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Rapid assessment of the biodiversity of sponges (Porifera) and other invertebrates in the coastal waters of Brijuni Islands, Northern Adriatic Sea, Croatia

The Adriatic Sea is a semi-enclosed sea forming a distinct sub-region within the Mediterranean Sea region. The Northern Adriatic basin is relatively shallow, considering that its depth does not exceed 50 m. It is earmarked by the stratification of its water column, great fluvial input, and high biological productivity. Restrained water exchange with the remaining Mediterranean sea led to the development of a very sensitive ecosystem. The geomorphology of its western part with its flat and uniform coast is distinctively different to its eastern part, which is rocky, steep and highly diversified with numerous islands, promontories and bays. The Brijuni islands, located along the southwestern coast of Istria close to the city of Pula, were proclaimed a national park in 1983. They cover a total area of 3, 635 ha with a marine area of 2, 651 ha. In total fourteen larger and small islands belong to the national park, of which the largest are Veliki and Mali Brijun. The aim of this study was to provide a first overview of the typical habitats focusing on sponges and other abundant invertebrates. Therefore, standard scientific diving methods including transects, photo documentation as well as the Stuttgart protocol for collecting sponges where used. Determination of the genera and species was done utilizing an integrative taxonomic approach consisting of morphological as well as molecular characters. The examination of shallow areas was carried out by experienced apnea divers. Underwater scooters helped cover long distances. This enabled efficient acquisition of the spread of two sea grass species, the abundance of the fan mussel Pinna nobilis and the spread of the green algae Caulerpa racemosa. Within five days of exploration, about 175 species could be observed covering mainly sponges, ascidians and molluscs.

Adriatic Sea ; sponges ; invertebrates ; scientific diving

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