ARE SOFT-SEDIMENT COMMUNITIES STABLE - AN EXAMPLE FROM A WINDY HARBOR

The macrobenthic soft-sediment communities at 6 sites in Manukau Harbo ur, New Zealand, have been quantitatively sampled at bimonthly interva ls since October 1987. Univariate (contingency-table analysis, Kendall 's coefficient of concordance and Jaccard's similarity index) and mult ivariate (non-metric multi-dimensional scaling and canonical community ordination) analyses were used to assess the absolute and relative st ructural stability of the communities at each of the 6 sites over the first 51/2 yr of sampling. Despite short-term, seasonal and inter-annu al variability, the communities have generally been persistent, in ter ms of their overall community structure, over the duration of the samp ling programme. Manukau Harbour is a dynamic and rigorous environment in terms of movement of water and sediments. Mean wind conditions were found to play an important role in contributing to variability in com munity structure at different sites in the Harbour, probably as a resu lt of sediment disturbance by wind-induced waves and bottom turbulence . In addition to local factors, there was also evidence that factors o perating at harbour-wide scales (e.g, water temperature) contributed t o variability in community structure. The populations of some species exhibited marked temporal fluctuations. Major recruitment events poten tially lead to altered physical, chemical or biological characteristic s of the benthic habitat with concomitant effects on other species in the community. Despite the physically and biologically dynamic environ ment, the communities were persistent and exhibited both resistance an d resilience to physical disturbance and major recruitment events. Oth er studies have reported these to be important factors contributing to instability in the structure of soft-sediment communities.