DISTURBANCE AND GAP FORMATION IN A MARINE BENTHIC MOSAIC - INFLUENCE OF SHIFTING MACROALGAL PATCHES ON SEAGRASS STRUCTURE AND MOBILE INVERTEBRATES

A field experiment was used to examine the interactions among structur ally complex, spatially shifting structure (macroalgae deposited by cu rrents), less-complex stationary structure (seagrass), and mobile bent hic invertebrates. I tested the effect of drift algal patches on under lying seagrass structure and fauna by establishing manipulated algal m ats over seagrass for comparison with control seagrass plots. Control and experimental plots did not differ significantly for any variable p rior to algal addition, but most seagrass structure was removed by thi s disturbance over a 6 mo period. In contrast, abundance of mobile fau na 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 o f dominance apparent on control plots. Although the structurally compl ex mats formed by drifting algae provided short-term habitat enhanceme nt for some fauna, longterm effects on fauna are probably negative due to mat ephemerality and degradation of seagrass.