The planktonic food web of Takapoto Atoll lagoon was studied using network analysis. This analysis includes four types of indices dealing with bilateral interactions of compartments, the trophic structure, biochemical cycles, and the topology of the flows. We found numerous parallel carbon pathways of similar importance, indicating a highly complex system compared to other marine ecosystems. Other characteristics were trophic levels not ranked in the same order as the size classes, the domination of system activity by processes at the first trophic level (and especially by herbivory), and cycling processes that involve many pathways. This is the first use of network analysis to describe completely a planktonic food web, and also the first comprehensive description of the trophic structure of the planktonic system in an atoll lagoon.

Current meter data on the northern slope of the island of Tahiti show the presence of internal waves principally at diurnal, inertial and sub-inertial frequencies. The amplitude of these internal waves is sufficient to bring nutrient-rich water to 30 or 40 m depth. This is the elevation of the base of the spur-and-groove system of coral reefs. From there the nutrients can readily be brought to the surface by wave-driven-upwelling in the grooves. The coupling of internal waves and upwelling in grooves on coral reef slopes may account for the elevated productivity of the coral reefs in oligotrophic surface oceanic waters.

Opunohu Bay is a narrow, straight, 3-km long bay on the island of Moorea, French Polynesia. The bay is open to the ocean with a water depth of about 80 m at the mouth. The sea floor slope reaches one-third offshore. Field observations show that a wind blowing to offshore along the axis of the bay generates an outflow at the surface and an inflow below 20 m depth. A localized upwelling results at the mouth of the bay which may also be detected in the phytoplankton population. This situation is modelled numerically and the results suggest that the wind stress must be taken to be not only a function of the wind speed but also of the wind fetch.

Large quantities of carbonate mud are found in suspension, with concentrations reaching 80 mg l−1, in the lagoon of Mataiva Atoll, French Polynesia. Residence time of water in the lagoon is about 73 days. Carbonate particles are exported offshore in a negatively buoyant plume that sinks in oceanic waters. The carbonate particles are from resuspension of abraded carbonate of biological origin. The negative buoyancy is induced by evaporative cooling of turbid lagoon water, turbidity resulting from wave-driven suspension of calcareous sediment. Contaminated mine water should be released at depth, offshore, as a negatively buoyant plume to sink in oceanic waters.

There has been in the last 13 years a marked increase of tourism pressure on the lagoon of Tiahura, (Moorea Island, French Polynesia). This increase may degrade the reef ecosystem. In particular, it has been suggested that the macro algal blooms are caused by waste water discharge. A field and numerical study of the water circulation was undertaken in order to evaluate this impact. The results show the existence of trapping zones where pollutants may accumulate under certain meteorological conditions. To remedy the situation, sewage should be discharged offshore on the reef slope in 30 m depth or used on land.

Quelques aspects de la biologie de Callichirus armatus A. Milne Edwards, 1870, un crustace fouisseur du groupe des callianasses, ont ete etudies pour la premiere fois. La distribution, les densites de peuplement, l'activite de creusement et la bioturbation dues a C. armatus ont ete etudiees dans differents lagons de Polynesie francaise. Des donnees preliminaires sur le cycle sexuel et les mues ont pu etre obtenues. La discussion porte sur la signification ecologique de la bioturbation sur les sediments lagonaires.