OUR COASTAL TREASURE
Pay a visit to a rockpool
Rockpools are magic places! They are miniature ecosystems, complete with all the drama of the savanna. They are filled with fascinating creatures including animals that look like rocks or plants, and plants that are not really plants. The best place to visit a rockpool in the St Francis area is in the vicinity of the Seal Point lighthouse or down on the rocky shore below Santareme or Otters’ Landing.
Take with you your hat and a pair of shoes to protect your feet from the sharp barnacles.
A refuge from the elements
Rockpools are filled with water when the tide comes in but do not drain completely when the tide recedes. They remain full of water and this provides a habitat for two different categories of intertidal creatures.
Firstly, there are those that naturally inhabit the higher zones of the shore. These include winkles (top shells), turban shells and the tiny periwinkles known as Littorina. These molluscs are well adapted to surviving long periods of exposure to air, as well as fairly warm conditions.
Littorina periwinkles
Winkles/Top shells (Oxystele)
Turban Shells (Turbo)
Sometimes, however, when conditions are very harsh in the high shore zone, or when it is time for these molluscs to lay their eggs, they take refuge in tidal pools. You can always see these species in the rockpools and, if you watch carefully, you can see them moving around slowly under the water as they graze.
Secondly, intertidal rockpools are inhabited by those species that can only survive when permanently covered in water. These include certain algae, anemones, sea urchins, fish, starfish and octopuses. They are often colourful and have interesting shapes and lifecycles.
Despite looking a lot like flowers, anemones and sea urchins are animals that live permanently submerged in rockpools.
Sea anemones are actually named after the anemone flower, which makes things even more confusing since they are animals and not plants!
Anemones are related to jellyfish but they cannot move around as easily as a jellyfish does. Anemones are usually found stuck to a rock; they have a column-shaped body that is closed at the top by a mouth. The many tentacles are slightly sticky and some may even carry stings (but along our shores these are not dangerous to humans). When the tentacles wave around in the water, they trap tiny animals and algae. These are brought to the mouth and swallowed.
Sadly for a sea anemone, it has no anus and so has to get rid of waste and undigested matter out of its mouth!
Sea urchins are related to starfish but they are herbivores that graze algae and pieces of drifting seaweed.
They can often be seen with empty seashells stuck to their bodies – these protect them from the UV radiation of the sun and help to camouflage them from predators.
If you observe a sea urchin carefully you will see that, in addition to its spines, it has tiny tube feet all over its body. It uses these to move around slowly over the rocks.
Luckily for a sea urchin, it has a mouth and an anus on different sides of its body. Its mouth is underneath and contains five calcium carbonate teeth that are used to graze and chew food. Sea urchins use their spines to defend themselves against predators such as fish, starfish and sea otters. You should not try to pick up a sea urchin – just as you would probably not try to touch a hedgehog or a porcupine!
Whelks are also commonly found in rockpools, where they scavenge or prey on other invertebrates.
Prey species, such as limpets and winkles will consciously move away from a whelk (albeit at a snail’s pace) in order to avoid being eaten.
One will often find clusters of white egg capsules stuck to rocks in tidal pools – these contain the eggs of whelks.
Small, well-camouflaged fish are also common inhabitants in rockpools on the shores around the greater St Francis area. These are mostly species of gobies, and they are notoriously difficult to identify accurately. The most common in the St Francis area is the banded goby, a species that is endemic to the South African rocky shores.
These fish are predators that hide under rocks and dart out into the light at any opportunity of food. It is very easy to attract them to one’s feet by dropping a few small pieces of bait into the water.
The photo above shows a beautiful spiny starfish in a local rockpool. Although not very colourful, this species is spectacularly camouflaged against the pink coralline algae on the rocks. It is a predator that feeds on mussels, sea urchins and other invertebrates such as whelks.
Cushion stars are rather small starfish that are commonly found in rockpools around the greater St Francis area.
They have poorly defined arms compared to other types of starfish, and are beautifully camouflaged as rocks and algae in the rockpools.
Cushion stars are herbivores and have the unusual habit of extruding their stomach out through their mouth and sticking it onto the rock, over the algae they wish to eat. Their stomach juices then digest the microscopic algae and the nutrients are absorbed into the stomach. Cushion stars lay eggs under the rocks; the eggs hatch directly into tiny, baby cushion stars.
Look out for an octopus while you are visiting an intertidal rockpool. Although the common octopus spends most of its time subtidally, individuals will often enter rockpools when the tide is high and then hide under the rocks while the tide recedes.
Octopuses are considered to be very intelligent invertebrates and are successful predators of fish, crabs and intertidal shellfish. They can pick up food items and manipulate them very dextrously with their eight arms.
If you find one under a rock in a rockpool, consider yourself lucky to have found such a fascinating and intelligent creature. But you should leave it in its hiding place for it can give a nasty bite with its beak-like mouth.
If you wish to find out any more information about the living creatures in rockpools, you could refer to the following publications.
Branch, M. & Branch, G. 1981. The living shores of southern Africa. Struik Publishers.
Branch, G. M., Griffiths, C. L., Branch, M. L. & Beckley, L. E. 1994. Two oceans: A guide to the marine life of southern Africa. David Philip Publishers.
Lubke, R. & De Moor, I. (Eds.) 1998. Field Guide to the Easter and Southern Cape Coasts. University of Cape Town Press.
Tietz, R. M. & Robinson, G. A. 1974. The Tsitsikama Shore: A guide to the marine invertebrate fauna of the Tsitsikama Coastal National Park. National Parks Board.
Photo Credits:
Patella granularis
https://commons.wikimedia.org/wiki/File:Patella_granularis_01.JPG
Turban Shell https://upload.wikimedia.org/wikipedia/commons/5/57/Turbo_cidaris_cidaris_01.JPG
Octopus
https://upload.wikimedia.org/wikipedia/commons/9/9f/Octopus_vulgaris_2.jpg
