The change in macroalgal assemblages through the Saldanha Bay/Langebaan Lagoon ecosystem (South Africa)

Saldanha Bay and Langebaan Lagoon form together one of the few sheltered ha bitats within the Benguela Marine Province; a wide gradient in environmenta l factors is found here. The West Coast National Park was established to pr otect this unique ecosystem, but at the same time an industrially expanding harbour marks this area. In an effort to understand the biological composi tion of the Saldanha/Langebaan ecosystem, the intertidal macroalgal assembl ages were studied in relation to the relatively well-known South African We st Coast flora. Three distinct floral entities were identified using variou s analytical techniques (similarity coefficients, CCA and TWINSPAN): (i) th e species poor, though distinct, salt marshes; (ii) the Lagoon sites; and ( iii) the Bay and West Coast sites. The transition between the latter two is located at the mouth of the Lagoon. The species richness of the Bay/West C oast entity is larger than in the Lagoon. The change in algal composition c an be explained in terms of the environmental variables of which wave expos ure is the most significant. Other important environmental parameters are w ater surface temperature and salinity, which were found to be negatively co rrelated with wave exposure. Biogeographical affinities of the different al gal entities of the Bay/Lagoon system were also determined in relation to t he entire South African shoreline. The Bay/West Coast entity supports a typ ical West Coast flora, with some noticeable effects of uplift of subtidal s pecies into the infralittoral fringe and morphological variation in less ex posed areas. The algal nora of the Lagoon is also dominated by West Coast s pecies, but is typified by species characteristic of sheltered habitats, an d with a number of species which otherwise only occur on the geographically distant South Coast least of Cape Agulhas). The algae from the salt marshe s occur widely in tropical mangroves and warm temperate salt marshes.