Species point records from 1988 OPRU HRE Taf, Tywi & Gwendraeth Estuaries survey

The estuaries of the Taf, Tywi and Gwendraeth are known locally as the `Three rivers` as they converge and enter into Camarthen Bay in South West Wales through a common mouth. The rivers drain agricultural catchments of 246, 1335 and 175 km2, respectively, and the underlying rocks are, for the most part slightly acidic. Of the three river estuaries, the Tywi is the larger at over 20 km in length. The Taf and Tywi are both typical coastal plain estuaries and the Gwendraeth is a bar-built estuary formed by the north westerly movement of sand from the Pembrey coast dune system. All three estuaries are presently undergoing substantial infilling by marine sediments originating from Camarthaen Bay and as a result are shallow and drain almost completely at low tide. Tidal flows within the system and in particular in the Taf and Tywi, are of considerable strength and the tidal wave symmetry is distorted producing a longer ebb than flood. This report describes the habitats and associated communities at twenty-one sites surveyed in the study area; eighteen intertidal sites and three dredge sites from the main channels. Species present have been identified and tabulated. Hard substrata communities are not well represented in the `Three Rivers` and those examples occuring are markedly sand scoured and support depauperate communities. Sedimentary habitats dominate the system, and there is a gradation of sand flats to mudflats from the mouth to the upper estuaries. The lower shore flats are generally unstable environments being subject to large tidal salinity fluctuations and strong tidal currents. More stable sand flats are found on the upper middle shore with considerably richer communities. Mussel scars occur at three sites in the system and are subject to scouring losses. Both mussels and cockles are collected commercially on a small scale and some netting also occurs. Mussel culture is presently being evaluated in the Gwendraeth Estuary. The Taf and Tywi have naturally low oxygen levels in their estuaries at times of continued fine weather, low river discharges and spring tides. These are compounded in the Tywi by effluent from a large sewage treatment works which significantly increases the biological oxygen demand (B.O.D.). The `Three Rivers` are flanked by Sites of Special Scientific Interest (SSSI) to the east, west and north. Notification of these was for the sand dune flora and fauna and maritime cliff communities. The south shore of the Gwendraeth, including Towyn Point, and Salmon Point Scar are the only marine habitats protected by the designations. The area is also of nature conservation interest for the populations of migrant and over-wintering waterfowl. Several species reach levels of National Importance, though they are not afforded any other specific site protection at the present time. rivers