The repeated disturbance of the deep seabed by bottom trawling has caused major environmental change. This is particularly evident in the deep sea where key species have long generation times. Repeated disturbance by commercial operations leads quickly to major ecosystem change which can only be restored over a long period or at exceptionally high cost. This is most evident in key structural taxa, such as deep-water corals and sponges, some of which may take thousands of years to recover from an individual impact of only a few minutes. However, vulnerability is also true of less charismatic, but no less important, species critical for ecosystem health.
Bottom trawling has an effect on seabed ecosystems several orders of magnitude greater than all other physical impacts of man in the deep sea put together. In addition, the effects of bottom trawling extend beyond areas of direct impact owing to the initiation of downslope sediment slides.
The rules of life change quickly with increasing depth in the ocean. Most species are dependent on food created by photosynthesis at the sea surface. Food availability decreases exponentially with increasing depth. Deep-sea animals, therefore, even on the upper continental slope, are adapted to an environment where food is limited. Typical life history characteristics include greater longevity, reduced reproductive output and longer generation times.
Spatial management approaches may be suitable in areas where bottom trawling has degraded ecosystems. Spatial management measures, however, should also be applied to deeper areas where collateral damage may have occurred. Most species occur on the continental margin within narrow depth limits. There is a continual change in species with increasing depth. Spatial management approaches, therefore need to have particular regard to variations in fauna relative to depth.