Impact of catchment land-use on an estuarine benthic food web

Long-term changes in agricultural land-use has resulted in enhanced nutrient (N) concentrations in the Ythan estuary, Aberdeenshire, Over the same time period there has been an increase in mat-forming macroalgae (Enteromorpha, Chaetomorpha, Ulva). These weed mats have both direct effects and indirect effects on the ecology of the estuary. Macro-algal biomasses in excess of 1 kg.m(-2) generate a highly reduced sediment environment through smothering of the sediment surface and local organic enrichment. The densities of many invertebrate species are significantly reduced under these weed mars, locally reducing the availability of prey to shorebirds. In contrast, the abundance of invertebrates and shorebirds may be enhanced in areas distant from the mats through subsidies of organic material from the mats themselves.