DISTRIBUTION AND SPATIAL VARIATION OF BENTHIC MICROALGAL BIOMASS IN ATEMPERATE, SHALLOW-WATER MARINE SYSTEM

Benthic microalgae are ubiquitous in Port Phillip Bay, southern Austra lia, where they occupy the dominant soft sediment habitats of this sem i-enclosed marine system. Sediment associated chlorophyll a and pheoph ytin a has been examined as a surrogate estimate of benthic microalgal biomass. The distribution of benthic microalgal biomass, in relation to water depth and sediment characteristics, and the variation of bent hic microalgal biomass across a range of spatial scales are discussed. Benthic microalgal biomass was vertically distributed with a signific antly greater biomass associated with the surficial sediment stratum ( 0-10 mm) compared to the deeper sediment stratum (10-20 mm). Sediments exhibited a significantly greater benthic microalgal biomass when ass ociated with shallow water sites as compared to deep water sites. Sedi ment type dissimilarities for benthic microalgal biomass were not sign ificant. The depth to which light penetrates both the water column and the surficial sediment may limit the distribution of benthic microalg aI biomass. Benthic microalgaI biomass followed a similar distribution to the total organic matter content of surficial sediments indicating that sediment geochemical processes such as nutrient release from the breakdown of organic matter may be important in determining the distr ibution of benthic microalgal biomass. Important scales of spatial var iation occurred at distances in the order of >10 km, 50 m and <2 m, wh ereas, scales in the order of 1 km and 10 m were comparatively unimpor tant. An appropriate sampling strategy to adequately examine benthic m icroalgal biomass in Port Phillip Bay is suggested. (C) 1998 Elsevier Science B.V.