Ostracoda
Methods

Representative samples of adults and the later juvenile stages are collected using plankton nets with 200-300 µm meshes, but larger species are also taken in trawls sampling micronekton. In open oceanic waters abundances are low, so about 2500 mö3 of water need to be filtered to give quantitatively meaningful samples, particularly from depths >500 m, i.e. a 1 mö2 net needs to be towed for one hour at 2 knots (1 m sö-1). This towing speed is the compromise most widely adopted which balances the needs to minimise avoidance, to filter enough water, and to collect material in identifiable condition. At depths of 100-400 m where the ostracods are usually most abundant, >25,000 specimens are likely to be collected. Vertically hauled nets provide good material but seldom provide enough specimens to describe the community structure adequately. Ostracod concentrations decline exponentially with depth, so if adequate numbers are to be collected, the nets need to be towed longer. The deeper-living species are also more fragile, so it is difficult to achieve the optimal balance between collecting a large enough sample by towing for a long time and collecting material that is not too damaged to identify. Sampling the benthopelagic realm requires the nets, either to be attached above bottom trawls, or fitted with echo-sounding devices to continuously monitor in real-time the height of the net above the bottom. Collections from research submarines and deep-towed instrument packages collect good qualitative, but poor quantitative, material. Results of repeated sampling of a community at a depth of 1000 m suggest that an accumulative sample of around 10,000 specimens is needed to provide representatives of all the species present.

Few efforts have been made to culture oceanic ostracods (e.g., Ikeda, 1992). Specimens are easily kept alive onboard ship for a few days - long enough to investigate experimentally many outstanding questions concerning their life-histories, diet, assimilation efficiencies, and ecological role.

Catches for taxonomic and distributional studies should be fixed as soon as they come onboard to avoid deterioration. Sea water-formalin is the most widely used fixative. A stock preserving solution is made up by adding one part of concentrated (40%) formaldehyde solution (neutralised with 5 g borax per litre) to nine parts of filtered sea water. Put the sample into a container, add filtered sea water until it is half-full, then top up with the stock preserving solution. Seal the container hermetically, trapping as little air as possible to minimise oxidation and mechanical damage when the ship rolls. Ideally the catch should only occupy only 10% of the container. Change the preservative after 24-48 h. For long-term storage transfer it into either Steadman's preserving fluid (10% propylene glycol, 0.5% propylene phenoxetol, 1% concentrated (40%) formaldehyde, and 88.5% distilled water), or 80% ethanol.