Other pollutants

Introduced species

There are no recorded cases of biotopes within this complex being seriously impacted by pollution processes other than organic enrichment, but on general biological principles it can be assumed that the various forms of contaminant shown to damage other benthic communities could also have adverse effects on the systems discussed here. Potentially harmful contaminants could include oil or oil-based drilling muds, pesticides, polychlorinated biphenyls (PCBs) and heavy metals.

Specific examples of known sensitivity to pollutants are rare, probably because burrowing megafauna are generally too difficult to sample to be included in standard pollution monitoring studies. In the North Sea, Daan et al. (1992) found that Callianassa subterranea decreased in density towards drilling sites contaminated by oil-based muds. Distribution patterns suggested that this was one of the more sensitive species in the sediment fauna, and experienced environmental stress even at distances of 1 - 2 km from the contaminant source. Following the wreck of the oil tanker Braer off the coast of Shetland in 1993, a fishery exclusion zone was established in the contaminated area. At present, Nephrops norvegicus is the only species for which this closure still operates (C.J. Chapman, personal communication). The low water currents associated with muddy sediments makes this type of habitat highly vulnerable to pollutants, which may persist in the environment for several years.

In the Scottish salmon farming industry, a variety of chemical compounds have been used to combat infestation of the fish by parasitic crustaceans (‘salmon lice’), and there has been concern about the possible effects of these pesticides on the benthic fauna. Ivermectin, an anti-louse treatment now coming into use within the industry, has recently been shown to be highly toxic to sediment-dwelling polychaetes (Black et al., 1997; Thain et al., 1997) and epibenthic shrimps (Burridge et al., 1993). It is reasonable to suppose that ivermectin (and perhaps other compounds used in the industry) might also be toxic to burrowing megafauna in the vicinity of salmon farms. In Washington State, USA, the pesticide carbamyl has been used to control populations of thalassinidean mud-shrimps whose activities are detrimental to the survival of cultivated oysters (Brooks, 1993).

Communities containing sea pens and abundant burrowing megafauna exist in the north-eastern Irish Sea in areas heavily contaminated by past discharges of long-lived radionuclides from the British Nuclear Fuels Plc reprocessing plant at Sellafield, Cumbria (Hughes & Atkinson, 1997). No obvious effects of Sellafield discharges could be observed here, although the burrowing fauna probably have a major influence on the distribution of radionuclides within the sediments (Kershaw et al., 1983).

In Nova Scotia, Pemberton et al. (1976) found that the extremely deep-burrowing mud-shrimp Axius serratus was most abundant in highly polluted sediments adjacent to urban, industrialised shores, areas barren of living foraminiferans, molluscs and ostracods. These observations suggest that the animal is one of the more pollution-tolerant members of the local benthic fauna, contrasting with the findings on North Sea Callianassa quoted above. The apparent diversity of responses and physiological abilities within the general category of ‘burrowing megafauna’ highlights the need for more research into the effects of environmental pollution on these animals.

There is currently increasing concern about the effects on marine ecosystems arising from the introduction of non-native species, this process often occurring accidentally as a result of human activities (eg. transport in ships’ ballast water) (Carlton, 1996). To date, a number of non-native species have become established in British waters, some very locally, others distributed more widely (Eno et al., 1997). The biotopes discussed here have not yet been subject to any biological invasions, but there is always the potential for this to occur.

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