274 research outputs found
Copepod hatching success rate in ecosystems with high diatom concentrations the paradox of diatom-copepod interactions revisited (abstract of paper presented at ASLO/AGU Ocean Sciences Meeting, Honolulu, HI, 11-15 Feb 2002)
No full textLatitudinal variation in plankton size spectra in the Atlantic Ocean
No full textThe size distribution of the pelagic community has the potential to compare ecosystems with different species composition as well as to identify the main functional properties of the system. Plankton size spectra are an effective approach of summarising the size structure of the community and have the potential to indicate the transfer of energy up the trophic food web. However, data on which open ocean plankton biomass-size structure can be constructed are scarce. Here we present the latitudinal distribution in the Atlantic Ocean of normalised biomass-size spectra (NB-S), plankton biomass and abundance, as well as mean zooplankton size between 70°N and 50°S. Samples were collected from three Atlantic Meridional Transect (AMT) cruises during May/June 2003, September/October 2003 and April/June 2004, as well as from a Marine Productivity (MarProd) cruise farther north in the Irminger Sea during spring 2002. The biomass-size distribution covered a body size range from nano- to mesoplankton and was based on a depth range of 50–0 m on the AMT and 120–0 m on the Irminger Sea cruise. The distribution of normalised biomass versus size was linear on a double log plot at all of the 95 stations. The slopes of the NB-S spectra ranged from ?0.93 to ?1.26 and ?1.12 to ?1.46 on the AMT and Irminger Sea cruises, respectively. A “dome-shaped” pattern in the slopes of community size spectra was observed in the Atlantic, indicating a decrease in the trophic transfer efficiency of energy with increasing latitude and phytoplankton biomass. Mesozooplankton biomass, abundance, and mean size followed a distribution similar to ecosystem productivity
North Atlantic Oscillation and spring bloom phytoplankton composition in the English Channel
No full textThe spring phytoplankton composition has been investigated at a 50 m deep station off Plymouth in the English Channel for 6 years (1993–1999). The percentage of diatoms during the spring bloom was significantly correlated with the North Atlantic Oscillation index. A similar relationship between phytoplankton and North Atlantic Oscillation has also been found in a Swedish lake, suggesting a possible link between atmospheric forcing and phytoplankton composition
Feeding and egg production of Oithona similis in the North Atlantic
No full textAlthough cyclopoids of the genus Oithona are considered the most abundant copepods in the marine environment, there is still very little information about what sustains their population and almost constant reproduction rate throughout the year. Feeding and egg production rate (EPR) of O. similis were measured at coastal and oceanic stations during 3 cruises in the North Atlantic between April and November 2002. O. similis ingested ciliates preferentially to other components of the nano- and microplankton (herein nano-microplankton), which only became a more important component of the copepod diet when the abundance of the former decreased to low concentrations. EPR did not show significant seasonal differences, with 2.13 ± 0.67 eggs female–1 d–1 in spring, 1.61 ± 0.32 eggs female–1 d–1 in summer and 1.60 ± 0.15 eggs female–1 d–1 in winter. The ingestion rates measured at many oceanic stations and in winter were often too low to sustain EPR.
Egg production efficiency (GGE) >100% indicated that sustained EPR might have relied, particularly in winter, on alternative food sources such as a more carnivorous diet and/or on the faecal pellets of euphausids
Zooplankton dynamics in a mesoscale eddy-jet system off California
No full textZooplankton in the central jet of the California Current and an adjacent mesoscale cyclonic eddy centered at 125.1°W, 38.4°N were studied in early July, 1993, using a SeaSoar-mounted Optical Plankton Counter. Within 3 d after the 2 d survey of these mesoscale features we completed a MOCNESS transect across the study area. Zooplankton in the rapidly moving (>40 cm s-1 near surface) jet were negatively correlated with the vertical distribution of phytoplankton biomass, which displayed strong fluorescence maxima in the upper 200 m. Zooplankton in the recirculating eddy, however, were positively correlated with fluorescence maxima at the pycnocline (ca 50 m) and at 150 m. Euphausiids, dominated by Euphausia pacifica, and the copepod Calanus pacificus accounted for most of the zooplankton in the upper 50 m of the eddy, while the copepod Metridia pacifica dominated the abundance maximum of medium size zooplankton at 150 m. These species were also present in the jet, but male:female ratios of the 2 copepod species differed greatly, suggesting that populations within the jet and the eddy were distinct from one another. Earlier observations of the cyclonic eddy indicate that it departed California coastal waters in April; resident zooplankton populations may have gone through several generations before they reached the position at which we found it in July. Waters of the jet, by contrast, probably departed from the California coastal region in mid-June, so that its populations of zooplankton may have been essentially the same as those advected to our sampling location
Feeding of Calanus finmarchicus nauplii in the Irminger Sea
