| Factor |
Category |
Definition |
| Salinity |
Fully marine |
30-40 ‰ |
| |
Variable |
18-40 ‰ |
| |
Reduced |
18-30 ‰ |
| |
Low |
<18 ‰ |
| Wave exposure |
Extremely exposed |
This category is for the few open coastlines which face into
prevailing wind and receive oceanic swell without any offshore breaks (such as islands or
shallows) for several thousand km and where deep water is close to the shore (50 m
depth contour within about 300 m, e.g. Rockall). |
| |
Very exposed |
These are open coasts which face into prevailing winds and
receive oceanic swell without any offshore breaks (such as islands or shallows) for
several hundred km but where deep water is not close (>300 m) to the shore. They
can be adjacent to extremely exposed sites but face away from prevailing winds (here swell
and wave action will refract towards these shores) or where, although facing away from
prevailing winds, strong winds and swell often occur (for instance, the east coast of Fair
Isle). |
| |
Exposed |
At these sites, prevailing wind is onshore although there is
a degree of shelter because of extensive shallow areas offshore, offshore obstructions, a
restricted (<90o) window to open water. These sites will not generally be exposed to
strong or regular swell. This can also include open coasts facing away from prevailing
winds but where strong winds with a long fetch are frequent. |
| |
Moderately exposed |
These sites generally include open coasts facing away from
prevailing winds and without a long fetch but where strong winds can be frequent. |
| |
Sheltered |
At these sites, there is a restricted fetch and/or open water
window. Coasts can face prevailing winds but with a short fetch (say <20 km) or
extensive shallow areas offshore or may face away from prevailing winds. |
| |
Very sheltered |
These sites are unlikely to have a fetch greater than
20 km (the exception being through a narrow (<30o) open water window, they face
away from prevailing winds or have obstructions, such as reefs, offshore. |
| |
Extremely sheltered |
These sites are fully enclosed with fetch no greater than
about 3 km. |
| |
Ultra sheltered |
Sites with fetch of a few tens or at most 100s of metres. |
| |
|
In the classification exposed (as in exposed littoral
rock) encompasses the extremely exposed, very exposed and exposed categories, whilst sheltered
(as in sheltered littoral rock) encompasses sheltered to ultra sheltered categories. |
| Tidal streams/currents (maximum at surface) |
Very strong |
>6 knots (>3 m/sec.) |
| |
Strong |
3-6 knots (1.5-3 m/sec.) |
| |
Moderately strong |
1-3 knots (0.5-1.5 m/sec.) |
| |
Weak |
<1 knot (<0.5 m/sec.) |
| |
Very weak |
Negligible |
| |
|
In the classification tide-swept habitats typically have
moderately strong or stronger tidal streams. |
| Zone |
Supralittoral |
Colonised by yellow and grey lichens, above the Littorina
populations but generally below flowering plants. |
| |
Upper littoral fringe |
This is the splash zone above High Water of Spring Tides with
a dense band of the black lichen by Verrucaria maura. Littorina saxatilis and
Littorina neritoides often present. May include saltmarsh species on shale/pebbles
in shelter. |
| |
Lower littoral fringe |
The Pelvetia (in shelter) or Porphyra (exposed)
belt. With patchy Verrucaria maura, Verrucaria mucosa and Lichina pygmaea
present above the main barnacle population. May also include saltmarsh species on
shale/pebbles in shelter. |
| |
Upper eulittoral |
Barnacles and limpets present in quantity or with dense Fucus
spiralis in sheltered locations. |
| |
Mid eulittoral |
Barnacle-limpet dominated, sometimes mussels or dominated by Fucus
vesiculosus and Ascophyllum nodosum in sheltered locations. Mastocarpus
stellatus and Palmaria palmata patchy in lower part. Usually quite a wide belt. |
| |
Lower eulittoral |
Fucus serratus, Mastocarpus stellatus, Himanthalia elongata
or Palmaria palmata variously dominant; barnacles sparse. |
| |
Sublittoral fringe |
Dominated by Alaria esculenta (very exposed),
Laminaria digitata (exposed to sheltered) or Laminaria saccharina (very
sheltered) with encrusting coralline algae; barnacles sparse. |
| |
Upper infralittoral |
Dense forest of kelp. |
| |
Lower infralittoral |
Sparse kelp park dominated by foliose algae except where
grazed. May lack kelp. |
| |
Upper circalittoral |
Dominated by animals, lacking kelp but with sparse foliose
algae except where grazed. |
| |
Lower circalittoral |
Dominated by animals with no foliose algae but encrusting
coralline algae. |
| |
|
Zone definitions primarily relate to rocky habitats or those
where algae grow (e.g. stable shallow sublittoral sediments). For use of the terms infralittoral
and circalittoral, especially for sediments, in the classification refer
also to Table 2.2 in Connor et al. (1997a, b). |
| Substratum |
Bedrock |
Includes very soft rock-types such as chalk, peat and clay. |
| |
Boulders |
Very large (>1024 mm), large (512-1024 mm), small (256-512
mm) |
| |
Cobbles |
64-256 mm |
| |
Pebbles |
16-64 mm |
| |
Gravel |
4-16 mm |
| |
Coarse sand |
1-4 mm |
| |
Medium sand |
0.25-1 mm |
| |
Fine sand |
0.063 - 0.25 mm |
| |
Mud |
<0.063 mm (the silt/clay fraction) |
| |
|
In the classification, bedrock, stable boulders, cobbles or
pebbles and habitats of mixed boulder, cobble, pebble and sediment (mixed substrata)
as well as artificial substrata (concrete, wood, metal) are collectively referred to as rock.
Highly mobile cobbles and pebbles (shingle), together with gravel, coarse, medium and fine
sand are collectively referred to as gravels and sands. Mixed sediment
consists of various mixtures of gravel, sand and mud and may often have shells and stones
also. |
