The effect of sewage pollution on the feeding behaviour and diet of Hediste (Nereis diversicolor (O.F. Müller, 1776)) in three estuaries in south-east England, with implications for saltmarsh erosion

• Nitrogen (sewage) pollution promotes surface deposit-feeding by Nereis diversicolor.
• In less polluted areas Spartina anglica detritus is important in Nereis diets.
• These two anthropogenic factors have probably increased Nereis densities.
• Deposit-feeding and herbivory by Nereis contributes to erosion of saltmarsh creeks.
• Saltmarsh management should attempt to alleviate this artificial cause of erosion.

Stable isotope analyses of the abundant infaunal polychaete Hediste diversicolor, recognised as an indicator of sewage pollution, support the hypothesis that nutrient enrichment promotes surface deposit feeding, over suspension feeding and predation. At sewage-polluted sites in three estuaries in SE England Hediste mainly consumed microphytobenthos, sediment organic matter and filamentous macroalgae Ulva spp. At cleaner sites Hediste relied more on suspension feeding and consumption of Spartina anglica. There were no consistent differences in Hediste densities between the polluted and cleaner sites, probably because of increased densities at the cleaner sites too, facilitated by the planting of Spartina and nitrogen enrichment there too, including from agricultural run-off. Increased nutrient enrichment and the artificial availability of Spartina have probably increased densities of, and deposit-feeding by, Hediste in the past half-century and contributed indirectly to saltmarsh losses, since deposit-feeding by Hediste has been implicated in recent saltmarsh erosion in SE England.