An introduction to zonation on intertidal shores

Where the land meets the sea two worlds join, one or air and the other of sea water.

As the tide rises and falls this stretch of land, refereed to as the intertidal zone, alternates between being exposed to the air and covered by sea.

The relative environmental pressures of submergence and exposure change retrospectively throughout the intertidal zone in relation to altitude from the low water mark. Other factors such as predation and competition also act to influence the communities found. 

The combination of all these factors can often result in repeated and definable communities of species at certain altitudes and/or exposures across the intertidal zone.

Such distributions of communities in relation to altitude or, height on the rocky shore is often referred to as zonation. Zonantion is often discussed in terms of dominant seaweeds present and is best exemplified on sheltered rocky shores. 

Zonation is not always clear cut (see previous blog post: http://thesaltyscavenger.blogspot.co.uk/2014/08/rockpooling-destination-mousehole-may.html) and is affected by factors for which altitude on the shore is often correlated. 

The following posts look at some of the characterising species of the general shore 'zones'; although these can be found else where, they are often characteristic of a particular zone of the shore.

Below are images of some of the different intertidal zones found on UK rocky shores.

The different zones of the intertidal rocky shore in relation to altitude.

The communities on this exposed rocky shore in Shetland exhibit distinct distributions in relation to rock altitude and exposure. Yellow and grey lichens occur at the highest elevation of the rock and mark the supralittoral zone. Below, the rocks of the littoral fringe appear black, from the tar lichen (Verrucaria maura) which is overgrown on the more sheltered vertical rock, by a fringe of the brown channel wrack (Pelvetia canaliculata); the rocks of the upper shore become increasingly grey due to the barnacle communities which are inter-dispersed by patches of the black, Lichina pygmaea.  Habitat classification: LR.FLR.Lic.YG (Yellow and grey lichens on supralittoral rock) EUNIS: B3.111, LR.FLR.Lic.Ver (Verrucaria maura on littoral fringe rock) EUNIS: B3.113 and LR.HLR.MusB.Cht (Chthamalus spp on exposed upper eulittoral rock) EUNIS: A1.112.

The communities on this sheltered rocky shore in Shetland exhibit distinct distributions in relation to rock altitude. Yellow and grey lichens occur at the highest elevation of the rock and mark the supralittoral zone. Below, the rocks appear black, from the tar lichen (Verrucaria maura) and the eulittoral is characterised by fucoids with a green patch of ephemeral greens marking fresh water run off entering the shore. Habitat classification: LR.FLR.Lic.YG (Yellow and grey lichens on supralittoral rock) EUNIS: B3.111, LR.FLR.Lic.Ver (Verrucaria maura on littoral fringe rock) EUNIS: B3.113, LR.LLR.F (Fucoids on sheltered marine shores) EUNIS: A1.31 and  LR.FLR.Eph (Ephemeral green seaweed communities - Fresh water influenced) EUNIS: A1.45.