The influence of macrofauna on intertidal sediment stability and biogeochemical properties.

Macrofauna are known to have a significant effect on intertidal sediment stability and biogeochemical properties. A series of manipulative in situ mudflat studies at Breydon Water, Great Yarmouth, UK investigated the effect of biodiversity on selected biogeochemical sedimentary properties related to mudflat sediment stability including the sediment erosion threshold and relative erosion rate, microphytobenthos biomass and health, sediment particle size and size distribution, sediment water content, chlorophyll a and b concentration, and colloidal carbohydrate concentration. Mudflat sediment macrofaunal biomass was removed using cryo-defaunation and the abundances of three common mudflat species Hediste diversicolor, Hydrobia ulvae and Corophium volutator manipulated to examine different aspects of macrofaunal biodiversity including species identity, density, biomass distribution, and richness. An additional laboratory study enabled two and three dimensional high resolution visualisation of fluid and particle mixing as a result of organism sediment bioturbation. Species identity was found to have a significant effect on sediment properties. The three species have distinct bioturbatory actions with consequences for sediment stability. In some circumstances a single organism was found to have as great an effect on selected ecosystem processes as a whole community. Variations in species density significantly changed the effect of the species on the measured sedimentary processes. Species richness effects were negatively interactive, with species mixtures underyielding in comparison to their monoculture counterparts. Changes in species biomass distribution and richness resulted in significant context dependent changes to sediment properties, moderated by inter- and intraspecific interactions. Species were also observed to exhibit a functional abundance threshold, below which they did not contribute significantly to ecosystem processes. Temporal and spatial variability observed in the experiments emphasised the potential of environmental and abiotic factors to also influence ecosystem processes. Investigating these subtle aspects of biodiversity will be key in the determination of the relationship between biodiversity and ecosystem processes