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Coolia monotis is a potentially toxic epiphytic dinoflagellate widespread along the Mediterranean coasts, where it is frequently detected year round at low concentrations. However, it only proliferates recurrently in some localities. The North Lake of Tunis is one of the affected areas in the southwestern part of the Mediterranean Sea. This site is one of the most productive aquatic Tunisian areas (Recreational Fisheries and shellfish collecting). In the south part of this area of study, recurrent C. monotis proliferation (5 x10(5) cells per liter) took place in late spring and early summer of 2006. During this proliferation, the spatial distribution of C. monotis species, phytoplankton community, and abiotic factors were studied. The composition of the phytoplankton community exhibited a clear dominance of dinoflagellates over other genera. We suggest that proliferation development of C. monotis was linked to climatic conditions, water temperature (r = 0.24, p < 0.05) and high concentrations of nitrogenous nutrients, essentially NH(4)(+) (r = 0.18, p < 0.05) and NO(3)(-) (r = 0.21, p < 0.05).

The influence of spatial and environmental factors in explaining the structure of large branchiopod assemblages at different spatial scales is still poorly explored. We hypothesized that the extent of actual spatial connectivity, and thus the spatial distribution of a metacommunity, may depend on the environmental conditions as represented by climatic gradients and the structural characteristics of the landscape. To test this hypothesis, the distributional patterns of 14 large branchiopod species in a set of 177 temporary water bodies repeatedly sampled across Tunisia and on its main islands were analysed. Physical, chemical, morphological and climatic characteristics of the studied water bodies were collected as well, and spatial structures were described using distance-based Moran’s Eigenvector Maps. Distance-based Redundancy Analysis and variance partitioning explained more than one-half of total variation. Mantel’s autocorrelograms demonstrated that species composition was spatially autocorrelated at shorter distances in the Mediterranean part of the country than in the southern, more arid part. These results suggest that both dispersal limitation and species response to spatially structured environmental gradients might be involved in determining large branchiopod distribution in Tunisia and that these patterns may greatly vary on a regional basis

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