S.E. Boyd

The structure and taxonomic composition of sublittoral meiofauna assemblages as an indicator of the status of marine environments

A study was conducted between 1997 and 1999 to investigate meiofauna assemblages from selected inshore and offshore locations around the UK coast. The main objective was to relate the differences in meiofauna distribution patterns to a number of measured environmental variables and to establish more clearly the sensitivity of meiofauna communities to anthropogenic disturbance. Results from univariate and multivariate data analyses show that distinct spatial differences in species distribution patterns exist and that these correlate with the natural physical characteristics and concentrations of trace metals in the sediment. Abundance and diversity of meiofauna assemblages were generally higher offshore than inshore and this difference can be attributed to both natural processes and anthropogenic impacts. The inclusion of meiofauna in applied monitoring programmes offers the potential for improving the resolution of the spatial extent of anthropogenic impacts over that achievable from macrofauna investigations alone.

Effects of simulated deposition of dredged material on structure of nematode assemblages – the role of contamination

Abstract Certain criteria must be satisfied before a licence for the deposition of dredged material at sea in UK waters is issued. These relate to the chemical quality of the material, the quantity to be disposed of, its nature and origin, and its predicted impacts at the disposal site. Although chemical analyses of dredgings provide an indication of the relative degrees of contamination, they do not provide a measure of any resultant biological effects. A laboratory experiment was therefore designed to investigate the effects of the degree of contamination and the role of burial associated with the deposition of dredged material on the meiofauna. Estuarine nematode assemblages were exposed to the simulated deposition of uncontaminated, oxic intertidal mud and anoxic sediments from the Mersey and the Tees estuaries, both of which were contaminated with heavy metals. The sediments, which differed little in terms of grain size, were deposited in two different frequencies. Nematodes showed a clear species-specific response to the experimental treatments, depending on the frequency of deposition and the chemical quality of the deposited material (e.g. metal and oxygen concentrations). The response of nematode assemblages was mainly determined by the deposition frequency rather than the type of sediment or the degree of contamination. The deposition of sediment in one large dose at the beginning of the experiment caused more severe changes in assemblage structure than the same quantity deposited in several smaller doses. Although lower than in uncontaminated mud, relatively high migration and survival rates in the contaminated high-frequency treatments were observed. This may have been due to reduced bioavailability of metals and the tolerance of estuarine nematodes to both metal contamination and the deposition of small sediment volumes at regular intervals. The observed trends demonstrate the potential of small-scale laboratory experiments for testing the quality of contaminated dredged material at the licensing stage, i.e. prior to the issue of a disposal licence.

Preliminary observations of the effects of dredging intensity on the re-colonisation of dredged sediments off the southeast coast of England (Area 222)

The re-colonisation of a site used for the extraction of sand and gravel for ca. 25 years off the southeast coast of the UK was examined 4 years after the cessation of dredging. Effects of different levels of dredging intensity on the rate of macrofaunal re-colonisation were investigated. Values of abundance and total numbers of species were significantly lower (p<0.05) in an area most recently exposed to the highest level of dredging intensity compared with samples taken from an area of low intensity, and those from a reference site. Differences between previously dredged sediments and the reference location were due to the reduced abundance of a range of macrofaunal species characterising nearby sediments. Multivariate measures of community structure also indicated that there were significant differences (p<0.01) between the macrofaunal assemblages in the areas exposed to different dredging intensities. Sediment from the area exposed to the highest dredging intensity contained proportionally more sand than other sampled sediments. The extent to which dredging intensity contributed to these differences was difficult to determine owing to the absence of any baseline data. Despite this, univariate and multivariate analyses indicated a strong relationship between macrofaunal community structure and dredging intensity at this site. Correlation analyses also demonstrated that the predominant influence on the macrofaunal community was that of the level of dredging that took place in 1995, the last year that the licensed site was dredged heavily. Preliminary observations indicated that the fauna remained in a perturbed state some 4 years after cessation of dredging. Therefore, relatively rapid ‘recovery’ rates, commonly cited as 2–3 years for European coastal gravelly areas, should not be assumed to be universally applicable. Implications for the future management and scientific study of marine aggregate extraction arising from preliminary observations on the physical and biological status of this site are discussed together with the options for selecting a reference site in the absence of baseline information.

