Tiny crustaceans called copepods rule the world, at least when it comes to oceans and estuaries.
The most numerous multi-cellular organisms in the seas, copepods are an important link between phytoplankton and fish in marine food webs.
To understand and predict how copepods respond to environmental change, scientists need to know not only how many new copepods are born, but how many are dying, say biological oceanographers David Elliott of the University of Maryland Center for Environmental Science and the Virginia Institute of Marine Science (VIMS), and Kam Tang of VIMS.
Elliott and Tang realized there was only one way to discover the answer: find the copepods' carcasses.
Mortality of copepods and other zooplankton is often assumed to be the result of predators.
Several studies have observed, however, that many dead copepods are found in samples of seawater. "This is more indicative of non-predatory mortality," says Elliott.
But traditional sampling often ignores the live/dead "status" of the copepods, Elliott says, and little is known about how many copepod carcasses are in fact floating around in the water.
Using a newly improved staining method to help distinguish between live and dead copepods in water samples from Chesapeake Bay, Elliott and Tang observed substantial numbers of intact copepod carcasses.
An average of 12 to 30 percent of the developmental stages of the abundant coastal copepod species Acartia tonsa were dead.
They found that these were likely the result of mortality for other reasons than predators.
"Using a relatively simple staining procedure to distinguish live from dead copepods, Elliott and Tang have been able to arrive at a more accurate picture of predation versus other sources of mortality for estuarine copepod populations," says David Garrison, program director in the National Science Foundation's (NSF) Division of Ocean Sciences, which
|Contact: Cheryl Dybas|
National Science Foundation