Weseloh, Annika (2007) The Role of Community Structure for Invasion Dynamics in Marine Fouling Communities in the South China Sea. (Diploma thesis), Universität Bremen, Bremen, Germany, 101 pp.

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Abstract

This study addressed the question whether the stability of marine fouling communities towards environmental changes is predictable by their age. If a marine fouling community is transported into a new habitat on a drifting object, the introduced community needs to cope with both: changes in abiotic conditions and the recruitment of local species at the new site to persist. If introduced communities persist for a long time, this enhances the risk that single species spread and/or reproduce, what can finally lead to a successful invasion. I investigated the 2nd step of the invasion pathway: the persistance of a marine fouling community after transport into a new environment. For this, I used marine fouling communities that established on artificial, vertically orientated, settlement substrata at two different study sites in the South China Sea. The sites differed in both abiotic and biotic conditions. At both sites two sets of communities established for 4 months and 2 months. Half of the replicated communities of each age were transplanted to the other study site and were paired statistically and spatially with a community of the same age (acting as a local reference community) that established at the recipient site. After the transplantation the communities were sampled biweekly for 8 weeks. At each sampling event I estimated the abundance (percent cover) of each macrofouler species. For both successional stages, I clearly observed a convergence process between transplanted and nontransplanted communities. On the base of the obtained data, I calculated the Bray-Curtis similarity between native and transplanted communities and derived the convergence rate over time. I found that community age is significantly affecting the rate of convergence between native and introduced assemblages. I related these findings to intrinsic communitiy properties, namely diversity, available settlement substratum and species identity. The influence of diversity on community stability has been controversially discussed for several decades. In my study, different diversity measures (Shannon-Weaver index, species number and functional richness) were correlated with the speed of convergence between transplanted and non-transplanted communities, i.e. community stability towards environmental change. All taxonomic diversity measures were poor predictors of stability. However, functional richness was the only diversity measure that significantly affected the convergence speed. On contrast, the functional identity, life strategy, and species identity were good stability predictors. The question is whether this correlation between functional richness and stability has to be considered as a “functional sampling effect”. In conclusion, the functional identities or the life strategies of the species in the community are better stability predictors than the tested taxonomic diversity measures. I will discuss the role of available settlement substratum, diversity, and the different functional traits in theobserved convergence process towards the resident communities.

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