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). |
