A quantitative evaluation of the effects ofAscophyllum harvesting on the littoral ecosystem

Abstract

Little is known of the ecological effects of harvesting littoral algae although this is a worldwide commercial activity. In 1976 an attempt to establish harvesting in Strangford Lough, Northern Ireland, was opposed on mainly theoretical conservation grounds. The attempt began and stopped within a single small bay leaving a sharp boundary between cut and uncut areas. A subjective survey apparently confirmed the predicted loss of cryptic fauna, decline through predation and the resorting of interboulder sediment. In April 1979 the cut and uncut areas were examined in detail to determine whether any of these effects had persisted and were demonstrable scientifically. Beach and boulder transects and various other studies showed some increases in the cut area. There was significantly moreFucus, Enteromorpha andUlva; Cirratulus (inhabitingRhodochorton-bound sediment on boulder surfaces) had a greater biomass. Some changes inLittorina colour morphs were apparent. Sediment in the cut area was coarser and had significantly more crustacean meiofauna.Ascophyllum internodal length and lateral branching were increased but it still provided 20% less shore cover than in the uncut area. There were significant decreases in the cover ofCladophora on the sides of boulders and ofHalichondria, Hymeniacodon andBalanus on undersurfaces. Indeed on the habitable underside of boulders total animal cover had been reduced by nearly two-thirds and the average number of species per boulder by one-third. It is concluded thatAscophyllum harvesting has a significant and persistent effect on shore ecology. Littoral algae are a valuable commercial asset but it is important that some fairly large intertidal areas should be left unharvested for general conservation purposes.