A Broad Review of Variability and Persistence in the Northumberland Benthic Fauna – 1971–85

Abstract

The long-term monitoring of two stations, 55 and 80 m depth, from 1971 to 1985 shows clear evidence of periods of stability interspersed with periods of change. These periods were identified by several different multivariate methods and persistence stability was quantified by the use of a between years similarity index. A short period of change at the shallow station, 1972–3, was followed by a prolonged period of stability 1974–80. The period 1981–3 witnessed a second period of change with rising total numbers and biomass with some evidence of a downward reversal in 1984–5. The deep station exhibited an essentially similar response except that the stable period 1974–80 was broken into two sub-periods 1974–6 and 1978–80 due to sequential changes in the dominant species which were regarded as evidence of biological interaction with the activities of the polychaete Ophelina acuminata possibly playing a key role. The shallow station showed little evidence of biological interaction and the majority of the species have exhibited similar responses throughout. The general rise in numbers and biomass at both stations is regarded as evidence of intermittent changes in organic flux to the bottom from the water column. The winter temperature fluctuations were shown to have short-term, but significant, effects on the diversity of the communities, bringing about year to year changes in the equitability and dominance.