Distribution and spatial variation of benthic microalgal biomass in a temperate, shallow-water marine system

Abstract

Benthic microalgae are ubiquitous in Port Phillip Bay, southern Australia, where they occupy the dominant soft sediment habitats of this semi-enclosed marine system. Sediment associated chlorophyll a and pheophytin 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 benthic microalgal biomass across a range of spatial scales are discussed. Benthic microalgal biomass was vertically distributed with a significantly 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 associated with shallow water sites as compared to deep water sites. Sediment type dissimilarities for benthic microalgal biomass were not significant. The depth to which light penetrates both the water column and the surficial sediment may limit the distribution of benthic microalgal biomass. Benthic microalgal 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 distribution of benthic microalgal biomass. Important scales of spatial variation occurred at distances in the order of >10 km, 50 m and <2 m, whereas, scales in the order of 1 km and 10 m were comparatively unimportant. An appropriate sampling strategy to adequately examine benthic microalgal biomass in Port Phillip Bay is suggested.