Now, understanding sharks and their significance as top predators--and the consequences of human activity towards them--has taken on new importance through a new study by scientists in San Diego and Spain.

Jordi Bascompte and Carlos Melin of the Integrative Ecology Group, Estacin Biolgica de Doana, Consejo Superior de Investigaciones Cientficas, in Sevilla, Spain, and Enric Sala of Scripps Institution of Oceanography at the University of California, San Diego, developed an unprecedented model of a Caribbean marine ecosystem and details of its intricate predator-prey interactions. This food "web" covered 1,000 square kilometers to a depth of 100 meters and included some 250 species of marine organisms. The study, published in the April 12 edition of the Proceedings of the National Academy of Sciences, included an intricate network of more than 3,000 links between these species.

The project was one of the largest and most detailed investigations of marine food webs and the first study to integrate food web structure, dynamics and conservation.

One of the most striking products of the study is a stark picture of human impacts on marine ecosystems and the consequences of targeted fishing. In the Caribbean, overfishing of sharks triggers a domino effect of changes in abundance that carries down to several fish species and contributes to the overall degradation of the reef ecosystem. Overfishing species randomly, the study shows, is not likely to cause these cascading effects.

"It appears that ecosystems such as Caribbean coral reefs need sharks to ensure the stability of the entire system," said Sala, deputy director of the Center for Marine Biodiversity and Conservation at Scripps.

When sharks are overfished, a cascade of effects can lead to a depletion of important grazers of plant life. This is because there are fewer sharks to feed on carnivorous fish
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Contact: Mario Aguilera or Cindy Clark
scrippsnews@ucsd.edu
858-534-3624
University of California - San Diego
11-Apr-2005