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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Sound production of 11 Mediterranean goby species, belonging to five different genera, have been comparatively analysed on the basis of the quantitative properties of the acoustic signal emitted by the male in both the reproductive and aggressive context. The results obtained showed that three groups of species can be recognized on the basis of signal similarity: the larger sized species (genus Padogobius and Gobius paganellus) producing tonal sounds, showing high values of pulse rate and low values of duration; the larger-sized species producing grunt sounds (genus Gobius and Zosterisessor) with low pulse rate and low duration; and the small-sized species producing grunt sounds (genus Pomatoschistus and Knipowitschia) with low pulse rate and high duration. The comparison between these results and those found in previous studies suggests congruence between the acoustic affinities among species and that obtained by means of morphological and genetic data. Furthermore, first hypotheses on the evolution of acoustic communication and the associated mechanisms in this fish group are suggested.

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