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.
||Uses: boats/shipping (oil spills)
|A number of studies have suggested that, in general, it is
the associated faunal communities that are more sensitive to oil pollution that the Zostera
plants themselves (Jacobs 1980; Zieman et al. 1984; Fonseca 1992). Epiphyte grazers
such as Hydrobia ulvae can contribute to the health of Zostera plants by
removing the algae that foul the leaves. Any factors (natural or anthropogenic) such as
oil pollution which reduce grazer populations may therefore have an indirect adverse
impact on the Zostera bed. As Z. noltii occurs highest up the shore, it is
likely to be most vulnerable to covering by oil, compared with sublittoral Zostera
species, which are protected from direct contact with oil. Since Zostera generally
occurs in sheltered, low energy sites, natural weathering of oil will be slow.
|Changes in nutrient
|Waste: sewage discharge
|Nutrient enrichment encourages rapid growth of blanket algae.
Some opportunistic species such as Enteromorpha spp. may cause severe shading of Zostera
(Den Hartog 1987). Den Hartog (1994) reported that at Langstone Harbour, S. England
the growth of a dense blanket of E. radiata in 1991 resulted in the loss of 10 ha
of Z. marina and Z. noltii, and that by the summer of 1992, Zostera
spp. were entirely absent. Eutrophication may have a detrimental affect on grazer
||Recreation: popular beach /resort
Uses: boats/shipping (anchoring, mooring, beaching & launching)
|Trampling is usually caused by recreational activities such
as walking, horse-riding and off-road driving. Trampling damage may also be caused by
environmental mitigation work. Thom (1993) reported that Z. marina beds in
Washington State were damaged by trampling when mitigation work was being carried out in
response to crab mortalities. Trampling damage resulting from oil clean-up attempts has
also been reported. After the Sea Empress oil spill near Milford Haven in Wales,
damage to Zostera appeared to be limited to those plants living on areas of shore
traversed by clean-up vehicles.
Abrasion may also be caused by boat anchoring, beaching
||Collecting: bait digging
|Eelgrasses are generally not physically robust. Their root
systems are typically located within the top 20 cm of the sediment and so can be dislodged
easily by a range of activities, including trampling, anchoring, digging, dredging and
powerboat wash (Fonesca 1992).