Lipids and life strategies of Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus in late autumn, Kongsfjorden, Svalbard

Stage IV and V copepodites were the dominant forms of Calanus finmarchicus, C. glacialis and C. hyperboreus in Kongsfjorden in late September 1997. Stage IV and V copepodites of C. glacialis and C. hyperboreus were rich in lipid, largely wax esters, and were well fitted to overwinter. Stage IV copepodites of C. finmarchicus were also rich in wax esters, but stage V copepodites of C. finmarchicus were less wax ester-rich. Large size increments between stage IV and V copepodites and between stage V copepodites and females were noted in C. finmarchicus. A very large increment between stage IV and V copepodites was noted for C. glacialis but the size difference between stage V copepodites and females was very small in this species. Particularly large increments were noted between stage IV and V copepodites of C. hyperboreus and also between stage V copepodites and females of this species. The very large, wax ester-rich C. hyperboreus is well adapted to survive the most extreme variations in the Arctic, in Arctic basin waters, whereas the smaller, wax ester-rich C. glacialis is adapted to survive less extreme Arctic variations, as in Arctic shelf waters. The smallest of the three, C. finmarchicus, is best adapted to survive the more predictable waters of the North Atlantic and the Barents Sea. Accepted: 3 January 2000     

Seasonal variations in copepod size: effects of temperature, food abundance, and vertebrate predation

Seasonal dry weights of female and male Cyclops bicuspidatusthomasi, Diaptomus ashlandi and Diaptomus minutus were studiedin southeastern Lake Michigan during 1975–1981. Smallestanimals occurred during summer and early fall, and largest animalsin winter and spring, a pattern reported for other copepods.The range of weights for the species and sexes decreased fromwinter to summer, and converged in summer to a value of approximately2 µg/animal. Surface water temperature and abundancesof young-of-the-year (YOY) fish were inversely correlated withweights of males and females of the three copepod species. Standingstocks of important phytoplankton groups, especially pennatediatoms and flagellates, were positively correlated with copepodweight. Seasonal change of copepod body size appears to be morethan simply a function of temperature; seasonal predation byYOY fish may be a factor influencing sizes of adult copepods.     

Effects of temperature, salinity and sex on the basal metabolic rate of the estuarine copepod Pseudodiaptomus hessei

Respiratory responses of Pseudodiaptomus hessei measured underdifferent conditions show an exponential increase in metabolicrate with temperature, but no changes with salinity. All metabolicdemands of this species are met through consumption of microalgaeduring the closed (winter) phase, but not during the open (summer)phase of the estuary.     

The metabolism of wax ters and other lipids by the marine copepod, Calanus helgolandicus

The polyunsaturated wax esters which occur in an oil droplet in Calanus helgolandicus apparently serve as a short term reserve metabolic fuel. The lipids of the copepods were labeled by feeding them (14)C-labeled diatoms, Skeletonema costatum, after which starvation and turnover experiments were carried out. During starvation both wax esters and triglycerides are largely depleted within 72 hr, whereas cholesterol and phospholipid decreased at much slower rates.     

Egg production of the marine,planktonic copepod,Calanus pacificus Brodsky: Laboratory observations

When acclimated to a continuous, superabundant food supply and constant temperature, Calanus pacificus Brodsky females produce eggs at a weight-specific rate ranging from 0.13 · day^?1 at 8°C to 0.21 · day^?1 at 15°C. Maximum weight-specific egg production rates do not change with seasonal changes in female body size. The relationship between egg production rate and food concentration is hyperbolic, with threshold and critical concentrations that are high relative to other species for which data are available. Food concentration and temperature influence spawning frequency (i.e., the time required for oocytes to mature) much more than the number of eggs in a single spawning event (i.e., clutch size). Clutch size is significantly related to female body size.     

The effects of tidal advection and mixing on the statistical dispersion of zooplankton

Series of six repeated vertical Zooplankton hauls 5 min apart were made on a hourly basis during 7 h at an anchor station in the upper St. Lawrence Estuary, Québec. A hierarchical analysis of variance showed that hour-to-hour variations in numbers of most Zooplankton components were of greater magnitude than those found within 30 min or caused by counting errors.The increase of variance for increasing lengths of the sampling period was investigated using a 175 h time series of Zooplankton samples taken 30 min apart at the same location. The results show that the confidence interval of a single observation at the anchor station increases as the scale of the experiment approaches that of the main advective processes (semidiurnal tidal currents) after which it remains relatively stable. For a given sampling scale, the statistical dispersion of Zooplankton is not permanent but varies in time and space under the effects of tidal advection and mixing. These results show that, in tidal estuaries, advection phenomena are more easily recognizable than turbulence effects.     

