Dwarf surfclam Mulinia lateralis (Say, 1822) populations and feeding during the Texas brown tide event
Montagna, Paul A.
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In 1990, there was an unusual brown tide bloom of an aberrant Chrysophyte sp, in Baffin Bay and Laguna Madre near Corpus Christi, Texas. Coincident with the bloom was a dramatic loss of shellfish in Baffin Bay and Laguna Madre, The dominant clam, Mulinia lateralis. disappeared for about two years. Wc performed a series of experiments to determine if disappearance of M. lateralis was related to negative feeding interactions with the brown tide organism, Radioactive tracers were used to compare feeding rates on brown tide, Isochrysis galbana, DUllalielia tertioleera. and Heterocapsa pygmeae. At low cell concentrations « I,000 cells' ml" I), M. lateralis grazing rates (ccll . h-I) increased with concentration and were similar among the microalgal species. At higher concentrations, grazing rates on lsochrysis were inhibited, but remained the same for the other microalgal species. Assimilation efficiency by M. lateralis was lowest on Heterocapsa, and was about the same for the three other species of algae. The high grazing and assimilation rates of brown tide by M. lateralis indicate that the loss of the clam population was not likely caused by a negative trophic effect of the brown tide. Other bloom factors, e.g. reproductive effects or toxic effects, may have contributed to the concomitant loss of the clam population and the occurrence of brown tide. It is also possible that non-bloom factors, e.g. natural population variability increased predation pressure, could have caused the population loss. The reduced populations of filter feeders could have been partially responsible for conditions conducive for the brown tide bloom.