Benthic responses to organic enrichment and climatic events in the western North Sea

Macrofaunal assemblages inhabiting stable offshore muddy sand substrata responded predictably to the effects of mild organic enrichment arising from sewage-sludge disposal off the north-east coast of England (western North Sea). At the disposal site, densities were elevated up to two-fold, but classical ‘indicator’ species were only marginally enhanced and there was no evidence of a significant waste-induced change in assemblage structure. The response following cessation of disposal was equally predictable, with a decline in densities to ‘reference’ levels some three years later. However, physical manifestations of disposal, including tomato pips and non-biodegradable artefacts, were still evident after this time. Changes in diversity at selected monitoring stations tended to track each other over time and the employment of treatment/reference ratios and limit values for acceptable change provided a useful model for the simplified expression of trends. Predictions concerning the limited scale and intensity of the effects of sewage-sludge disposal appear to have been met, indicating that the management option of sea disposal was, at the time, an environmentally acceptable one. Temporal trends in the benthic fauna were also correlated with winter values of the North Atlantic Oscillation Index for the preceding year. The densities and variety of species tended to be lower in response to warmer winters characterized by westerly airflows which were commonly encountered in the 1990s. Finally, the increasing importance of extended time-series data for the investigation of man-made impacts on the marine environment is highlighted, along with the accompanying requirement for continuity and quality assurance of sampling programmes.

Response of estuarine meio- and macrofauna to in situ bioremediation of oil-contaminated sediment

Numerous studies have demonstrated the efficacy of bioremediation for enhancing oil removal but the ecological effect on shoreline biota is unclear. Therefore, a field experiment was designed at an intertidal sandflat in SW England to assess the effects of nutrient addition to oiled sediments on meio- and macrofauna for a period of up to 45 weeks. Natural assemblages were exposed to different types of experimental treatments (no oil, oil alone, oil treated with slow-release fertiliser or liquid fertiliser). Bioremediation stimulated the microbial population and increased oil biodegradation. This, however, did not result in faster recolonisation rates of fertilised versus non-fertilised oiled sediments. Mild effects of oil and bioremediation treatments on benthic fauna were observed, including short-term shifts in dominance patterns. Decreased abundance of dominant species in the oiled compared to unoiled sediments resulted in significantly higher evenness of benthic assemblages within the first 11 weeks of the experiment.

A comparative study of a 0.1 m2 and 0.25 m2 Hamon grab for sampling macrobenthic fauna from offshore marine gravels

This paper is concerned with comparing the relative performance of small (0.1 m 2 ) and large (0.25 m 2 ) Hamon grabs for sampling the benthic macro-invertebrates from coarse offshore marine sediments. We present results based on an actual survey near the Isle of Wight, UK, but we also summarize and develop a statistical theory as well as demonstrate the theory using a small simulation study. Our results show that: the larger grabs are more difficult to handle, especially from small vessels; for a given sampling area the small grab can provide a more precise estimate of abundance than the larger grab if the individuals are clustered; the smaller grab can detect more species than the larger grab if individuals from the same species are clustered together (in our study, approximately 5% more species); and the smaller grab may undersample larger macrofaunal species and also species that live on larger cobbles. We present theoretical equations to demonstrate the two samplers abilities to capture cobbles of different sizes. Multivariate techniques suggest that differences in the composition of the fauna collected using the different sized grabs are statistically significant, but small. It is more expensive to process samples from the smaller grab per unit area. However, per grab, the smaller grab is cheaper. We also present a model to demonstrate the effect on species occurrence and abundance.