The interaction between physical disturbance and organic enrichment: An important element in structuring benthic communities

The interaction between physical disturbance and organic enrichment, with r espect to its effect on the diversity and community structure of a macroinf aunal assemblage, has been examined in a benthic mesocosm experiment. The e xperiment was conducted at the Solbergstrand mesocosm (Norwegian Institute for Water Research) using subtidal sediment collected from Bjornhordenbukta , a small sheltered bay in Oslofjord. Ninety-eight areas of homogenized sed iment were subjected to one of seven levels of organic enrichment, combined with one of seven different frequencies of physical disturbance, each repl icated once. This structured matrix of physical disturbance and organic enr ichment treatments demonstrated the combined effects of these factors to be nonadditive. Diversity was lower than expected when low frequencies of phy sical disturbance acted in conjunction with high levels of organic enrichme nt or when high frequencies of physical disturbance were combined with low levels of organic enrichment. Diversity was higher than expected when both disturbance and enrichment were either high or low. The implications of thi s interaction between physical disturbance and organic enrichment for the a pplication of the dynamic equilibrium model (Huston 1979) to sediment commu nities are discussed, Multivariate analysis also showed community structure to be significantly affected by physical disturbance, organic enrichment, and interactions between the two. It is concluded that strong interactions between physical disturbance and organic enrichment, coupled with both smal l- and large-scale variability in these factors, could promote heterogeneit y and diversity in benthic infaunal assemblages. However, this remains to b e tested in field conditions. Additionally, interactions between physical d isturbance and organic enrichment may have important implications for matte rs of coastal zone management.