Habitat requirements

Habitat factor Range of conditions
Salinity Fully marine. Kelps are stenohaline in that they do not tolerate wide fluctuations in salinity. Laboratory studies have shown Norwegian species to tolerant salinities as low as 15 ‰ although 25 ‰ to 30 ‰ was found to be favourable (Sundene 1964b). Sporophytes of Laminaria hyperborea grew optimally from 20-35‰ but did not survive at 6‰ (Hopkin & Kain 1978).
Wave exposure Moderately exposed, Sheltered
Tidal streams Very strong, Strong, Moderately strong, Weak, Very weak
Substratum Bedrock; stable boulders and cobbles
Zone Sublittoral fringe; Infralittoral
Depth range 0-20m
Temperature The kelp species of western Europe have relatively limited geographical ranges, which suggests that they are stenothermal and as such unable to tolerate large fluctuations in temperature. Laminaria digitata found in cold temperate waters have a range of 0oC – 20oC (Kain 1969). Laminaria hyperborea shows a narrower range of temperature tolerance for growth 0oC – 15oC (Kain 1964). Seasonal adaptations to temperature tolerance do occur though increased temperatures during the winter months are less well tolerated than increased temperatures during the summer months (Luning 1990).
Water quality The critical depth for Laminaria corresponds roughly to the depth at which irradiance levels, averaged over the whole year, fall to about 1% of their values at the surface. If light penetration is good and kelp plants can grow at greater depths. For example, kelps are found below 100m in the clear waters of the Mediterranean but are restricted to around 35m in the coastal waters off the far western coasts of Europe. In the turbid waters of Helgoland and Norway, kelps are found at depths of only 6-7m.

Light is also used as an environmental signal by Laminaria hyperborea. New frond growth is induced in winter when the daylength falls below a certain value (Luning 1986).

Nutrients All kelp species are thought to be efficient scavengers of nitrate and phosphate from seawater. However the quantity of these nutrients in seawater varies throughout the year, with maximum levels being attained during the winter months. In spring when the nitrate concentration of the water is almost zero kelps continue to grow by means of their own internal reserves. However, after depletion of all reserves the growth rates decline in late spring and early summer, then external supply governs growth activity (Conolly and Drew 1985a, b).

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