Copepods cope with climate change

Natural History, Dec, 2008 by Stephan Reebs

A small zooplankton species, the copepod Ca/anus finmarchicus, is the dietary mainstay of many economically valuable fishes in the North Atlantic Ocean. Climate change is shifting the region's cool waters northward, and some of the copepods have managed to tag along. Scientists have worried, however, that most are trapped in dangerously warming waters by vast, circular oceanic currents called gyres. Indeed, as a result, C. finmarchicus numbers have plummeted 70 percent during the past four decades, sparking fears that there may soon be too few to maintain a viable population--or food web. Now, Jim Provan and four colleagues, all at the Queen's University of Belfast in Northern Ireland, have shown that the copepods are more mobile and resilient than had been feared.

If C. finmarchicus couldn't successfully disperse, genetic differences would have cropped up among the populations living near Nova Scotia, Greenland, Iceland, and Norway. Yet after extensive sampling throughout the North Atlantic, Provan's team found no evidence of such genetic isolation. Some individuals must escape their gyres and follow the cool waters north.

Moreover, though there was little genetic variability among C. finmarchicus populations, there was a moderate amount within them. For that to happen, Provan calculated, the species would have had to maintain fairly high numbers for the past 350,000 years. Several warm spells occurred during that time, including the one that ended the last ice age 18,000 years ago. The little critters appear to be climatic survivors--but the unprecedented speed of the current warming may test their survival skills. (Proceedings of the Royal Society B)

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