Benthic Faunal Dynamics during Succession Following Pollution Abatement in a Swedish Estuary

Abstract

The recovery of benthic communities was studied continuously since the closure of a sulfite pulp mill in 1966. The previous, increasing organic enrichment in the estuary had deteriorated the marine environment and reduced the fauna over large areas. The succession of the macrobenthic communities to a level where the recovery process was indistinguishable from annual fluctuations took about 8 yr. By then the composition of the community was similar to that recorded 40 yr earlier. The successional changes in number of species, individuals and biomass are illustrated for the total fauna and for dominating groups. The sequential changes of some numerically dominant populations showed a bell-shaped curve pattern. During the 1st years after pollution abatement, when polychaetes dominated, these population changes were drastic but evened out in later seral stages. The role of larval recruitment in succession is discussed. Three diversity indices were used to assess the community structure: Shannon''s formula, its measurement of evenness, and Sanders'' rarefaction technique. As tools for assessing pollution or recovery, the 2 former had to be used with care, as the highest values were recorded at the beginning of the recovery process when the individuals found were few but evenly distributed among the few species present. The rarefaction technique and the measure of species richness were more satisfactory for this kind of assessment.