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.
||Extraction: navigational/ maintenance dredging
|Dredging and aggregate extraction will affect the sediment
and hydographic regimes. Dredging of sandbanks will occur where they interfere with
navigation and also to deepen and widen channels for shipping. The activity can also cause
loss and damage by the indirect effects of increased scour and erosion on artificially
steepened slopes. Dredging will disturb the benthic community and possibly reduce the
number and diversity of benthic species and affect larval recruitment (Rosenberg 1977).
However, it is emphasised that subtidal sandbanks are the result of relatively high energy
conditions and as such will be naturally disturbed by changes in hydrographic conditions.
The ability of the community to recover from sediment disturbance is therefore high (Rees
1994; Kaiser & Spencer 1996).
|Changes in turbidity
||Waste: spoil dumping
|Dredged material disposal over subtidal sandbanks may occur
adjacent to dredged areas. However, in areas of strong tidal current dispersion of dredge
plumes may be high and thus the effects minimal. Any increase in the amount of suspended
particles will influence turbidity, light penetration and primary production of the water
column and substrata (Iannuzzi et al. 1996). Suspension- feeding invertebrates may
also be affected by suspended dredge spoil, as it will clog their respiratory or breathing
apparatus. However, it is emphasised that subtidal sandbanks are the result of relatively
high energy conditions and as such will be naturally disturbed by changes in hydrographic
conditions and will accommodate man-induced conditions such as dredge spoil.
|Changes in temperature
||Climate change/global warming
|Infralittoral sandbanks are not subjected to such extreme
changes in temperature as intertidal areas although fluctuations will occur in stratified
waters or on the boundaries of frontal systems. Variation in water temperature may affect
the succession of macrobenthic species with the occurrence or survival of different groups
of species related to periods of mild or cold winter temperatures.
||Uses: boats/shipping (oil spills)
|Infralittoral sediments will be less at risk from oil spills
than intertidal sediments unless dispersants are used in clean-up operations or if wave
action allows sediment mobility and thus oil to be incorporated into the sediments.
|Changes in nutrient levels
||Waste: sewage discharge
|In contrast to the low-energy areas, the higher-energy
sediment biotopes are less likely to receive and/or retain such contamination. The coarse
sediments and hydrodynamic characteristics, including high dispersion, of subtidal
sandbanks dictates that there are few cases of severe pollution in this habitat.
||Fishing: benthic trawling
|Commercial shell and fin-fisheries can potentially have a
large effect on the integrity of infralittoral sand. The affects of fishing will depend on
the type of gear used. Megafaunal species are in general more vulnerable to fishing
affects than macrofaunal species because they are slow growing and thus slowly recover
from disturbance. Removal of non-commercial-sized fish will affect the nursery function of