Deep-sea benthic community and environmental impact assessment at the Atlantic Frontier

The seabed community provides a sensitive litmus for environmental change. North Sea analysis of benthic populations provides an effective means for m onitoring impacts from man's interventions, such as offshore oil exploitati on and fishing, against baseline knowledge of the environment. Comparable k nowledge of the benthic biology in the deep waters of the Atlantic Frontier beyond the N.E. Atlantic shelf edge is poorly developed. But uncertainties should not encourage assumptions and extrapolations from the better-known conditions on the continental shelf. While sampling at present still provid es the best means to assess the health of the deepwater benthic habitat, pr otocols developed for deep-sea fauna should be applied. These are necessary because of (a) lower faunal densities, (b) higher species richness, (c) sm aller body size, and (d) to ensure comparability with other deep-sea data. As in the North Sea, species richness and relative abundance can be analyse d from quantitative samples in order to detect impacts. But analysis based on taxonomic sufficiency above species level is premature, even if arguably possible for coastal communities. Measures also need to ensure identificat ions are not forced to more familiar coastal species without proper study. Species-level analysis may be applied to seabed photographs of megafauna in relation to data on bottom environment, such as currents and the sediment, to monitor the health of the deep-water community. Although the compositio n of higher taxa in the benthic community is broadly similar to soft sedime nts on the shelf, concordance in sensitivities is speculative. Moreover, ne w organisms occur, such as giant protozoan xenophyophores, unknown on the c ontinental shelf, whose sensitivities remain conjectural. Past knowledge of the benthic biology of the deep-water areas off Scotland is based on scatt ered stations and some more focussed, multidisciplinary studies, and should be significantly augmented by the results from the oil industry-funded Atl antic Margin Environmental Study cruises in 1996 and 1998. A predominantly depth-related pattern in variability applies here as found elsewhere in the deep ocean, and just sufficient knowledge-based predictive power exists to make comprehensive, high-resolution grid surveys unnecessary for the purpo se of broad-scale environmental assessment. But new, small-scale site surve ys remain necessary because of local-scale variability. Site survey should be undertaken in the context of existing knowledge of the deep sea in the U K area of the Atlantic Frontier and beyond, and can itself usefully be stru ctured as tests of a projection from the regional scale to reduce sampling effort. It is to the benefit of all stakeholders that environmental assessm ent aspires to the highest scientific standards and contributes meaningfull y to context knowledge. By doing so it will reduce uncertainties in future impact assessments and hence contribute usefully to environmental risk mana gement. (C) 2001 Elsevier Science Ltd. All rights reserved.