Disturbance and gap formation in a marine benthic mosaic: Influence of shifting macroalgal patches on seagrass structure and mobile invertebrates

Abstract

A field experiment was used to examine the interactions among structurally complex, spatially shifting structure (macroalgae deposited by currents), less-complex stationary structure (seagrass), and mobile benthic invertebrates. I tested the effect of drift algal patches on underlying seagrass structure and fauna by establishing manipulated algal mats over seagrass for comparison with control seagrass plots. Control and experimental plots did not differ significantly for any variable prior to algal addition, but most seagrass structure was removed by this disturbance over a 6 mo period. In contrast, abundance of mobile fauna on experimental plots increased after 6 mo of algal cover relative to abundance on control plots. There was also greater evenness in the canopy fauna of the algal plots which contrasted with the high level of dominance apparent on control plots. Although the structurally complex mats formed by drifting algae provided short-term habitat enhancement for some fauna, long-term effects on fauna are probably negative due to mat ephemerality and degradation of seagrass.