Particulate matter in Takapoto lagoon waters: potential food for cultivated pearl oysters

Results of research concerning the food of the pearl oyster Pinctada mai ma rgaritifera are presented, by taking Takapoto atoll (Tuamotu archipelago, F rench Polynesia) as a study site. Monthly sampling of several parameters re presentative of bivalve environment and food (water temperature, salinity, mineral and organic matter, proteins, lipids and carbohydrates, chlorophyll a and phaeopigments) confirm and increase knowledge of the Takapoto lagoon hydrobiology. The variability of these parameters was analysed. Takapoto l agoon showed a remarkable spatial stability. Temporal variations showed a l ow seasonal trend. Local meteorology (wind, precipitation) had an influence on short-term variability (especially for mineral matter). Night and day r hythm also affected some parameters (temperature, chlorophyll a, lipids and carbohydrates). In this shellfish environment, carrying capacity appears t o be low: organic matter is around 0.35 mg.L-1, chlorophyll a concentration is below 0.30 mu g L (- 1) and energetic content of particulate material i n waters, approx. 2 J.L (- 1), is ten times lower than in temperate areas. On the other hand, seasonal effect is reduced and particulate food is alway s available. Preliminary results on carrying capacity show that cultivated pearl oysters play an insignificant role on the system in comparison with t he natural trophic bivalve population. (C) 2000 Ifremer/CNRS/IRD/Editions s cientifiques et medicales Elsevier SAS.