide a classic illustration of evolution in action. The peppered moth is nocturnal, resting during the day on light coloured trees, where it is reasonably well camouflaged. However, during the industrial revolution, trees in forests between London and Manchester became covered in soot and dark coloured morphs increased in frequency from 0.01% of the population to 98% due to increased bird predation on the less camouflaged light coloured morph.The light (top) and dark (bottom) coloured morphs of the peppered moth, Biston betularia (images Wikipedia)Although we don't often think of ourselves as predators, hunting and fishing are essentially the same thing. Like predation on peppered moths by birds, they can produce evolutionary change in the target populations. For instance, trophy hunting of bighorn sheep, Ovis canadensis, results in sheep with smaller horns and lighter body weight over time. A couple of recent studies show that behavioural traits are selected too.Bighorn sheep in Montana (image Wikipedia)Using GPS devices, Ciuti et al. tracked 122 (77 females and 45 males) elk, Cervus elaphas, to monitor their movements over the course of a year. The males that were the most likely to fall victim to hunters were those that moved more often, traveled the furthest and made greater use of open areas. The pattern was similar, but less pronounced, in females. Older females tended to move less and use of open areas less than younger females, suggesting that they may learn to avoid hunters. They could not assess learning with age in males as all the tracked males were of the same age.A male elk (image Wikipedia)Ciuti et al. suggest that the bolder behaviour of the elk that were harvested may provide them with protection from other predators, like wolves and bears. Moving long distances and using open areas may make it easier for elk to avoid natural predators, but it favours harvesting by humans with high-powered rifles. It's a neat hypothesis and they say that they intend to test it in future experiments.A second study in rainbow trout, Oncorhynchus mykiss, looked at growth rate, a trait closely correlated with activity rate. To fuel a fast growth rate, it's thought that fish must spend more time actively searching for food, which is supported in the literature. Biro stocked four fishless lakes in Canada with trout that were slow-growing, intermediately-growing and fast-growing. By stocking the lakes, Biro knew the numbers of fish present in each lake and in each experimental group. He then randomly sampled the four lakes using a sampling method that wasn't size-selective.Rainbow trout (image US Fisheries and Wildlife Service)There was substantial variation in the proportion of each of the experimental groups that was caught in each lake. However, faster growing trout were consistently more likely to be caught than intermediate or slow-growing trout. Overall, fast-growing trout were nearly twice as likely to be caught than the two groups with slower growth rates. Importantly, size did not matter; small, slow-growing fish were still less likely to be caught than small, fast-growing fish.Biro's study has the issue that it did not directly assess behaviour, but relied on growth rate as a proxy measure. However, it is consistent with other studies that show fish personalities influence the probability that they are caught by different collection techniques. Bluegill sunfish, for instance, are more likely to be caught in the wild by angling when they're less active. Intriguingly, there is also an interaction between habitat and capture method as less active bluegill sunfish are also less likely to be caught by angling in the open areas of artificial ponds.  I'm troubled by the correlation between growth rate and supposed personality traits. It suggests that what is being measured as personality might actually be a by-product of physiology and not a separate trait. But, other studies I looked at showed that in some situations less active fish grow faster than more active fish, which suggests that they are independent traits.In any case, the Cuiti et al. and Biro studies show quite nicely that humans are probably influencing the direction of evolution in the populations that we harvest by hunting and fishing. Their work adds to a ... Read more »

Biro PA. (2012) Are most samples of animals systematically biased? Consistent individual trait differences bias samples despite random sampling. Oecologia. PMID: 22885993  

Ciuti, S, Muhly, T B, Paton, D G, McDevitt, A D, Musiani, M, & Boyce, M S. (2012) Human selection of elk behavioural traits in a landscape of fear. Proceedings of the Royal Society: B, 279(1746), 4407-4416. DOI: 10.1098/rspb.2012.1483  

Palumbi, S R. (2001) Humans as the World's greatest evolutionary force. Science, 293(5536), 1786-1790. DOI: 10.1126/science.293.5536.1786  

Wilson, A D M, Binder, T R, McGrath, K P, Cooke, S J, & Godin, J J. (2011) Capture technique and fish personality: angling targets timid bluegill sunfish, Lepomis macrochirus. Canadian Journal of Fisheries and Aquatic Sciences, 68(5), 749-757. DOI: 10.1139/f2011-019  

