The structure and functioning of estuarine fish assemblages have been analysed using data sets for 38 transitional waters covering all European latitudes, including NE Atlantic estuaries, Mediterranean lagoons and Scandinavian fjords. The fish species were assigned to functional guilds covering estuarine use, mode of feeding and reproductive strategy, thus describing the use made of transitional waters by fishes. The importance of estuaries as temporary biotopes (migration and nursery routes) for fish species has been identified together with the predominance of feeding on the detritivorous hyperbenthos and infauna. The high incidence of protective breeders in estuaries, as a mechanism to prevent the flushing out of young, has also been identified. These findings allow the validation of the functional guild approach, emphasising its use for the understanding of the functioning of estuaries and for their management and the protection of their ecological goods and services.

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The morphological organization of the male brood pouch skin of three different species of syngnathids (Nerophis ophidion, Syngnathus abaster and Hippocampus hippocampus), investigated using light and electron microscopy, showed that each pouch had a skin with a different ultrastructure. This reflected different relationships between the paternal body and the developing embryos. In N. ophidion, the bilayered epidermis of the pouch consisted mainly of pavement cells (filament-containing cells) typical of fish skin. In S. abaster, pavement cells were interspersed with many mitochondria-rich cells. These cells varied in number during the different functional stages of the pouch and died by apoptosis after the breeding period. Modified secretory ' flame cone cells ' rich in vesicles and granules characterized the epidermis of H. hippocampus. Although there were specific differences, the vascularized dermis was the only feature common to all three types of pouch. These findings suggest that the brood pouch in Syngnathidae has different functions, which may be related to the different reproductive strategies and ecology of each species.