The intertidal sediment habitats of the lower medway estuary, Kent

Abstract

During an ecological survey of the benthic invertebrate macrofauna of the lower Medway estuary, Kent, sediment cores were analysed for particle size, redox potential profiles, total organic matter and free sulphide ions, to characterise the sediment habitats at ten shore sites. Visual assessments of the percentage cover of green algae, predominantly Enteromorpha intestinalis (L.) and Ulva lactuca L., over the mudflats are presented. Sediment parameters ranged from less favourable conditions at BP Horseshoe Bay to the relatively healthy conditions at the Isle of Grain. In general, those sites sheltered from the influences of the main tidal channel supported green algal blooms which, on decay, resulted in a depletion of oxygen in the sediment which was characterised by negative redox potentials, high organic matter levels and high free sulphide ion estimates. Numbers of the tubificid Peloscolex benedeni (Udekem) and Hydrobia ulvae (Pennant) increased during these periods with the appearance of the capitellid Capitella capitata (Fabricius). At sites more open to the flow of the main channel, green algae were absent from the mudflats and sediment conditions were characterised by higher redox potentials, lower organic matter levels and lower free sulphide ion estimates. Nereis diversicolor Müller was the most common polychaete at these sites. A number of polychaetes found at the Isle of Grain were either absent, or did not occur in as high numbers, at other sites.