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. Anal ysis of samples collected from areas of different sizes furnished info rmation on the distribution of microphytobenthic organisms (diatoms an d 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 distri bution on all spatial scales for the majority of dominating microalgal species and the existence of 2 orders of aggregation. The spatial str uctures formed by aggregates of the first and second orders are notice ably different from each other in the degree of aggregation (Cassie In dex of 0.5 and >2 on average, respectively), overlapping of species di stributions (Pianka Index of 0.5 and 0.3 on average) and degree of sim ilarity of species structure (Pianka Index of 0.9 and 0.5 on average). This indicates the existence of several structural associations on th e studied intertidal sandflat which differed from each other in specie s 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 severa l main biotic (interspecies interaction) and abiotic (granulometric co mposition of sediments and emersion period during low tide) factors. T he degree of influence of these factors on the character of spatial di stribution of microalgae is related to the selected spatial scale.