Particulate matter in the sublittoral zone of an exposed coast and its ecological significance with special reference to the fauna inhabiting kelp holdfasts

Abstract

As part of an ecological investigation of the kelp holdfast fauna in northeast Britain, research has been made into the physical conditions responsible for the ecologically significant ‘sediment factor’. Bottom-mounted apparatus at Robin Hood's Bay and Flamborough Head (Yorkshire, England) has been used to study fluctuations in sediment deposition. Membrane filtration of sea water has given data on suspended material. The total dry weight of deposited sediment has been related to prevailing onshore winds (in excess of 6.6 m/sec) and turbulence. The coarseness of the sediment deposited is proportional to the total sample dry weight. Sediment sorting is shown to vary according to the relative contribution of the particle size range incorporating a median diameter of 180 μm. ‘Organic’ content of deposited sediment fluctuated seasonally, with highest values after the settlement of detritus during periods of summer calm. Suspended solids showed a marked seasonal variation with high values in winter and low values in summer. Statistical analysis, has enabled a grouping of months into two significantly different periods, i.e. ‘summer’ and ‘winter’ to be made. A generally comparable seasonal trend in suspended solids has been observed over a two year period. A multiple linear regression equation is presented, linking suspended solids at Robin Hood's Bay with the environmental parameters of sea state, tidal range, and river flow: the regression accounts for 28 % of the total variance. Sea state is shown to be the single most important factor influencing suspended solids. The ecological significance of the environmental complex governing the expression of a ‘sediment factor’ is discussed in relation to the kelp fauna. The difficulty of accurately interpreting data on faunal dynamics is outlined in the light of these and other factors. The suggestion is made that such data would be of little use in an assessment of temporally changing pollution effects.