SHORT-TERM BIOTURBATION ACTIVITY IN THE LAGOONAL SEDIMENTS OF TIKEHAUATOLL (TUAMOTU-ARCHIPELAGO, FRENCH-POLYNESIA)

To quantify bioturbation activity in Tikehau lagoon, a tracer made of black basaltic sand was poured over the natural white calcareous sedim ent surface. Three stations respectively located on the inner flat (-3 m), the inner slope (-9 m); and the lagoon floor (-19 m), were studie d for short periods of time (48 hours). Bioturbation by macrofauna was quantified by volume of sediment elected onto the experimental surfac e and by volume of tracer incorporated into sediment. The results show ed a rapid incorporation of sedimented particles at the interface by w ay of the funnels and burrows of surface deposit feeders and carnivore s. Expelled quantities varied with respect to site location: 213 cm(3) .m(-2).24 h(-1) in the inner flat; 98.9 cm(3).m(-2).24 h(-1) in the in ner slope; 7.9.m(3).m(-2).24 h(-1) in the lagoon floor. Bioturbation b y decapod megafauna appeared to be important in the dynamics of the se diments in the deepest areas of the lagoon. In these areas, with almos t no hydrodynamical impacts on sediments, bioturbating events were res ponsible for sediment mixing (despite lower absolute rates than in sha llow area). Hydrodynamics controlled the spatial distribution of macro invertebrate trophic groups by its effects on sedimentation.