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Warmer, lower-oxygen oceans will shift marine habitats

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Rock crab habitats are predicted to shift away from warm temperatures at the equator and toward shallower, more oxygenated water.
Credit: J. MacCausland / U.S. Geological Survey

Modern mountain climbers typically carry tanks of oxygen to help them reach the summit. It’s the combination of physical exertion and lack of oxygen at high altitudes that creates one of the biggest challenges for mountaineers.

University of Washington researchers and collaborators have found that the same principle will apply to marine species under global warming. The warmer water temperatures will speed up the animals’ metabolic need for oxygen, as also happens during exercise, but the warmer water will hold less of the oxygen needed to fuel their bodies, similar to what happens at high altitudes.

The study, published June 5 in Science, finds that these changes will act together to push marine animals away from the equator. About two thirds of the respiratory stress due to climate change is caused by warmer temperatures, while the rest is because warmer water holds less dissolved gases.

“If your metabolism goes up, you need more food and you need more oxygen,” said lead author Curtis Deutsch, a UW associate professor of oceanography. “This means that aquatic animals could become oxygen-starved in the warmer future, even if oxygen doesn’t change. We know that oxygen levels in the ocean are going down now and will decrease more with climate warming.”

The study centered on four Atlantic Ocean species whose temperature and oxygen requirements are well known from lab tests: Atlantic cod that live in the open ocean; Atlantic rock crab that live in coastal waters; sharp snout seabream that live in the subtropical Atlantic and Mediterranean; and common eelpout, a bottom-dwelling fish that lives in shallow waters in high northern latitudes.

Deutsch used climate models to see how the projected temperature and oxygen levels by 2100 due to climate change would affect these four species’ ability to meet their future energy needs. If current emissions continue, the near-surface ocean is projected to warm by several degrees Celsius by the end of this century. Seawater at that temperature would hold 5-10 percent less oxygen than it does now.

Results show future rock crab habitat would be restricted to shallower water, hugging the more oxygenated surface. For all four species, the equator-ward part of the range would become uninhabitable because peak oxygen demand would become greater than the supply. Viable habitats would shift away from the equator, displacing from 14 percent to 26 percent of the current ranges.

The four animals were chosen because the effects of oxygen and temperature on their metabolism are well known, and because they live in diverse habitats. The authors believe the results are relevant for all marine species that rely on aquatic oxygen for an energy source.

“The Atlantic Ocean is relatively well oxygenated,” Deutsch said. “If there’s oxygen restriction in the Atlantic Ocean marine habitat, then it should be everywhere.”

Climate models predict that the northern Pacific Ocean’s relatively low oxygen levels will decline even further, making it the most vulnerable part of the ocean to habitat loss.

“For aquatic animals that are breathing water, warming temperatures create a real problem of limited oxygen supply versus elevated demand,” said co-author Raymond Huey, a UW professor of biology who has studied metabolism in land animals and in human mountain climbers.

“This simple metabolic index seems to correlate with the current distributions of marine organisms,” he said, “and that means that it gives you the power to predict how range limits are going to shift with warming.”

Previously, marine scientists thought about oxygen more in terms of extreme events that could cause regional die-offs of marine animals, also known as dead zones.

“We found that oxygen is also a day-to-day restriction on where species will live, outside of those extreme events,” Deutsch said. “Ranges will shift for other reasons, too, but I think the effect we’re describing will be part of the mix of what’s pushing species around in the future.”

Source: University of Washington

Originally published here: www.sciencedaily.com/releases/2015/06/150604162455.htm

 

Posted June 9th, 2015.

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Genetic analysis of the American eel helps explain its decline

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American Eels of the upper St. Lawrence grow slowly but attain larger sizes (top) compared with eels in coastal areas (bottom).
Credit: Guy Verreault/Current Biology 2015

The American eel has been a concern for the U.S. Fish and Wildlife Service since 2007, when it was first considered for, but failed to receive, Endangered Species Act protection. The numbers of these slender, slimy, ancient fish in freshwater areas have been decreasing rapidly due to dams, pollution, and overfishing, but scientists have been puzzled as to why the fish can’t recolonize. Now, a new look at eel genetics published on May 28 in Current Biology finds that there are differences between eels that feed in freshwater and eels that feed in brackish environments that were previously thought to be genetically interchangeable.

