Intertidal habitats and benthic macrofauna of the Forth estuary, Scotland

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Abstract
The intertidal habitats of the Forth estuary are dominated by fine-grained muds, which experience a salinity range of 0–32%, j over the length of the estuary from Stirling to Queensferry. The current total area of the intertidal zone is 23.3 km2, the majority of which is found in the three central bays of Skinflats, Kinneil and Torry Bay. Over the centuries, agricultural and industrial reclamation has reduced by almost 50% the size of the Forth estuary intertidal habitat. The upper estuary has narrow intertidal shores, inhabited almost exclusively by oligochaete worms, which are very abundant due to organic enrichment of the area. The middle estuary is responsible for the greatest biomass and production of the intertidal benthic macrofauna. The lower estuary has a greater diversity of species than the upper and middle estuary, but has a lower biomass and abundance of macrofauna. It is shown that the production/biomass (P/B) ratio of several species in the Forth estuary is lower than that of the same species in other estuaries. This depression cannot be explained by natural environmental variables, and is suggested as being due to the levels of pollutants throughout the area. Despite this depressed productivity, and the threats from further reclamation, the Forth estuary retains abundant populations of intertidal animals, which are an important food source for birds and fish.