Environmental and nutritional factors determining seasonal variability in the fecundity and egg viability of Calanus helgolandicus in coastal waters off Plymouth, UK

Abstract

Fecundity of the copepod Calanus helgolandicus was monitored at a coastal station in the western English Channel during January to September 1994 and varied seasonally from 3 to 33 eggs female-' d-l (mean 17 eggs female-' d-'). Particulate fatty acid levels, particularly in the <20 pm size fraction, were more highly correlated with fecundity than either chl a, particulate carbon or nitrogen. and this reflected the size and species composition of the microplankton. Diatoms, dinoflagellates and ciliates all sustained high fecundity. The mean volume of eggs produced by C. helgolandicus was inversely related to both food availability and fecundity, with increased numbers of smaller eggs produced during per~ods of high food availability. Female C helgolandicus with the highest body nitrogen and carbon produced eggs with the highest carbon and nltrogen contents, although these eggs were also smaller. Hatching viability was consistently high with a seasonal mean of 83% and both viability and the incidence of deformed nauplii were negatively correlated with the carbon and nitrogen content of females and eggs. Hatching viability was not correlated with the abundance of diatoms, but was closely correlated with the levels of 18:2(n-6) and 20:4(n-6) fatty acids in both the environment and in the eggs. Particulate concentrations of the polyunsaturated fatty acids 20:5(n-3) and 22:6(n-3), although abundant in the environment and therefore good indicators of food availability, were not correlated with either egg viability or naupliar survival. The levels of saturated and monounsaturated fatty acids in the eggs were important factors determining naupliar survival under starvation conditions. Although food availability limited fecundity, female recruitment was possibly limited by predation pressure. particularly during the late summer. This study highlights the value of seasonal and nutritional based studies in understanding variability in zooplankton fecundity.

Composition of wax esters is linked to diapause behavior of Calanus finmarchicus in a sea loch environment

“…Since only comparatively small amounts of lipid are contained within individual copepods, extraction procedures were simplified to reduce losses and minimize the introduction of contaminants into the samples (Pond and Tarling 2011). After the addition of 125 mL KCl (0.88% w : v), samples were initially whirlimixed before being centrifuged for 2 min at 400 3 g to promote phase separation.…”

“…Lipid analysis-Lipids were extracted from stage CV C. finmarchicus following Pond and Tarling (2011). Individual copepods preserved at 280uC were initially transferred to 1.1-mL tapered vials (Chromacol) containing 500 mL of chloroform : methanol (2 : 1 v : v).…”

“…A recent study of the dominant calanoid copepod in the Southern Ocean, Calanoides acutus, has suggested a critical role for the composition of the wax esters in regulating buoyancy while at depth (Pond and Tarling 2011;Pond et al in press). Analysis of the levels of unsaturation (number of double bonds) of the wax esters in CV Calanoides acutus has indicated that those copepods migrating into the deep ocean contained similarly high levels of polyunsaturated wax esters, while those from the surface were highly variable.…”

“…Wax esters derived from saturated and monounsaturated fatty acids did not exhibit these pressure effects. Thus, Pond and Tarling (2011) proposed that a combination of both the total amount and the degree of unsaturation of the wax esters would be key determinants of the depth of neutral buoyancy in diapausing copepods.…”

“…Analysis of the levels of unsaturation (number of double bonds) of the wax esters in CV Calanoides acutus has indicated that those copepods migrating into the deep ocean contained similarly high levels of polyunsaturated wax esters, while those from the surface were highly variable. Pond and Tarling (2011) analyzed Calanoides acutus wax esters using high-pressure differential scanning calorimetry, a technique that can be used to simultaneously determine the influence of temperature and pressure on the solid-liquid phase changes of lipids and other materials. It was discovered that wax esters with high levels of unsaturation (.…”