ALBERT

Description: Distribution and abundance of the horned octopus Eledone cirrhosa in the Tyrrhenian Sea are described on the basis of stratified-random bottom trawl surveys in spring and summer of the years 1985–1987. Specimens were caught between 25 and 630 m depth (higher densities between 50 and 200 m depth); mature males were found to prefer deeper bottoms than mature females. Young specimens occurred in spring samples from the Western Ligurian Sea and in summer samples from the Lower Tyrrhenian Sea, but were scarcely represented in the Higher Tyrrhenian Sea. Thus recruitment seems to be progressively delayed later in the season from north to south. The greatest abundance was recorded in the Higher Tyrrhenian Sea; wide seasonal variations of minimum stock biomass estimates have been observed and total biomass decreased from 1985 to 1987 in the surveyed areas.

Description: An investigation was carried out on the morphology, growth and microstructure of statoliths of 833 specimens of Sthenoteuthis pteropus (Steenstrup) mantle length (ML): 2–548 mm collected in the open waters of the Gulf of Guinea in 1984–1988. Statolith morphology is similar to that of other species of the subfamily Ommastrephinae and is similar to the sibling species S. oulaniensis. Statolith development includes five stages resembling those of Illex illecebrosus and other ommastrephids. Statolith growth is characterized by negative allometry. Increments visible in ground sections of statoliths can be grouped into four main growth zones, differing mainly in colour and increment width. Age and growth rates of S. pteropus were calculated using increment counts. The life span of females of all size groups does not exceed 1 yr, that of males is 1–2 months shorter, probably due to preliminary mating. Instantaneous relative growth rage (G) of paralarvae is high (up to 16% of body weight (BW)). G values for juveniles decline, but remain relatively high (7–8% BW). Juveniles attain 100–110 mm ML by age 100–110 days. G values for adults are the lowest (1.8–2% BW), but daily growth rates reach maximum values (40–70 g per day in large females of 450–500 mm ML). Each ontogenetic phase of S. pteropus corresponds to features of morphology, growth and microstructure of the statolith.

Description: The presented data on indirect and direct calorimetry in Halicryptus spinulosus, a species with prominent ecological significance in parts of the Baltic Sea, provide a basis for a better understanding of the metabolic adaptation of these animals to low oxygen availability in their environment. Metabolic rates in H. spinulosus were measured respirometrically as oxygen consumption and calorimetrically as heat dissipation. Oxygen uptake rates are in the range of M O2 = 3.81 ± 1.37 μmol O2·g−1 dry mass·h−1. Upon reimmersion into normoxic seawater after an anoxic incubation of 7 days, the animals exhibit an overshoot of oxygen consumption by a factor of 2.4. It takes at least 2 days for the animals to balance their oxygen consumption to previously measured rates. Direct calorimetry exhibits different strategies of H. spinulosus to cope with declining oxygen and anoxia. During the first 2 transitional days to anoxia in the calorimeter, the animals decreased heat dissipation moderately down to 53.4 and 26%, respectively, of aerobic values. The animals are not necessarily quiescent at the beginning of anoxia, but at the end of the experiments after 14 days metabolic rates have dropped substantially down to ≈2% of normoxic values. These findings are discussed with regard to an effective adaption to frequently changing oxygen regimes in deeper parts of the Baltic Sea.

Description: CO2 partial pressure in surface water was measured in the Northeast Atlantic and in the Hebride Shelf/North Sea area during a cruise with R.V. Poseidon in June 1991. A mean pCO2 of 303 μatm was found in the Atlantic between 50°N and 60°N. For an atmospheric CO2 content of 357.5 ppm(v) this corresponds to a partial pressure difference of −55 μatm. This supports the view that the subarctic Atlantic is a significant sink within the CO2 cycle between the ocean and the atmosphere. A comparison of our measurements with other data reveals that the pCO2 distribution changes significantly during May/June. This explained by seasonal warming, CO2 exchange with the atmosphere and biomass production. The contribution by each of these processes to the seasonal variations is calculated. It was found that during a plankton bloom the production of biomass is the dominating factor and may lower seawater pCO2 by almost 100 μatm. The shelf areas are charactrized by strong pCO2 gradients which are explained by water exchange with the Atlantic, temperature effects and biomass production.

