Seaweek!

Seaweek is coming up fast. It's organised by the Marine Education Society of Australia and running from the 2nd to the 10th of March. I've been invited to participate in a day of activities at Rickets Point Marine Sanctuary on the 7th. I'll be talking to primary and high school students about marine introduced species. The day will bring together marine experts from MESA, Parks Victoria, Melbourne Aquarium, Monash University, the Earth Watch Institute, the Ocean Ark Alliance, the Gould League, Marine Care Ricketts Point, Pelican Expeditions, Nautilus Educational and the Australian Youth Climate Coalition (and me, who is not from any of those organisations).

The theme for Seaweek 13 is ‘Sustainable Seas’. The theme provides a focus for students in schools and for communities to inform and inspire them about the diversity of our marine and coastal environments and how, through good management and individual action, we can all contribute towards the sustainability of these environments.

Aims

• Highlight the sustainable management of Australia’s marine environment;
• Identify factors that threaten the sustainability of marine and coastal ecosystems;
• Facilitate the communication of sustainable marine management projects to the education community;
• Initiate interest and actions for supporting sustainable marine management that help us learn more about and contribute towards the sustainability of our marine and coastal environments; and
• Provide schools with educational resources available on the MESA website for school’s classroom based activities.

Find out more about Seaweek here.

The anti-science, anti-environment Victorian Government

The Victorian Government is at it again. They've allowed a "scientific trial" of cattle grazing in Victoria's Alpine National Park against all scientific advice (why conduct a trial when you've already got a robust answer?). They've provided funding to find the Victorian panther, the Australian version of Bigfoot. They've decided to allow private tourist developments in National Parks, when the best thing that National Parks do for the environment is to limit access to people. Now they've decided to redraw the boundaries of the Alpine National Park to allow business at the Falls Creek ski resort to expand. You'd probably be surprised to know that the Victorian Premier is a former director of a real estate company...

Flying squid really fly

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).

*** Correction - While flying fish have been documented to travel over 400 meters in a single jump, their typical jumps are about 50 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

A stepping stone of rotting wood

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.

A hypothetical succession of animals on submerged wood in the deep sea over a year. Initially wood-boring bivalves move in, followed by predators and detritus feeders (e.g. polychaetes and sipunculids). The respiration of the colonisers creates anoxic niches that allow the chemosynthetic mussels to move in (diagram from Bienhold et al. 2013).

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

Attack of the jellyfish swarm

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.

 

Condon, R., Duarte, C., Pitt, K., Robinson, K., Lucas, C., Sutherland, K., Mianzan, H., Bogeberg, M., Purcell, J., Decker, M., Uye, S., Madin, L., Brodeur, R., Haddock, S., Malej, A., Parry, G., Eriksen, E., Quinones, J., Acha, M., Harvey, M., Arthur, J., & Graham, W. (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

Evolution, climate change and coral

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., Muthiga, N., Bradbury, R., Dubi, A., & Hatziolos, M. (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

The aquatic ape hypothesis is rubbish

I mentioned the aquatic ape hypothesis in a recent post on wrinkly fingers improving grip when handling submerged objects. As if on cue, I then received this email:

Dear colleague,

Humans are very different from other primates, and many evolutionary hypotheses have been proposed to explain this remarkable fact. Is there scientific consensus on which of those hypotheses are most substantiated? If not, do opinions differ among researchers with different backgrounds?

Please help to establish the state of the art by answering a survey on this topic. You receive this invitation because you have recently published in a scientific journal covering paleoanthropology, paleontology or (human) biology, which indicates that you have expertise in a relevant field. 

A link to the survey is provided in the end of this message. 

Your responses will be anonymous. If you wish to be informed about the outcome of the survey, you can add your e-mail address to the mailing list after having completed the main survey. The present mailing list will only be used to send the invitations. My apologies if you receive this message more than once. 

Thank you for participating! 

Yours sincerely,
[Name and contact details redacted]

The first couple of pages were reasonable enough, containing questions on a variety of theories for how human traits evolved. Which is as you would expect from a survey that is trying to "establish the state of the art" on human evolution. But, the survey then degenerated into asking questions solely about the aquatic ape hypothesis. A quick bit of googling later and I find that the sender is a proponent of the hypothesis.

I am baffled by the persistence of the aquatic ape hypothesis. It has received almost no attention in the scientific literature because on more then superficial examination it fails to provide a parsimonious explanation of human evolution. In fact, to accept the aquatic ape hypothesis you would not only have to find its scant evidence convincing, but assiduously ignore the contradictory evidence.

