The general patterns of zonation on rocky shores can be explained in terms of physical
factors affecting the outcome of biological interactions. The diversity of species on
rocky shores increases towards the lower shore where conditions are damper. A major
biological influence on community structure is the presence of algal canopies and shorter
algal communities at mid and low shore levels. Macroalgae provide a variety of resources
that are not available on bare rock. Most importantly, they increase the amount of space
available for attachment, they provide shelter from wave action, desiccation and heat, and
they are an important food source.
Many rocky shore species have a planktonic dispersal phase. These species produce
propagules or larvae that spend their early life in the open sea and may eventually settle
on shore some distance from where they originated. This strategy allows species to rapidly
colonize new areas that become available. The level of larval supply and its fluctuation
plays a considerable role in structuring rocky shore communities and has been appreciated
for a long time (Southward & Crisp 1956; Lewis 1964; Kendall et al. 1985)
Macroalgae exude considerable amounts of dissolved organic carbon which are taken up
readily by bacteria and may even be taken up directly by some larger invertebrates. Only
about 10% of the primary production is directly cropped by herbivores (Raffaelli &
Hawkins 1996). Dissolved organic carbon, algal fragments and microbial film organisms are
continually removed by the sea. This may enter the food chain of local, subtidal
ecosystems, or be exported further offshore. Rocky shores also make a contribution to the
food of many marine species through the production of planktonic larvae and propagules
which supply essential biochemicals to pelagic food chains.
Keystone (structuring) species
Pelvetia canaliculata, Fucus spiralis, Fucus vesiculosus, Ascophyllum
nodosum, Fucus serratus
Importance of habitat for other species
Fish and crustaceans migrating into the intertidal to feed as the tide rises, are
important predators of rocky shore species. Juveniles are commonly found in rockpools.
Shore birds also feed on the rocky shore (Feare & Summers 1985). The invertebrates
attracted to seaweed on the strandline are a particularly important food source. Rich
pickings can also be had under macroalgae canopies. Otters Lutra lutra often use
rocky shores and will feed on animals such as shore crabs Carcinus maenas which, in
turn feed on rocky shore species.
Rocky shore communities are often highly variable in time, due to the combined effects
of physical disturbance, competition, grazing, predation and variation in recruitment.
However sheltered shores tend to be less variable than exposed or moderately exposed
shores and are therefore more stable.
Time for community to reach maturity
No information available.