ABSTRACT: Filter-feeding behaviours of the mussel Perna viridis and the oysters Crassostrea belcheri, Crassostrea iradelei, Saccostrea cucculata and Pinctada margarifera were compared during natural tidal variations in the concentration (6 to 40 dry mg total particulate mass l^-1) and organic content (6 to 22%) of seston available in the Merbok mangrove system, Malaysia. In P. viridis, C. belcheri and S. cucculata, declining retention efficiencies for the largest available particle size classes of more than 6 to 12 µm diameter were associated with an overall organic enrichment of filtered relative to available matter. As seston availability increased, a minimum average of 71% of the additional filtered matter was rejected by each species as pseudofaeces prior to ingestion. And in all 5 species, preferential rejection as pseudofaeces of filtered particles with higher average inorganic content resulted in the net organic enrichment of ingested relative to filtered matter. In P. viridis and C. belcheri, the efficiency of that net organic selection declined for seston of lower organic content. Combining all data from each species, absorption efficiencies from ingested organics increased exponentially with the organic content of ingested matter. Collective findings suggest that key interrelations between component processes of nutrient acquisition were similar to those that have been established for the modeling of feeding, growth and environmental impact among filter-feeding bivalves from temperate latitudes. However, especially fast growth in P. viridis stemmed from higher average (± 2 SE) clearance rates (13.2 ± 7.0 l h^-1 g^-1 when particulate organic matter < 1 mg l^-1), greater average organic enrichment of filtered relative to available matter (0.99 ± 0.67) and greater average organic enrichment of ingested relative to filtered matter (0.63 ± 0.03) than have hitherto been recorded in any species of bivalve filter-feeder. In contrast, P. margarifera was least well adapted for the pre-ingestive selection of organic matter, with no differential retention on the gill and little selective rejection as pseudofaeces, representing at least part of the physiological basis for characteristically slow growth in pearl oysters.

KEY WORDS: Filter-feeding behaviour · Particle selection · Seston composition · Perna viridis · Crassostrea belcheri · Crassostrea iradelei · Saccostrea cucculata · Pinctada margarifera

Published in MEPS Vol. 166 (1998) on May 28
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1998