Population dynamics of naturalised Manila clams Ruditapes philippinarum in British coastal waters

The Manila clam Ruditapes philippinarum was introduced to Poole Harbour (lat 50°N) on the south coast of England in 1988 as a novel species for aquaculture. Contrary to expectations, this species naturalised. We report on individual growth patterns, recruitment, mortality and production within this population. On the intertidal mudflats the abundance of clams (&gt;5 mm in length) varied seasonally between 18 and 56 individuals m?2. There appear to be two recruitment events per year and there were 6 year classes in the population. A mid-summer decline in abundance was partly due to increased mortality but probably also a result of down-shore migration in response to high water temperatures and the development of anoxic conditions. A winter fishery removes c 75% of clams of fishable size (maximum shell length ?40 mm) and c 20% of the annual production. The fishery depresses the maximum age and size attained by the clams but appears to be sustainable. Clam mortality due to factors other than fishing is highest in late-winter to early spring. The growth of the clams is intermediate in comparison with many published studies but remarkably good given their intertidal position. As on the coasts of the Adriatic Sea, where the clam is also non-native, the Manila clam has thrived in a shallow, eutrophic, lagoon-like system on the English coast. While the Poole Harbour population is currently Europe’s most northerly reported self-sustaining, naturalised population, given forecasts of increasing air and sea temperatures it might be expected that this species will eventually spread to more sites around the coasts of Northern Europe with associated economic and ecological consequences. <br/

Birds in estuaries Synopsis

SIGLEAvailable from British Library Document Supply Centre- DSC:GPC/06117 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Birds in estuaries Volume 1 - summary and predictive studies

SIGLEAvailable from British Library Document Supply Centre- DSC:GPC/06119 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Microbiological mediation of spectral reflectance from intertidal cohesive sediments.

Analysis of upwelling radiation (spectral reflectance) by remote sensing may provide valuable information on the nature and distribution of the primary producers, the microphytobenthos, on intertidal mudflat systems. Spatial and temporal variation in the spectral reflectance signal (400-900 nm) from the surface of an exposed intertidal mudflat was investigated in relation to the density and vertical position of microphytobenthos assemblages within the sediment. Spatial measurements were obtained from areas of sediment colonized by different assemblages of microphytobenthos (mainly mixtures of diatoms and euglenids). In addition, a station was selected to examine temporal changes in spectral reflectance (corrected for variations in ambient light) over an exposure period. It was shown that the spectral reflectance signal varied, depending on the pigment compliment and biomass of the surface assemblages of microphytobenthos. The qualitative variation in composition of the assemblages visualized by low-temperature scanning electron microscopy was confirmed by analysis of species composition (light microscopy) and by pigment fingerprinting (diode array high-performance liquid chromatography [HPLC]). Time-series analysis showed that the migration of cells to the surface of the sediment during a daytime emersion period rapidly changed the optical properties of the sediment surface. Analysis of sediment pigment content was conducted using standard surface scrapes (0.5-cm depth) and a high resolution sectioning technique (200-mu m layers). The migration influence was only detected by fine-scale analysis of pigments. This was demonstrated by a step-wise elimination analysis, which showed that correlations between the absorbance characteristics of the sediment and pigment content improved as premigration data were excluded. Maximum light penetration into the natural sediment was of the order of 2 mm under light conditions comparable with ambient levels. Two main conclusions were drawn from this study: (1) interpretation of spectral reflectance data must be consistent with knowledge of the ecology and behavior (cyclic migration patterns) of intertidal microphytobenthos, and (2) ground truthing of pigment-related signals from intertidal Bats should be conducted on a scale relevant to the process of spectral reflectance from sediments. The implications of these findings are discussed