Biodiversity & Conservation

Ecological relationships within MLR.Salv are not especially complex. Nevertheless, diversity of associated fauna may be high. Collins (2001) found 59 faunal taxa and 18 floral taxa associated with Sabellaria alveolata reefs at Criccieth in North Wales, dominated by annelids, molluscs, nematodes and hexapods. Dias & Paula (2001) recorded a total of 137 taxa in Sabellaria alveolata colonies on two shores on the central coast of Portugal. Sheets of Sabellaria alveolata can form ridges on flat shores which can trap water and create small pools (Cunningham et al., 1984) (see Habitat Complexity). This may also result in an increased species diversity, as might the stabilization of mobile sand, shingles, pebbles and cobbles (Holt et al., 1998) often attributed to the presence of extensive Sabellaria alveolata sheets.

Algae use older reefs as substratum. Some of these are perennials such as Fucus serratus and others annual ephemerals such as Ulva sp. The attached community may themselves have epifaunal species (Collins, 2001). In addition, the space between the epiphytic algae and the reef provide shelter for mobile organisms.

Several grazing molluscs, including Patella vulgata and Littorina littorea, feed directly on these algae as well as on epiphytic microalgae.

Some temporal changes may be apparent in Sabellaria alveolata reefs with a cycle of decay and settlement over several years. Recruitment is very sporadic so cycles are not very predictable. Decay is primarily through the effects of storms and wave action. There will also be changes with season in the amount of algae growing in the biotope. Annual species will come and go and perennial species such as Fucus serratus exhibit changes in the level of surface cover they provide. Epiflora such as Fucus serratus, particularly if dense, may act as nursery grounds for various species including Nucella lapillus.

Habitat complexity varies temporally with the cycles of development and break up of the reefs. When growing actively as sheets or hummocks the entire sea shore can be covered. Ridges can be formed on flat shores which may trap water leading to the formation of pools (Cunningham et al., 1984). These extensive sheets ('placages'), can stabilize otherwise mobile sand, shingle, cobbles and pebbles (Holt et al., 1998). However, increased habitat diversity, and therefore increased species diversity, are found as the reef begins to break up, cracks, crevices and a greater variety of available surfaces develops, creating a more diverse and complex habitat. Collins (2001) found that reefs in poor condition had a significantly higher diversity of associated infauna than intermediate condition reefs at Criccieth in North Wales. Porras et al. (1996) reported similar findings, in addition to the observation that eroded reefs have higher structural complexity. Collins (2001) also reported that, within reefs in poor condition, the sediment size was significantly larger than in other reefs. In contrast, the levels of organic content were found to be significantly higher in reefs in condition. Sabellaria alveolata reefs, due to their structure, maintain a high level of relative humidity during low tide, thereby protecting some associated flora and fauna from desiccation, which may permit some species to occur at higher levels on the shore than normal.

Sabellaria alveolata reefs can support diverse communities (see Ecological Relationships). For example, colonies may support several species of annual and perennial algae, particularly if the reefs are older and beginning to break up. This algal growth can support several species of grazing mollusc (including Littorina littorea and Patella vulgata). Where hummocks or reefs form, the density of Sabellaria alveolata can be very high, causing high secondary productivity.

Sabellaria alveolata recruits from pelagic larvae that spend from 6 weeks to 6 months in the plankton. Although reproduction occurs each year, recruitment is very sporadic and unpredictable. Larval settlement appears to favour areas with existing Sabellaria alveolata colonies, or their dead remains (e.g. Wilson, 1971; Cunningham et al., 1984). Fucus serratus also recruits from tiny pelagic plants.

Sabellaria alveolata has been recorded as living for up to 9 years but most worms survive for four years or so. The growth of Sabellaria alveolata appears to slow after its first year after settle. Wilson (1971) reported that the growth in the second and third years after settlement in some colonies was about half that of growth in the first year. Such active growth effectively prevents any other species from colonizing the reef. When growth is less active then algae can begin to colonize, as the reef begins to break up the available substratum becomes more heterogeneous permitting establishment of more species. If further recruitment does not then occur, allowing new growth, the reef will disintegrate. There is no real 'mature stage' as such, rather a cycle of growth and decay. Although settlement of Sabellaria alveolata is sporadic, areas that are good for Sabellaria alveolata tend to remain so because larval settlement appears to favour areas with existing Sabellaria alveolata colonies, or their dead remains (e.g. Wilson, 1971; Cunningham et al., 1984).

Cunningham et al. (1994) noted the presence of large numbers of Mytilus edulis on the remains of Sabellaria alveolata colonies in several locations including Llwyngwril in Wales and at Dubmill Point in West Cumbria. In some circumstances therefore, the mussels could potentially interrupt the usual cycle of growth and decay of the reef.