Sensitivity to human activities

Activities listed are those which influence, or are likely to influence this habitat and which are assessed in the UK marine SAC project review. The sensitivity rank may require amendment in the light of new information becoming available.

Sensitivity to: Human activity Rank Comments
Substratum change Waste: sewage discharge

Intermediate

Smothering by algae may be linked to eutrophication. Zostera marina / angustifolia plants were overwhelmed by Enteromorpha spp.in Langstone Harbour, but their final demise may have been due to grazing by Brent geese (den Hartog 1994).
Changes in temperature Climate change/global warming

Low

Den Hartog (1970) suggested that Zostera marina generally tolerates temperatures up to 20oC without showing signs of stress. There is likely to be damage through frost to beds exposed at low water (den Hartog 1987).
Changes in turbidity Waste: spoil dumping

High

Prolonged increases in turbidity would reduce light penetration and prevent adequate photosynthesis by deeper populations of Zostera marina. Geisen et al. (1990) suggest that turbidity caused by eutrophication, deposit extraction and dredging activities were major factors in the decline of Zostera in the Wadden Sea.
Synthetic compound contamination Uses: coastal farming

Uses: boats/shipping (anti-fouling)

Intermediate

Terrestrial herbicides have been found to inhibit growth and cause decline in Zostera marina (Delistraty & Hershner 1984). Some effects may be indirect. For instance Zostera marina readily uptakes heavy metals and TBT (Williams et al. 1994). Whilst plants appeared unaffected, any loss of grazing prosobranchs due to TBT contamination in the leaves or externally would result in excessive algal fouling of leaves, poor productivity and possible smothering.
Hydrocarbon contamination Uses: boats/shipping (oil spills)

Intermediate

Apparently healthy Zostera marina beds are known to exist in areas subject to low-level chronic hydrocarbon contamination (see, for instance, Howard, Baker & Hiscock 1989). Smothering by stranded oil is likely to occur on lower shore populations but little is known of its effects.
Changes in nutrient levels Waste: sewage discharge

Intermediate

High nitrate concentrations have been implicated in the decline of Zostera marina by Burkholder et al. (1993). Such eutrophication may increase the cover of epiphytic algae and prevent photosynthesis of sea grass plants. Eutrophication may increase abundance of Labrynthula macrocystis (see below). However, nutrient enrichment may stimulate growth of Zostera marina (Fonesca et al. 1994)
Changes in oxygenation Aquaculture: fin-fish

High

No evidence of effects found in the literature but the de-oxygenation of water would be likely to adversely affect plants.
Abrasion Uses: Boats/shipping (anchoring, mooring, beaching & launching)

Fishing: benthic trawling

Intermediate

Eelgrass is generally not physically robust. Their root systems are typically located within the top 20 c, of the sediment and so can be dislodged easily by a range of activities. including trampling, anchoring, digging , dredging and powerboat wash (Fonseca 1992).

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