The invasive Anadara transversa (Say, 1822) (Mollusca: Bivalvia) in the biofouling community of northern Adriatic mariculture areas

The composition of biofouling communities on colonised terracotta tiles was assessed in mariculture areas of the northern Adriatic Sea (Croatia) according to a hierarchical nested sampling design. Significant differences in the composition of biofouling assemblages were detected between depths (1 and 5 m) and at the larger spatial scale (tens of km). Additionally, the biofouling community showed different patterns in relation to the time of immersion (2, 4, 6 and 8 months). The most abundant taxa were Spirobranchus triqueter, Spirorbis spirorbis, Ostrea edulis, Mytilus galloprovincialis, Schizoporella sp., Balanus sp. and Botryllus sp. The invasive Anadara transversa was consistently an important component of these biofouling assemblages. It was able to spawn throughout the duration of a survey (April to January) showing peak recruitment during the summer. A maximum density, up to 500 individuals m(-2), were assessed at the depth of 5 m. Maximum shell length of 30 mm was recorded at the end of the experiment. These results suggest that, besides the native fouling community species, the invasive and opportunistic A. transversa might cause additional problems in mariculture facilities of the northern Adriatic Sea.