Summer reproduction of the planktonic copepod Calanus sinicus in the Yellow Sea: influences of high surface temperature and cold bottom water

We have observed that Calanus sinicus retreated from neriticareas in the Yellow Sea and concentrated in the Yellow Sea ColdBottom Water (YSCBW) area in summer. To investigate the summerreproductive strategy of C. sinicus in this situation, effectsof high temperature on reproduction and hatching, as well asgeographical variation of in situ egg production rate, werestudied by onboard incubation in August 2001. Diel verticalmigration (DVM) of females was investigated within and outsidethe YSCBW, respectively. Onboard incubation at 27°C (i.e.surface temperature) resulted in lower fecundities than thatat 9.8 and 12°C (i.e. bottom temperature inside and outsidethe YSCBW) together with decreased hatching rates and increasednaupliar malformation. Egg production was more active at stationsoutside the YSCBW than inside, where chlorophyll-a concentrationwas also relatively low. Females inside the YSCBW underwentDVM although they rarely entered the surface layer, but DVMwas not observed outside the YSCBW. We conclude that surfacetemperature in summer has deleterious effects on C. sinicusegg production and hatching, and that it cannot reproduce successfullyover the whole area. Inside the YSCBW, egg production is depressedby low food availability, while females outside suffer fromhigh temperatures because of strong vertical mixing.     

Reproduction of the calanoid copepod Calanus propinquus in the southern Weddell Sea,Antarctica: observations in laboratory

Reproduction of the dominant Antarctic copepod Calanus propinquus was studied in February–April, 1989 aboard the R.V Dmitry Mendeleev during cruise N° 43 to the Weddell Sea. Single females were kept at 0 °C in the laboratory for 56 days with abundant food concentration (above 300 µg C l^–1 of Platymonas viridis). Females released clutches at night at 2–3 day intervals. Most clutches contained from 10 to 40 eggs, mean 37.3 eggs female^–1. Average carbon content of an egg was 0.37 ± 0.05 µg C. The maximum daily egg production rate of 30–50 eggs female^–1 d^–1 was observed for the first 3 days of the laboratory incubation, corresponding to 3.7–6.2% body C. The state of gonadal development of females showed the decline of the reproductive season in late February. The data suggest that egg laying in the region under study starts in December and lasts until March. The state of ovarian maturation, changes in vertical distribution and biochemical body composition of females suggest the possibility of two-year life cycle in C. propinquus in the southern Weddell Sea.     

The influence of salinity on the kinetics of NH inf4 sup+ uptake in Spartina alterniflora

Summary The effects of short- and long-term exposure to a range in concentration of sea salts on the kinetics of NH _inf4 ^sup+ uptake by Spartina alterniflora were examined in a laboratory culture experiment. Long-term exposure to increasing salinity up to 50 g/L resulted in a progressive increase in the apparent K_m but did not significantly affect V_max (mean V_max=4.23±1.97 mole·g^–1·h^–1). The apparent K_m increased in a nonlinear fashion from a mean of 2.66±1.10 mole/L at a salinity of 5 g/L to a mean of 17.56±4.10 mole/L at a salinity of 50 g/L. These results suggest that the long-term effect of exposure to total salt concentrations within the range 5–50 g/L was a competitive inhibition of NH _inf4 ^sup+ uptake in S. alterniflora. No significant NH _inf4 ^sup+ uptake was observed in S. alterniflora exposed to 65 g/L sea salts. Short-term exposure to rapid changes in salinity significantly affected both V_max and K_m. Reduction of solution salinity from 35 to 5 g/L did not change V_max but reduced K_m by 71%. However, exposing plants grown at 5 g/L salinity to 35 resulted in an decrease in V_max of approximately 50%. Exposure of plants grown at 35 g/L to a total sea salt concentration of 50 g/L for 48h completely inhibited uptake of NH _inf4 ^sup+ . For both experiments, increasing salinity led to an increase in the apparent K_m similar to that found in response to long-term exposure. Our data are consistent with a conceptual model of changes in the productivity of S. alterniflora in the salt marsh as a function of environmental modification of NH _inf4 ^sup+ uptake kinetics.     

The reproductive cycle and life history of the Arctic copepod Calanus glacialis in the White Sea

Seasonal variations in the gonad development and sex ratio of copepodite stage V (CV) and adults were examined from February to November in order to understand the reproductive cycle and the life history of Calanus glacialis in the White Sea. Gonad maturation, sexual differentiation and moulting to adults take place during the 2nd year of development. Energy accumulation takes place in the spring and summer of the 2nd year. The following autumn/winter is the major period of CV maturation, which occurs independent of food supply. Maturation of males precedes that of females by 2–3 months. The maximum proportions of CV and adult males are found in the population in October and November. The onset of female maturation is observed in February and March, ca. 2 months prior to the spring phytoplankton bloom. Reproduction takes place between April and June. Its termination in the second half of June coincides with the warming of the surface water layer where egg laying takes place. Variations in the gonad morphology throughout the year suggest long life spans and iteroparity of females of C. glacialis in the White Sea. Many of them survive for several months after reproduction and are able to overwinter again. Therefore, females with different life histories co-occur in the population in winter: “young” females recently moulted from the overwintering CVs, and “old” females which have spawned at least once in their life, after which they return to overwintering conditions. In contrast, males have shorter life spans of 3–4 months resulting in a sex ratio skewed toward females at all seasons. Accepted: 27 April 1999     

