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.
|Extensive areas of intertidal sand/mudflats 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 their area, most of which has been
the land claim of intertidal sand and mudflats. The greatest impact of land claim is the
reduction in area and biological integrity of this habitat, which will reduce the carrying
capacity for supporting bird and fish predator populations.
|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.
|Changes in wave exposure
||Development: land claim
|Land claim may also disrupt the hydrophysical regime in an
area resulting in changes in wave action. Increased wave action causes stress to the
infauna by disrupting feeding and burrowing activities and reduces species richness,
abundance and biomass. The appearance of the intertidal region may also alter as the top
20cm of sand may be removed by storm events (Dolphin, Hume & Parnell 1995). Infauna
will be sensitive to this change in sediment as they are adapted to burrow through only
certain grades of sediment (Trueman & Ansell 1969).
|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, radionuclides and
synthetic organic compounds. The lethal and sub-lethal effects of these pollutants vary
according to the state and availability of the compound, its characteristics and the
organisms. 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).
Sheltered, low-energy areas in enclosed bays will be most susceptible to these pollutants
as dispersion is low and the finer substrata in these areas will act as a sink (McLusky
1982 ; Somerfield, Gee & Warwick 1994; Ahn, Kang & Coi 1995; Nedwell 1997). The
pollutants will enter the food chain and be accumulated by predators, as shown by the
seasonal loading of heavy metals in tissues of wading birds in the Wash (Parslow 1973).
Silt which is often associated with industrial pollution may be deposited onto the
mudflats thus raising their height and therefore increasing the exposure time of infaunal
communities at low tide.
||Uses: boats/shipping (oil spills)
|Oil-spills can cause large-scale deterioration of communities
in intertidal and shallow sub-tidal sedimentary systems (Majeed 1987). Oil covering
intertidal muddy sand prevents oxygen transport to the substratum and produces anoxia
resulting in the death of infauna.
|Changes in nutrient levels
||Waste: sewage discharge
|High organic inputs coupled with poor oxygenation leading to
conditions of slow degradation will produce 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 chemicals
such as hydrogen sulphide and methane. The changed status to anaerobiosis will limit the
sediment macroinfauna to species which can form burrows or have other mechanisms to obtain
oxygen from overlying water. Moderate enrichment provides food to increase the 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 Manayunkia
aestuarina. Organic enrichment may result in increased coverage by opportunistic green
macroalgae such as Ulva sp. and Enteromorpha sp. resulting in the formation
of green tide mats. Anoxic conditions form below the mats, reducing the
diversity and abundance of infauna (Simpson 1997).
|Removal of non-target species
||Collecting: bait digging
|The effects of bait diggers are to reduce community diversity
and species richness, especially by commercial digging for worms and other macrofauna on
intertidal muddy sand (Brown & Wilson 1997). This removal of target species leading to
community and population changes at the ecological and genetic levels will affect
predators e.g. the removal of bait organisms such as Arenicola from intertidal
mudflats will effect shorebird predation.