Both freshwater and brackish American eels are the same species, but they vary in size and have very different growth rates and life spans. Once a year, sexually mature eels from both groups migrate thousands of miles to spawn in the Sargasso Sea (located in the North Atlantic Ocean east of Bermuda). The offspring are carried off by the current to their new homes. It’s been thought that young American eels can detect whether they’ve ended up in brackish or freshwater habitats and acclimate accordingly. But this new study suggests that eels are predisposed to survive in these environments, depending on what genes they inherited.

“People have considered these differences in growth and age to be 100 percent due to phenotypic plasticity, independent of the genotype,” says lead author Scott Pavey, a postdoctoral fellow at the Integrated Biology Institute of Laval University in Quebec, Canada. “But what we found is that genes affect whether an eel can survive freshwater or brackish environments.” This helps explain why some conservation efforts to preserve the freshwater eel haven’t been successful, as more plentiful brackish eels cannot easily change their traits to survive in freshwater environments.

Pavey, in collaboration with ecologist Louis Bernatchez and colleagues, used new sequencing technologies to screen the eel genome in 45,000 places. The analysis identified 99 genes that differ between freshwater and brackish eels, including those associated with growth rate, heart development, and smell. It’s unknown whether this type of genetic differentiation exists in other, non-eel marine species with high levels of phenotypic plasticity.

The question remains, though, as to why eels would have such a strange approach to survival. The fish is considered evolutionarily ancient, so they must be doing something right. “It’s a different strategy, a kind of hedging your bets,” speculates Pavey. His team is now working to publish and release the entire genome of the eel. This will provide an important tool for other researchers to conduct similar studies on different aspects of eel ecology.

Source: Cell Press

Originally published here: www.sciencedaily.com/releases/2015/05/150528124204.htm

Posted May 29th, 2015.

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Iconic Indian fish on the brink of extinction

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Humpback Mahseer.

Credit: Bournemouth University

The legendary humpback Mahseer, one of the world’s most iconic freshwater fish, is on the brink of extinction according to scientists from Bournemouth University in the UK and St. Albert’s College in Kochi, India.

Ever since the publication of HS Thomas’s A Rod in India in 1873, this giant member of the carp family has been known to anglers around the globe as ‘one of the largest and hardest fighting freshwater fish in the world’. With its distribution having always been limited to South India’s River Cauvery basin, this fish is now believed to be so endangered it may be extinct in the wild within a generation.

Adrian Pinder of Bournemouth University and Dr Rajeev Raghavan of St. Albert’s College have been studying the ecology, taxonomy and conservation status of 17 species of mahseer which populate rivers throughout south and southeast Asia since 2010. Four of these species are already listed as ‘Endangered’ on the IUCN [International Union for Conservation of Nature] Red List. Along with co-author Dr Robert Britton, the paper, published in the international research journal Endangered Species Research, clearly demonstrates that the endemic humpbacked Mahseer is now of the brink of extinction having been replaced by non-native relatives (blue-finned Mahseer) which have been artificially bred and introduced to the river in the name of species conservation.

The paper acknowledges that many pressures are placed upon the fish of India’s rivers, including pollution; poaching (using dynamite and poisons); sand and gravel extraction; low river flows due to abstraction; and India’s continuing thirst for electricity, which has resulted in dozens of hydro-electric which restrict the ability of fish to migrate to their spawning grounds.

Against this backdrop of threats, this research suggests that the introduction of non-native Mahseer has acted as the catalyst which has had a catastrophic effect on the numbers of endemic Mahseer remaining in the River Cauvery and its tributaries.

Adrian Pinder said, “This research all stems from my interest as an angler, when as a boy I had read about this great fish. In 2010 I made my first trip the River Cauvery, where I realised the fish I was catching did not match the appearance of the iconic specimens I’d seen in historic photos.

“On returning to the UK, I interrogated the scientific literature and made contact with Dr Rajeev Raghavan based at St Albert’s College Kochi, to ask his opinion. Comparing photographs over the internet opened a can of worms and confirmed that very little was known about all of the Mahseer species found throughout south and south East Asia.

“As large monsoonal rivers are extremely difficult to survey, and angling was banned in all protected areas in India in 2012, I started to look for alternative data sources and discovered that the Galibore Fishing Camp [one of three former angling camps in the Karnataka jungle] had kept detailed angler catch records. This not only allowed us to analyse the temporal trends in population size over the previous 15 years but also form a detailed understanding of how the type and species of Mahseer had changed over time.”

