Using a combination of field samples from the Norwegian Sea and a new method for analyzing sea life populations, researchers have shown that tiny marine crustaceans called copepods use cannibalism as a mechanism to limit their population.

Traditional notions have assumed that fluctuations in marine populations can be explained mainly by physical processes. That is, if you understand ocean circulation and other physical functions affecting marine life, then you can understand how and why populations fluctuate. Other theories of marine populations are based on birth rates, including the processes of feeding and growth that lead to the production of new offspring.

Mark Ohman of Scripps Institution of Oceanography at the University of California, San Diego, and colleague Hans-Jrgen Hirche of the Alfred Wegener Institute for Polar and Marine Research in Germany, have provided evidence that there is much more to the story. Instead of birth rates, they flipped conventional notions and analyzed the death rates of copepods.

In their study, published in the August 9 edition of the journal Nature, Ohman and Hirche found that egg mortality in the copepod species Calanus finmarchicus is directly related to the abundance of females in the population.

"We found that a tenfold increase in adult egg-producing female copepods will not result in a similar increase in the number of surviving eggs," said Ohman, a professor in the Integrative Oceanography Division at Scripps. "Rather, half as many eggs will survive. We believe the reason is cannibalism and we think its a self-regulating mechanism that no one has found before in the open sea."

Copepods, tiny marine crustaceans (about four Calanus finmarchicus fit end to end on a dime), are the most numerous multicellular animals in the oceans, and possibly the most numerous on Earth. T
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Contact: Mario Aguilera or Cindy Clark
scrippsnews@ucsd.edu
858-534-3624
University of California - San Diego
8-Aug-2001