Sensitivity to Natural Events

Several authors have noted that brittlestar beds are long-lasting features of the benthic environment. Brun (1969) concluded from the results of repeated sampling off the southern Isle of Man that the beds there were stable structures, and quoted local fishermens’opinion that their spatial extent had increased (the time-scale over which this increase had occurred was not given). Garner (1878) and Chadwick (1886) also provide early records of brittlestar beds from the Isle of Man. Davoult & Gounin (1995) stated that the Ophiothrix population in the Dover Strait had remained stable, dense, and with a precise and unchanged location for ‘several years’. Cabioch (quoted in Holme, 1984) stated that beds in the eastern Channel and near Roscoff were sufficiently constant features to be given names by local fishermen. However, in most areas the lack of long-term records prevents any more precise estimation of the longevity of brittlestar aggregations. Long-term data are available only for the western English Channel. These indicate a cycle of bed expansion and contraction over a scale of decades, possibly driven by oceanographic factors and consequent changes in predator populations. In a few other locations, authors have recorded the disappearance of previously extensive brittlestar aggregations, demonstrating their sensitivity to particular forms of environmental change.

This chapter will describe the known case studies of naturally-driven fluctuations in brittlestar beds, and list the agents of change that appear to underlie them. On general biological principles, several other factors can be identified that one would expect to have the potential to affect brittlestar beds. These will also be briefly summarized.

Recorded examples of fluctuations in brittlestar beds

Other potential agents of change