ALBERT

Description: The only known population of coelacanths, in the Comores, western Indian Ocean, is endangered by human predation. Historical catch data from Grande Comore reveal that annual catch rates increased steadily from 1954 until the 1970s. This trend was temporarily interrupted due to an international policy introducing motorized boats and promoting offshore fishing techniques. Coelacanths are only caught from traditional unmotorized outrigger canoes as an incidental by-catch of deep water line fishing. A complete survey of all motorized and unmotorized vessels in 1995 at Grande Comore in comparison to earlier years indicated that a recent decreased use of motors and increase of unmotorized canoe fishing has led to an increase in coelacanth catches. Conservation measures and strategies for reducing the fishing pressure exerted on coelacanths are discussed. The southwest coast of Grande Comore should be designated as a nature reserve and protected area where immediate protection measures should be taken, an opinion which is supported by Comorian authorities.

Description: VHF telemetry was used in November and December 1995 on 8 Humboldt penguins Spheniscus humboldti breeding at Pan de Azúcar Island (26°S, 70°W), Northern Chile, to determine at-sea behaviour of the birds. We obtained 2710 locations, 90% of which were within a radius of 20 km around the island. Mean travelling speed of the birds was 0.92 m s-1 and speed distribution showed peaks at 1.6 and 3 m s-1. Penguins travelling between foraging areas remained submerged for an average of 8.4 s between surfacings, whereas foraging dives lasted on average 61 s. The analysis of 79 complete foraging trips showed that tracks deviated from a straight course, and range (maximum distance from island) was only 0.37 times total horizontal distance swum. Birds did not forage synchronously or in the same foraging areas. However, foraging ranges were correlated between birds, indicating similar search strategies during periods of low food availability. The results obtained here via VHF telemetry agreed well with those of previous studies employing satellite transmitters and data loggers.

Description: The tissue of 31 demosponge and 7 hexachnelhd species was analyzed for its composition of organic and lnorganic matter With one excephon (Hahclona cf gausaana) inorganic matter i e n~ostly the siliceous skeleton, accounted for most of the dry weight, varying between about 60 and 95%dry wt There were no general trends in the ratio of organic to inorganic matter within sponge orders or genera, and within one species, the ratio could vary between stations For one of the hexactinellids Bathydorus spmosus, several size classes were analyzed and there was no systematic change in the organic inorganic matter ratio w t h specimen size For some species the results from the Weddell Sea sponges are in good agreement with earlier data from McMurdo Sound The low organic matter content in Weddell Sea sponges mphes that sponge biomasses are much lower than hitherto assumed on the basis of then high abundances and large sizes In consequence Antarctic sponges despite their ubiquitousness, may only channel a m n o r fractlon of the general bentho-pelagic flow of matter and energy and their maln role in the ecosystem is likely structural rather than dynamic

Description: During 5 consecutive summer seasons (1990 to 1994) both Aureliaaurita medusa and mesozooplankton abundances were investigated at 2 stations in the Kiel Bight (western Baltic Sea). Stocks of medusae varied considerably between the years, with median abundance of 1 and 0.3 ind. 100 m-3 in 1990 and 1991, 3 and 4 ind. 100 m-3 in 1992 and 1994, but 9 ind. 100 m-3 in 1993. Significant differences in the mesozooplankton stock and community composition were observed in 1993 when compared with the year of rather low Aurelia abundance (1991). Total zooplankton and copepod numbers both exhibited an inverse relationship with the abundance of medusae and were thus considerably lower in 1993 than in 1991. However, not all copepod species were affected by A. aurita. Pseudo- and Paracalanus spp. and Oithonasimilis showed dramatically reduced stocks in the bloom year when compared with the medusa-poor situation, but no significant changes were found for Centropageshamatus and Acartia spp. Also other zooplankton groups with the exception of bivalve larvae were reduced by the medusae. The differential response of zooplankton to varying abundance of medusae led to a shift in the trophic structure of the zooplankton community. Fine-filter feeders and raptorial feeders were much more important in years when medusae occurred in low densities, whereas coarse-filter feeders dominated in the opposite situation.

Description: From the Gulf of Aden along a transect to the central-northern Red Sea the abundance and taxonomic composition of metazoan plankton was studied during the southwest monsoon period (summer 1987). Samples were taken with 0.055 mm mesh nets down to a maximum depth of 1050 m. In the epipelagic zone, a distinct decrease in total plankton abundance was observed from south to north, which was much more pronounced in biomass (by a factor of up to 10) as compared to numbers (by a factor of 2). This could partly be explained by differences in the taxonomic and/or size composition of the planktonic fauna. Among non-calanoid copepods, 40 out of 75 species or taxa investigated decreased in abundance from south to north. Sixteen of these species were completely absent in the central-northern area. Nineteen species or taxa, however, showed the opposite feature of a higher abundance in the central-northern Red Sea. The stations were grouped according to similarities in the taxonomic composition of non-calanoid copepods in the epipelagic zone. The following 3 geographical regions could be separated: (1) Gulf of Aden and Strait of Bab al Mandab; (2) southern Red Sea; and (3) central-northern Red Sea. In the meso- and bathypelagic zones, regional differences were not evident. The results are discussed in relation to hydrographic conditions during summer 1987.

