EFFECT OF SHOOT DENSITY ON THE INFAUNAL MACROINVERTEBRATE COMMUNITY WITHIN A ZOSTERA-MARINA SEAGRASS BED

A seagrass (Zostera marina) bed in south-west United Kingdom was mappe d using SCUBA in July 1996. Within the bed, three seagrass density ran ges (shoots m(-2)) were sampled, low (1-50), medium (51-100) and high (>100), to assess infaunal macro-invertebrate community structure. At each of the sites seagrass and sediment parameters were measured (shoo t density, number of leaves per shoot, root-rhizome biomass, median gr ain size, sorting coefficient, silt fraction). As seagrass density inc reased, a corresponding increase in infaunal diversity was observed, m ultivariate analysis indicating that there were significant difference s in community structure between the shoot density ranges sampled. The main factors explaining community structure were above-ground paramet ers (leaf number per shoot, shoot density), whilst sediment and root-r hizome measures were apparently unimportant in structuring the infauna l community. The influence of increased seagrass structural complexity on the infauna is possibly indirect (e.g. increased detrital depositi on, reduced predator efficiency), however, the direct influence of roo t-rhizome complexity requires further investigation. (C) 1998 Academic Press.