The distribution and ecology of British shallow-water tanaid crustaceans (Peracarida, Tanaidacea)

Summary

Twenty-eight species of tanaid, belonging to fourteen genera, occur in waters to a depth of 200 metres around the British Isles. Two species are exclusively intertidal whilst seven others inhabit both intertidal and shallow sublittoral waters. Many of the remaining species also occur in waters deeper than 200 metres in other areas, especially off the Norwegian coast. Typhlotanais pulcher, previously known only from below 3000 metres off Greenland is recorded from Scottish waters, and Agathotanais ingolfi, another deep-water species, is recorded from the North Sea. Only Pseduotanais jonesi and Tanaissus elongatus have not been recorded from outside British waters. All known localities for the twenty-eight species are plotted on distribution maps and all available ecological data is collated, although for many species it is scant. Those species in the intertidal and shallow sublittoral zones occupy a wide variety of microhabitats, but the majority of offshore species are found associated with soft substrates, such as mud and muddy sand, with densities sometimes exceeding 100 m^-2. Only Tanaissus lilljeborgi is commonly found in intertidal sands, sometimes at densities of 600 m^-2 or more. Only one offshore species, Typhlotanais aequiremis constructs a tube, although a number of species inhabiting the intertidal, and both the intertidal and shallow sublittoral zones do. The tubes of the intertidal species, Parasinelobus chevreuxi, may reach densities of over 6000 m^-2 on suitable shores.

A survey of two Scottish sea-lochs has revealed six sublittoral species at depths of 17–40 metres. Both species diversity and abundance increases towards the seaward end of the lochs where there is stronger tidal movement. At one open sea site near to the entrance of the lochs a total of eight tanaid species, three of which were common, were obtained in only two combined grab samples.

A table is given of the tanaids occurring in nine regions of the North-east Atlantic down to a depth of 200 metres and the species common to the various regions are discussed.