Take the claim that bipedalism evolved in our ancestors as an adaptation to an aquatic conditions, from a situation much like how gorillas and chimpanzees walk when wading. It's a fine and very plausible claim, but it doesn't fit with what we know from the fossil record. All of the putative human ancestors, such as Australopithecus and Orrorin, retain features that show they were still capable tree climbers when they first started walking upright. For the aquatic ape hypothesis to be true, they would have had to come to the ground first then moved to water before becoming bipedal. There is nothing to support this in the fossil record.

Another problem that the human fossil record poses for aquatic ape proponents is that several of the traits claimed to be adaptations to aquatic conditions appeared separately. For instance, it's claimed that only a seafood diet rich in omega-3 fatty acids could support the expansion of brain size in the human lineage. Brain expansion, however, came after bipedal locomotion, indicating that the association with water had to have lasted several million years for both of these claims to be true.

Hairlessness is one of the traits that is central to the aquatic ape hypothesis. Again it is a fine and plausible claim to make, but hairlessness is poorly associated with an aquatic lifestyle. There are some notably hairless aquatic mammals, such as whales, dolphins and walruses, but there are many more aquatic animals that retain hair. Moreover, there are some hairless mammals that are clearly not aquatic, such as naked mole rats, rhinoceros[1] and elephants. Hairlessness is clearly neither necessary for an aquatic life nor is it uniquely associated with aquatic mammals.

A feature that is far more commonly associated with aquatic mammals is that they are testicond, that is they have internal testicles (at least the males do!). In fact, I know of no aquatic mammal that is not testicond. There are some mammals that are not aquatic and are also testicond, like our friends the rhinoceros and elephant[2], but the far more common condition for terrestrial mammals is to have external testicles. So, the external testicles of human males suggests that humans are typical terrestrial mammals and not aquatic apes.

There are a whole host of other features that aquatic ape proponents cite as evidence consistent with aquatic ancestry and it would take an entire website to debunk them all (like this one). Individually, none of these traits are very compelling evidence for their hypothesis, and taken together they're a complete mish-mash. While some are highly derived features, like hairlessness, others have barely changed from the ancestral condition, like webbing between the fingers.

More parsimonious explanations for the evolution of human traits involve multiple causes, not a single cause as proposed by the aquatic ape hypothesis. The aquatic ape hypothesis is neither simple[3], nor does it fit well with the available evidence. Proponents of the aquatic ape hypothesis need to bend the evidence to fit their hypothesis and resort to special pleading to explain away the inconsistencies in their arguments. It's a textbook example of adaptationist just-so storytelling.


[1] An interesting aside is that the species of rhinoceros that is most closely associated with water is often called the hairy rhinoceros.

[2] Another interesting aside is that both the rhinoceros and elephant are thought to have aquatic ancestors. The support for this is much stronger for the elephants, which are part of a clade (the Tethytheria) who's other members are all aquatic (the extant Sirenia and the extinct Desmostylia). This may explain why they and rhinoceroses are testicond. It does not explain their hairlessness, as we know that as recently as 10,000 years ago there were a number of very hairy rhinos and elephants, indicating that the common ancestors of modern rhinos and elephants were also hairy.

[3] The transition from arboreal to terrestrial to aquatic back to terrestrial is not a simple evolutionary scenario. A simpler assumption would be that human ancestors were all terrestrial after descending from the trees.

Ed Yong is treading on my turf

Ed Yong is treading on my turf (or should that be seagrass meadow?). Worse though, is that he is doing it better than me...

I have been writing a post about the longevity of coral reefs under future climate conditions. Yesterday, Ed (I hope I can call him that) posted a piece on the future prospects of retaining coral reefs into the next century. You should go read it, but come back in a few days when I post my own piece that will look at the issues from an evolutionary perspective.

*** UPDATE *** I've published my piece.

Online nature sound archive

Cornell University has just released their full archive, the World's largest, of bird calls and other animal sounds. It comprises nearly 150,000 recordings dating back to 1929. The Cornell press release says that they are trying to make the sound recordings as accessible as possible, to the broadest audience possible. If you're interested go check it out.

A first look at the giant squid footage

A fleeting glimpse of the footage of a live giant squid in its typical deep sea habitat, captured by filmmakers in Japan. You might want to watch it with the sound off...