Linkages to other Habitats
Large Shallow Inlets and Bays
The extensive and dominant nature of the sedimentary biotope complexes dictates that
the present report also mentions related habitats such as Estuaries (Habitats
Directive Annex I and Large Shallow Inlets And Bays (see Appendix I). In addition, an
additional habitat, Lagoons will support these sedimentary Biotope Complexes under
Depending on the precise definition used, there are more than 100 estuaries in the
British Isles which gives the UK the largest part of the European estuarine resource (27%
by area) compared to other north-eastern Atlantic countries. The status, number and type
of these habitats is described fully in Davidson et al (1991) and they range from
shallow coastal embayments which receive a freshwater input to deep fjordic systems. The
predominant habitat types within estuaries, and often the reason for their biological and
physical importance, are the habitats considered here - intertidal sand and mudflats and
subtidal sandbanks. The mosaic of biotopes which constitutes an estuary dictates that each
sub-area may require consideration and management as well as taking an overall view (D.
Connor pers. comm. 1998).
Estuaries are primarily controlled by salinity combined with structuring due to their
topographical features which create the hydrophysical regime (McLusky, 1989). The
modification of salinity by changes to the hydroclimate regime is likely to lead to
changes in species' distributions, especially the degree of landward penetration of marine
organisms. In addition, the input of organic materials, from both allochthonous and
autochthonous sources are required to support these primarily detritus-driven systems.
Decreases in these inputs can lead to an oligotrophic condition whereas increases can
produce hypernutrification and possibly eutrophication. In addition, the importance of
estuaries is not only for those species resident during much of the year but also for
migrant fish and bird populations (Elliott et al, 1990). The movement of predators
to estuaries for feeding, reproduction, nursery and refuge is well described, as is their
role as migration routes for fishes passing between sea and freshwaters.
Large Shallow Inlets and Bays
There is no readily available inventory of the habitat as a whole although the
component biotopes have been recorded (Connor et al, 1997). Most coasts of the UK
have some shallow inlets and bays although many are relatively small. By definition many
will have a soft sedimentary substratum in the body of the inlet or bay and will be
bounded by hard substratum. The bays and inlets are created primarily by the underlying
geological features and then infilled with the prevailing mobile substrata and modified by
the hydrographic regime. The size and shape of the area together with these
characteristics thus creates the available niches for colonisation.
The areas may be heterogeneous where there is a complicated coastline and where
different niches are created. Although the shape of these habitats are relatively easy to
define, the seaward boundary and thus the area is rather more difficult to specify. The
areas are primarily marine and thus fully saline with little dilution by river runoff
although they may have diffuse inputs of freshwater from land-runoff.
The sedimentary regime will be dictated by the hydrographic regime and thus may have
high and low energy areas depending on the tidal, wind-induced and residual current
patterns. Where the habitats are open features, such as coastal embayments, then the
direction of the prevailing currents and the length of fetch will be of importance in
structuring the habitat. These features will dictate the relative composition of the
component habitats, especially the subtidal sandbanks, the intertidal sand and mudflats,
lagoons and reefs. The depth of the area will be defined by the tidal regime and
underlying geology and bathymetry and will be variable. The coastal waters will allow good
light penetration and thus support an extensive
infralittoral area of algal and angiosperm growth. Each of the above conditions will
create a mosaic of habitats which will include intertidal, infralittoral and circalittoral
biotopes covering both hard and soft substratum.