EFFECTS OF A CYCLONE ON CORAL-REEF PHYTOPLANKTON BIOMASS, PRIMARY PRODUCTION AND COMPOSITION (MOOREA ISLAND, FRENCH-POLYNESIA)

Observations on the phytoplankton biomass, primary production and comp osition of a French Polynesian barrier reef, following the passage of cyclone Wasa in December 1991, led to outline two effects: a transient washout of the lagoonal waters replaced by oceanic ones, and an incre ase in phytoplankton biomass and primary production together with a pr edominance of diatoms over other phytoplankton classes. These results are compared and discussed with the few previous studies either concer ning the same reef or other tropical reefs. The increase in biomass an d primary production, although less marked than in other areas, may be related to nutrient enrichment either from terrestrial run-off or res uspended sediments. The predominance of diatoms seems to be a general pattern which can be related to higher growth rates of diatoms compare d to other phytoplankters, thus allowing diatoms to take advantage of the nutrient enrichment in the first place. The phytoplankton increase is frequently followed by a bloom of benthic macroalgae. This micro- and macroalgal development may prevent the loss of dissolved nutrients out of the coral reef ecosystem.