The diversity and distribution of bryozoans have been surveyed at two localities, Cape Struga on Lastovo Island (South Adriatic) and Cape Š ilo on Prvić Island near Senj (North Adriatic), with similar characteristics of topography and exposure but markedly different sea temperature conditions. Continuous measurements over one year have shown that temperature conditions differ in two aspects. First, the annual range of temperature is much larger in the North. Second, in the South during summer, marine life within the thermocline layer is exposed to large high-frequency temperature oscillations, partly due to an internal diurnal tide, a phenomenon recorded for the first time in the Adriatic. Altogether, 78 species have been recorded, 57 in Lastovo and 50 in Prvić, and 29 in both localities. The comparison of mean zooid lengths of 14 bryozoan species occurring at both localities indicates no consistent difference in zooid size between northern and southern sites. Seventeen bryozoan species have been recorded in the Eastern Adriatic Sea for the first time.

Large carbonate, bryozoan-serpulid constructions, made by Pentapora fascialis and Salmacina dysteri respectively, were found around karstic freshwater springs, called vruljas, in the Senj Archipelago (Velebit Channel, Croatia). In June 2002, several sites were investigated by SCUBA divers on the rocky cliffs of Grmac and dralova at depths ranging from 19 to 32 m. Mean colony diameter decreased with increasing distance from the vruljas: in the vicinity the mean diameter was 65.8€21 cm, at 2-m distance it was 40.4€8.2. Carbonate contribution was to a great extent due to the bryozoan (5,784€1,186 gÁm 2 CaCO 3 ) rather than to the serpulid (383€218 gÁm 2 CaCO 3 ). P. fascialis carbonate standing stock was remarkably high if compared with data from literature for shallow carbonate producers. The bryozoanserpulid constructions can be indicated as important, even if localised, contributions to the carbonate budget in the Adriatic Sea.

Bryozoans are aquatic invertebrates that inhabit all types of aquatic ecosystems. They are small animals that form large colonies by asexual budding. Colonies can reach the size of several tens of centimeters, while individual units within a colony are the size of a few millimeters. Each individual within a colony works as a separate zooid and is genetically identical to each other individual within the same colony. Most freshwater species of bryozoans belong to the Phylactolaemata class, while several species that tolerate brackish water belong to the Gymnolaemata class. Tissue samples for this study were collected in the rivers of Adriatic and Danube basin and in the wetland areas in the continental part of Croatia (Europe). Freshwater and brackish taxons of bryozoans were genetically analyzed for the purpose of creating phylogenetic relationships between freshwater and brackish taxons of the Phylactolaemata and Gymnolaemata classes and determining the role of brackish species in colonizing freshwater and marine ecosystems. Phylogenetic relationships inferred on the genes for 18S rRNA, 28S rRNA, COI, and ITS2 region confirmed Phylactolaemata bryozoans as radix bryozoan group. Phylogenetic analysis proved Phylactolaemata bryozoan's close relations with taxons from Phoronida phylum as well as the separation of the Lophopodidae family from other families within the Plumatellida genus. Comparative analysis of existing knowledge about the phylogeny of bryozoans and the expansion of known evolutionary hypotheses is proposed with the model of settlement of marine and freshwater ecosystems by the bryozoans group during their evolutionary past. In this case study, brackish bryozoan taxons represent a link for this ecological phylogenetic hypothesis. Comparison of brackish bryozoan species Lophopus crystallinus and Conopeum seurati confirmed a dual colonization of freshwater ecosystems throughout evolution of this group of animals.

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This study examines the ecology and thermal regime in the Živa Voda anchialine cave on Hvar Island (Adriatic Sea, Croatia). The cave, which has no direct connections with the open sea, contains a dense population of the deep‐sea hexactinellid sponge Oopsacas minuta Topsent, 1927. Several species of polychaetes, molluscs and crustaceans were also recorded. Two‐year temperature data recorded simultaneously at two depths within the cave and at a nearby outside site provide information on thermal conditions in the system. The temperature oscillations within the cave are strongly dampened – varying from 14.6 °C in winter to 17.9 °C in summer – the annual range being four times smaller than in the adjoining sea. These data suggest that O. minuta can withstand higher temperatures than previously expected from deep‐sea or cold‐water cave occurrences, and that other environmental factors must be playing an important role.