A multivariate study of biotic and abiotic relationships in a subtidal algal stand

Abstract

The distribution patterns of Gelidium sesquipedale, Saccorhiza polyschides and Laminaria ochroleuca in relation to depth, sediment loading and substrate topography were investigated in a commercial stand of G. sesquipedale off Cape Espichel, Portugal. There were significant positive relationships between G. sesquipedale cover and substrate slope, and negative relationships among G. sesquipedale, sediment loading and S. polyschides density. Within the depth range studied (0-18 m), S. polyschides abundance was the only variable correlated with depth. The only interaction significantly correlated with G. sesquipedale local distribution was that between L. ochroleuca density and depth. Data suggest that steep slopes and reduced sediment loading favour G. sesquipedale development; S. polyschides dominated in shallow zones with low slope surfaces and high sediment loading; L. ochroleuca by itself was not significantly correlated to the distribution of G. sesquipedale, but its interaction with depth suggests that at greater depths it dominates G. sesquipedale. -from Author