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The Seashore

Rocky Shore Trail
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The lower shore (sheltered shores)

For our purposes the lower shore is that part from the average low water neap tide (MLWN) to the lowest the tide ever get ie. extreme low water spring tides (ELWS).

As we move down into the lower shore abiotic (physical) factors become less and less of a problem for most inter-tidal species. Most of them do better when immersed (underwater) and worse when emersed (out of the water). The sea is so enormous that it is very slow to change in temperature, pH, salinity (and anything else you can think of). By the time you get to the bottom part of the lower shore it's almost like being permanently under the water. Most inter-tidal organisms originated in the sea and do better wetter and in this relatively cushioned constant environment. Abiotic environmental factors now start to become of less importance in controlling what can live where. The benign environmental conditions means that there are lots more species (increased diversity) and much greater abundance of those species. This means that biotic factors (interactions with other living organisms) become more important than abiotic factors (interactions with the non-living part of the environment) in determining the distributions of organisms.

Most algae are shade plants and are adapted to absorb low amounts of light energy. This applies especially to red algae and many of them begin to appear on the lower shore. Most of the time the light they receive there is attenuated by its passage through the covering sea water. eg. Dulse (Palmaria palmata), Irish moss (Chondrus crispus), coral weed (Corallina officinalis) and many other species of red algae. The saw wrack (Fucus serratus) is common in the upper part of the zone and may dominate it.

Kelps (like the sugar kelp, L. saccharina) are large brown algae that can dominate the shore towards the lower end of this zone. In very sheltered conditions this will be accommpanied by the bootlace (Chorda filum) seaweed. As wave action increases the sugar kelp will be replaced by the oarweed.

Greater productivity of algae means more herbivores can survive (eg. Blue rayed limpets (Helcion pellucida), grey topshell (Gibbula cineraria), and more herbivores means more carnivores like shore crabs (Carcinus maenas), blennies (Lipophrys pholis) and starfish (Asterias rubens). Not only that but the food available to filter feeders is increased due to longer feeding time so sponges like the breadcrumb sponge (Halichondria panicea) can do very well in these regions. Filter feeding tube worms like the spiral tube worm (Spirorbis borealis) and the keeled tube worm (Pomatocerous triqueter) also can be found in great quantity here.

All these creatures die at some point and detritivores (who eat dead stuff) also abound here. Porcelain crabs (Porcellanus platycheles) use their massive front claws to stir up the sediment and feed on decaying material trapped on the bristles. Soft bodied predators/detritivores like the snake locks anemone (Anemonia viridis) and the beadlet anemone (Actinia equina) also do well here (although A. equina can live on the higher levels of the shore (see sheltered rocky shore upper shore section). Shrimps and prawns are generalist feeders who will consume large amounts of dead animal material. All this means that factors like competition and predation and interactions between organisms become more important as we move down this zone.

In fact the list will go on and on. A search around the kelp base will show and incredible variety so have a look at the species list for rocky shore under the headings of the main phylum groups like echinoderms, crustraceans and molluscs.

Compare this zone (lower shore) with the one on exposed shores.

Table of Zones - click to go

 


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