The use of natural microphytobenthic assemblages as laboratory model systems

The use of complex species mixtures is becoming more common in laboratory investigations of ecological theory. Natural assemblages of microphytobenthos provide a model system of considerable species richness that can be examined and manipulated easily under laboratory conditions. However, the relative temporal stability of these assemblages maintained under laboratory conditions in terms of species composition and community metabolism is not known. This information is required before the results from model systems employing assemblages of microphytobenthos can be properly interpreted. Natural assemblages of microphytobenthos were sampled, prepared and incubated in the laboratory under light levels representative of those found in the literature. Analysis of microphytobenthic assemblage composition (gross community change); biomass (chlorophyll a), composition of pigments and photophysiological status were assessed after a 14 d period. No changes in species richness were found, whilst diversity declined from the initial field values, but were similar when compared between assemblages maintained at different light levels. Field assemblages contained greater numbers of larger diatoms compared to the cultured assemblages. Photophysiological responses were similar between the 2 light treatments, although signs of photophysiological stress were observed. It was therefore shown that estuarine microphytobenthic assemblages appear to possess a certain degree of inertia when brought from the field into the reduced light regime of a laboratory. Microphytobenthic assemblages therefore provide a useful experimental model with relevance to natural conditions.