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January 2011 Issue

Scientists Question Common Indicators of Fisheries Health
The most widely adopted measure for assessing the state of the world's oceans and fisheries led to inaccurate conclusions in nearly half the ecosystems where it was applied, according to an international team led by a fisheries scientist at the University of Washington (UW). Their findings were published in a November issue of the journal Nature.

"Applied to individual ecosystems, it's like flipping a coin: Half the time you get the right answer, and half the time you get the wrong answer," said Trevor Branch, a UW assistant professor of aquatic and fishery sciences and the paper's first author.

Over the last decade, the prevailing means of measuring the health of world fisheries has been to rely on trends in the trophic levels of fish that are caught. The analysis in the recent paper, however, reveals weaknesses in this assessment of ecosystem health.

"This is important because that measure is the most widely adopted indicator by which to determine the overall health of marine ecosystems," Branch said.

An example of the problem with the measure is found in the Gulf of Thailand, where the average trophic level of what is being caught is rising, which should indicate improving ecosystem health, according to proponents of that measure. Instead, it turns out that populations of fish at all levels have declined tenfold in the gulf since the 1950s because of overharvesting.

"The measure only declines if fisheries aimed for top predators first, but for the Gulf of Thailand the measure fails because fisheries first targeted mussels and shrimps near the bottom of the food web before shifting to predators higher up in the food web," Branch said.

Including the Gulf of Thailand, Branch found that changes in the average trophic levels of what was being caught and what was found when fish populations were surveyed differed in 13 of the 29 trawl surveys from 14 ecosystems.

Branch and his co-authors are the first to combine so many trawl surveys for analysis. The data came from efforts started three years ago by fisheries scientists and ecologists gathered at University of California, Santa Barbara's National Center for Ecological Analysis and Synthesis (NCEAS). They consolidated global catch data, stock assessments, trawl surveys, small-scale fishery data and modeling results.

The study paints a different picture from previous catch data and has revealed another major finding: On a global scale, humans do not appear to be fishing down the food web.

The new data also reveal that, following declines in the 1970s in the average trophic levels of caught fish, catches at all trophic levels have generally gone up since the mid-1980s, meaning that averaging the trophic levels tells very little about if overfishing is occurring and to what extent. For more information, visit www.eurekalert.org.

Scientists Discover Microbial World in Deep Ocean Crust
The first study to explore biological activity in the deepest layer of ocean crust has found bacteria with a remarkable range of capabilities, including eating hydrocarbons and fixing carbon.

The research, published in the journal PLoS ONE, shows that a significant number and amount of bacterial forms are present in this deep-ocean crust, even in temperatures near the boiling point of water.

"This is a new ecosystem that almost no one has ever explored," said Martin Fisk, a professor in the College of Oceanic and Atmospheric Sciences at Oregon State University. "We expected some bacterial forms, but the long list of biological functions that are taking place so deep beneath the Earth is surprising."

At a site in the Atlantic Ocean near the Atlantis Massif undersea mountain, core samples were obtained from gabbro rock formations that were closer to the surface than usual because they had been uplifted and exposed by faulting. This allowed the researchers to investigate for the first time the microbiology of this deep rock.

The research expedition drilled more than 4,600 feet into this formation, into rock that was very deep and very old, and found a wide range of biological activity. Microbes were degrading hydrocarbons, some appeared to be capable of oxidizing methane, and there were genes active in the process of fixing both nitrogen and carbon.

The findings are of interest, in part, because little is known about the role the deep ocean crust may play in carbon storage and fixation. They may lend credence to one concept for reducing carbon emissions in the atmosphere—pumping carbon dioxide into deep subsurface layers where it might be sequestered permanently.

Microbial processes in this subseafloor environment "have the potential to significantly influence the biogeochemistry of the ocean and the atmosphere," the researchers wrote. For more information, visit www.plosone.org.

Faster Water Flow Linked to Greater Invertebrate Diversity
One of the biggest factors promoting the diversity of coastal ocean life is how fast water flows, according to new research by ecologists at Brown University. Experiments and observation in Palau, Alaska and Maine showed that the faster the flow, the greater the number of invertebrate species that live on rocks under the water.

The findings, recently published in the journal Ecology Letters, could help improve management of delicate and complex coastal ecosystems, said James Palardy, a former Brown doctoral student and the paper's lead author. Finding the fastest water could point scientists to areas where diversity is likely greatest—and perhaps especially worthy of protection—and to zones where invasive species could establish their first beachheads.

"It totally blew us away that we got almost identical results in two marine regions of the world separated by 4,000 miles with completely different regional diversities and no species shared in common," said Jon Witman, professor of ecology and environmental biology and Palardy's co-author on the paper. "It's a wake-up call saying that water flow is a really strong predictor of how many species are present in a particular area of the ocean."

The reason why faster flow seems to promote diversity, Witman said, is that it allows for the larvae of rock-dwelling invertebrates, such as barnacles, sea squirts, corals and sponges, to spread farther. For more information, visit http://onlinelibrary.wiley.com.


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