Quest for Illegal Gain at the Sea Bottom Divides Fishing Communities By karla zabludovsky

Species at top of freshwater food web can indirectly limit buildup of carbon dioxide in the atmosphere

By Janet Raloff

Web edition: February 17, 2013

In ecosystems around the world, big guys eat littler guys, who in turn eat plants and other organisms at the base of the food web. A study now finds that removing top predators in freshwater environments allows their prey to flourish — and overgraze on plants and algae. The result of the missing plant matter: a 93 percent reduction in uptake and storage of carbon dioxide.

Several research teams have explored the importance of predators in protecting organisms that store carbon, notes ecologist James Estes of the University of California, Santa Cruz, who was not involved in the new research. The new study is particularly strong, he says, because it demonstrates predators’ influence across a broad range of ecosystems. It therefore suggests “that the phenomenon may be fairly general.”

When pesticide runoff, overfishing or other human activities impact ecosystems, the first species to disappear are usually the bigger, top predators, notes freshwater ecologist John Richardson of the University of British Columbia in Vancouver and coauthor of the study, published online February 17 in Nature Geoscience. The new work shows that predator losses have effects beyond the loss of biodiversity: “We can see climate effects as well,” he says. “We start seeing a higher flux of carbon dioxide into the atmosphere.”

Study leader Trisha Atwood, then also at the University of British Columbia, and colleagues simulated three freshwater ecosystems outdoors to study the effects lower in the food web of predator loss at the top. They diverted water from streams near Vancouver into six channels they had constructed. Those channels accumulated critters and debris for about six weeks. To simulate ponds, Atwood’s team added water and sediment from ponds in Vancouver to 10 tanks, each about 2 meters across, and let them acquire organisms over 18 months. And to study the water-holding reservoirs among leaves of some plants, the ecologists went to Costa Rica and let the center well of 20 bromeliads — flowering plants found mainly in tropical regions — collect a little water and wildlife over a two-week period.

In half of the simulated ecosystems in each location, the researchers added top predators. For streams, that predator was the three-spined stickleback (Gasterosteus aculeatus), a 10-centimeter-long fish that feeds on zooplankton in stream water. Stonefly larvae served as the predator in the simulated ponds. And the researchers introduced damselfly larvae to feed on zooplankton in the bromeliads.

At the end of these accommodation periods, the researchers made daylong measurements of carbon dioxide in water. Then they compared the values for environments with and without their top predators.

Adding the top predators decreased the amount of carbon dioxide in the water by an average of 93 percent, Atwood and her colleagues report. When predators are absent, the researchers think the unchecked zooplankton aggressively feed on plants and algae in each ecosystem. Those photosynthetic organisms, had they not gotten eaten, would have used and stored carbon, removing it from the water. That in turn would have pulled more carbon dioxide from the atmosphere.

1. 
   What is the normal food web described in the beginning of the article?
   
2. 
   If the plant matter is overeaten, what happens?
   
3. 
   What are some causes of top predators disappearing?
   
4. 
   In at least 4 sentences, describe the “pond” the research team assembled and what results they found.
   

5. 
   Is there a direct link between top predators and gas levels in the ponds?
   

The Sensible Seafood program helps consumers make sustainable seafood choices in stores and restaurants. Working in partnership with Monterey Bay Aquarium and an Advisory Panel of regional seafood experts, our Sensible Seafood program provides you with a handy reference pocket guide​ that rates the most popular seafood items as green, yellow or red. Green items are best choices for seafood that is abundant, well-managed, and fished or farmed in environmentally friendly ways. Yellow items are good alternatives to consider when best choices are not available, though there may be some concerns with how they are caught or farmed. You should avoid red items, at least for now, because they are over-fished or are caught or farmed in ways that harm other marine life or the environment. Click here for more information on Monterey Bay's program.

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  How is the species population doing? – This seems like an obvious question, but in order to know if the seafood we are consuming is a good choice, we need to know about the life history of the species and if its population is abundant or disappearing. Some species easily reproduce in large numbers and grow to maturity very fast. Others, such as sharks, reproduce and mature more slowly. Understanding these factors is critical for good fisheries management. Abundant species from well managed fisheries make good seafood choices.
  
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  Where does the seafood come from? – Is the seafood from local sources, from other parts of the U.S, or imported? This is important because, like many other commodities, seafood can now be transported all over the globe. Seafood from local sources has the potential to be fresher and reduces the financial and environmental costs of long distance transport. Additionally, U.S. fisheries may be better managed than some foreign fisheries. These factors are important when considering where a seafood item might originate.
  
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  Is the seafood wild-caught, or is it farmed? – As seafood has become more popular, many species are now raised on farms, a process called aquaculture. In some cases, the wild stock of a species may be depleted, but there is a good supply from aquaculture, like catfish. In other cases, the farmed stock has been associated with problems and the wild-caught stock is the better choice, like some shrimp. Of course, most of our seafood choices still come mostly from wild-caught stocks.
  
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  How is the seafood harvested? – Are the fishing or aquaculture practices environmentally sound? To answer this question, we must understand fisheries and aquaculture techniques and how they are applied for harvesting different seafood species. Some fisheries techniques, like bottom trawling or dredging, have the potential to damage ocean bottom communities like corals. Others may have unintended catches of unwanted animals, called bycatch. Bycatch can include unwanted fishes and even sea turtles or marine mammals. Finally, poorly managed aquaculture operations can damage coastal ecosystems. Well managed fisheries and aquaculture, utilizing sound techniques to minimize bycatch and ecosystem impacts, provide the best seafood choices.
  

Buy local sustainable seafood – not only does buying local usually ensure the freshest seafood, it also helps support an important segment of the local economy. Virginia’s seafood industry is the third-largest in the country, producing vast amounts of blue crabs, scallops, clams, croaker, spot, striped bass, and oysters that are shipped all over the world. Puchase sustainable seafood in your area, where you know and understand the harvesting or growing process, to think globally and act locally.​

1. 
   What is the Sensible Seafood program?
   
2. 
   Who has the Virginia Aquarium worked with to create the Sensible Seafood booklet?
   
3. 
   What is sustainable seafood and why does it matter?
   
4. 
   How do they determine if seafood is sustainable or not?
   
5. 
   How do they want you to make sustainable choices.
   
6. 
   Look at the list, are there any surprises?
   
7. 
   Is there something you eat often that is on the avoid list?
   
8. 
   Would this be easy for you to do?