Benthic ecology of Dublin Bay in relation to sludge dumping: Fauna

Abstract

The Dublin Bay area in 1971 received sewage from about three quarters of a million people most of which was discharged or dumped off Howth to the north-east of the bay. Much sludge appeared to settle up and down the tide from the dump site, though finer particles entered the bay to the south. Additionally, dredge spoil was dumped south-east of the Baily up to 1971, but not in 1972. In 1971 and 1972 the effects of these organic wastes on the benthos were investigated. The fauna in the main part of the bay resembled the Acrocnida/Clymene community of Glémarec. On the sand banks there were also species of the Ophelia facies of Glémarec's deep Venus community. In the dumping area and in the southeast of the bay downtide of the dump site, where depths are greater, the faunas resembled the Nucula/Sabellaria community of Caspers. As well as having pollution indicator species, this latter community generally had greater faunal densities and diversities than elsewhere in the bay (except low divcrsities at the dump sites in 1971). Apart from a possible effect of depth, this suggests that the dumping was having an enriching rather than a degrading effect, although the probable sediment change since 1874 may imply a change in community type. Microvores (comprising surface-deposit and suspension feeders) were a prominent isotrophic group in the sampling area, and at the sludge-dumping site in 1971 particle feeders were abundant. All feeding types were more numerous in the organic waste settlement areas, though proportionally they appeared to be receiving differential benefits from the sludge and dredge spoil.