Polychaete fauna of Cymodocea nodosa meadow and Caulerpa racemosa settlement in Vrsar (Croatia, Northern Adriatic Sea)

Polychaetes are the dominant macrobenthic group of Cymodocea nodosa meadow and are considered as excellent descriptors of the whole faunal community associated to seagrasses. The aim of this study was to compare the structure and composition of polychaete fauna of native C. nodosa meadow and settlement of highly competitive invasive green algae Caulerpa racemosa, in the region of Vrsar (Northern Adriatic Sea). Samples were collected with PVC corers on three different locations within C. nodosa, C. racemosa and on bare soft bottom nearby. Altogether 63 polychaete taxa were found: 43 within C. racemosa, 40 on non-vegetated sediment and only 22 taxa in C. nodosa community. Polychaete abundance in C. racemosa was very high, and the number of taxa on all three locations was always the highest within C. racemosa and the lowest within C. nodosa community. High correlation was shown between both number of taxa and diversity indices, and the organic matter content in the sediment: the said parameters were the the highest in C. racemosa and non-vegetated stations in the most sheltered location within the harbor, characterized by the highest percentage of organic matter and high amount of fine silty-clay fraction. Further analyses of the whole macrobenthic fauna would be necessary to give the more accurate insight on the impact of C. racemosa on benthos in Vrsar area.