Spatial structure of an intertidal sandflat microphytobenthic community as related to different spatial scales

Investigations were carried out on an intertidal sandflat (Kandalaksha Gulf, the White Sea, Russia) during the summers of 1988 to 1992. Analysis of samples collected from areas of different sizes furnished information on the distribution of microphytobenthic organisms (diatoms and dinoflagellates) over 3 spatial scales: microscale (10 to 1000 cm(2)), mesoscale (1000 cm(2) to 100 m(2)) and macroscale (100 to 10 000 m(2)). Analyses of the data disclosed the aggregated character of distribution on all spatial scales for the majority of dominating microalgal species and the existence of 2 orders of aggregation. The spatial structures formed by aggregates of the first and second orders are noticeably different from each other in the degree of aggregation (Cassie Index of 0.5 and >2 on average, respectively), overlapping of species distributions (Pianka Index of 0.5 and 0.3 on average) and degree of similarity of species structure (Pianka Index of 0.9 and 0.5 on average). This indicates the existence of several structural associations on the studied intertidal sandflat which differed from each other in species composition and the character of spatial distribution of organisms. The studied community had a highly complicated spatial structure. The presence of several orders of aggregation probably results from several main biotic (interspecies interaction) and abiotic (granulometric composition of sediments and emersion period during low tide) factors. The degree of influence of these factors on the character of spatial distribution of microalgae is related to the selected spatial scale.