In 2012 Adrian Pinder and Dr Raghavan set up the Mahseer Trust, an NGO working to protect Mahseer and its habitats. The Trust is now working with national and international stakeholders to educate and promote better informed fisheries management practices and to save the humpback Mahseer from extinction.

Adrian Pinder concluded, “The blue-finned Mahseer, is not native to the River Cauvery, yet our studies over the last two years have shown that they are now one of the most abundant fish in the river. Without a doubt, their success has been at the expense of the humpbacked Mahseer that historically occurred throughout the entire river catchment. Despite the positive intention of conservationists, this is clearly a conservation programme which has backfired. The state of confusion surrounding Mahseer taxonomy means the humpback Mahseer currently lacks a valid scientific name and could potentially go extinct before being named!”

“My current priority is on sourcing specimens of the endemic humpbacked Mahseer. If we are not already too late, obtaining DNA from this animal will allow us to name the fish and, based on our data, get it classified as ‘Critically endangered’ on the IUCN Red List. When you consider that the iconic Giant panda and tiger are classified as ‘endangered’ this puts things in context and demonstrates the urgency to act in sourcing native fish for culturing in local hatcheries.”

Source: Bournemouth University

Originally published here: www.sciencedaily.com/releases/2015/05/150514085703.htm

Posted May 26th, 2015.

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Clever fish around the coast of Mallorca Island avoid fishing lines

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A clever painted comber in its natural habitat at the coast of Mallorca.

Credit: Josep Alós

To avoid overfishing and aid in sustainable exploitation, the status of the fish stocks has to be monitored regularly. In many cases stock assessment is based on fishery-dependent data generated from fish markets or creel surveys. The assumption is: the lower the catches in a certain unit of time, the smaller the stock of fish should be. The scientists Dr. Josep Alós and Prof. Dr. Robert Arlinghaus from the German Leibniz-Institute of Freshwater Ecology and Inland Fisheries and the Humboldt-Universität zu Berlin have now shown that some fish species show enhanced gear-avoidance behavior in regions with high angling intensity compared to fish exposed to low levels of exploitation near marine protected areas. The consequence is the impression that there are less fish in the sea, which does not necessarily agree with underwater reality.

The coast of the Spanish Island Mallorca is a holiday paradise for sun worshippers and for those loving water sports. But few are aware of the exiting phenomena that happen below the water surface. Here, a competition between increasingly clever fishes and the catch-addicted fishers takes place. Within a project funded by the European Union, the Spanish scientist Josep Alós and the German-Spanish scientist Robert Arlinghaus from the German Leibniz-Institute of Freshwater Ecology and Inland Fisheries and the Humboldt-Universität zu Berlin have investigated the fish populations at the coast of Mallorca using novel mathematical models and monitoring methods . Their research aims at understanding the behavior of fish in response to recreational fisheries. Based on standardized angling catch methods in a study from 2013 the scientists concluded that marine protected areas host higher fish quantities and bigger fishes than sites with a high exploitation pressure. A follow-up study now released in the Canadian Journal of Aquatic Sciences, which used underwater video analysis in addition to angling as a method to quantify the fish stock, puts these former results into doubt. The reason for this: clever fishes that escape the pursuit of the anglers without a corresponding decline in fish stock levels.

More anglers means less painted comber on the hook

The research team investigated two fish species popular among recreational anglers along the Mediterranean Sea. Both have the same size and the same habitat but differ in their eating habits. The painted comber (Serranus scriba) show a carnivorous foraging mode and feeds on fish and small crustaceans while the annular sea bream (Diplodus annularis) lives on mobile algae and bivalves. The sea bream can afford to carefully examine the potential prey and takes its time moving around the baits, inspecting them and is generally less vulnerable to capture in comparison with the comber. By contrast, the comber evolved a carnivorous life-style: too much hesitation and the mobile prey is gone. As a result of this, the painted comber is much more aggressive towards baits than the annular sea bream in their natural habitats where fishing pressure is low, which makes the comber much more vulnerable to be harvested by the anglers.

The recent study by the researchers has now shown a starkly different behavior in sites where the fishing pressures is high. The researchers studied the behavioral responses towards baits in 54 different locations with the same habitat characteristics but different angling pressures. An autonomous underwater video recording was used to measure the behavior of the fish when they were exposed to baited hooks.

