SAKKA, A. GIROQ, UNIVERSITƒ LAVAL, aae264@agora.ulaval.ca
LEGENDRE, L. GIROQ, UNIVERSITƒ LAVAL, Louis.Legendre@bio.ulaval.ca
GOSSELIN, M. DƒPARTEMENT D'OCƒANOGRAPHIE, UNIVERSITƒ DU QUƒBEC Ė RIMOUSKI, Michel_Gosselin@uqar.uquebec.ca

 
TROPHIC INTERACTIONS IN THE MICROBIAL FOOD WEB IN THE LAGOON OF TAKAPOTO ATOLL (TUAMOTU ARCHIPELAGO, FRENCH POLYNESIA)
 
Trophic interactions in the microbial food web were investigated in the lagoon of Takapoto Atoll (Tuamotu Archipelago, French Polynesia). The growth and grazing mortality rates of bacteria, cyanobacteria and eucaryotic algae were assessed, in the presence and absence of the large grazers (35-200 µm microzooplankton), by serial dilution experiments. Grazing on bacteria was low even when the large grazers were removed, only 28% of bacterial production being consumed. Cyanobacteria were the main primary producers in the lagoon, and were largely consumed by microzooplankton. The grazing mortality rates of cyanobacteria were 55-80% of their growth rates. These results are significant for the fate of biogenic carbon, indicating that a high proportion of the primary production could be channelled to larger metazoan via microzooplankton grazing on cyanobacteria and not on bacteria. The large algae (> 3 µm; dominated by 3-5 µm chlorophyceae) were grazed at rates equivalent to their own growth rates, indicating a steady-state situation with rapid cycling of the biomass of the large algae. When the 35-200 µm grazers were absent from the incubated samples, the phytoplankton grazing mortality rates significantly increased, indicating that the small consumers (< 35 µm protozoa) were controlled by the large ones. The specific growth rates of large eucaryotic algae were higher when these were exposed to high grazing, indicating a close coupling between the growth of large algae and protozoan grazing. This linkage was likely mediated by increased nutrient regeneration.
 
Day: Wednesday, Feb. 3
Time:
Location: Sweeney Center
 
Code: CS60WE0248S