Summary of the Management Issues Relating to Zostera Biotopes

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.


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

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