Ascidians in the succession of marine fouling communities
Frederike Lindeyer, Adriaan Gittenberger
a venue for the exchange of information on the biogeography, ecology, genetics, impacts, risk assessment and management of invasive tunicates worldwide. Abstract Approximately 200 grey PVC settlement plates were hung along at sites along the Dutch coast at a depth of 1 meter. The cover of each species that could be identified on the plates was recorded every three months from March 2009 to March 2010 to study the role of native versus non-native ascidians in the succession of marine fouling
... unities. Three native ascidian species, Ciona intestinalis, Ascidiella aspersa and Botryllus schlosseri, and five species of cryptogenic and/or non-native origin, Molgula socialis, Styela clava, Diplosoma listerianum, Botrylloides violaceus and Didemnum vexillum, were recorded. After the Cnidaria, Ascidiacea were found to be the group that explained most of the differences found in species communities on settlement plates at different stages in the succession. Regardless of the fact that non-native ascidian species were very abundant at times, their role in the succession of the studied marine fouling communities appears to be limited. After the polyp stage of the moon jelly Aurelia aurita and hydroid species of the genus Obelia, the two native ascidian species Ciona intestinalis and Ascidiella aspersa explained most of the differences that were found between the successive stages in the fouling communities. In general, the three native ascidian species appeared to determine the succession of the fouling communities more than the five cryptogenic and/or nonnative ascidian species. Whether this is linked to species being either native or non-native is questionable however. The various ascidian species differed strongly in the period of settlement, the ability to settle on prior settlers and the ability to survive the winter. The non-native ascidians settled mostly in June to December, while the native ones settled from March to December. Although the native ascidians M. socialis and B. schlosseri were found to be restricted in their settlement by the presence of prior settlers, the non-native species B. violaceus and D. vexillum were not. Native and non-native ascidian species survived the winter equally well. Native C. intestinalis and A. aspersa and non-native B. botrylloides and D. vexillum were most successful in surviving winter water temperatures of just below 0°C. Thus the results of this study, based on one year of data, suggest that the roles of ascidian species in the succession of fouling communities vary, and that being native or non-native is not necessarily linked to the degree to which species influence the development of marine fouling communities. Their individual seasonality, abilities to overgrow prior settlers and survival of winter temperatures appear to be more important.