ON A ROCKY SHORE
by Andy Horton
Because the distance that the tide comes up the shore varies from
day to day, this provides different environmental conditions, and therefore
different habitats supporting different communities of more or less permanent
fauna, together with the errant animals that will be present when the conditions
and availability of food suit them.
Splash Zone (above Highest Astronomical Tide):
The very highest zone on the shore is called the splash zone, and as the name indicates this zone is not directly flooded with the rising water. Therefore, it has more in common with terrestrial habitats, although some of the animals move down to the sea to discharge their eggs or young at the highest spring tides.
The dominant fauna is a few species of lichens which are fed on by two very small species of winkle.
Upper Shore Zone (around Mean High Water Springs):
This zone is only immersed by the spring tides, and then only for a
short time. Two brown seaweeds, the Channelled Wrack, Pelvetia
canaliculata, and the Spiral Wrack, Fucus spiralis, have
adaptations to prevent drying out and can survive when the tide is out.
Acorn Barnacles settle in this zone.
Middle Shore Zone (around Mean Tide Level):
For half the day the tide will be in, even during the period of neap
tides. The common brown wrack of this zone is the Bladder Wrack,
vesiculosus. Mussel beds will form and both
and periwinkles will graze the rocks. Beadlet
Anemones are resident and Shore Crabs will
be found from spring to autumn.
Lower Shore (around Low Water Neaps):
For most of the day the sea will cover this part of the shore, so that the rockpooler will need to consult his tide tables to ascertain when the shore is accessible.
This will be longest during the spring tide period. The important brown seaweed is the Serrated Wrack, Fucus serratus, which straddles large areas where there are suitable attachments.
The range of crabs, molluscs, small fish and prawns is much greater in this zone.
Infralittoral Fringe (around Low Water Springs):
This is the exciting area with conditions in the larger pools matching
the shallow seas, and almost any of the fish and invertebrates that live
around the British Isles can be found on occasions.
Sublittoral (below Lowest Astronomical Tide, or Chart Datum):
In most literature this refers to the submerged sea area below the low water mark.