Direct effects - Kelp harvesting
Case studies of the effects of kelp harvesting in UK and
Case studies on the effects of harvesting of kelp
elsewhere in the world
Around the world numerous kelp species have been exploited over the
years as a source of chemicals for industry. Since early times, kelp cast up on the shore
has, along with other seaweeds, been collected for use as an agricultural fertiliser (rich
in potash and phosphate) and also to improve the soil structure. In more recent times,
kelp has been burned to produce iodine-rich ash but now is the basic resource used in the
important alginate industry which produces valuable emulsifying and gelling agents. In
Europe, kelp is now harvested from living kelp beds, the most commonly harvested species
being Laminaria hyperborea and L. digitata. Commercial interest has also
been increasing recently in utilising Alaria esculenta and L. saccharina as
"sea vegetables" and it is possible that these species also will be harvested in
the near future. This harvesting may alter or destroy the structure of the kelp forest
ecosystem and reduce the POM and DOM available to other biotopes in coastal areas.
As a result of the importance of L. digitata and L.
hyperborea to the chemical industry, several reviews of the effects of harvesting on
kelp populations have been produced in recent years in France, Scotland and Norway.
The following brief discussion of the effects of harvesting on kelp
biotopes has been extensively abstracted from the work of Martin Wilkinson (1995):
"Information review on the impact of kelp harvesting".
Examples discussed below include non-European kelp species as these
include some useful information on the effects of kelp harvesting on the non-kelp species
in the kelp beds. Relatively little work on other species in kelp biotopes has been
undertaken in the UK as commercial, mechanical harvesting of kelp has not occurred.
Case studies of the effects of kelp harvesting in UK and European
Impact information comes from two sources: the removal of kelp for
scientific experiments, and from observations made on harvested grounds in Norway and
Brittany. The observations and data need to be considered in two different ways, the
effect of harvesting on the resource itself and the effect of kelp harvesting on the
complete kelp forest ecosystem. Not surprisingly most published work concerns the resource
rather than the entire ecosystem. The international scientific community recognises the
difficulty of determining both the short-term impacts of kelp harvesting and the long-term
consequences to the coastal environment. Around the coasts of Brittany 75-80,000 t of
seaweed are collected each year and yet there is no data on the effects of this biomass
loss from coastal ecosystems (Dauvin, 1997).
Experimental canopy removal and clearance experiments
Laminaria hyperborea harvesting
Harvesting of Laminaria digitata
Case studies on the effects of harvesting of kelp elsewhere in the
The following information has been abstracted from Wilkinson 1995,
(chapter 6, prepared by T. Telfer).
Most of the information on kelp harvesting that is available in the
literature concentrates on community dynamics of the kelp and the effects on grazers of
total or partial canopy removal. This may give an indication of harvesting effects but
must be interpreted with great care. The major effects shown by the removal of kelp plants
are centred on the influence of grazing populations, particularly the urchins which can
increase in abundance and change kelp-dominated areas into coralline "barrens"
Harvesting of Laminaria longicruris
Harvesting of Ecklonia species
Harvesting of Lessonia species.