ALBERT

Description: The effect of variable CO2 concentrations on the elemental composition (C:N:P) of marine diatoms was investigated in 2 strains of Skeletonema costatum (Grev.) Cleve. Five or 6 concentrations of dissolved molecular carbon dioxide [CO2 (aq)], ranging from 0.5 to 39 µmol l-1, were applied in dilute batch cultures. In both strains, elemental ratios were clearly dependent on [CO2 (aq)]. With decreasing CO2 concentrations, a decline in C:P and N:P and an increase in C:N was observed. The close correlation between C:P or N:P and [CO2 (aq)] corresponded to a ca 45 to 65% decrease in elemental ratios from highest (〉=30 µmol l-1) to lowest (ca 1 µmol l-1) CO2 concentrations. C:N at low [CO2 (aq)] was up to 24% higher than at high [CO2 (aq)]. To date, the elemental composition of marine phytoplankton has been considered to be independent of CO2 availability. If dependency of the C:N:P ratio on [CO2 (aq)] proves to be a general phenomenon in marine phytoplankton, changes in the elemental composition may be expected in response to the currently observed increase in partial pressure of atmospheric CO2.

Description: The response of epilithic microphytobenthos to in situ nutrient enrichments was studied in the Kiel Fjord, Western Baltic Sea. For this purpose an experimental setup with continuous nutrient supply was designed and installed. Experiments followed the colonization of artificial substrates and the responses of benthic algae to different concentrations and combinations of nitrogen and phosphate. They revealed nitrogen limitation of epilithic microflora from late spring to autumn, such that there was higher biovolume with increasing nitrogen concentrations. Diatoms became dominant in all experiments except one in which the rhodophyte Ceramium strictum prevailed. Species composition was altered by nutrient treatments; one to several species were highly favoured by nutrient enrichment. Consequently, diversity was negatively correlated with final yield. These findings support the hypothesis that competition is an important factor structuring microphytobenthic communities.

Description: Snails Littorina littorea with and without artificial epibionts were exposed in situ for nearly 1 mo. Measurement of individual shell length increase over this period revealed that clean snails grew 3 times faster than fouled snails. These results compare well with previously conducted flume experiments (Wahl 1996). This epibiosis effect is thought to be due to increased drag-the only feature distinguishing the 2 treatment groups-caused by the presence of epibionts on the shell. Increased drag probably entails higher energy expenditure for pedal activities (attachment and locomotion) and a reduced allocation of resources towards growth and, possibly, reproduction

Description: Stomach contents from 30 long-finned pilot whales Globicephala melas captured incidentally in the Distant Water Fleet (DWF) mackerel fishery off the northeastern United States were examined. Several methods of assessing prey importance were used in order to construct a true representation of the pilot whale diet. Separate analyses of trace (free, durable body parts from well-digested prey) and non-trace (relatively intact prey) food materials were conducted to address biases caused by differential rates of digestion and passage. Squids dominated the diet and long-finned squid Loligo pealei was the most important prey, but we noted large yearly fluctuations in prey importance. Metric multidimensional scaling analyses of trace and non-trace stomach contents of individual whales suggest that many animals were cuaght while feeding opportunistically near fishing operations, resulting in a bias of non-trace (intact) stomach contents. The diversity of prey in this study was greater than previous reports of the food habits of western North Atlantic non-finned pilot whales.

Description: We investigated the foraging location, diving behaviour, dietary composition, feeding rates and foraging trip durations of emperor penguins Aptenodytes forsteri raising chicks at the Auster and Taylor Glacier colonies on the Mawson Coast of Antarctica in the winter, spring and early summer of 1993, to examine seasonal changes in the penguins' foraging ecology. As day-length increased after winter, the penguins' daily swimming time increased from 7.83 ± 1.50 h in August to 12.23 ± 1.25 h in September and 12.95 ± 1.24 h in October. Accordingly, the penguins' dive rate increased from 92.7 ± 28.5 to 149.4 ± 23.4 and 161.6 ± 19.3 dives d-1 in the respective months. The birds targeted prey in the vicinity of the continental slope mainly at depths 〈100 m, although some individuals frequently hunted at depths 〉200 m, and the maximum depth achieved was 438 m. Antarctic krill Euphausia superba were the most common prey taken overall, 41% of the diet by mass, and dominated the diets between August and October. The contribution of Antarctic krill to the diet reduced over time from 68% in August to 1% in early December. In November, the glacier squid Psychroteuthis glacialis dominated the diet (47 to 63%), and in early December the diet comprised various species of fish, Trematomus species (27%), Pagothenia borchgrevinki (24%), and Pleuragramma antarcticum (8%), and squid, P. glacialis (13%) and Alluroteuthis antarcticus (9%). The birds' prey consumption rates more than doubled between late winter and early summer, from 4.0 ± 1.0 to 8.7 ± 1.7 kg d-1 spent foraging; these values are equivalent to metabolisable energy intakes of 628 ± 134 and 1422 ± 308 kJ kg-1 d-1, respectively. During brooding (late winter to early spring), females spent less time at sea than males (8.7 ± 2.7 vs 17.7 ± 3.8 d); thereafter trip durations of both sexes were similar and declined from 15-19 d in spring to 〈10 d in early summer. Between hatching and about 1 wk prior to fledging each parent fed its chick 7 or 8 times. To raise a chick, females and males consumed approximately 410 and 470 kg of prey respectively, or 880 kg for each breeding pair. Seasonal variations in the penguins' foraging were probably influenced by fluctuating sea-ice conditions, differences in the prey types available, changes in day-length toward summer, and increasing demands of the growing chicks.