Description: A spring investigation of the phytoplankton in the western Alboran Sea (Mediterranean) was undertaken using chlorophyll and carotenoid biomarkers to characterize the community in the water column and in drifting sediment traps set at 100 and 200 m. During 2 drifter experiments, calm and sunny conditions induced a progressive thermal stratification that reduced pigment sedimentation into deeper water and confined the phytoplankton to the surface layer, resulting in an increase in chlorophyll biomass. 19'-Hexanoyloxyfucoxanthin (prymnesiophytes) and chlorophyll b (chlorophytes, prasinophytes, prochlorophytes) were the major accessory pigments, while fucoxanthin, alloxanthin and peridinin indicated the presence of diatoms, cryptophytes and dinoflagellates, respectively. The proportional contribution of each algal group to the chlorophyll a (chl a) biomass, as derived from multiple regression analysis, revealed that prymnesiophytes, cryptophytes and the green algal group collectively accounted for at least 75% in the upper 100 m, emphasizing the importance of the nanophytoplankton. Phaeopigments, dominated by phaeophorbide a2, were the main pigments observed in sediment traps, although chl a, fucoxanthin and 19'-hexanoyloxyfucoxanthin were detected in smaller concentrations as well as traces of chlorophyll b (chl b). In deep water, fucoxanthin and 19'-hexanoyloxyfucoxanthin were the only accessory pigments present while total phaeopigment/chl a molar ratios 〉1 reflected the active transformation of fine phytogenic material at depth. High particulate organic carbon (POC)/chl a ratios (〉100 in surface water; 〉1000 in deep water) suggested that phytoplankton was a relatively small component of the total carbon biomass down the water column. Using simple budget calculations, we determined that 58 to 65% of the chl a produced in the upper 100 m accumulated in the water column over both experiments. During Expt 1, 29% of the chl a sedimented out, mostly as phaeopigment, at 100 m (24%), and 6% was degraded to colourless residues in the water column. In contrast, only 12% of the chl a sedimented in Expt 2, while 20% was degraded to colourless residues.

Description: Five hormone-treated female Japanese silver eels Anguilla japonica were tagged with ultrasonic transmitters and released by submersible in the West Pacific at seamounts of the West Mariana Ridge, their supposed spawning grounds. Four eels were tracked for 60 to 423 min in the vicinity of the seamounts. They did not settle at the seamounts but swam at a mean speed of 0.37 m s-1 into open water above deep ground. Their mean swimming depth ranged from 81 to 172 m. Experiments suggest that pre-matured A. japonica migrate to their spawning grounds in temperate warm water and at shallow depths.

Description: A method to derive salinity data from RAFOS float temperature and pressure measurements is described. It is based on evaluating the float's in situ density from its mechanical properties and in situ pressure and temperature data. The salinity of the surrounding water may then be determined, assuming that the float has reached equilibrium with its environment. This method, in comparison with the possible use of floatborne salinity cells, has the advantage of being both cost and energy neutral and highly stable in the long term. The effect on the estimated salinity of various parameters used in the determination of the float's in situ density is discussed. Results of seven RAFOS Boats deployed in the Brazil Basin are compared with corresponding CTD data to estimate the magnitude of these errors. At present, an accuracy of 0.3 psu is achieved. The accuracy may be improved to 0.02 psu by referring the float's calculated density to a reference density established by a CTD cast at the time of launch. Results from five floats deployed in the heterogeneous water masses of the Iberian Basin are compared with the corresponding CM casts to demonstrate the variability and interpretation of p-T-S float datasets from different areas.

Description: Data from a surface mooring located in the Sargasso Sea at 34°N, 70°W between May 1982 and May 1984 were compared with satellite data to investigate large diurnal sea surface temperature changes. Mooring and satellite measurements are in excellent agreement for those days on which no clouds covered the site at the time of the satellite pass. During the summer half-year at this site, there is a 20% charm of diurnal warming of more than 0.5°C, with values of up to 3.5°C observed in the two-year period. Diurnal warming observed at the mooring has been simulated well by a one-dimensional model driven by local beat and momentum fluxes. Under the conditions of very light wind and strong insolation that produce the Largest surface warming, the surface mixed-layer depth reduces to the convection depth, and wind-mixing becomes unimportant. The thermal response is then limited to depths between 1 and 2 m, making it likely that such events have been underreported in routine ship observations. In all cases observed, the spatial extent of warming events as determined by satellite data are well correlated with the corresponding atmospheric pressure patterns. Conditions giving rise to the largest diurnal warming events are often associated with a westward-extending ridge of the Bermuda high. In the region studied, 57°–75°W and 29°–43°N, diurnal warming of more than 1°C was found on occasion to cover areas in excess of 300 000 km2, with warming of more than 2°C coveting areas in excess of 130 000 km2.

Description: Historical data from the region between the Greenwich meridian and the African continental shelf are used to compute the offshore geostrophic transport of the Benguela Current. At 32°S, the Benguela Current is located near the African coast, transporting about 21 Sv (1 Sv = 106 m3 s−1) of surface water toward the north relative to a potential density surface lying between the upper branch of Circumpolar Deep Water and the North Atlantic Deep Watar. Two warm core eddies of probable Agulhas Current origin an observed west of the Benguela Current at 32°S. Near 30°S, the Benguela Current turns toward the northwest and begins to separate from the eastern boundary. It carries about 18 Sv of surface water across 28°S. The current then turns mainly toward the west to flow over a relatively deep segment of the Walvis Ridge south of the Valdivia Bank. A surface current with northward surface of about 10 cm s−1 flows along the western side of the Valdivia Bank, while another northward surface current flows at about 20 cm s−1 some 300 km west of the bank. About 3 Sv of surface now do not leave the Cape Basin south of the Vaidivia Bank, but instead drift northward as a wide. sluggish flow out of the northern end of the Cape Basin. Because of the more southerly seaward extensions of most of the Benguela Current, there are no deep-reaching interactions observed between this current and the cyclonic gyre in the Angola Basin east of the Greenwich meridian. Beneath the surface layer, about 4–5 Sv of Antarctic Intermediate Water are carried northward across 32° and 28°S by the Benguela Current, essentially all of which turns westward to cross the Greenwich meridian south of 24°S.