Energetics and interactions with other ecosystems
Fate of primary production by macroalgae
Rocky shores as nursery grounds
Rocky shores as feeding areas for birds and mammals
One of the defining characteristics of a rocky shore is that it exists at the interface
between marine and terrestrial ecosystems. Consequently, there are strong interactions
between the communities of the shore, land and sea. Coasts, including rocky shores, are
highly productive (Hawkins et al. 1992). Shallow water allows the penetration of
light which promotes primary production in macroalgae and the microbial film which coats
the rock. Rocky shores also benefit from primary production in phytoplankton which are
washed over the shore with each tide. The sea also brings detritus in a range of particle
sizes. Whole kelp plants and other algae washed up on the shore are eaten by littorinids,
crustaceans and limpets. Banks of mixed seaweeds can accumulate on the strandline, where
they support populations of invertebrate scavengers of both terrestrial and marine origin.
Small detrital fragments and phytoplankton are consumed by filter feeders such as
barnacles and mussels. Particulate organic matter in this form is the main route of
material flowing up the detrital food chain.
Fate of primary production
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). On exposed shores, grazers feed mainly on the microbial
film. 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.
Rocky shores as nursery
The rocky subtidal is an important nursery area for many commercially
important species of fish including herring and gadoids. These can migrate into the
intertidal zone at high tide but there is little evidence of any dependence on littoral
communities. However, fish and crustaceans, migrating into the intertidal to feed as the
tide rises, are important predators of rocky shore species. Corkwing wrasse, which are
important to the aquaculture industry as a cleaner species rely heavily on the intertidal.
Juveniles are commonly found in rockpools.
Rocky shores as feeding
areas for birds and mammals
Shore birds also feed on the rocky shore (Feare and 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 often use rocky shores and will
feed on animals such as shore crabs which, in turn, feed on rocky shore species.
Opportunistic mammalian species such as rats, rabbits and even sheep will forage on
available rocky shores.