Temporal variation in body composition and lipid storage of the overwintering, subarctic copepod Neocalanus plumchrus in the Strait of Georgia, British Columbia (Canada)

Neocalanus plumchrus (Marukawa) was sampled between October 1996 and August 1997 in the upper 400 m of the water column in Strait of Georgia (49 degre es 15' N, 123 degrees 45' W), a large, partly enclosed basin in British Col umbia, Canada. The overwintering vertical stage distribution of N, plumchru s is described together with the temporal variations in total body length, dry weight, Lipid and body composition in copepodite stage V (CV) and adult females. Adult males and females were found at depths of less than 200 m f rom January to March. Regressions of total body length to total dry weight showed significant correlations for CVs and females. Carbon and nitrogen is otopic analysis (delta(15)N and delta(13)C) indicated no temporal increase, suggesting a lack of feeding in CVs (October to December) and females (Jan uary to March) at depth and a dependency on stored Lipid reserves accumulat ed during times of high primary production in the euphotic zone. Total Lipi d content per individual copepod showed significant decreases from 0.5 to 0 .2 mg during the time of adult female gonadal development between January a nd February. A decrease in total dry mass per copepod from 0.9 to 0.4 mg al so occurred during this time period. Lipid composition showed preferential retention of long-chained fatty acids until the onset of egg release in Mar ch. Significant decreases in carbon and nitrogen from January to February a nd, to a lesser extent, between February and March were observed, correspon ding to periods of gonad maturation and egg release, respectively. Signific ant increase in nitrogen content suggests the possibility of bacterial inge stion by late moulting CVs. The significant decrease in C:N ratio, from 8.7 to 4.1, suggests a depletion of lipid reserves and resultant reliance on p roteins as an energy source for egg release. Variations in organic content verify that the CVs remain in a state of dormancy in which minimal lipid re serves are depleted, while the onset of maturation and reproduction is the major energy consumer.