EFFECTS OF TRICHODESMIUM SPP. BLOOMS ON PENAEID PRAWN LARVAE

The effects of blooms of the cyanobacterium Trichodesmium spp. on pena eid prawn larvae were examined using in situ and laboratory rearing ex periments and plankton surveys in Albatross Bay, Gulf of Carpentaria, Australia. The in situ experiments demonstrated that, during a bloom o f Trichodesmium spp., larvae of the prawn Penaeus merguiensis did not develop beyond the first protozoea stage, and survival was low compare d with times when diatoms were dominant in the same study area. Labora tory experiments confirmed the in situ results. None of the prawn larv ae fed Trichodesmium sp. in laboratory experiments developed beyond th e first protozoeal stage. In contrast, 94% of prawn larvae fed the gre en flagellate Tetraselmis suecica successfully developed to the second protozoea stage. Electron microscopy of larvae gut-contents revealed that Trichodesmium spp. were ingested by larvae but were of no nutriti onal value, resulting in starvation. A 7 yr plankton survey, from 1985 to 1992, showed that minimum abundance of prawn larvae occurs during the annual summer blooms of Trichodesmium? spp. and that maximum abund ance of prawn larvae generally occurs just after the bloom. There was a negative correlation between the abundance of larvae and the abundan ce of Trichodesmium at individual sites, one offshore and one inshore, indicating that the blooms affect the survival of larvae. We conclude that variations in both timing and magnitude of Trichodesmiun? blooms are important determinants of prawn larvae abundance in Albatross Bay .