Habitat requirements

Habitat factor Range of conditions
Salinity Full. Kelps are stenohaline in that they do not tolerate wide fluctuations in salinity.
Wave exposure Extremely exposed, Very exposed, Exposed. Laminaria hyperborea is unable to survive where wave action is extreme, since its stiff stipe, topped with a large lamina, is prone to being snapped. In some areas, wave action depresses the upper limit of the L. hyperborea habitat to several metres below MLWS and under very severe wave conditions, the species may be absent. In such areas (e.g. Rockall) Alaria esculenta will be found in the infralittoral zone owing to its flexible stipe and thickened mid-rib which acts as reinforcement.
Tidal streams Very strong, Strong, Moderately strong, Weak, Very weak
Substratum Bedrock; stable boulders
Zone Sublittoral fringe; Infralittoral
Depth range 0-50 m
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 hyperborea grows in a temperature range of 0oC – 15oC (Kain 1964), whereas Saccorhiza polyschides grows between 3oC-24oC (Norton 1970). Alaria esculenta is tolerant of temperatures up to 16oC (Sundene 1962). Seasonal adaptions 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 light quantity and quality that is available to a kelp plant is dependent on the depth of water above the plant and its clarity. Absorption of light in coastal waters is influenced by the amount of particulate matter in suspension as well as by the dissolved oxygen components. Wavelengths of light are attenuated differentially as a result of these factors, altering the spectrum of wavelengths available at different depths. These effects may have a strong influence on kelp distribution and density within a kelp biotope.
Nutrients All kelp species are thought to be efficient absorbers of nitrate and phosphate from seawater. However the quantities of these nutrients in seawater vary 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 & Drew 1985 a, b).

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