| 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). |
