The role of macroalgal morphology and community structure on the accumulation of sediment and the subsequent effects on the dynamics of marine intertidal communities

This study examines the influence of intertidal macroalgae on sediment accumulation, and the effect of sediment cover on intertidal community structure.Three shores on the North Yorkshire coast, England, were used to investigate differences in the quantity of sediment trapped by ten morphologically different algal species, and the relationship between morphology and the quantity of sediment trapped. The quantity of sediment accumulated in quadrats of four different macroalgal communities (canopy, turf, canopy/turf and bare rock) was also examined. Differences in sediment cover and community structure were investigated on the intertidal rocky shore at Holbeck, North Yorkshire. The distribution and position of both were described using transects across three sites, whilst relationships were examined using 54 fixed quadrats in the mid shore.Across three different shores the mass of dried sediment g⁻¹ macroalgal dry mass was found to differ between macroalgal species. All measured aspects of macroalgal morphology correlated with the quantity of sediment trapped. Macroalgae with different morphologies trapped different gram size compositions but no differences were found hi the quantity of sediment accumulated by turf, canopy, bare rock or unmanipulated algal communities. At three different sites at Holbeck, the site with the greatest sediment cover had lower macroalgal species diversity, richness and total abundance, patellid and littorinid abundance. Although differences were found in sediment cover between sites in the mid shore, no differences were found hi community structure. Sediment cover had negative correlations with macroalgal richness and diversity in algal quadrats, but positivecorrelations with macroalgal abundance and diversity in bare rock quadrats. Within individual macroalgae morphology was found to affect the quantity of sediment trapped, however at quadrat level macroalgal morphology had no effect. At both the level of the quadrat and the whole shore sediment cover influenced community structure, whilst within the mid shore alone sediment cover did not affect community structure. This work suggests that relationships/interactions between sedimentation and intertidal community structure are scale dependent