The community structure and ecology in and around a Sabellaria alveolata biogenic reef

Justin Grainger BSc (Hons) Marine Biology, Ecology and Conservation, Anglia Ruskin University


Cei-Bach is a semi sheltered bay within the Cardigan Bay Special Area of Conservation (SAC) in West Wales, and designated for its honeycomb worm (Sabellaria alveolata) biogenic reef habitat, which provides a biodiverse substratum on an otherwise scouring benthos. The study objectives were to make a rapid and effective assessment of the community structure and ecology with limited resources. GIS was used to measure the reef extent and environmental gradients for direct comparison with taxa response.
With some 52 species of macro-epifauna identified, there was much noise in the data and challenges in identifying the key players shaping the community. Indirect ordination techniques of Cluster Analysis and Principal Components Analysis (PCA) were used with MVSP to resolve three clear community assemblages and their defining species. This enabled direct ordination with five environmental variables of shore position, stability, salinity, turbulence and submersion through Canonical Correspondence Analysis (CCA); whilst mitigating the characteristic “horseshoe” effect when resolving noisy data, or rare taxa, with Correspondence Analysis.
The results showed significant heterogeneity in the community structure and higher biodiversity within the reef extent. The reef was effectively “framed” by limiting factors of transition from an intertidal environment to the North; desiccation to the south, and east; excessive seston and salinity reducing inundation of freshwater to the west, where the honeycomb worm was competitively excluded by functioning guilds of Ulva sp. The study found that the assemblages were defined most strongly by shore position, substrate stability and salinity, and highlighted the challenges of effective environmental variable selection in direct ordination.

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