Seasonal abundance, reproduction and development of four key copepod species on the Faroe shelf

The copepod community on the Faroe shelf is dominated by Calanus finmarchicus, Temora longicornis, Acartia longiremis and Pseudocalanus spp. The species composition, abundance and development of the copepod community varied considerably during the season 2004. These variations reflected to a large extent the different life strategies of the copepods. Both nauplii and copepodites of C. finmarchicus were most abundant during spring and early summer. The two neritic copepods T. longicornis and A. longiremis were present in low numbers during spring but dominated the copepod community later during the productive period. Pseudocalanus spp., on the other hand, occurred throughout the year, but showed no clear numerical response in abundance to the spring bloom. The egg production measurements of C. finmarchicus and T. longicornis showed some pre-bloom egg production, but as the spring bloom started the egg production rate increased significantly, especially for C. finmarchicus. There seemed to be a substantial loss of nauplii and copepods from the shelf ecosystem during the productive season. It was, however, not possible to determine whether this was mainly due to mortality or advective loss.     

Effects of diet and starvation on digestive enzyme activity and feeding behavior of the marine copepod Calanus pacificus

In this paper we look at the response of Calanus pacificus overa period of several weeks to both starvation and diet as reflectedby survival rates, feeding rates and digestive enzyme activities.Phytoplankton species used as food were the diatom Thalassiosiraweissflogii, two dinoflagellates, Gymnodinium simplex and Scrippsiellatrochoidea, and the chlorophyte Dunaliella tertiolecta. In general,C.pacificus appeared to be resistant to starvation for periodsup to 1 week. Survival remained high for at least 6 days ofstarvation, while maximum feeding rates remained constant forseveral days and then declined by 50% after a week of starvation.When initial digestive enzyme activities were low, they didnot change appreciably during the experiments. However, activitylevels dropped rapidly during starvation experiments in whichthey were initially high. Other evidence indicates that starvationmay induce changes in the digestive system before it affectsingestion rates or survival. In general, long-term changes indigestive enzyme activity under different dietary regimes weregradual. An exception to this pattern was S. trochoidea, whosepresence in the diet induced a precipitous, though reversible,decline in digestive enzyme activity, a phenomena possibly relatedto the toxic reaction to this species reported by other researchers.A positive induction of digestive enzymes occurred over a time-scaleof 1–5 days in response to a change in diet. The absenceof laminarin in the diet of C.pacificus for nearly 3 weeks (whenfeeding on G.simplex), during which time laminarinase activitydeclined by {small tilde}50%, did not adversely affect subsequentassimilation of a laminarin-rich food (T. weissflogii).     

The effects of temperature and salinity on Tilapia rendalli Boulenger 1896

Temperature and salinity tolerances of Tilapia rendalli were determined experimentally. Results indicate that they are tolerant over a wide range of temperatures (11-37°C), but are incapable of surviving in salinities above 19 ‰ The maximum salinity tolerance is at temperatures between 20–28°C. The osmotic concentration of the blood rises from 255 mosmol/1 in freshwater to 340 mosmol/1 in a salinity of 19‰ T. rendalli is restricted to the warmer waters of the Zambezi river system in central Africa and southwards to the Pongolo river, as well as certain tropical and subtropical brackish water lagoons and lakes. Evidence from these experiments suggest that the distribution of T. rendalli isgoverned by both temperature and salinity.     

The relationship between Gulf Stream position and copepod abundance derived from the Continuous Plankton Recorder Survey: separating biological signal from sampling noise

The mean annual abundance of copepods was calculated from ContinuousPlankton Recorder records for the period 1966-1992, and foran area to the north of the UK bounded by latitudes 58-64Nand longitudes 3E and 21W. Spatial heterogeneity of copepodabundance, when combined with changing tow routes, introducedconsiderable noise as well as an artifactual increasing trendin copepod abundunce into the time series. We therefore defineda more homogeneous subarea spanning {small tilde}270 km eitherside of the shelf edge between latitudes 59 and 6IN, withinwhich the noise introduced by changing tow routes was considerablyless. There was a significant (P < 0.01) positive linearrelationship between the annual copepod abundance for this smallhomogeneous subarea and the annual Gulf Stream position betweenlongitudes 79 and 65W. The copepod abundances for the last4 years of the time series (1989-1992) were, however, significantly(P < 0.01) lower than those predicted from the Gulf Streamposition in these years. Evidence suggests that the anomalyof these years was not an artifact caused by poor sampling orchanging tow speeds.