Effect of patch size and in-patch location on the infaunal macroinvertebrate assemblages of Zostera marina seagrass beds

Much recent work on patch-occupancy dynamics has been concentrated in terre strial ecosystems, with few examples evident from soft-sediment marine habi tats. Seagrass landscapes have recently been recognised to be potentially i deal marine models for the study of such ecological concepts. Infaunal macr oinvertebrate assemblages of two patch sizes of the seagrass Zostera marina were compared: small (< 15 m diameter) and large (> 30 m diameter), using an unreplicated random block design. Further comparison was made between in faunal assemblage composition at the edge and centre of each patch. Univari ate statistical analysis of data indicated significantly greater total numb ers of taxa in samples from large patches than in small. Multivariate analy ses indicated significant differences in assemblage composition due to both patch size and in-patch location, and revealed that differences were due t o small changes in the relative abundances of many taxa. Possible mechanism s underlying the observed variations of assemblage composition with patch s ize and in-patch location are discussed. Although the present results suppo rt some of the theories relating to the control of infaunal assemblage comp osition, explanations are not applicable across all taxonomic groups. At th e scale of the present study, seagrass patch size and edge-effects appear t o be less significant than 'regional' factors, which relate to relatively s mall variation in environmental parameters, for the structuring of infaunal macroinvertebrate assemblages. (C) 2001 Published by Elsevier Science B.V.