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

Abstract

The overwintering vertical stage distribution of N. plumchrus 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 from January to March. Regressions of total body length to total dry weight showed significant correlations for CVs and females. Carbon and nitrogen isotopic analysis ( 6 "~ and 6I3C) indicated no temporal increase, suggesting a lack of feeding in CVs (October to December) and females (January to March) at depth and a dependency on stored lipid reserves accumulated during times of high primary production in the euphotic zone. Total lipid content per individual copepod showed significant decreases from 0.5 to 0.2 mg during the time of adult female gonadal development between January and February. A decrease in total dry mass per copepod from 0.9 to 0.4 mg also occurred during this time period. Lipid composition showed preferential retention of long-chained fatty acids until the onset of egg release in March. Significant decreases in carbon and nitrogen from January to February and, to a lesser extent, between February and March were observed, corresponding to periods of gonad maturation and egg release, respectively. Significant increase in nitrogen content suggests the possibility of bacterial ingestion 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 proteins 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 reserves are depleted, while the onset of maturation and reproduction is the major energy consumer.

Seasonal and spatial dynamics of the planktonic trophic biomarkers in the Strait of Georgia (northeast Pacific) and implications for fish

“…They found that, similar to our data, Neocalanus plumchrus, E. bungii, and C marshallae generally had DHA/ EPA < 0.5, whereas DHA/EPA of P. elongata was in the range of 1-1.5. In addition, a similar nutritional value for N. plumchrus (i.e., DHA/EPA < 0.5) was found in the SoG in 1996-1997 50 . This might suggest that DHA/EPA of zooplankton in the region has not varied substantially in the last two decades and thus the nutritional value of copepod prey for juvenile salmon and herring in the SoG has been suboptimal for at least 20 years.…”

Evaluating the utility of stable isotope analyses of archived freshwater sample materials

“…Overall, the d 13 C values of ethanol preserved samples were 13 C enriched, which, together with the lower C:N ratios in preserved samples, indicate that ethanol acted as a lipid-extracting agent as also observed by Kelly et al (2006) for fish muscle. This would explain why copepods showed the greatest variability in ethanol treatments, as the lipid contents of copepods can be highly variable (Kuosa & Gyllenberg, 1989;Evanson et al, 2000). In fact, values for ethanol treated zooplankton d 13 C-control d 13 C and ethanol treated C:N-control C:N correlated significantly (Pearson r = -0.686, P = 0.005).…”

Growth and development of Calanus helgolandicus reared in the laboratory

“…It is more common to find a drop in female weight after moulting (as, in fact, also occurred with our females but only after the first 10 d, see Rey-Rassat et al 2002, this volume). This drop in female weight occurs particularly in large copepod species with lipid reserves, which build eggs from internal resources (Evanson et al 2000). Moreover, the period during which females have a positive growth must vary with species.…”