Kelp Wrack and the Flow of Energy through a Sandy Beach Ecosystem

Abstract

One of the most distinctive and frequently cited features of exposed sandy beaches as ecosystems is their almost complete lack of in situ primary production (e.g. Brown, 1964; Munro et al., 1978; McLachlan et al., 1981a). This results directly from the mobility of the sediments, which renders them unsuitable for the attachment of macrophytes or the development of dense benthic diatom communities. In the absence of these potential food resources macrofaunal organisms on exposed beaches must obtain their nutrition from imported materials. These may take the form of finely divided detritus or phytoplankton particles, many of which may originate from rich blooms of phytoplankton in the surf zone (McLachlan et al., 1981b), or large items of carrion. The macro-fauna associated with these food resources normally comprises two major trophic elements, namely filter feeders, including bivalves (such as Donax) and crustacea (such as Emenita and Gastnosaccub); and predator/scavengers (e.g. Bullia, Ocypode,various isopods and polychaetes). The proportion of these two trophic elements differs widely, depending on the relative availability of plankton and detritus versus carrion (McLachlan et al., 1981a), but filter feeding bivalves are frequently the overwhelming dominants in terms of biomass (e.g. McLachlan et al., 1981b).