Global patterns of macro invertebrate biomass in marine intertidal communities

We examine global patterns of benthic macroinvertebrate biomass and its distribution among functional feeding guilds in marine intertidal cOnmlunities. Variation in ash-free dry biomass was related to physical variables (mean annual air and water temperatures, sediment grain size, intertidal slope, tide range and type, wave height and exposure) by least-squares regression analysis of data for 36 rocky shores and 245 sedimentary shores. Linear combinations of physical variables explain up to 44 % of the variance in total biomass on sedimentary shores and 40 % of the variance in the biomass on rocky shores. Grain size and wave exposure are the best single predictors of total biomass for sedimentary shores and rocky shores, respectively. Biomass estimates peak in temperate regions and are an order of magnitude higher on rocky shores than on sedimentary shores. In fact, macroinvertebrate biomass on temperate rocky shores attains levels 10 to 100 times higher than those documented for other benthic marine environments. Suspension feeders tend to dominate temperate intertidal communities (they typically comprise> 30 to 60 % of the macroinvertebrate biomass), reflecting the importance of benthic-pelagic coupling in these ecosystems. Contrary to consumer stress models for rocky shores,. there is no compelling evidence for biomass limitation of grazers and carnivores at high wave exposure.