The health and community structure of the biogenic reef at Cei Bach, Cardigan Bay

For six weeks during May-July, Cardigan Bay Marine Wildlife Centre (CBMWC) volunteer Justin Grainger – an undergraduate student from Anglia Ruskin University, Cambridge – undertook research to asses and consider the health and age of the honeycomb worm reef, Sabellaria alveolata, along with its associated and neighbouring community structure. S. alveolata reefs in Cardigan Bay SAC are BAP protected habitats as they create stable substrate for diverse flora, invertebrates and vertebrates that would otherwise be absent in the mobile and scouring benthos of sandy and boulder scar habitats. The increased species richness supports higher biodiversity throughout the food web.

The worm secretes mucus that it utilises to cement sand grains into dwelling tubes and with many congeners these “join up” cobbles, pebbles and boulders on the sand, creating increased rock pool frequency and a foothold for epibionts. These polychaetes require suspended sediment, seston, and are usually associated with freshwater outfalls that increase turbidity and suspension duration. However, west Wales represents the northern tip of the species habitat and most reef tends to be of moderate or poor quality and patchy in distribution.

Quadrat cell over mature honeycomb worm reef

A quadrat cell over mature honeycomb worm reef with the diagnostic “porches” visible, indicating live worms (Image: Justin Grainger 2012).

Over the last six weeks some 58 non invasive quadrat samples, each with 25 subsamples, have been used to record reef health and age along with substrate type, temperature and presence, abundance and coverage of macro flora and fauna. GPS was used to create random points and log the extent of the reef and surrounding communities. Early indications from the data suggest three quite distinct communities.

Firstly, gutweed (Enteromorpha intestinalis), Ulva and Porphyra in and around the freshwater channel with few Sabellerids, bivalves or other flora and fauna.

Sabellaria reef to the northeast of the freshwater outfall and association with bladder wrack (Fucus vesiculosus), pepper dulse (Osmundia pinnatifida), Irish moss (Chondrus crispus), Corallina officinalis, velvet horn (Codium tomentosum), periwinkles (Littorina), top shells (Gibbula), and some serrated wrack (Fucus serratus), at the lower shore. As the condition of the reef decreases, presence of opportunistic Ulva and gutweed seems to increase.

North east edge of the honeycomb worm reef with the Mytilus dominated zone visible in the foreground (Image: Justin Grainger 2012)

North east edge of the honeycomb worm reef with the Mytilus dominated zone visible in the foreground (Image: Justin Grainger 2012)

Thirdly, a very dense coverage of Mytilus edulus, and little else, to the southeast of the freshwater outflow where sand grain availability may be low. Full multivariate data analysis will be undertaken over the coming months to consider further associations and other biotic and abiotic factors.