No full textRecent studies have shown that the passage from nauplius to copepodite is a key event in the population dynamics of Calanus finmarchicus. As a first step towards understanding if and how trophic interactions influence this event, we investigated the feeding of C. finmarchicus nauplii IV-VI in the Irminger Sea during spring and summer in a series of incubation experiments. Generally, feeding efficiencies were highest on large cells, whereas small flagellates were ingested at very low rates. Colonies of Phaeocystis sp. were not ingested. Among the larger cells, the diatoms Chaetoceros pelagicus and Tropodineis sp. and the ciliate Strombidium sp. were the main food sources. We observed a negative relationship between the percentage of diatoms in the food environment and the filtration rate on Strombidium sp. We therefore suggest that the combination of low feeding efficiency on small cells and the generally low concentrations of ciliates in oceanic waters explains why C. finmarchicus relies on phytoplankton blooms for recruitment from nauplius to the first copepodite stage
Regional and temporal variation of Oithona spp. biomass, stage structure and productivity in the Irminger Sea, North Atlantic
No full textOithona spp. standing stock and production is considered relatively stable in space and time as a result of continuous breeding, low metabolism, reduced predation mortality and the ability of these small cyclopoids to exploit microbial food webs more efficiently than larger copepods. However, through a review of the published literature we show that Oithona spp. biomass can vary widely both over the year and with latitude. Thus, the present study set out to investigate the basin scale variability in biomass, stage structure and reproduction of Oithona spp. in relation to changes in hydrographic, physico-chemical and biological parameters encountered during three cruises conducted between April and November 2002 in the Irminger Sea, North Atlantic. Here we found that Oithona spp. biomass varied significantly with temperature and with dinoflagellates biomass concentration. On the other hand, O. similis egg production rates (EPR) increased with both ciliates and dinoflagellates concentrations, rather than with temperature. The inverse relationship we found between Oithona spp. naupliar recruitment with Calanus spp. and fish larvae abundance suggests that predation pressure may contribute to control the spatial variation in the stage structure and biomass of Oithona spp. and that the nauplii of this genus may serve as a food source for other planktonic organisms prior to the spring phytoplankton bloom
Growth and movement patterns of early juvenile European anchovy (Engraulis encrasicolus L.) in the Bay of Biscay based on otolith microstructure and chemistry
No full textVarious hypotheses have been put forward to explain the mechanisms in the Bay of Biscay that result in a good recruitment of European anchovy. Anchovy larvae from the spawning area in the Gironde River plume are advected towards off-shelf waters, where juveniles are commonly observed. Otolith microstructural and chemical analysis were combined to assess the importance of this off-shelf transport and to determine the relative contribution of these areas for anchovy survival. Chemical analysis of otoliths showed that anchovy juveniles in the Bay of Biscay can be divided into two groups: a group that drifts towards off-shelf waters early in their life and returns later, and a group that remains in the low salinity waters of the coastal area. The first group presents significantly faster growth rates (0.88 mm day-1) than those remaining in the coastal waters (0.32 mm day-1). This may be due to off-shelf waters being warmer in spring/summer, and to the fact that the lower food concentration is compensated for by higher prey visibility. Furthermore, the group of juveniles that drifted off the spawning area and had faster growth rates represents 99% of the juvenile population. These findings support the hypothesis that anchovy in the Bay of Biscay may use off-shelf waters as a spatio-temporal loophole, suggesting that transport off the shelf may be favourable for recruitment. © 2010 Blackwell Publishing Ltd
Feeding and reproduction of Calanus finmarchicus during non-bloom conditions in the Irminger Sea
No full textSimultaneous ingestion and egg production experiments were conducted with female Calanus finmarchicus in April/May and July/August 2002 in the Irminger Sea. Experimental animals were provided with natural microplankton food assemblages and incubated under in situ conditions for 24 h. The quantity of food consumed was significantly related to the concentration of prey cells, with total daily ingestion rates ranging from 0.6 to 8.1 µg of carbon female–1 day–1, corresponding to carbon-specific rates of 0.6–4.7% day–1. Egg production rates (EPRs) remained relatively low (0.3–11 eggs female–1 day–1) during both periods of investigation and were not influenced by food availability. The data were used to construct energetic budgets in which the microplankton carbon ingested, including ciliates, was compared with the carbon utilized for egg production and respiration. These budgets showed that ingestion alone could not provide the necessary carbon to sustain the observed demands for growth and metabolism. Although ciliates constituted >80% of the total material ingested at times, they were not sufficient to provide the metabolic shortfall. Indeed, the females were typically lacking 5 µg of carbon each day, 5% of their carbon biomass. Our study results highlight the possible importance of internal reserves in sustaining reproduction in C. finmarchicus during periods of food scarcity
- …
