Catherine Johnson, Andrew Leising, Jeffrey Runge, Erica Head, Pierre Pepin, Stéphane Plourde, and Edward Durbin
| HTML version | PowerPoint version |
Abstract
Demographic time-series from four fixed stations in the Northwest Atlantic Ocean show variable timing of entry into and emergence from dormancy in subpopulations of the planktonic copepod Calanus finmarchicus. A proxy for timing of entry was established as the date each year when the proportion of stage CV in the subpopulation rose to half its overall climatological maximum CV proportion at that station. The proxy for timing of emergence at each station was set as the first date when adults were more than 10% of the total abundance of copepodid stages. An alternate emergence proxy date was determined by back-calculating the spawning dates of the first early copepodid stages appearing in spring, using a stage-structured, individual-based model. No single environmental cue (photoperiod, surface temperature, or average surface layer chlorophyll a concentration) consistently explained entry or emergence dates across all stations. Among hypotheses put forward to explain dormancy in Calanus species, we cannot eliminate the lipid accumulation window hypothesis for onset of dormancy or a lipid-modulated endogenous timer controlling dormancy duration. The fundamental premise of these hypotheses is that individuals can only enter dormancy if their food and temperature history allows them to accumulate sufficient lipid to endure overwintering, moult, and undergo early stages of gonad maturation.