The following table draws together the main conclusions from the
preceding chapters to summarize the important processes and activities which must be taken
into account in the development of an SAC management scheme for Zostera biotopes.
| Process |
Possible consequences |
Impacts on Zostera beds |
Coastal development
(eg. Dredging, flood defences, marina construction) |
- Complete removal of habitat
- Changes in balance of sediment accretion/erosion
- Increased water turbidity
|
Biotope
destruction
Smothering or erosion of
beds
Shading of plants, reduced depth limits to growth |
Increased nutrient input
(eg. From sewage, fertilizers, fish farms) |
- Increased nitrate concentrations
- Eutrophication: Proliferation of planktonic, benthic or epiphytic algae
|
Metabolic
imbalance
Smothering of plants by epiphytes or benthic algae
Shading of plants by increased turbidity
Increased susceptibility to wasting disease |
Water pollution (dissolved contaminants) |
- Heavy
metals
- Antifoulants (triazine herbicides)
- Terrestrial herbicides
- Other pollutants (eg. industrial effluents)
- Loss of epiphyte grazers due to pollutants
|
May affect nitrogen fixation
Inhibition of photosynthesis
Growth inhibition
May be toxic to Zostera or to epiphyte grazers
Smothering by epiphytic algae |
Oil pollution |
- Chronic exposure to refinery effluent
- Major oil spills
- Chemical dispersants
|
No evidence of significant effects
Smothering effect: may halt or reduce growth
Highly toxic to Zostera and associated community |
Physical disturbance (eg. Trampling, bait
digging, Dredging) |
- Removal of sediment
- Crushing, physical damage
|
Increased erosion and shading (turbidity)
Damage to leaves and rhizomes |
Spread of non-native species (Spartina,
Sargassum) |
- Potential competitive displacement of Zostera
|
Little evidence of serious competition so
far
Herbicides used to control Spartina may be harmful
|
Wasting disease |
- Large-scale loss of Zostera beds
|
- Environmental stress may increase susceptibility to infection
|
Wildfowl grazing |
- Can result in consumption of high percentage of Zostera biomass
|
- Beds can normally tolerate grazing pressure, but may be more seriously affected if
stressed by other factors
|
Climatic change |
- Possible effects:
- Warmer temperatures
- Sea level rise
- Increased storm frequency and severity
|
- Increased flooding and erosion of beds
- Increased stress, resulting in greater susceptibility to wasting disease
|
