Chauvaud, L. L. IUEM,
Jean, F. L. IUEM,
Ragueneau, O. O. IUEM/CNRS,
Thouzeau, G. G. IUEM/CNRS,

Observation of the joint evolution of pelagic and benthic compartments of a western european coastal bay (Bay of Brest) over 20 years, suggests a novel hypothesis on the way this ecosystem withstands eutrophication. Increase in nitrate inputs has slumped the Si:N ratio over the last 20 years. Since 1981, maximum concentrations of Chl a of the first spring blooms have evenly decreased, whereas they increased during secondary blooms. Concomitantly, the extensive spreading of Crepidula fornicata onto bottoms changed the trophic structure of the benthic communities with an increase of the suspension feeders biomass within large areas all over the bay. From our observations, the following synthetic hypothesis can be made: the observed decrease of chlorophyll biomass during the first spring bloom would result from an increased activity of suspension feeders, which would also increase silica retention in the bay. Then, the recycling of retained silicon would maintain the populations of diatoms in summer and would reduce the primary production seasonality. By grazing the spring primary production (storing BSi), the benthos limits the advection rate of BSi towards the neighboring ocean. Thus, benthos control the specific composition of secondary phytoplankton blooms in the bay, avoiding non-siliceous production thanks to remineralization of BSi previously stored.
Day: Friday, Feb. 5
Time: 02:45 - 03:00pm
Location: Sweeney Center
Code: SS13FR0245S