Patterns of benthic invertebrate biodiversity in intertidal seagrass in Moreton Bay, Queensland

The nature and biodiversity of invertebrate macrobenthos in intertidal seagrass beds along the northwest coast of North Stradbroke Island, Moreton Bay (Australia) are reviewed, especially those features of potentially wider relevance. Three attributes seem of particular note. (i) Although species rich, the fauna is dominated by four tiny animals (<8mm max.), of which very little indeed is known and two have only been recently described: the leaf-biofilm consuming microgastropods Calopia imitata and Pseudoliotia spp, the amphipod Limnoporeia yarrague (a micro-predator), and the crab Enigmaplax littoralis of uncertain ecology. Seagrass ecology cannot afford to ignore such tiny animals that may require a disproportionate amount of time and effort to detect and/or identify. (ii) Change from the seagrass macrofaunal assemblage to that in adjacent areas of unvegetated sand can be extremely abrupt, the more diverse and abundant seagrass community effectively switching to the species poor and less dense sandflat fauna across a distance of only 0.1 m. Transition is spatially asymmetric, but abundance and species density of both faunas decline as the boundary region is approached. (iii) Notwithstanding that distribution of individual species is patchy and that assemblage composition and abundance vary markedly at all spatial scales, the total number of species per unit area is remarkably constant across space at all spatial scales investigated, a feature suggesting that the faunal assemblage is held well below carrying capacity by top-down control (as is also suggested by its very low density). Functional groups are likewise distributed homogeneously across space.