Post-bloom grazing byCalanus glacialis,C. finmarchicus andC. hyperboreus in the region of the Polar Front,Barents Sea

The plankton community in the Polar Front area of the Barents Sea was investigated during a cruise from 14 to 28 July 1987. The colonial algaePhaeocystis pouchetii andDinobryon pellucidum dominated the phytoplankton. Depth integrated carbon assimilation rates varied from 190 to 810 mg C m^–2 d^–1. A high carbon:chlorophyll ratio (which varied from 123 to 352) prevailed at the three stations investigated, which may relate to facultative heterotrophic behaviour byD. pellucidum. The herbivorous zooplankton community was dominated byCalanus glacialis, C. finmarchicus, andC. hyperboreus. Maximum zooplankton biomass was found in the same depth strata as phytoplankton chlorophyll maximum. The herbivorous copepod populations did not display consistent day-night vertical migration patterns. Phytoplankton consumption rates of the various life stages were estimated from the turnover rate of plant pigments in the gut. The gut defecation rate constant (R) varied from 0.014 to 0.027 min^–1 at 0°C in copepodites (Stage II to adult female) ofC. glacialis, independent of developmental stage.Calanus spp. community carbon ingestion rates calculated from particulate carbon:chlorophyll ratios, were 10, 65 and 400% of daily phytoplankton carbon fixation rates at Stations 1, 2 and 3, respectively.     

Circadian rhythms in the chromatophore movements of Dictyota dichotoma

In the brown alga Dictyota dichotoma Lamour the phaeoplasts move to the anticlinal walls (profile position) in strong light and to the periclinal walls (face position) in dim light. By these movements transmittance changes are caused. If the algae were grown in light:dark cycles of about natural daylengths, circadian oscillations of the amplitudes and the kinetics of these transmittance changes are initiated. The lengths of the free running periods vary between 24 and 29 h. In addition, light:dark grown thalli were transferred into continuous dim or strong light or darkness, in order to check whether or not the rhythms continued under these conditions. By taking photomicrographs of intact thalli and of isolated cortical cell layers, prepared by bisecting, it could be shown that the maxima and minima of circadian transmittance changes correspond well with the number of phaeoplasts at the periclinal cell walls. The ecological relevance of these phenomena is discussed.Presented in part by the first author at the XI. International Seaweed Symposium, Qingdao, People's Republic of China, 19 to 26 June, 1983     

An investigation on the anaerobic metabolism of Nephtys hombergii (Annelida: Polychaeta)

In Nephtys hombergii Savigny (Annelida: Polychaeta: Errantia), succinate and less pronounced L-alanine are accumulated as endproducts during an initial phase of anaerobiosis. In this phase aspartate is utilized as substrate for anaerobic energy production in addition to glycogen. Prolonged anaerobiosis results in the formation of propionate and acetate which, to a large extent, are excreted into the water. The concentrations of aspartate and succinate were found to remain unchanged down to a Pw_{O 2}(oxygen partial pressure in incubation water) of approximately 20 torr, indicating a fully aerobic metabolism. At a Pw_{O 2}of 15 torr characteristic changes can be observed: energy production becomes partially anaerobic. At a Pw_{O 2}of 7 torr the level of aspartate is largely reduced, but the accumulation of succinate is still significantly less than at anoxia. [In the habitat of N. hombergii, the intertidal mud flats, a Pw_{O 2}in the range from 0 torr (Pamatmat, 1968) to 12 torr (Wells and Warren, 1975) was measured.] The activities of some important enzymes involved in anaerobic energy production (among them pyruvate kinase, phosphoenolpyruvate carboxykinase and lactate dehydrogenase) were measured. Although N. hombergii has a high glycolytic capacity, no lactate dehydrogenase was detected. Instead strombine and alanopine dehydrogenases were present in comparatively high activities.     

Effect of limpets on the fouling of ships in the Mediterranean

Limpets reduce the cover of algae and barnacles on intertidal rocks, but do not inhabit ship-fouling communities. Patella caerulea (L.) from Israeli Mediterranean shores were successfully transplanted onto 20x20 cm initially non-fouled steel panels in 1983–1984, hung vertically in a commercial port at depths of 1 and 5.5 m. The limpets (15 individuals of ca 20 to 25 cm in length on each panel) controlled the fouling organisms that settled on the panels throughout a month of lowest settlement (December) and throughout a month of highest settlement (August). After 7 d of immersion the limpets restricted the total cover of fouling organisms from 2.4 and 4.8% to 0.6 and 0.2% (at 1 and 5.5 m depths, respectively), and brought down the barnacle density from 1.2 and 2.6 to 0.3 and 0.4 individuals per cm² (at 1 and 5.5 m depth, respectively). After 26 d the equivalent figures were a cover of 72 and 92% reduced to 14 and 9% and a density of 2.9 and 1.1 reduced to 0.3 and 0.2 individuals per cm². The limpets presumably achieved this by preventing the attachment of propagules and by removing already settled organisms through their movements during grazing excursions.     

Nontransitive patterns of historecognition phenomena in the Red Sea hydrocoral Millepora dichotoma

Allogeneic assays were conducted in situ on the Red Sea hydrocoral Millepora dichotoma. Forty-five pairwise combinations among ten colonies and ten control isografts were set up in four replicates each (180 and 40 pairs, respectively) and followed for up to 8 mo in the Gulf of Eilat, Red Sea in 1992–1993. In 42 allogeneic combinations we recorded a reproducible and unilateral tissue and skeleton overgrowth which developed within the first 10 wk up to 20 mm. Following the development of these primary overgrowths, four types of secondary responses were observed among most incompatible combinations: reversals in overgrowth directionality, tissue necroses, stand-offs and abnormal growth patterns. Secondary responses within a given set of replicates of most allogeneic combinations were characterized by high variability in type and intensity of response. Based on the outcomes of primary overgrowths, a complex nontransitive hierarchy was constructed for the ten colonies. All isografts and three allogeneic combinations fused within 3 wk. Fusion pattern between the three allogeneic combinations was nontransitive: one M. dichotoma colony repeatedly fused with two other colonies (four assays each). However, these two colonies not only did not fuse with each other, but one of them repeatedly overgrew its confrére. In the third compatible combination, the most superior and the most inferior colonies in the network of hierarchies among the ten colonies, fused in all tested assays. These results are compared with allogeneic outcomes in other enidarians, where nontransitive fusion between allogenic colonies have never been recorded.