SOURCES OF VARIABILITY IN BENTHIC MACROFAUNA OFF SOUTH NORTHUMBERLAND COAST, 1971-1976

Spatial and temporal variability for the period 1971-76 has been assessed, using data from five monitoring stations and two broad surveys of the Northumberland coast. Ordination of the broad survey stations relates the faunal assemblages to depth and the silt content of the sediment, and suggests that their distribution has remained essentially stable for more than a decade. Diversity is negatively correlated with silt content of the sediment but shows no correlation with depth. Biomass is negatively correlated with depth but shows no correlation with sediment type. Temporal variation over the period implicates winter temperatures. The period 1965-70 was characterized by cold winter sea temperatures, but 1971 saw a reversal in this temperature regime and, in the period 1971-76, the winter temperatures were above average. The community response was a progressive change in the pattern of species relative abundance, leading towards a new stabilized ranking condition. At the same time, the number of individuals in the communities progressed towards an equilibrium condition under the influence of density-dependent recruitment and mortality. It is suggested that, in areas with an unstable temperature regime, different suites of species enjoy competitive advantage at different points of the temporal range of temperature variability. This in turn allows the community to maximize its performance throughout a broad range of environmental variability. © 1978, Marine Biological Association of the United Kingdom. All rights reserved.