A habitat that I really miss is the rocky shore habitat. The shore line of the Netherlands consists mostly out of sandy shore, in other words beaches. We have some rocky parts but these are mostly dykes and piers. These man-made structures have some rocky shore life, but I really miss the little tidal rock pools of water with so much life in them you can’t stop looking. During my study of Coastal and Marine management, we had an entire module about the rocky shore habitat. However because the Netherlands lacks beautiful rocky shores we travelled to Pembrokeshire Wales, and look at the rocky shore biology. While living in Scotland I also lived at a rocky coastline and its always so interesting to look at everything that lives on these rocks. But it is more than just looking at the biology of the rocky shore, it is also the pure beauty of a rocky coastline. As it seems so much rougher and feels wilder than a soft beach. I love seeing how the waves hit the rocks in all there force. So in this blog I want to look at the ecosystem of the rocky.
The rocky shore is a very harsh ecosystem to live in. It is under influence of the tides, waves, sun and sometimes even fresh water. The rocky shore can be divided in different zones. These zones are the splash zone, upper shore, middle shore and lower shore. On different zones live different organisms who are able to cope with different levels of being emersed and submerged. Emerged and submerged are the two terms associated with being above water and under water on the rocky shores. The period where the animals and plants on these shores are washed by the falling and/or rising of the tides is referred to as awash.
The splash zone is the highest zone of the rocky shore. And as the name suggest it is mostly splashed by waves, although the splash zone can be submerged during a high spring tides and storm surges. In this zone you can mostly find salt loving plants and lichen.
Upper shore
The next zone is submerged during high tide and emerged during low tide. This zone is thus only submerged for a couple of ours in the day. In this zone you can mostly find species like periwinkles, barnacles and limpets. Here you can also find some algae. The animals all have adapted to survive the dry times and the extreme temperature changes. When submerged the temperatures are stable but when emerged the temperatures can rise quickly. How do they survive above water? Lets take the barnacle as an example. Barnacles are small crustaceans (family of crab and lobster) they have a white cone which is made up of six calcium plates that forms a circle around the crustacean. Within this circle there are four more plates which form a sort of ‘’door’’ which can be opened and closed. This depends on the tide, during high tide when the barnacles are submerged these plates are open and they can feed by rapidly extending and retracting their feather-like appendage called cirri from the opening. The cirri sifts through the water column for microscopic organisms. When emerged during low tide the barnacles close the ‘’door’’ and trap water inside their shells and keep moist.
Middle shore
The middle zone submerges and emerges with every tidal cycle. As this zone has more water coverage and for longer there is more life to find. Besides the barnacles and limpets which can also be found in the upper shore, you could find mussels, crabs, anemones and brown seaweed. All of these animals are also capable of being emerged.
Like the splash zone and the upper shore, the middle shore has the challenge of living out of water. And besides the challenge of keeping moist, they also have the challenge of temperatures. During a low tide the temperatures on the emerged parts rise when the sun shines, but in colder regions (higher latitudes) the animals and plants also might have to cope with extreme cold temperatures.
Lower shore
The lower shore is completely submerged and only emerged for a short period during a spring tide. This is the zone where a wide range of different animals can be found. Like snails, crabs, starfish, sea urchins, anemones, shrimps, fishes and different types of seaweed. This zone is the most stable with temperature and salinity levels, however because there are more animals there is also more competition between the species
Rock pools
During low tide the rocky shore is emerged from the water, but not everything is emerged, some water stays behind on the shore and creates rock pools also known as tidal pools. Life in these rock pools can be very harsh as well. There are many challenges of living in a rock pool. Once the tide has gone out, there is no way back to the sea. It depends on the weather and other animals, which challenges are meant to overcome in a rock pool. When the sun shines the pool water temperature might increase and the water starts evaporating. The evaporating water means that the salinity of the pool increases as well. On the other hand when it rains the salinity levels might decrease. Many marine animals can only tolerate small differences in temperature and salinity. There is also a challenge with the oxygen levels. Marine animals need oxygen to breath, oxygen is present in the water column through the photosynthesis of algae. During the day algae can keep on producing oxygen in the pool. However during the night, algae can't produce oxygen, the challenge during nighttime is to preserve oxygen until the tide comes back in. Another challenge depends on your fellow marine animals in the rock pool. As we have seen above there are many different types of marine animals that can live on the rocky shore and any of them could get stuck in a rock pool. For example star fishes will keep on eating when they are stuck in a pool and they feed on crustaceans but also on snails. So besides dealing with the changing temperatures and salinity you might also need to evade certain fellow pool dwellers.
Rocky shore as indicator of climate change
The rocky shore ecosystem is one of the most researched marine ecosystem. And research has been done to the effect of climate change on the rocky shore communities. What has been found is that over the years many species have redistributed to the north. And some species are and stat smaller in size then they used to. It is thought that this is due to the warming of the oceans waters.
Sources:
Book: The Biology of Rocky Shores. C. Little, G.A. Williams & C.D. Trowbridge Second edition. ISBN: 978-0-17-856491-1