Weather and storms

The exposed position of many CFT biotopes places them at risk from severe weather conditions. However, two factors will mitigate against damage. One is the depth of most biotopes, usually 20 m or greater, and the rapid rate at which wave induced exposure attenuates with depth is described in section II.D. The other is the generally robust nature of exposed CFT species, which are adapted to withstanding severe water movement. In coral reef biotopes there are records of storm damage to substantial depths - to 27 m in Hawaii (Walsh, 1983), to 30 m in Jamaica (Huston, 1985), and to over 35 m in French Polynesia (Harmelin-Vivien & Laboute, 1986). However there are no confirmed reports of similar effects in British CFT biotopes, though the systematic recording to detect such damage is probably lacking. In the Gulf of Maine rock wall communities were monitored by Sebens (1985a) through a series of violent storms, but no damage was observed. In fact a modest amount of storm damage would not necessarily have adverse effects. By creating patches of free space it can limit dominance by a few species and maintain high levels of biodiversity - the ‘intermediate disturbance hypothesis’.

There are two biotopes more likely to suffer storm damage. Scour-prone biotopes on unstable substrata are clearly at risk, from scouring action, and from covering by mobile sediments. However these generally have an impoverished community of scour-tolerant species, so storm effects may be difficult to detect. CFT communities in relatively shallow waters, normally on vertical or steeply sloping surfaces, would also be sensitive to storm damage. These shallow biotopes are relatively scarce, and their accessibility gives them added value and requirement for management consideration. Only intensive monitoring programmes will determine the extent to which storm damage actually occurs.

Indirect effects of weather can arise from the effects of heavy rains and floods, which can be mediated by climatic cycles such as the N.A.O. These can affect rate of nutrient transport to the sea, water stratification, and the initiation of plankton blooms. These effects are more likely to impact shallow and semi-enclosed biotopes.

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