Description: Sixteen samples (588 individuals) of the Argentine shortfin squid Illex argentinus were collected by commercial vessels from Falkland and surrounding waters (42°06–51°17S) between February and May 1990 and subjected to starch gel electrophoresis. Levels of electrophoretically detectable generic variability and the extent of population differentiation were determined from allele frequencies at 25 enzyme-coding loci. Low levels of genetic variability were detected, with the overall proportion of polymorphic loci, P = 0.28, mean heterozygosities per locus, H1 = 0.011, and the average effective number of alleles, Nc = 1.23. Marked population differentiation was indicated by significant differences in allele frequency among samples, and unbalanced genotypic distributions with heterozygote deficits at most loci. Nei's mean genetic distances (D) and identities (I) ranged from 0.000 to 0.130 and 1.000 to 0.878, respectively, underlining the marked genetic divergence detected. Some evidence of microgeographic differentiation (between replicates within sites) was observed. Individuals collected from northerly limits of the sampled area (42: 06 S, 58:09 W) were most genetically distinct (I = 0.878−0.904), suggesting the existence of a hitherto unrecognised subspecies or species of Illex. Emphasis is placed on the need to delimit putative stock boundaries, and develop appropriate population models to ensure conservation of genetic resources.

Description: Coccolith and dinoflagellate cyst assemblages have been investigated in five sediment cores from the Norwegian Sea and Fram Strait. Both fossil groups are characterized by similar patterns of composition. The assemblages contain high proportions of single species. The coccolith flora is of low diversity and consists almost entirely of Coccolithus pelagicus and Emiliania huxleyi. The dinoflagellate cysts are generally dominated by Operculodinium centrocarpum and Nematosphaeropsis labyrinthus. Other species, especially Bitectatodinium tepikiense, Peridinium faeroense and Impagidinium pallidum, sometimes contribute considerably to the assemblages. Based on the abundance of the assemblages and the ratio change between the dominating species it has been possible to establish three intervals of distinct major changes in surface water mass conditions. Sparse occurrences of coccoliths and dinoflagellate cysts have been observed before 10,000 yrs. B.P., indicating harsh environmental conditions with a distinct influence of meltwater and temporarily very slight inflow of Atlantic water. The modern surface-water circulation pattern was reinitiated during Termination IB. The assemblages suggest slightly cooler and probably less saline surface water conditions than are present today until 7500 yrs B.P. Solar insolation may have caused a first temperature peak which is responsible for the early Holocene productivity maximum. A considerable change in the composition of dinocyst and coccolith assemblages occurs corresponding approximately to the onset of the Holocene climatic optimum. This change was most probably linked to an almost synchronous reorganization of the hydrographic properties in the entire North Atlantic realm after the ice sheets had vanished. Since 6000 yrs B.P. the Norwegian Current with its modern oceanographic and ecological properties has been fully established.

Description: The alimentary tracts of 12 species of Antarctic squid were examined visually and serologically for the presence of Euphausia superba. Only four species, Alluroteuthis antarcticus, Galiteuthis glacialis, Martialia hyadesi and Psychroteuthis glacialis, contained material which was identifiable to species visually. Myctophid fish and euphausiids were the most common prey item. Serology showed that specimens of six species had eaten euphausiids. Where antisera showed cross-reactions with other potential prey species, biogeographical and haul data was used to determine the species of Euphausia consumed. P. glacialis (n=19) had consumed E. superba. Mastigoteuthis psychrophila (n=10) had eaten E. superba and/or E. triacantha. Brachioteuthis picta (n=6), M. hyadesi (n=27), and two Moroteuthis spp. (n=2) had consumed unidentified euphausiids. Bathyteuthis abyssicola (n=13) and Histioteuthis eltaninae (n=13) had not preyed on euphausiids. B. picta appeared to have fed in the net.

Description: Analysis of growth by year of hatching was estimated from the statolith growth increments of the oceanic squid Todarodes angolensis in three consecutive years. Samples were taken between November 1987 and February 1990 in the northern Benguela upwelling system. Growth increments suggested that hatching took place throughout the year and that the life cycle was ≈ 1 yr. From the onset of sexual maturity in the final third of the life cycle, growth rates were subject to considerable individual variation. Growth rate was significant highest in the 1987 year class, presumably because of exceptionally cool environmental conditions in the Benguela region. The response of T. angolensis to interannual environmental variability in the northern Benguela system is discussed. The results from this study suggest that it will be important to consider variability in growth rate in relation to environmental conditions, in future studies of squid age and growth.