| 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). |
