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Site- and habitat-dependent variations in the diversity of polychaetes associated with golden kelp <i>Ecklonia radiata</i> holdfasts along the southeast coast of South Africa


Polychaetes are important components of the macrofaunal communities associated with golden kelp Ecklonia radiata holdfasts across different spatial scales. However, the polychaete component varies in different habitat types in response to varying environmental conditions. Here, we compared patterns of variation in Ecklonia radiata holdfast-associated polychaetes between rock pools and gullies along South Africa’s southeast coast. Eighteen species were found in gullies and 28 species in rock pools, with 13 and 16 families represented, respectively. The study sites at Cwebe, Dwesa and Nqabarha had 12, 11 and 20 species, respectively. The rock pools were more species-rich than the gullies, while Nqabarha was the most species-rich site. The composition of species varied both among habitat types and between sites, with a separation in polychaete composition observed between Cwebe and Dwesa. The species that contributed >60% to the distinction between habitat types and among sites were Lepidonotus semitectus, Cirriformia capensis, Eunice aphroditotis, Syllis sp., Chaetopterus variopedatus, L. durbanensis, Arabella iricolor, Lysidice natalensis and Gunnarea gaimardi. The polychaete distribution on kelp holdfasts was influenced by the sediment and geomorphological characteristics of the sampling sites. Our findings highlight the importance of sediment in creating habitat heterogeneity and how this facilitates high species richness in rock pools. However, physical factors explained a small proportion of the variance in the polychaete assemblages. Therefore, biological factors could be more important drivers than abiotic elements, particularly between habitat types.