L. Connell, K.A. Welling, R.A. Cattolico-1997
Journal of Shellfish Research, 16 (2) : 493-501 (from Current Contents)
Abstract:
Cell-free conditioned media obtained from high-density Heterosigma cartel ae isolate Carter cultures caused mortality of larval Pacific oysters Crassostrea gigas in 48-h exposures. Streptomycin sulfate added to test vessels prevented mortality at all concentrations of conditioned medium analyzed. These results indicated that bacterial infection of the larvae, and not an algal-produced toxin, was responsible for larval mortality. To explore this hypothesis further, bacteria were isolated from both healthy and diseased larvae. Of the 11 bacterial isolates recovered, 5 belonged to the genera Pseudomonas and Vibrio, both known to be pathogenic to larval oysters. The Vibrio isolate caused mortality when inoculated into healthy cultures of larvae. The growth rate of the bacterium was enhanced by the addition of H. carterae-conditioned medium. It was shown that the amount of dissolved organic carbon (DOC) in conditioned medium increased as algal cell density increased and that this conditioned medium significantly influenced the capacity of pathogenic bacteria to divide. Conditioned medium of the cryptophycean alga Isochrysis galbana was also shown to produce DOC, although at lower amounts. This observation suggests that many algal sources have the potential to induce both bacterial growth and larval mortality, at differing levels. H. carterae-conditioned medium was shown to have no effect on oyster fertilization response, even though it completely inhibited sea urchin fertilization. Further, H. carterae-conditioned medium slightly enhanced the fertilization efficiency in starfish, a predator of bivalves.
(Univ. Washington, Dept. Bot., BOX 35-5325, Srattle, WA 98195, USA)