Indirect effects

Kelp has traditionally been collected for use as an agricultural fertiliser and to improve soil structure. The change to mechanical harvesting from live kelp beds is the most significant human activity directly affecting the kelp in the kelp forests. Other important activities which impact on kelp beds include eutrophication from domestic and agricultural nutrient run-off, which can result in increased turbidity in coastal waters due to blooms of phytoplankton as well as affecting the physiology of the kelp plants. Turbidity increases also occur as the result of increased silt loads in rivers draining agricultural areas and from the particulate components of sewage. The removal of predator species is known to have had major effects in Pacific and Eastern Canadian kelp beds. Effects of predator removal and of the limited harvesting of edible urchins in the UK are not yet known. Very little information is available on the effects of human activities on species other than the kelps themselves and this is a consequence of past research in response to the commercial interest in the kelp species, rather than interest in the kelp bed ecosystems as a whole.

Detecting the environmental impacts of human activities on natural communities is a central problem in applied ecology. It is a difficult research topic because human perturbations must be separated from the considerable natural temporal variability displayed by most populations. In addition, most human perturbations are generally unique and thus un-replicated. This raises the problem of deciding whether observed local effects are due to human intervention or to the natural differences in temporal patterns that often occur among different sites. These problems can be successfully addressed with the Before-After/Control-Impact (BACI) sampling design, in which Impact and Control sites are sampled contemporaneously and repeatedly in periods Before and After the human perturbation of interest (Schroeter et al., 1993).

Direct effects - Kelp harvesting

Marine Aquaculture effects on kelp biotopes

Eutrophication

Pollution

Channel dredging and coastal alteration

Sediment loading

Effects of the removal of predator species.

Effects of introduced species

Global warming and ozone layer depletion

References