Microalgae, macrofauna and sediment stability: an experimental test of a reciprocal relationship

A manipulative field experiment was conducted at Blackness in the Firth of Forth, Scotland, to study the effects of differences in microphytobenthos abundance on sediment stability and macrofauna. Opaque and transparent Perspex was used to construct shaded and controlled treatments, respectively. Shading resulted in significantly lower levels of chlorophyllarecorded from the sediment. Shaded treatments showed significant reductions in populations ofMacoma balthica,Hydrobia ulvaeandCorophium volutator, 3 of the dominant species at this site. Largely as a result of changes in the abundance of these species, multivariate analyses showed significant differences between shaded and control communities. The impacts of shading on individual species depended on the sediment characteristics. There were no significant differences between treatments in recorded sediment accretion/erosion rates. These results demonstrate the importance of microphytobenthos for the deposit feedersM. balthica,H. ulvaeandC. volutator. The absence of any effect on sediment stability might result from the reciprocal, opposite effects of macrofauna and microphytobenthos on sediment stability cancelling each other out in this experiment.