Sensitivity to human activities

Activities listed are those which influence, or are likely to influence this habitat and which are assessed in the UK marine SAC project review. The sensitivity rank may require amendment in the light of new information becoming available.

Sensitivity to: Human activity Rank Comments
Substratum change Waste: spoil dumping


Heavy sedimentation will inhibit bed occurrence by clogging the brittlestar feeding organs. Aronson (1989) refers to the demise of Warner’s (1971) Ophiothrix bed in Torbay, and tentatively attributes this to increased sedimentation caused by the localised dumping of construction materials.
Changes in temperature Climate change/global warming


Leewis, Waarenburg & van der Tol (1994) described fluctuations in the abundance of Ophiothrix fragilis in the Dutch Oosterschelde Estuary over the period 1979-90. These changes appeared to be driven by winter temperatures. Following the mild winters of 1979-80 and 1987-88, populations of brittlestars increased enormously, the animals occupying 60-90% of the available hard substrata in layers up to 5 cm deep. Populations were greatly reduced (to less than 10% spatial coverage) following cold winters in 1978-79, 1984-85 and 1985-86. The populations undergoing these changes were living in very shallow water (5-7 m depth) and were therefore vulnerable to spells of unusually cold weather.
Heavy metal contamination Waste: industrial effluent discharge

Not sensitive

Gounin, Davoult & Richard (1995) studied the transfer of heavy metals (iron, manganese, lead, copper and cadmium) through Ophiothrix beds. They concluded that heavy metals ingested or absorbed by the animals transited rapidly through the body and were expelled in the faeces. The brittlestars did not appear to accumulate metals in the tissues and so would not act to decontaminate the near-bottom water mass.
Hydrocarbon contamination Uses: boats/shipping (oil spills) Low The water-accumulated fraction of diesel oil has been found to be acutely toxic to Ophiothrix fragilis and Ophiocomina nigra (Newton 1995). So far, however, there are no field observations of epifaunal brittlestar beds being damaged by any of these forms of pollution. It is logical to suppose that brittlestar beds would be adversely affected by major pollution incidents such as oil spills.
Changes in nutrient levels Aquaculture: fin-fish


The expansion of cage aquaculture of Atlantic salmon along the fiordic coastlines of western Scotland and Ireland over the past few decades has led to increased local inputs of organic material into many semi-enclosed water bodies (Black 1996). The effects of this on brittlestars have not been studied in detail, but some relevant observations have been made in Killary Harbour, western Ireland (Keegan & Mercer 1986). A dense aggregation of Ophiothrix and Ophiocomina was recorded in 1974 from a site at the mouth of the harbour, mainly on rocky outcrops but extending out onto adjacent sand silt areas. A salmon farm was established at the site in the late 1980s, within 100 m of the main beds. Despite the presence of this farm for ten years, the extent and density of the brittlestar beds appeared not to have changed (B. Ball pers. com.), although an increase in siltation had taken place.
Changes in oxygenation Aquaculture: fin-fish


High levels of organic enrichment such as that expected from aquaculture waste would have deleterious effects on brittlestars and other suspension feeders by excessive sedimentation and hypoxia.
Displacement Fishing: benthic trawling


Brittlestars themselves are of no economic value, and their aggregations are not significant habitats for any commercially important fish or shellfish. Fishermen tend to avoid areas with dense brittlestar populations because the animals foul their nets (Aronson 1989). There is little likelihood of damage to brittlestar beds by fishing activities. In fact Aronson & Harms (1985) speculated that human overexploitation of fish resources could favour the spread of brittlestar aggregations by reducing predation pressure on the animals.

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