Non-indigenous bryozoan species from natural and artificial substrata of Mediterranean submarine caves

Abstract

Numerous non-indigenous bryozoan species or NIBs (= non-indigenous bryozoans) have been recorded in the Mediterranean Sea, some in marine cave habitats. Recent surveys, mostly of submarine caves, led to the discovery of new NIBs and documented the spreading of NIBs already known from the basin. Cradoscrupocellaria hirsuta, Catenicella paradoxa, and Smittina nitidissima were recorded at several localities of central sectors of the Mediterranean. Only Ca. paradoxa was previously known from the area, while S. nitidissima had previously been recorded only from the Eastern Mediterranean, and Cr. hirsuta is new to the area. Within the examined area, Cr. hirsuta has a wide distribution, occurring on artificial panels and natural substrates. S. nitidissima and Ca. paradoxa were detected only on artificial panels, except for a few Ca. paradoxa colonies from a single locality, which had settled on algae. Artificial substrates offer additional surfaces available for colonisation, often more suitable than natural substrates. As such, they can be rapidly exploited by new settlers and particularly by opportunistic taxa as most alien species are. Although artificial substrates can be advantageous tools for the early detection of non-indigenous species (NISs), submerged anthropogenic substrates, such as artificial reefs and coastal protection structures, may selectively attract non-indigenous species favouring their spreading alongshore. Shipping appears to be one of the main pathways for species introduction and the main vector for dispersion.