SHORT-TERM VARIATION IN THE QUANTITY AND QUALITY OF SESTON AVAILABLE TO BENTHIC SUSPENSION FEEDERS

Recent studies have demonstrated that short-term and small-scale variation in seston availability can have significant effects on individual and population characteristics of benthic suspension feeders. To provide a better understanding of in situseston dynamics 1-2 cm above the substrate surface we measured hourly variation in seston quantity and composition (total C and N, chlorophyll a, bacteria, energy content, and particle size spectra) over a tidal cycle. Mean seston concentration was significantly lower in water collected during ebb tide than in water sampled during flood tide (37·1 vs.78·1 mg 1-1). The range of seston concentrations observed in a single tide was almost as great as the range of seston concentrations measured at this site over an entire year in other studies. Particles 2-20 μm in diameter comprised most (>80%) of the volume of the seston throughout the entire tidal cycle. The organic portion of the seston remained fairly constant when tidal velocities increased during flood tide; the seston was not 'diluted' by inorganic particles. In general, mean seston concentration for the entire tide (57·1 mg l-1) was greater in our study than has been reported in the majority of comparable studies. This may be a consequence of our sampling much closer to the substrate surface. The patterns of variation in seston concentration and quality were not predictable solely from measurements of physical factors responsible for particle suspension (e.g. current speeds, wind speeds). © 1992 Academic Press Limited.