Field Studies Council

ABSTRACT Recent attention to bioremediation of stranded oil on shorelines has identified some of the conditions under which nutrient addition to oil may prove successful. However, relatively little is known of the interactions between substrate texture and natural biodegradation rates to determine the residual hydrocarbon content and composition. The effects of varying shoreline energy levels on the balance of physical versus biological oil removal rates from a range of sediment substrates was investigated in a series of oil spill field experiments in southwest Britain. Two oil types (medium fuel oil mousse and lightly weathered Nigerian crude oil) were used on five shore types (coarse sand to salt marsh). Hydrocarbons were determined in the sediment at intervals up to a year. Selected extracts were analysed by gas chromatography (aliphatics). In a further phase, the contribution to the removal process made by treatment of the stranded oil with chemical dispersant was assessed. Results indicated that on shores where the most rapid physical removal occurred, biodegradation was minimal during the short time scale involved. On shores where oil persisted more than 20 days, biodegradation was more noticeable when oil concentration in the sediment was less than about 1 percent. These data show that physical processes (waves, tides, evaporation) remain the dominant removal mechanism across a range of shore types. The use of chemical dispersant on stranded oil appeared to accelerate physical removal of oil, but may have slowed down biodegradation rates. It would seem, however, that the stage at which biodegradation becomes quantitatively important may be reached more quickly if shoreline countermeasures (including dispersant use) are successful in accelerating physical removal.

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ABSTRACT On the 19th of August 1989 at 2:30 p.m., a fracture occurred in a pipeline carrying Venezuelan crude oil from a shipping terminal at Tranmere to the Shell (U.K.) Ltd. oil refinery at Stanlow, on the Mersey Estuary, England. 150 metric tons of oil were released into the estuary before the pipeline was sealed; tidal currents widely distributed the oil within a tidal cycle. The Mersey Estuary is heavily industrialized and urbanized but does retain extensive areas of salt marsh and intertidal mud flats which are internationally important for wildfowl and wading birds. Cleanup operations were coordinated by the two local fire brigades whose areas of responsibility included impacted shoreline. Input to the response came from government, local authorities, specialist consultants, and various other interested parties. The occurrence of the spill on one of the highest spring tides of the year and under favorable weather conditions served to lessen the environmental impacts. Less than two weeks after the spill, Shell (U.K.) and Cheshire County Council set up the Mersey Oil Spill Project Advisory Group, with a membership drawn from independent scientific groups, which would monitor the environmental effects of the spill and publish its findings. The primary report of the advisory group is a detailed historical record of the spill incident, the response to it, and the coordination of that response, as well as the lessons learned by the involved parties. Further studies consider the persistence of the oil, and its effects on birds, invertebrates, vegetation, and algae. Recommendations have already led to a review of the local contingency plan and the commissioning of work to produce specific cleanup guidelines and sensitivity maps for the region. In February 1990, a court action brought by the newly formed National Rivers Authority led to Shell (U.K.) Ltd. being fined £1 million due to the pollution arising from this incident.

The third instar larvae of two closely-related blowfly species, Chrysomya megacephala (Fabricius) and Chrysomya regalis Robineau-Desvoidy (=marginalis Wiedemann) are described and illustrated, and a simple key is given to separate them. As with some other blowfly larvae, it was found that the structure of the spines was a most useful diagnostic feature. Although the natural ranges of these two species do not overlap to any extent, the recent introduction of Ch. megacephala into Africa (part of the range of Ch. regalis) makes it desirable to separate these two species in the larval stage.

Research has always been one of the functions of the Field Studies Council. One facet of this is the great diversity of small projects which support educational courses at the Field Centres. There has also been the growth, from small beginnings in 1967, of the Oil Pollution Research Unit at Orielton. OPRU has operated internationally for many years and undertakes both basic research and contract work for industry and governments. A more recent development involving contract work is ‘acid rain’ monitoring. These industrial facets of FSC Research have useful educational spin-offs.

Iridophora clarki gen. nov., sp. nov., Megaselia sembeli sp. nov. and M. kodongi sp. nov. are described. The females of I. clarki attack the workers of the ant Iridomyrmex cordatus (Smith). The same ant species is also attacked by M. sembeli, and the morphology of this species indicates that it is close to P. beirne Brues, the typespecies of the genus Plastophora. The loss of the type-material of the latter species prevented synonomy of the genus when it was re-evaluated (Disney, 1978). The detailed examination of M. sembeli now indicates that the genus Plastophora is a synonym of Megaselia (syn. nov.). A consequence is that P. dubitata Brues, 1935 becomes a homonym of M. dubitata (Malloch, 1912) and the replacement name M. bruesi nom. nov. is proposed. The females of M. kodongi attack workers of a species of Pheidologeton which forages on the forest floor. The habit of Iridomyrmex cordatus in using covered ways up trees appears to be related to its extreme vulnerability to attack by these two phorides.

SynopsisThe identity and abundance of animals passing through a 1·0 mm mesh but retained on a 0·5 mm mesh is detailed for a number of seabed samples of medium, fine and very fine sand taken in the Beatrice Oilfield in 1981. Comparisons are made with the corresponding 1·0mm-sieved fractions, and the effects on community parameters of combining the two data sets are considered.In general fewer animals were found on the 0·5 mm mesh than on the 1·0 mm mesh above it. The 0·5 mm mesh samples added comparatively few taxa to the faunal list of the survey. The quantitatively-scored taxa from the 0·5 mm mesh were therefore essentially a sub-set of those already recorded on the 1·0 mm mesh. Several taxa of Foraminiferida were found only on the 0·5 mm mesh, and one of these appeared to be relatively abundant. However. Foraminiferida were not scored quantitatively in this study.In all samples, when 0·5 mm and 1·0 mm data were combined an increase was noted in the number of taxa recorded compared with 1·0 mm data alone. This recruitment of taxa was largely a reflection of the greater number of individuals in the combined data, rather than the inclusion of taxa unique to the 0·5 mm material. Similarly, the improved precision of abundance estimates of dominant taxa in replicate samples in the combined data probably resulted from the greater number of individuals included in the analysis.It is argued that the choice of a particular mesh size imposes an essentially arbitrary cut-off along the size spectrum of benthic organisms. A 1·0 mm mesh has been found to yield adequate data in a number of offshore surveys undertaken by the Oil Pollution Research Unit (OPRU). Although a greater number of animals per sample is collected by sieving on a 0·5 mm mesh, the time taken to extract and identify this material must be considered. The alternative of spending an equivalent time analysing extra 1·0 mm samples may in fact yield a greater increase in confidence in the results.

Abstract Amphicteis midas and A. gunneri are redescribed from British and North Sea material including the types of A. gunneri. The two species have long been confused under the name A. gunneri but are readily distinguished morphologically and appear to be separated ecologically. Amphicteis midas was only found in shallow < 30 m) waters including the intertidal whilst A. gunneri was restricted to deeper waters. On the basis of an examination of limited material from other areas, it was concluded that the cosmopolitan status of A. gunneri is unjustified.