Kelp communities contain a large number of habitats available for colonization by other species. The faunal diversity of kelp biotopes is extremely rich owing to the available primary, secondary and microbally-recycled production and also to the structural diversity within the biotope with many and various exploitable niches available. The floral diversity within kelp communities can also be great with colonisation occurring epiphytically on kelp plants or less independently on the surrounding substrata. Drach (1949) pointed out the importance of this and calculated that the rugose stipes of Laminaria hyperborea provide a settlement area of one-and-a-half times that of the rock surface. Epiflora recorded for Laminaria hyperborea stipes include Palmaria palmata, Phycodrys rubens, Membranoptera alata, Ptilota gunneri and Cryptopleura ramosa (Marshall 1960). Stipes of Laminaria digitata, although smooth, can support a considerable epiphytic flora, mainly of smaller species (Gayral & Cosson 1973).

Kelp beds are dynamic ecosystems where competition for light, space and food result in the species rich but patchy distribution patterns of flora and fauna on the infralittoral reefs. Kelp plants themselves support a diverse epiflora and epifuana, with their holdfasts forming a sheltered habitat for a diverse assemblage of animals.

Kelp biotopes, with their large numbers of species, high biomass and high rates of productivity are an important nursery area for a diverse range of species. It is likely that juvenile forms of all the animals that are present as adults in the kelp bed make use of the habitat as a nursery area. Other species may make use of the kelp beds during only parts of their life cycles.

Kelp plants are the major primary producers in the marine coastal habitat. Within the euphotic zone (from high water to the depth of light penetration) kelps produce nearly 75% of the net carbon fixed.

Laminaria hyperborea, Alaria esculenta, Echinus esculentus.

Although kelp species often dominate their environment, they also supply extra substrate available for other organisms. Holdfasts provide refuge to a wide variety of animals. Jones (1971) listed upto 53 macrofaunal invertebrate species obtained from an individual holdfast. A few meiofaunal species may actively burrow into kelp. Benwell (1981) showed how the nematode Monhystera disjuncta may help weaken the distal areas of the kelp where it feeds on decomposition-associated microbiota.

Urchin predators such as lobsters Homarus gammarus and wolfish Anarhichas lupus may also be found amongst kelp forests.

A very obvious change that has been noted in kelp forests throughout the world is that of either at a certain depth (Kain 1971) or in an area of kelp at a certain time, the kelp plants are lost and the bedrock becomes covered with encrusting coralline algae. The populations of the local species of sea urchin were found to increase at the same time. The resulting kelp-free areas within or adjacent to kelp forests are frequently referred to as "urchin barrens" and may remain kelp-free for years. Large-scale overgrazing of Laminaria hyperborea forests by the green sea urchin Strongylocentrotus droebachiensis has occurred off the coast of northern Norway (Hagen 1987). The resulting overgrazed ‘Isoyake’ bottoms dominated by crustose coralline algae and sea urchins persisted for more than five years in the Vestfjord area.

Long-term fluctuations or permanent shifts in the biodiversity of kelp forests may occur in the UK; however long-term monitoring has not been undertaken. Long-term studies on kelp beds on the Atlantic coast of Canada have continued since the original study in the late 1960s (Mann 1972). Temporal changes within kelp beds seem to be on a decadal scale, making long term monitoring projects necessary.

Leinaas & Christie (1996) examined re-colonisation of a kelp forest after severe reductions in urchin numbers. The succession of algal growth followed a predictable pattern. The substratum was colonised initially by filamentous algae, then Laminaria saccharina. Only after 3-4 years after urchin removal did the slower growing, long-lived kelp Laminaria hyperborea become dominant.

Kain (1963) determined the age of individual plants by counting the number of growth rings or lines in the stipe. Laminaria digitata was reported as having no more than three growth lines (Kain 1979). Gayral & Cosson (1973) estimated the life expectancy of L. digitata to be approximately 4-6 years. Laminaria hyperborea is the longest-living species with plants as old as 15 years being recorded off the Outer Hebrides (Kain 1977). A plant with 18 rings was found in Norway by Grenager (1956). Many populations are limited by conditions to a life span of less than half of these extremes (Kain 1971). Alaria esculenta was estimated to live for between 4-7 years (Baardseth 1956) and Saccorhiza polyschides plants between 8-16 months.

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