ALBERT

Description: A culture of juvenile Sepia officinalis L. was kept during summer 1985 in the aquaria of the “Station Marine”, Wimereux, France. During the first four months of juvenile development, oxygen consumption under increasing hypoxia was measured with a closed respirometer. The experiments revealed a high regulatory capacity of juvenile S. officinalis. The critical oxygen concentrations were calculated and their ontogenetical evolution was studied. The critical oxygen concentration increased with increasing development. A linear relationship emerged between the critical oxygen concentration and the logarithm of the wet weight [COc (mg O2 l-1)=-0.393+0.893×log10(Ww)]. The decreasing regulatory capacity of growing S. officinalis is most probably related to adaptations to a changing ecological environment during development. Another possibility is a physiological change, most probably related to the shift from embryonic to adult hemocyanin.

Description: Aquatic animals directly influence the cycling of phosphorus in lakes through feeding and excretion. Traditionally, animals (zooplankton, benthic invertebrates and fish) have been assigned only minor roles in the process of freshwater phosphorus cycling. They were regarded as consumers without much regulating influence. Today there is growing evidence that animals, predators and herbivores, directly or indirectly can control biomass of primary producers and internal cycling of phosphorus. This paper summarizes different mechanisms of transformation and translocation of phosphorus via different groups of organisms.

Description: The present paper describes composition and abundance of meso- and macrozooplankton in the epipelagic zone of the Weddell Sea and gives a systematic review of encountered species regarding results of earlier expeditions. Material was sampled from 6 February to 10 March 1983 from RV Polarstern with a RMT 1+8 m (320 and 4500 μm mesh size). In agreement with topography and water mass distribution three distinct communities were defined, clearly separated by cluster analysis: The Southern Shelf Community has lowest abundances (approx. 9000 ind./1000 m3). Euphausia crystallorophias and Metridia gerlachei are predominating. Compared with the low overall abundance the number of regularly occurring species is high (55) due to many neritic forms. Herbivores and omnivores are dominating (58% and 35%). The North-eastern Shelf Community has highest abundances (about 31 000 ind./1000 m3). It is predominated by copepodites I–III of Calanus propinquus and Calanoides acutus (61%). The faunal composition is characterized by both oceanic and neritic species (64). Fine-filter feeders are prevailing (65%). The Oceanic Community has a mean abundance of approximately 23 000 ind./1000 m3, consisting of 61 species. Dominances are not as pronounced as in the shelf communities. Apart from abundant species like Calanus propinquus, Calanoides acutus, Metridia gerlachei, Oithona spp. and Oncaea spp. many typical inhabitants of the Eastwind Drift are encountered. All feeding types have about the same importance in the Oceanic Community.

Description: Many cephalopods have lines of ciliated cells on their head and arms. In the cuttlefish Sepia and the squid Lolliguncula, electrophysiological recordings clearly identify these epidermal lines as an invertebrate analogue to the mechanoreceptive lateral lines of fish and aquatic amphibians and thus as another example of convergent evolution between a sophisticated cephalopod and vertebrate sensory system. Stimulation of the epidermal lines with local water displacements, generated by a vibrating sphere, causes receptor potentials that have many features known from lateral line microphonic potentials. The minimal threshold of the head lines is 0.2 micron peak-to-peak water displacement (calculated at the skin surface) at 75-100 Hz.

Description: Laboratory culture of 40 Octopus bimaculoides from April 1982 to August 1983 through the full life cycle at 18°C vs 23°C provided information on the growth, reproductive biology and life span of this California littoral octopus. At 18°C, the cephalopods grew from a hatchling size of 0.07 g to a mean of 619 g in 404 d; the largest individual was 872 g. Octopuses cultured at 23°C reached their highest mean weight of 597 g in 370 d; the largest individual grown at this temperature was 848 g after 404 d. Growth data revealed a two-phase growth pattern: a 5 mo exponential phase followed by a slower logarithmic (power function) phase until spawning. At 5 mo octopuses grown at 23°C were over three times larger than their 18°C siblings. However, beyond 6.5 mo, growth rates were no higher at 23°C than at 18°C. At 13.5 mo, the mean weight of the 18°C group surpassed that of the 23°C group. The slope of the length/weight (L/W) relationship was significantly different for the two temperature regimes, with the 23°C octopuses weighing 18% less than their 18°C siblings at a mantle length of 100 mm. Females weighed more than males at any given mantle length. Males grew slightly larger and matured before females. The L/W relationship indicated isometric body growth throughout the life cycle. Higher temperature accelerated all aspects of reproductive biology and shortened life span by as much as 20% (from approximately 16 to 13 mo). O. bimaculoides has one of the longest life cycles among species with large eggs and benthic hatchlings. Extrapolations to field growth are made, and the possible effects of temperature anomalies such as El Niño are discussed.