Habitat point records from 1985 OPRU HRE Fal Estuary survey

1. Falmouth bay and the Fal estuary are situated on the south coast of Cornwall at the western entrance to the English channel. The estuary and its various branches extend 17 Km from the open coast to the head of the Tresillian river with the major port, Falmouth, situated close to the mouth on the west side. The estuary is considered to be rich in biota because of its biogeographical position. 2. Previous biological studies have been largely concerned with the oyster industry, heavy metal contamination or specific areas of high biological interest such as the St Mawes maerl bed. The present work includes a review of previous studies in addition to a wide ranging intertidal and subtidal survey through out the estuary. 3. Intertidal work was carried out between Thursday 2nd May and Thursday 9th May, 1985. Various types of shore with rocky, muddy or mixed substrata were surveyed. The subtidal work was carried out between Fiday 29th June and Friday 12th July, 1985, mainly using diving techniques, plus some trawling and dredging which was carried out on the 10th July. During the two surveys, 24 intertidal and 57 subtidal sites were surveyed and photographs were obtained from almost all sites during the periods of fieldwork. Aerial photographs were taken during a flight on Saturday 4th May, 1985. 4. The predominant features of the Fal estuary are the very slow tidal currents in all but a few areas, the consequent degree of sediment deposition which is taking place, the scarcity of subtidal rock habitats and the large extent of the shallow subtidal banks. 5. During the surveys 9 different intertidal and 14 subtidal habitats were distinguished. Several communities are characterised by a range of silt tolerant species which occur commonly through out the estuary. The richness of algal and animal populations is reduced due to lack of hard substrata and it is clear that many species present offshore are unable to penetrate far northwards into the estuary. Some habitats are very rich in species although these areas represent only a small proportion of the total area surveyed and are found almost entireley in the vicinity of St Mawes and the Percuil River. There are also rich intertidal communities in gullies between Trefusis Point and Penarrow point. Many of the other expensive habitats such as the various shallow banks in Carrick roads are species poor. 6. The maerl bed on St Mawes bank is an unusual habitat being the furthest south in the british isles. In view of its importance many sites there were surveyed during the 1985 survey. The majority of species found are fairly typical of maerl beds but some were lower in abundance than expected. The presence of mud and silt combined with the relatively slow tidal currents is probably detrimental to many organisms. 7. An assesment of scientific interest and nature conservation importance has been undertaken through a general evaluation and by ranking the conservation importance of the habitats and communities encountered and also of species considered to be of conservation interest. Although the whole region of the Fal estuary must be considered of scientific interest because of its physiographical features, our surveys have revealed fairly impoverished communities over much of the area. However the outer part of the estuary has many features which make it of high scientific interest. 8. The maerl bed and adjacent areas to the south were designated as the Roseland Voluntary Marine Reserve in 1982 and these areas are confirmed as being of high scientific interest. There are many significant threats to the future security of the reserve including damage by anchors, bait digging, collection of shellfish, pollution by organotin compounds and also the construction of a modern container complex south of Falmouth Docks. The latter is likely to have some adverse effects on communities within the reserve. Records currently considered sensitive have been removed from this dataset.

Organization: Joint Nature Conservation Committee