The Distribution of Nephtys on the Scottish Coast

Abstract

Only two species of Nephtys, N. hombergi and N. cirrosa, are common on the coast of south and south-western England and Wales (Clark & Haderlie 1960). Two other species N. caeca and N. longosetosa, have been recorded from various beaches on this part of the coast, but there appear to be no substantial intertidal populations of them there now and both must be accounted rarities in the area. The two common species suffer an almost complete ecological isolation. N. hombergi is confined to muddy substrata while N. cirrosa lives in clean and fairly coarse sandy beaches. The grade composition of optimum and tolerable substrata can be defined for each species and only a small number of beaches with poorly sorted substrata satisfy the requirements of both worms, and so support mixed populations. In Scotland, to judge from the literature, N. cirrosa is rare and is replaced on clean sandy beaches by N. caeca. The former species occurs in the Firth of Clyde (Clark 1960), on St Kilda (Gauld, Bagenal & Connell 1953, Scott 1960) and at Aberdeen (McIntyre 1961), but has been reported from nowhere else on the islands or mainland of Scotland. Admittedly, little collecting has been done on the remote and inaccessible west coast of Scotland, but Stephen (1929, 1930) and Scott (1958) have made fairly extensive collections on the east coast from the Firth of Forth to the Moray Firth and have reported the commonest species of Nephtys from that area to be N. caeca. Although N. caeca appears from the accounts of Stephen and Scott to be characteristically associated with clean sandy beaches, as N. cirrosa is in the south-west, a surprising number of Scottish beaches are reported to contain both it and N. hombergi. If, as this information might suggest, N. caeca tolerates muddier substrata than N. cirrosa can, then N. hombergi must experience greater competition in the northern part of its range than it does in the south. In an attempt to study this question and also to investigate the limits of distribution of N. cirrosa, we have examined the fauna of some seventy beaches from the Solway to the Forth (Fig. 1). Relatively few west coast beaches could be visited and our greatest effort has been concentrated on the north and east coasts where practically every accessible sandy and muddy beach has been sampled. The general procedure has been broadly similar to that used in previous surveys (Clark & Haderlie 1960, 1962). Beaches on the west coast of Scotland and the Hebrides were visited in August and September 1960, those on the north and north-east coasts in July and August, and those between Aberdeen and Edinburgh at various times between March 1960 and February 1961. The most thorough examination of beaches has been at and below M T L since it has now become clear that this is where the most numerous populations of Nephtys are generally to be found, although on beaches where the worms are scarce the search has been extended to all tidal levels. Soil samples were brought