DYNAMICS OF SPATIAL PATTERNS OF MICROPHYTOBENTHIC BIOMASS - INFERENCES FROM A GEOSTATISTICAL ANALYSIS OF 2 COMPREHENSIVE SURVEYS IN MARENNES-OLERON BAY (FRANCE)

Microphytobenthos plays an important role as primary producer in shall ow embayments subject to a tidal regime. The present paper aims to cha racterize the spatial patterns of sedimentary chlorophyll a (chl a) bi omass in 2 seasons in the wide intertidal mudflats of the Marennes-Ole ron Bay (France); furthermore, it provides estimates of total microphy tobenthic biomass. Accordingly, a systematic sampling scheme was perfo rmed in June 1995 and in January 1996. On average, biomass was higher in June (ca 120 mg chi a m(-2)) than in January (ca 85 mg chi a m(-2)) . Moreover, the geostatistical analysis revealed that spatial similari ties were propagated over larger distances in June (6 km) than in Janu ary (2.2 km). In order to account or this result, we suggest that seas onal dynamics of benthic microalgae biomass obeys a 'constant-density model' that describes the alternating spreading/shrinkage phenomenon a round the few persistent patches of maximum biomass (ca 300 mg chi a m -2). Total biomass estimates were ca 13 t chl a (SE = 0.26) in June an d 10 t chi a (SE = 0.28) in January. Calculating a raw approximation o f the growth rate (0.1 d(-1)) of that biomass and considering that the total produced biomass is resuspended at flood tide, we found that mi crophytobenthos supplies about 2 mu g chi a l(-1), which corresponds t o 30-90 % of the chi a suspended in the water column, depending on the season. This suggests that microphytobenthos could be a major food so urce for secondary producers in both pelagic and benthic ecosystems of the Marennes-Oleron Bay.