Habitat requirements

Habitat factor Range of conditions
Salinity Fully marine and variable
Wave exposure Sheltered, Very sheltered, Extremely sheltered
Substratum Muddy fine sand; sandy mud
Height band Upper shore, Mid shore
Zone Eulittoral
Temperature Although Z. noltii is adapted to intertidal conditions and can tolerate broad temperatures ranges, the upper shore habitat exposes the species to extremes of cold or heat at low tide or in very shallow bays. Den Hartog (1987) suggested that cold winters could result in significant losses. In extreme winter conditions, the formation of ice amongst the sediments of exposed intertidal eelgrass beds can lead to the erosion of surface sediments and the uprooting of rhizomes, as well as direct frost damage to the plant. Covey & Hocking (1987) observed in the Helford River that, during exceptionally cold weather in January 1987, ice formed in the upper reaches of the mudflats and led to the defoliation of Z. noltii (the rhizomes survived).
Water quality Like all plants, Zostera requires a particular light regime to photosynthize and grow. Turbidity affects light penetration thus influencing Zostera growth by restricting the amount of photosynthetically active radiation available to the submerged plants. Increases in turbidity are a commonly cited factor in the decline of eelgrass beds. Jimenez, Niell & Algarra (1987) found that Z. noltii is better adapted to high light intensities than Z. marina and this is probably one of several adaptations that allows Z. noltii to occur higher up the shore.
Nutrients Nutrient uptake by Zostera from the water column occurs through the leaves and from the interstitial water via the rhizomes. Nitrogen is usually the limiting element and is most easily absorbed as ammonium. In sandy sediments, phosphate may become a limiting factor due to its adsorption onto sediment particles (Short 1987).

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