||Range of conditions
||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).
||Sheltered, Very sheltered, Extremely sheltered, Ultra
||Weak, very weak
||Clean sand, muddy fine sand, mud
||Lower shore, Upper infralittoral
||Lower shore 0-5 m
||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).
||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.
||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).