  • September 18, 2012
  • 08:49 AM
  • 435 views

Unflappable albatrosses

by Mostly Open Ocean in Mostly Open Ocean

Wandering albatrosses, Diomedea exulans, are among the largest flying birds in the world and are renowned for soaring flights of thousands of kilometers to feed. Several adaptations allow their flight to be extremely energy-efficient. For instance, their extremely long wings allow them to glide remarkably long distances and a modified tendon allows them to hold their wings open without the use of their muscles.A wandering albatross showing its fight position (photo Wikipedia)For a long time, it's been clear that albatrosses are using wind energy to power their flight. Indeed, Lord Rayleigh proposed that albatrosses were using wind shear to soar in 1883. Although other mechanisms have been proposed, dynamic soaring in wind shear has since been cited as the principle mechanism that they are able to gain energy from the wind. At the ocean surface the wind travels more slowly because of friction, but as you move away from the surface wind speeds get higher. Albatrosses can gain airspeed by rising away from the sea into the faster winds and then dropping back into the slower winds at the surface. They first turn into the wind and rise followed by a turn with the wind as they descend, gaining energy in both directions while losing some to drag.The dynamic soaring cycle of an albatross. It starts with a turn into the wind, then a climb in altitude, then a turn with the wind and a descent back to the sea surface. The length of yellow arrows to the left of the figure indicate the strength of the wind at different altitudes (Image taken from Sachs 2005).Penncuick argued that albatrosses couldn't get enough energy from the wind-gradient and must be deriving a large amount of energy from moving in and out of the pockets of almost still air in the lee of wave crests, which he termed 'gust soaring'. Other authors have suggested that they slope-soar off the windward side of wave crests. But, the debate over how albatrosses are gaining enough energy for their long distance flights has played out in the theoretical literature, sometimes accompanied by anecdotal observations of flight behaviour.The gust soaring cycle of an albatross. As the albatross moves through the 'separated boundary layer' (blue line) from the leeward side of a wave crest it gets a kick of energy from the wind allowing it to gain altitude and potential energy to power its soaring flight (Image taken from Richardson 2011)With their paper published recently in PLOS One, Sachs et al. have added some empirical data to help resolve the issue. They attached small GPS devices to the backs of 16 albatrosses, which measured the position and altitude of each individual once every second and the velocity 10 times a second. This allowed them to look at the small scale of the flight cycle and draw inferences about the physics of the manoeuver. A plot of a recorded dynamic soaring cycle. The numbers indicate each stages from the ascent [1], to the turn at peak altitude [2], to the descent [3] and the turn to restart the cycle [4] (Image taken from Sachs et al. 2012).They used the data to calculate the total energy over the entire dynamic soaring cycle by summing the potential and kinetic energy. Contrary to the expectations of gust soaring and slope soaring, the maximum energy in the cycle was reached on the descent. And the energy accumulation was gradual, without any large spikes that would result from a big kick in energy close to the surface.A two-dimensional plot of the soaring cycle showing the point at which maximum and minimum energy are reached. The track shown here is the same as the one above (Image taken from Sachs et al. 2012).Sachs et al. also calculated the energy gain that the albatrosses could achieve throughout the cycle. The maximum energy in the cycle was ~360% of the minimum energy and provided enough surplus to overcome drag forces. Indeed, the energy gain... Read more »

Sachs G, Traugott J, Nesterova AP, Dell'omo G, Kümmeth F, Heidrich W, Vyssotski AL, & Bonadonna F. (2012) Flying at no mechanical energy cost: disclosing the secret of wandering albatrosses. PloS one, 7(9). PMID: 22957014  

Richardson P. L. (2011) How do albatrosses fly around the world without flapping their wings?. Progress in Oceanography, 88(1 - 4), 46-58. DOI: 10.1016/j.pocean.2010.08.001  

Pennycuick CJ. (2002) Gust soaring as a basis for the flight of petrels and albatrosses (Procellariiformes). Avian Science, 2(1), 1-12. info:/

  • September 6, 2012
  • 08:28 AM
  • 356 views

Rapid speciation in starfish

by Mostly Open Ocean in Mostly Open Ocean

Australian waters are extremely rich in starfish species. Indeed, a little over 15% of all known species of starfish occur in Australia. For at least two of these starfish, speciation occurred extraordinarily fast. At most, they became separated about 22 thousand years ago, but the best estimate for the timing of the split is about 6 thousand years ago.We know that evolution can be very rapid (e.g. sticklebacks) and that sometimes this leads to speciation (e.g. cichlids). But, in these cases selection is probably acting on a small number of alleles that are already present in the population. What makes the starfish study so breathtaking is that there has been profound changes to life history in the two species, which likely involved selection on many morphological and physiological traits.Puritz et al. looked at Cryptasterina pentagona and its sister species C. hystria. Like most starfish, C. pentagona has separate sexes and reproduces by 'broadcasting' sperm and eggs into the water column where fertilisation occurs. In stark contrast, C. hystria produces both sperm and eggs simultaneously, and it exclusively self-fertilises within its own body cavity. The embryos of C. pentagona develop in the plankton, while C. hystria broods its offspring within the gonad until they are ready to emerge as small starfish.It takes an expert to distinguish Cryptasterina hystria (top) and C. pentagona (bottom) in the wild. In fact I've seen the bottom picture shown as C. hystria and C. pentagona, but I think I got it right (photo Jon Puritz).Puritz et al. speculate that water temperature may have provided the selective pressure that favoured the evolution of the C. hystria life history. Viviparity, like that seen in C. hystria, has been documented in a number of other starfish species. And it is consistently associated with species that occur in colder water. The two Cryptasterina species are separated by about 375 kilometers, with C. pentagona in the warmer north and C. hystria to the cooler south.The authors also argue that small population size may have selected for self-fertilisation. If there are so few individuals in the population that your gametes are unlikely to meet another individual's, it's better to fertilise your own than to not reproduce at all. It's expected that genetic variation in a population that self-fertilises should be very low. But, genetic variation in C. hystria is so low it suggests the whole species derived from very few individuals, perhaps just a single one.The transition from broadcast spawning with planktonic larval development to self-fertilisation with larvae brooded within the gonad has occurred in another Cryptasterina species, C. pacifica. In the closely related genus Parvulastra, a similar transition has occurred too, but probably over 500 thousand years. This suggests that the genetic variation required for the dramatic shift in life history is widely present in the group of starfish to which the genera Cryptasterina and Parvulastra belong. But, the speed at which evolution has occurred is truly astonishing.Parvulastra exigua, note its similarity to the Cryptasterina species (photo Museum Victoria).Puritz JB, Keever CC, Addison JA, Byrne M, Hart MW, Grosberg RK, & Toonen RJ (2012). Extraordinarily rapid life-history divergence between Cryptasterina sea star species. Proceedings. Biological sciences / The Royal Society, 279 (1744), 3914-3922 PMID: 22810427... Read more »

