A Seasonal Survey of the Lipids in Calanus helgolandicus Claus from the English Channel

198

180

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.

Section: Fecunditymentioning

confidence: 99%

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

Pond¹,

Harris²,

Head³

et al. 1996

198

180

“…Tande (1982) concluded that the source of materials and energy for sexual differentiation, molting and the first stages of gonad maturation is the female's lipid reserves, but that the final stages of oogenesis, in which large quantities of yolk are accreted, require materials derived from feeding on sufficiently high phytoplankton concentrations. However, it has also been proposed that lipid reserves are sufficient to sustain considerable egg production without an external food supply (Gatten et al 1979(Gatten et al , 1980, which may account for observations of spawning in C. finmarchicus before the spring bloom. Diel & Tande (1992) suggested that there is a direct relationship between the level of lipid reserves at the initiation of gonadal development and the stage of oocyte maturation achieved at the time of the spring bloom.…”

Section: Introductionmentioning

confidence: 99%

Reproduction of the planktonic copepod Calanus finmarchicus in the Lower St. Lawrence Estuary: relation to the cycle of phytoplankton production and evidence for a Calanus pump

Plourde¹,

Runge²

1993

152

Due to the dynamic physical environment of the Lower St. Lawrence Estuary, the spring phytoplankton bloom in the Laurentian Channel occurs late in the season, typically in mid-June, but the high phytoplankton biomass is sustained throughout the summer months. In this study, relationships between the phytoplankton production cycle, water temperature, and the reproductive cycle of Calanus finmarchicus Gunnerus, a predominant planktonic copepod in the Lower Estuary, were investigated during spring-summer 1991. Field observations showed that the final stages of oocyte maturation in C. finmarchicus females did not begin until the onset of the spring phytoplankton bloom in midJune. High egg production rates, as estimated by the number of eggs released by females incubated immediately after capture, commenced 1 wk later and persisted until late August. Egg production rates were significantly correlated with an index of gonadal maturity in females and were consistent with a rectilinear or curvilinear relationship with chlorophyll a standing stock. Laboratory experiments showed that: (1) in presence of food (the diatom Thalassiosira weissfloggii), maturation of oocytes would proceed and females could spawn eggs at least 2 mo before the spring bloom; (2) without food, the oocytes did not develop past immature stages, except in a small minority of the population; and (3) colder temperatures in early spring would prolong the lag between the onset of the spring bloom and the start of egg production by less than 4 d. Combined with concurrent microscopic measurements of oil sac volume, the results do not rule out the possibhty that lipid reserves were used to support the early stages of oogenesis, but do show that the majority of females did not use lipid reserves for vitellogenesis prior to the spring phytoplankton bloom. It is suggested that the Lower St. Lawrence Estuary is an important region of C. finmarchicus production in summer which, because of the residual surface circulation, may act as a Calanus 'pump' to influence levels of zooplankton biomass in the Gulf of St. Lawrence and on the shelf off Nova Scotia.

“…lb). Gatten et al (1979) concluded that fluctuations in phytoplankton lipid did not explaln the seasonal fluctuations of lipid in C. helgolandicus. Deevey (1960Deevey ( , 1964 investigated the relative effects of temperature and phytoplankton concentration on the seasonal variations of cephalothorax length of marine copepods from various geographical areas.…”

Section: Discussionmentioning

confidence: 99%

“…A seasonal survey of body size of Calanus helgolandicus (Gatten et al, 1979) showed dry weight to be correlated with total lipid and nitrogen for copepodite stage V and males, but only with nitrogen for females. The seasonal fluctuations of total lipid exhibited the same seasonal pattern as fluctuations in dry weight of Calanus from the English Channel (Bogorov, 1934 ) and from the Celtic Sea (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…(e.g. Rees, 1949;Jaschnov, 1955;Brodsky, 1959;Matthews, 1967) there has been only one seasonal survey of body size of Calanus helgolandicus (Claus) (Gatten et al, 1979); this dealt primarily with total lipid and lipid classes, and reported equations relating dry weight, carbon and nitrogen to total lipid for copepodite stage V, male and female C. helgolandicus from the English Channel, but did not report seasonal changes in dry weight.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Seasonal variations in length, dry weight, carbon and nitrogen of Calanus helgolandicus from the Celtic Sea

Bottrell¹,

Robins²

1984

Seasonal fluctuations in mean dry weight of the copepod Calanus helgolandicus were large and contrasted markedly with the small seasonal fluctuations of cephalothorax length. Dry weight was related linearly to cephalothorax length on logarithmic axes by a series of regression equations which were significantly different for each of 8 cruises. Carbon and nitrogen were likewise linearly related to dry weight on logarithmic axes and followed the seasonal fluctuations in dry weight. Dry weight and cephalothorax length showed little or no correlation with food concentration, ingestion rate, population numbers, population biomass or temperature. However, seasonal changes in dry weight could be explained in terms of Vidal's (1980a, b: Mar. Biol. 56: 111-134; 135-146) laboratory studies which relate growth rate and development time to body size, food concentration and temperature.