Environmental variables explaining structural and functional diversity of seagrass macrofauna in an archipelago landscape

Thirteen seagrass beds located over a 80-km range in the brackish waters of SW, Finland, northern Baltic Sea were investigated in order to determine the environmental variables important for univariate community measures and for number, composition and redundancy of functional groups of benthic macrofauna. For species assemblages, fetch and shore angle were the best explanatory variables, followed by sediment granulometry (fine gravel) and then sediment organics. Similarly, fetch, shore angle and Zostera marina shoot density were the best explanatory variables for functional group patterns. Small (< 50 m²) inner-archipelago beds were functionally and structurally equal to the most extensive (500 to > 1000 m²) seagrass beds in the study area. Community measures (density, number of species and diversity) and functional diversity (number of functional groups) equalled or exceeded levels previously recorded in deeper, non-vegetated communities in the northern Baltic Sea. In comparison with marine seagrass assemblages, the total number of species and number of species per function were low. However, species density and derived diversity measures (Shannon-Wieners index H′) equalled or exceeded those reported for other seagrass ecosystems. It is concluded that in terms of seagrass infauna, the Baltic Sea should not be regarded species poor, as is often generally stated, and that conservation initiatives and management strategies should consider both minor as well as more extensive occurrences of seagrasses in coastal waters.