MICROPHYTOBENTHOS AND PHYTOPLANKTON IN BA NYULS BAY (GULF OF LIONS) -STANDING STOCKS AND HYDROCLIMATIC FACTORS

A three year survey of the microphytobenthic biomass in Banyuls bay (G ulf of Lions) was performed from May 1990 to March 1993. The sediments investigated had different characteristics in granulometry and bathym etry: from shallow sands to a deeper muddy sediment. In order to estab lish comparisons between pelagic and benthic microphytic biomasses and their temporal variations, the phytoplankton standing crop was also m easured in the bay. A geographical gradient appeared: the highest bent hic biomasses were associated to the muddy sediment (P-5, 32 m deep: o n an average 2.5 mu g Chl a g(-1) sediment Dry Weight, 5 mu g Phaeo a g(-1) DW; 7.5 mg Chl a m(-2)), 2 whereas very low pigment concentratio ns characterized the sands - 5 to 20 m deep - (on an average 1 mu g Ch l a g(-1) DW, 0.5-1 mu g Phaeo a g(-1) DW; 7 mg Chl a m(-2)). A season al trend, well marqued at Ps, but also at the other stations, was evid enced. These temporal variations are characterized by a summer maximum : up to 1 mu g Chl a g(-1) DW in the sands and more than 4 at Ps, when expressed by surface units it corresponds to 14 mg Chi a m(-2) in san ds and 18 mg Chl a m(-2) in the P-5 muddy sediment. These pigment conc entrations are relatively low. Chi a and Phaeo a variations are simult aneous in the sands and disynchronous at P-5. Some hydroclimatic param eters (temperature, insolation, wind and roughness of sea) are illustr ated and their variations compared to those of pigment concentrations in the sediments. The summer increase of the microphytobenthic biomass may be related to the stability of the substratum and the high level of insolation. The seasonal variations of phytoplankton biomass are qu ite different: decrease in pigment concentrations in summer and increa se in winter (up to 2 mu g Chl a l(-1); annual mean concentration: 0.7 mu g Chl a l(-1) corresponding to 20 mg Chi a m(-2) at P-5).