PATTERNS OF MACROALGAL SPECIES-DIVERSITY DANISH ESTUARIES

We analyzed species number of macroalgae in relation to environmental variables at two spatial levels comprising 202 individual sites and 26 entire estuaries in Denmark. The species number of macroalgae increas ed with salinity and declined with nutrient concentrations both at the sites and in the estuaries. Availability of hard substratum was assoc iated with higher species richness at the sites. The number of macroal gal al species in the estuaries increased with higher mean depth and l onger coastline, suggesting that both the vertical and horizontal exte nsion of the colonization area are important for the maximum represent ation of macroalgal species. Mean depth explained as a single predicto r 60% of the variability in species number in entire estuaries. Estuar ies with high mean depth also tend to be large and have high salinity and transparent waters due to efficient exchange with open waters. In conclusion, we find that the regulation of species richness of macroal gae in Danish estuaries, though complex, is influenced predictably by salinity, water transparency, nutrient concentration, and availability of hard substrata.