Habitat requirements

Habitat factor Range of conditions
Salinity Full; Variable; Reduced; Low.

McRoy (1966) suggests optimum salinities of 10 to 39‰; den Hartog (1970) reports tolerances as low as 5‰ in the Baltic. Laboratory studies indicate that maximum germination occurs at 30oC and 1‰ salinity (Hootsmans et al. 1987). Field studies indicate that germination occurs over a wide range of temperatures and salinities (Churchill 1983, Hootsmans et al. 1987). In brackish waters along the Atlantic coast, Zostera marina behaves as an annual plant, shedding its leaves in winter (Jacobs 1982). Low salinities may encourage production of reproductive shoots and stimulate leaf production. Zostera marina beds survived disease especially in low salinity conditions in the eastern United States (Muehlstein, Porter & Short 1991).

Wave exposure Sheltered, Very sheltered, Extremely sheltered, Ultra sheltered
Tidal streams Weak, very weak
Substratum Clean sand, muddy fine sand, mud
Zone Lower shore, Upper infralittoral
Depth range Lower shore 0-5 m
Temperature Optimum temperature range for Zostera marina appears to be between 5 and 30 oC (Marsh et al. 1986; Bulthius 1987). Seasonal growth is closely associated with temperature. Yonge (1949) suggested that growth ceases below 10 oC and that flowers could only open and seeds form when the temperature exceeded 15 oC. Zostera marina beds, which occur intertidally, may be damaged by frost although the rhizomes most likely survive (Covey & Hocking 1987).
Water quality Zostera marina requires high light levels. It most commonly occurs shallower than 2 m below chart datum, exceptionally to 5 m and the deepest recorded depth it has been found in Britain and Ireland is 13 m below chart datum off south-west Ireland (Cullinane et al. 1985). Harrison (1987) describes how the extent of a Zostera marina bed expanded after construction of a causeway blocked the flow of silty water.
Nutrients It seems most likely that nitrogen is the limiting nutrient. In carbonate-based sediments, phosphates may be limiting due to adsorption onto sediment particles (Short 1987). Mild nutrient enrichment of sediments may stimulate growth of Zostera marina shoots (Roberts et al. 1984).

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