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.
||Waste: sewage discharge
|Although sheltered infralittoral kelp is tolerant of
siltation, excessive siltation which occurs in the vicinity of sewage outfalls can exert a
number of detrimental influences on marine benthic algal communities (Fletcher 1996). The
sediment can cover all available substrata interfering with the processes of spore
attachment. They can smother young germlings and inhibit their growth and development.
|Changes in temperature
||Climate change/global warming
|This would affect the biogeographical distribution of kelp
according to their temperature tolerances. Unfortunately, global warming effects span
multiple generations of scientists and governments and the need for very long term
monitoring research has only recently been appreciated.
|Changes in turbidity
||Extraction: navigational/ maintenance dredging
||Dredging results in the suspension of the fine silt and clay
fractions of the sediment that is deposited by inshore currents. This will increase
turbidity and decrease the amount of penetrating light.
||Uses: boats/shipping (oil spills)
|The mucilaginous slime covering kelps is thought to act as a
protective device (OBrien & Dixon 1976). However, Laminaria hyperborea
would probably never come into contact with freshly released crude oil as a result of its
|Changes in nutrient levels
||Waste: sewage discharge
||The increase in levels of macronutrients in European coastal
waters results in the excessive growth of ephemeral macroalgal species. Increased
turbidity in coastal waters may also occur as a result of prolific phytoplankton growth.
The localised increase in nutrient levels as a result of marine aquaculture could produce
local eutrophication effects, particularly at slack tide.
|Changes in oxygenation
|Plumes of waste could stream over kelp forests leading to
anaerobiosis as a result of the oxygen demand of the decomposing material. Detrital rain
could also smother the surfaces of plants. Anti-microbial agents could be particularly
harmful to kelp biotopes because of the importance of bacteria in detrital cycling.
|Removal of target species
||Collecting: kelp/wrack harvesting
|Svendensen (1972) examined kelp beds over periods of up to 3
years after harvesting. He found the Laminaria population to be dense after one
year but in terms of biomass considered the population to have completely regenerated
after 3-4 years. Sivertsen (1991) has compared the re-growth of kelp in areas trawled 1-5
years previously with areas freshly trawled and control areas. Large canopy-forming plants
were absent until 4 years after harvesting, but the structure of the kelp population was
beginning to stabilize with little change in plant density from years 4-5. A further
interesting observation was the replacement (for one year only) of the L. hyperborea-dominated
forest with a population of S. polyschides as in the clearance experiments by Kain
(1975). Harvesting may also affect those species associated with the kelp biotope. Rinde et
al. (1992) carried out a survey to establish the affects of kelp harvesting on common
organisms within the kelp biotope. They found the forest structure to recover to almost
normal after 3-4 years, but argue that the forest does not provide the same physical
environment for the other organisms that it shelters.