Biodiversity & Conservation

The sub-biotopes of SIR.LsacRS illustrate the importance of ecological relationships in determining the presence of different species assemblages in apparently similar situations with regard to physical and chemical conditions. In some examples of low water movement and reduced salinity, rocks are dominated by algae (£SIR.LsacRS.FiR£ and £SIR.LsacRS.Phy£) but in others, the sea urchin Psammechinus miliaris grazes algae so that few foliose seaweeds are present (£SIR.LsacRS.Psa£). In the absence of grazing, algae dominate this biotope most likely providing a habitat for a community of small worms, crustaceans and molluscs but making movement difficult for larger species that require attachment to the surface. For instance, brittle stars, Ophiocomina nigra, occur extensively in the grazed sub-biotope but not in those dominated by foliose algae. Some other species may have difficulty settling onto bare rock in areas dominated by algae although the richness of communities in the £LsacRS.FiR£ sub-biotope in south-west Britain suggests that algal growth may not be a great impedance to settlement. A significant fauna may also be associated with sponges (Peattie & Hoare, 1981).

No specific information has been found in relation to this biotope.Saccharina latissima is a short-lived perennial. Sporophytes typically have a life span of 2 to 4 years although plants may occur as annuals suggesting the possibility of some seasonal fluctuation in abundance. Where surfaces have been cleared, Kain (1975) recorded that Saccharina latissima (studied as Laminaria saccharina) was abundant six months after substratum was cleared. Foliose algae are likely to show a seasonal change in condition of the fronds and in abundance (see Hiscock, 1986c). Also, solitary ascidians are short lived and may fluctuate in numbers through the year and from year to year. For instance, Svane (1988) describes Ascidiella scabra as "an annual ascidian".

There are a wide range of microhabitats within this biotope. They include sediments, sometimes maerl, where infauna will occur, underboulder habitats, the sides and tops of boulder which often have different dominant species, the interstices of massive sponge growths, the holdfasts of kelp plants and the fronds of kelps and other algae.

No specific information found has been found but the communities in this biotope are likely to be highly productive. The biotope occurs in shallow depths where high light intensity will result in high primary productivity. Secondary productivity is also be high although due mainly to active suspension feeding by such species as ascidians, barnacles and mussels largely unassisted by external water movement.

The characterizing species in this biotope all have planktonic spores or larvae and are fairly short-lived. There is therefore high recruitment and high turnover. In sub-biotopes with significant algal presence (especially SIR.LsacRS.Phy), algae might attract a high abundance of solitary ascidians (see Schmidt, 1983) relative to the erect tubes of the hydroid Tubularia indivisa).

The community would probably reach maturity within 2-3 years although recruitment of additional species to the biotope would continue for some further time.

Examples of this biotope are notably rich for areas subject to low or variable salinity. It might be that, in areas not subject to grazing, the stability of physical conditions allows for settlement and survival of progressively more species with time.