Habitat point records from 1984-85 Harris lower Torridge estuary littoral survey

In common with all estuaries, that of the Torridge has a wide range of habitat types, ranging from fine, clean sand to pure mud with high organic content. Such diversity of habitats might be expected to support a similarly high diversity of organisms, especially since the estuary is so thoroughly scoured by tidal activity - thus preventing the kind of accumulation of organic material which leads to eutrophication but whilst still permitting the organisms to take advantage of the rich, detrital food supply borne by river and sea. This expected diversity is absent. It is only those shores which are either rocky or sufficiently stony to act as rocky shores which support a variety of plant and animal species - a situation which is, of course, common on 'ordinary' sea-shores - i.e. outside estuaries. Whilst it is true that estuarine faunas are always restricted, it is surprising to find, for example, that the sandy shores support such very reduced faunas of errant species and that, despite considerable searching, no evidence could be found for the presence of either the gastropod Hydrobia ulvae nor the amphipod Corophium volulator on any of the muddy shores. Both of these species are usually very common in estuaries. It is not inconceivable that the lack of these species was due to the season during which this survey was carried out - but that would not entirely explain the apparent total absence of the accumulated shells of the gastropod along strand lines where they frequently occur in enormous quantities in other situations. There is no doubt that some of the muddier shores in the Appledore region accumulate very large quantities of organic debris, apparently washed down in the river-flow and deposited on these shores due to the flow pattern of the river near its mouth. Such organic material is one of the prime sources of food for invertebrates - but an excess of this material, especially when it is not effectively cleared away by water movements, can lead to ecological trouble due to the accumulation in the colloidal muds of hydrogen sulphide, with accompanying anoxia. Whilst the larger, naturally occuring debris of this sort (leaf-litter and remains of salt-marsh plants) were readily detectable, more metabolised debris, such as sewage waste, was not detectable by methods employed fro this study - but would, if accumulated in these sites, exacerbate the problem due to its more rapid bacterial breakdown. Despite the lack of species diversity, the plants and animals do exist within the Torridge estuary appear to be successful. The abundance of Scrobicularia plana and Mytilus edulis at their representative sites has already been recorded, along with comment concerning the large size to which both species grow. Algal cover on the hard shores is good and, for an estuary, interestingly diverse. There is apparently no accumulation of Ulva lacuta thus indicating that no stagnation of dissolved plant nutrients occurs within the estuary - a situation which could scarcely be expected to arise in an estuary with such sweeping tidal activity.

Organization: Joint Nature Conservation Committee