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.
||Development: land claim
|Extensive areas of intertidal sandflats have been removed
through land claim coupled in some areas with rising sea levels (Davidson et al.
1991; Burd 1992). Some estuaries have lost up to 80% of the area, most of which has been
the land claim of intertidal mud and sandflats. The greatest impact of land claim is due
to depletion of the main prey rather than simply the area loss and each prey and predator
species will differ in their response (McLusky, Bryant & Elliott 1992).
|Changes in temperature
||Climate change/global warming
|Many intertidal species have wide tolerances for temperature
and can also alter metabolic activity, or simply burrow deeper in the sediment or move
seaward to combat temperature change (Brown 1983). Severe changes in temperature in
intertidal areas will result in a seasonal reduction in benthic species richness and
abundance, although the species are well adapted to such changes.
||Uses: boats/shipping (oil spills)
|Oil-spills can cause large-scale deterioration of communities
in intertidal and shallow sub-tidal sediment systems (Majeed 1987). Tidal-pulsing will
push oil into intertidal sands. Oil pushed into coarse sands will destabilise the sediment
and produce an oxygen demand where oxygen is available but little degradation at depth
where aeration does not occur.
|Synthetic compound contamination/
|Waste: industrial effluent discharge
|Industrialised and urbanised estuaries and coastlines may
receive effluent discharges which contain conservative contaminants i.e. those with a long
half-life, are likely to bioaccumulate (remain within the food chain) and thus have a
toxic effect (Clark 1997). Such contaminants include heavy metals, radionucleides and
synthetic organic compounds. The lethal and sub-lethal effects of these pollutants vary
according to the state and availability of the compound and its characteristics and the
organism it affects. Some effects may be lethal, by removing individuals and species and
thus leaving pollution-tolerant and opportunistic species. Other effects may be
sub-lethal, in affecting the functioning of organisms such as their reproduction,
physiology, genetics and health, which will ultimately reduce their fitness for survival
(Nedwell 1997). In contrast to low energy areas (e.g. mudflats), the higher energy
sediment biotopes are less likely to receive and/or retain these contaminants. The coarser
sediments of exposed intertidal sandflats and the hydrodynamic characteristics, including
high dispersion, dictates that there are few cases of severe pollution in such habitats.
However, chemical pollution of intertidal sands can occur and will remove elements of the
|Changes in nutrient levels
||Waste: sewage discharge
|High organic inputs coupled with poor oxygenation lead to
conditions of slow degradation and produces anaerobic conditions in the sediments. In turn
this increases microbial activity and reduces the redox potential of the sediments
(Fenchel & Reidl 1970). Ultimately this increases the production of toxic substances
such as hydrogen sulphide and methane. Moderate enrichment provides food to increase the
species abundance and a mixing of organisms with different responses increases diversity
(Elliott 1994). With greater enrichment, the diversity declines and the community becomes
increasingly dominated by a few pollution-tolerant, opportunistic species such as the
polychaete Capitella capitata. In grossly polluted environments, the anoxic
sediment is defaunated and may be covered by sulphur-reducing bacteria. Such a change will
affect the palatability of any remaining prey and thus impair functioning of marine areas.
|Removal of non-target species
||Collecting: bait digging
|The effect of bait digging is to reduce community diversity
and species richness, especially by commercial digging for worms and other macrofauna on
intertidal sandflats (Brown & Wilson 1997). This removal of target species leading to
community and population changes at the ecological and genetic levels will effect
predators e.g. the removal of bait organisms such as Arenicola from intertidal
sandflats will effect shorebird predation.