Plankton abundance and feeding characteristics of Thysanoessa raschii from Godthabsfjord, Greenland

Despite being a key zooplankton group, knowledge on krill biology from the Arctic is inadequate. The present study examine the functional biology and evaluate the trophic role of krill in the Godthabsfjord (64°N, 51°W) SW Greenland, through a combination of fieldwork and laboratory experiments. Krill biomass was highest in the middle fjord and inner fjord, whereas no krill was found offshore. The dominating species Thysanoessa raschii revealed a type III functional response when fed with the diatom Thalassiosira weissflogii. At food saturation, T. raschii exhibited a daily ration of 1% body C/d. Furthermore, T. raschii was capable of exploiting plankton cells from 5 to 400 µm, covering several trophic levels of the pelagic food web. The calculated grazing impact by T. raschii on the fjord plankton community was negligible. However, the schooling and migratory behaviour of krill will concentrate and elevate the grazing in specific areas of the euphotic zone.

Parameters of population dynamics and energetics of ctenophore Mnemiopsis leidyi in Sevastopol Bay from January 1995 to March 1996

Population dynamics of abundance and biomass were studied and specific production of population of ctenophore Mnemiopsis leidyi was estimated in the Sevastopol Bay from January 1995 to March 1996. The ctenophores achieved maximum abundance and biomass in July during period of intensive reproduction. Young specimens (<5 mm) contributed during that period as much as 50-87% to total abundance of population. Annually averaged daily specific growth rate was 0.039. Growth, food consumption, and rate of filtration were measured in a laboratory under two concentrations of food (Acartia clausi and Moina micrura: 60 and 100 specimens per liter, 0.35 and 0.60 mg wet weight/l). Both concentrations sustained growth of animals with dry weight less than 20 mg. However these concentrations were insufficient to sustain growth of larger ctenophores. Specific growth rate of the ctenophores with dry weight <20 mg under favorable food conditions was 0.20-0.30 l/day. Specific growth rate of the ctenophores in the Sevastopol Bay never exceeded 0.093 l/day, mean biomass of fodder zooplankton in the bay being 90 mg/m**3 in terms of wet weight. Hence a conclusion was made that population of M. leidyi in the bay was limited by lack of food.

Feeding parameters of copepods from upwelling areas

Feeding patterns of mass herbivorous copepods in upwelling areas are investigated. Daily rations and aspects of their formation are examined in Calanoides carinatus (Benguela upwelling), Calanus pacificus (off the California coast), and Calanus australis (Peru upwelling). Rations were calculated based on gut plant pigment contents obtained at daily stations using laser spectrofluorometry, experimental data on the rate of gut evacuation and data on the carbon/chlorophyll ratio in phytoplankton and particulate matter at the respective stations. When phytoplankton was abundant, diel feeding rhythms were not pronounced and gut pigment level was high during the entire 24-h period. When phytoplankton biomass was low, distinct feeding rhythms were pronounced with a nocturnal maximum. During active upwelling intensive feeding on phytoplankton supports energy (respiration) and plastic (growth, development, reproduction, accumulation of reserves) metabolism of copepods. When upwelling was inactive, the surface part of the population feeds less actively and is able only partially to cover its energy expenditures. The actively growing and reproducing populations of C. pacificus and C. carinatus may consume close to 20% of primary production, whereas the inactive population of C. australis consumed only 0.2% of primary production when upwelling weakened.

Food composition of beryx-alfonsino over submarine rises near Azores

Qualitative and quantitative food composition, as well as intensity of feeding of beryx-alfonsino Beryx splendens was examined on banks near the Azores. Data are presented with respect to size groups and taking into account type of feeding of males and females. Crustaceans and fishes were constituents of their feeding ration. A tendency toward increase in the number of consumed fishes in the course of ontogenetic development of beryx-alfonsino was noted. Beryx-alfonsino was shown to occupy the trophic level of consumers of the third order performing function of a deep-water predator.

Feeding of Sagitta setosa in the Black Sea

Gut dissection of fixed individuals from samples collected during Cruise 6 of R/V Vityaz-2 in April-May 1984 was used to study feeding of Sagitta setosa in the layers of daytime plankton accumulation at the lower boundary of the oxycline. The principal food was copepodite stage V of Calanus and females of Calanus and Pseudocalanus. Analysis of daytime and night data with reference to length of migratory alterations of Sagitta populations and gut passage time indicates that they feed actively in the layers of day¬time plankton accumulations. Total food consumption during time spent in the subsurface layers ranged from 0.025-0.097 cal/indiv. in 12 h, equivalent to 37-143% of their metabolic energy expenditure. Over the course of 12 h Sagitta population consumes 0.3-5% and 0.5-6% of population of stage V copepodites and females of Calanus and Pseudocalanus females, respectively.

(Table 1) Indices of feeding of natural populations of Infusoria in antarctic and subantarctic waters

Ration of mass species of infusoria and their consumption of phytoplankton in the 0-200 m layer of antarctic and subantarctic waters of the Pacific Ocean are evaluated from microscopic study of digestive vacuoles and counts of algae present in them. In antarctic waters tintinnids, which make up 63-75% of total biomass of infusoria, consumed 19-27% of biomass of nannophytoplankton or 0.1-0.3% of biomass of all phytoplankton. In Subantarctic the main infusorial consumers of phytoplankton were large strombidia, which were dominant in infusorial biomass and in their areas of maximum development consumed 14% of biomass of nannophytoplankton, equivalent to about 10% of total biomass of phytoplankton in the 0-200 m layer.

Abundance, biomass, ingestion rates and daily ratios of Salpa thompsoni individuals sampled during POLARSTERN cruise ANT-XVIII/5b to the Eastern Belingshausen Sea

Distribution, density, and feeding dynamics of the pelagic tunicate Salpa thompsoni have been investigated during the expedition ANTARKTIS XVIII/5b to the Eastern Bellingshausen Sea on board RV Polarstern in April 2001. This expedition was the German contribution to the field campaign of the Southern Ocean Global Ocean Ecosystems Dynamics Study (SO-GLOBEC). Salps were found at 31% of all RMT-8 and Bongo stations. Their densities in the RMT-8 samples were low and did not exceed 4.8 ind/m**2 and 7.4 mg C/m**2. However, maximum salp densities sampled with the Bongo net reached 56 ind/m**2 and 341 mg C/m**2. A bimodal salp length frequency distribution was recorded over the shelf, and suggested two recent budding events. This was also confirmed by the developmental stage composition of solitary forms. Ingestion rates of aggregate forms increased from 2.8 to 13.9 µg (pig)/ind/day or from 0.25 to 2.38 mg C/ind/day in salps from 10 to 40 mm oral-atrial length, accounting for 25-75% of body carbon per day. Faecal pellet production rates were on average 0.08 pellet/ind/h with a pronounced diel pattern. Daily individual egestion rates in 13 and 30 mm aggregates ranged from 0.6 to 4.8 µg (pig)/day or from 164 to 239 µg C/day. Assimilation efficiency ranged from 73 to 90% and from 65 to 76% in 13 and 30 mm aggregates, respectively. S. thompsoni exhibited similar ingestion and egestion rates previously estimated for low Antarctic (~50°S) habitats. It has been suggested that the salp population was able to develop in the Eastern Bellingshausen Sea due to an intrusion into the area of the warm Upper Circumpolar Deep Water