The researchers were amazed when finding a strong correlation between high fishing intensity and hook-avoidance behavior of painted comber: this species had starkly changed the behavior from aggressively attacking the baited hooks in the natural environments with low fishing pressure to being shy in exploited sites where they were able to recognize the fishing gear and avoid hooking. No such response was detected in the sea bream. The explanation may involve both genetic change towards increased shyness and learning to avoid future capture.

Less fish on the hooks does not necessarily mean less fish in the sea

Although the catch rates of comber in areas with high fishing intensity were half of those in low exploited and marine protected areas both sites showed similar fish densities as recorded by underwater video. Therefore, the benefits of marine protected areas previously determined by the same authors in 2013 were not supported by underwater video footage now. “These results suggest that recreational angling may contribute to patterns of hyper depletion in catch rates without a corresponding change in the fish population where catch rates declines stronger than the abundance of fishes,” the first author of the study, Josep Alós, comments. And further: “Reports on the dramatic decline of fish populations in the ocean which were only based on fishery-dependent data, for example data from the long-line fishery of tuna, cod or swordfish, could also have their cause in enhanced gear-avoidance behavior of those fishes. We have to rethink our monitoring of fish stocks and take the behavioral changes into account. Maybe some areas with high fishing intensity host more fish than we believe,” concludes study leader Robert Arlinghaus.

Story Source: Forschungsverbund Berlin e.V. (FVB)

Originally published here: www.sciencedaily.com/releases/2015/05/150520083129.htm

Posted May 20th, 2015.

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Deadly Sponges Snuffing-Out Coral Colonies

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Brain coral (Diploria labyrinthiformis) overgrown and smothered by the lavender branching sponge Aplysina cauliformis.

Joseph Pawlik, UNCW

It sounds like the plot of a B-movie, but researchers have determined that sponges in over-fished areas are using deadly tactics — such as smothering and toxic mucus — to kill coral colonies so that the sponges can grow on what’s left: skeletons.

The discovery shows how disruption of even just a few members of an ecosystem — in this case, tasty fish — can hurt many other organisms that live in the same area.

The problem, highlighted in the latest issue of the journal PeerJ, is particularly evident at Caribbean coral reefs, where the combined effects of warming seawater temperatures, storms, and diseases have already decimated populations of corals.

While coral looks sort of like an undersea plant, groupings actually consist of tiny marine creatures that live together within compact colonies. They usually grow slowly. Sponges, on the other hand, grow either quickly or more slowly, depending on the species.

“If the goal is to save the corals that build Caribbean reefs, we have to protect the angelfishes and parrotfishes that eat sponges,” lead author Tse-Lynn Loh, now a Postdoctoral Research Associate at the Haerther Center for Conservation and Research at Chicago’s Shedd Aquarium, said in a press release.

Loh and colleagues surveyed reefs from 12 countries across the Caribbean. The scientists compared 25 sites where fish abundance is very low (because of decades of intensive fish trapping) with 44 sites where fishes are plentiful (because they’ve been protected from fishermen).

Both fast and slow-growing sponges tended to dominate coral colonies at overfished sites, adversely impacting at least 25 percent of them. The damage was more than double the incidence of this seen at less-fished reefs. At the latter, angelfishes and parrotfishes munched on the sponges, helping to keep their dominant ways in check.

Even when the fish were around, slower-growing sponges still made a dent in coral colonies, since these sponges can unleash their arsenal of “weapons” that allow them to compete aggressively for reef real estate. In addition to the smothering tactics and toxic mucus, the sponges can kill coral by releasing other toxins and by shading out light.

In past studies, seaweed was also found to hurt coral, but the new research led to the surprising discovery that seaweeds were more abundant on reefs with greater numbers of fish. The outcome is contrary to the conventional wisdom that fishes eat seaweeds and keep them in check. It now looks like the relationship between seaweeds and fishes is more complicated than previously imagined.

Conservationists in earlier years based some of their claims about needed regulation of fishing at reefs on the idea that fish kept damaging seaweed under control. Now, there is convincing evidence that sponges, and perhaps not so much seaweed, are heavily impacted by over-fishing, which sets the stage for the sponges to kill and take over coral reefs.

“Caribbean nations can now base their fishing policy decisions on the clear connection between overfishing and sponge-smothered corals,” said co-author Joseph Pawlik of the University of North Carolina at Wilmington. “Coral conservation requires a healthy population of reef fishes.”

Author: Jennifer Viegas

Originally published here: http://news.discovery.com/earth/oceans/deadly-sponges-are-snuffing-out-coral-colonies-150427.htm

Posted May 18th, 2015.

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