Habitats in submerged karst of Eastern Adriatic coast--Croatian natural heritage.

of the Dalmatian coast type, formed primarily from karst limestone, Eastern Adriatic coast shows great diversity of habitats. This diversity is also influenced by the position of the Adriatic Basin, stretching from northwest to southeast, climatic differences along its length, and the direction of sea currents. Habitats in the submerged karst characteristic for the Croatian side of the Adriatic Sea are anchihaline caves, sea caves, cold sea caves and pits with bathyal elements, vruljas, karst estuaries, submerged river canyons, submerged tuffa barriers, marine lakes, and bare karst in the sea. Though sea caves, vruljas, coralligen, marine lakes, and Posidonia beds are today threatened by direct and indirect anthropogenic influences (pollution, eutrophication, tourism, nautical tourism, coastal development, aquaculture), only a few of these habitats have been declared as areas of special interest for conservation or as threatened habitats under the relevant international conventions. There are still too few targeted studies that could contribute to better understanding of these habitats and their levels of threat. Therefore, some of these specific and valuable habitats are in danger to be destroyed before they can be investigated (1). Sea caves, vruljas, and coralligen are quite inaccessible and, therefore, there is insufficient information on the organisms living there. The mechanisms how deep-sea organisms settle into cold-water sea caves and how they survive and reproduce in these caves are insufficiently investigated. All the ecological factors which result in such a large diversity of sponges in the semi-dark cave communities are also unknown. Preliminary research of anchihaline caves shows that it might be possible that karstification processes occur just beneath the sea surface (2). Marine lakes, ecologically separate from the surrounding sea due to limited contact, are very rare at the eastern Adriatic coast and, therefore, very threatened. The benthos of these lakes includes a small number of organisms that have very large populations, which is contrary to what we find in the surrounding sea. All the preliminary research has proven these habitats to be very interesting.