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Rocky Shore Trail
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The splash zone (sheltered shores)

Splash zone on a sheltered shore

Splash zone on a sheltered shore

For our purposes we are defining this zone as the bit of shore above the highest tides (extreme high water spring tides (EHWS)) and below the start of truly terrestrial vegetation. The upper limit of the splash zone cannot be identified precisely because it depends on the size of the waves causing the splash and these are different on every shore and every day has different wave conditions. On sheltered shores the splash zone may be very restricted in height because the waves are usually small and do not splash very high up. On a typical sheltered shore around Dale you'd expect a zone of about 1 metre height.

PROBLEMS

Lichens are the most obvious organisms in the splash zone. They are colonisers of bare rock and are slow growing but long lived. As they grow the action of acids and expansion of their cells can help to break up the rock into tiny fragments to produce a raw soil. This may then be colonised by mosses and as humus collects in crevices, by flowering plants able to tolerate the high salt content eg. thrift (Armeria maritima). This is an example of succession called a lithosere.

Lichens are made up from two different organisms, a fungus and an alga, together they form a symbiotic, mutualistic relationship. Separately, they would require moist, sheltered conditions, together they survive in very hostile places.
The fungal partner makes up about 80% of the lichen. The algal partner is almost always either a green alga (Chlorophyta) or a blue-green alga (Cyanobacteria). Some grow particularly well where there is a high nitrogen content eg. from sea bird droppings. Xanthoria may be prolific for this reason; it releases spores continually through the year. Spores consist of an algal cell encased in strands of the fungus. The orange (eg. Caloplaca) and grey lichens (eg. Ochrolechia) in this zone are slow growing and therefore intolerant of grazing by marine snails. Verrucaria spp. found further down the shore are faster growing and more resistant to grazing. These salt-tolerant lichens form an important community between the inter-tidal zone and the truly terrestrial communities on the cliff tops. Lichens are very susceptible to pollution and can be used as indicators of sulphur dioxide in the air. Splash zone lichens are killed by oil pollution and some of the detergents used to disperse spills.

The flowering plants surviving here depend on their ability to cope with the salt and desiccation, coupled with the almost total lack of soil. Thrift deals with all of this and grazing. Sea plantain (Plantago maritima) also grows here, both are members of tundra communities. To avoid water loss leaves of these plants are narrow and succulent. This will reduce the surface area. Around the stomata of the leaves may be a dense cover of hairs, helping to retain moisture. Lichens dominate in this zone, in more favourable environments they would be easily out-competed for space, light and nutrients by rapidly growing flowering plants.

Few marine animals survive in the splash zone. The rough periwinkle (Littorina saxatilis agg.) is one that can. It can graze on lichens, has a protective shell and all manner of other attributes that allow it survive here. Having said that it tends to be just in the lower section of the splash zone. Therefore with grazing only happening in the bottom section of the splash zone it is more likely that the lichens tolerant of grazing will be in that same area. Look at the image below:
A splash zone

A small section of splash zone with Channel Wrack (just visible at the bottom) and is the start of the upper shore. Note that the splash zone has an upper area of white and yellow lichens - the slow growers intolerant of grazing - and a lower area dominated by tar lichen. Also visible in image at the top of page.

An insect that has adapted to live here is the primitive bristletail that may be seen darting across the rocks of the upper splash zone.

There are no seaweeds in the splash zone because they need to be covered by the water (immersed) for at least some of the time to avoid drying out, to obtain nutrients, to reproduce and for support.

Compare this zone (splash zone) with one from an exposed shore.

Table of Zones - click to go

 


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