Seagrass-associated macrobenthic functional diversity and functional structure along an estuarine gradient

Changes in the relative importance of the 27 component functional groups (FGs) of seagrass-associated macrobenthos were assessed up the long axis of an estuarine system. Although previously observed division of the estuary into two sections with respect to species diversity was confirmed, this did not correspond to any functional compartmentalisation. Functionally, division was into the terminal extremes and the large intervening marine/lagoonal/lower-estuarine zone, within which no linear segregation of sites occurred. 40% of individual FGs in the latter showed no variation at all, and variation in the remainder was only axially related in two cases, one positive and one negative. Overall structure of the dominant FGs at each locality remained uniform, although rank orders of proportional importance varied widely. Only one major marine/lagoonal FG failed to penetrate the upper estuary at the time of sampling. Estuarine components may change spatially, sometimes dramatically, but overall functional pattern shows considerably less change than the species numbers usually used in characterisation.