The ecology of the Tamar Estuary VI. An account of the macrofauna of the intertidal muds

Abstract

The macrofauna of the intertidal mud-flats of the River Tamar have been investigated. Quantitative samples were taken by sieving the mud through a o·8 mm. sieve. Traverses of series of stations were worked at successive intervals up the river, and the tidal level of each station ascertained.The characteristic species which inhabit the mud-flats are listed and the data secured regarding (1) population density, (2) up-river penetration, and (3) vertical distribution, are summarized and related to previous information on these points.While some species are more or less uniformly distributed intertidally, others show marked zonation, with maxima in one part or another of the intertidal zone. Marine species which penetrate into the estuary tend to show the same intertidal distribution as in marine habitats. All five of the more strictly estuarine species are concentrated in the upper tidal levels.In considering the limiting factors which cause a decrease of population at lower tidal levels, emphasis is placed on the probable importance of the increase in strength of water currents towards low water.