Puritz JB, Keever CC, Addison JA, Byrne M, Hart MW, Grosberg RK, & Toonen RJ. (2012) Extraordinarily rapid life-history divergence between Cryptasterina sea star species. Proceedings. Biological sciences / The Royal Society, 279(1744), 3914-3922. PMID: 22810427  

  • September 4, 2012
  • 03:05 AM
  • 385 views

An unusual crustacean meets its parents

by Mostly Open Ocean in Mostly Open Ocean

Many animals living in the ocean have complex life histories where the young look nothing like the adults and often occupy different habitats. Frogs, with their early tadpole stage, are classic examples of animals with complex life histories. But, tadpoles look far more like frogs than the larvae of other animals resemble their adult forms. Different species of distantly related crustacean larvae, for instance, can look far more like each other than they resemble the adults of their own species.The nuaplius larvae stage (left) of a cylopoid copepod (top) and penaeid shrimp (bottom) and their adult forms (right). These distantly related crustaceans appear similar as larvae, but not as adults (images Wikipedia) Because larvae look so different from the adult form, identifying the species that larvae belong to can be tricky. Often it requires the larvae to be carefully reared in the laboratory to see what they eventually turn into, but this isn't always possible. In some cases, it is possible to place larvae within a species using genetic techniques, but this requires a DNA sequence from the adult to compare to.One type of crustacean larva that has been difficult to assign to an adult form are the Cerataspids. There are three known species that have been placed in two genera, Cerataspis monstrosa, C. petiti and Cerataspides longiremus. Like many unusual crustacean larvae, the first to be discovered (C. monstrosa in 1828) was thought to be an adult of the crustacean order Leptostraca. However, it later became apparent that they were probably larvae of shrimp within the Penaeoid superfamily, possibly from the family Aristeidae.The crustacean larva Cerataspis monstrosa (image from Bracken-Grissom et al. 2012)Through a combination of skill and luck, Bracken-Grissom et al. were able to resolve the adult identity of C. monstrosa. The luck involved getting their hands on a specimen of the larva that was suitable for DNA analysis. Almost all we know about C. monstrosa comes from examining specimens in the gut contents of its predators, like skipjack tuna. But, Bracken-Grissom et al. unexpectedly obtained a single specimen from a trawl at a depth of 420 meters in the Gulf of Mexico.Bracken-Grissom et al. collected DNA sequence data from the specimen and compared it to sequences of crustaceans available from a database of genetic sequences. Because C. monstrosa had been liked with Penaeoid shrimp in the family Aristeidae, they concentrated their analysis within those taxonomic groups. And they hit pay dirt. The DNA from the C. monstrosa specimen was a near perfect match with a deep-sea Aristeid shrimp Plesiopenaeus armatus.The Aristeid shrimp Plesiopenaeus armatus (image from Bracken-Grissom et al. 2012)Plesiopenaeus armatus has a similar geographic distribution to C. monstrosa, but it is known from deeper water. The contrast between the larval habitat and  adult habitat is not unusual for organisms with complex life histories. Indeed, many complex life histories involve much more dramatic habitat shifts. However, the transition from mid-water pelagic larvae to abyssal adults is not known in many species.The findings of Bracken-Grissom et al. have implications for the other species of Cerataspis larvae that haven't been linked to their adult form. They suggest that C. petiti is the larva of the only other known species in the genus Plesiopenaeus, P. coruscans. Further they suggest that Cerataspides longiremus is the laval stage of a closely related Aristeid shrimp, possibly an unidentified representative of the same genus.Bracken-Grissom HD, Felder DL, Vollmer NL, Martin JW, & Crandall KA (2012). Phylogenetics links monster larva to deep-sea shrimp Ecology and Evolution DOI: 10.1002/ece3.347... Read more »

Bracken-Grissom HD, Felder DL, Vollmer NL, Martin JW, & Crandall KA. (2012) Phylogenetics links monster larva to deep-sea shrimp. Ecology and Evolution. DOI: 10.1002/ece3.347  

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