The transition zone between land and the marine environment is not a simple transition area between rocks and water. It constitutes a unique environment that gives rise to a set of specific communities. Here we will focus on the intertidal zone, its zonation in rocky shores and what plant and animal communities live.
WHAT IS THE INTERTIDAL ZONE?
The intertidal zone is the transition between the terrestrial and marine environment, which is limited by the height of the higher tide and the height of the lowest tide, that is, between the highest and lowest water height due to tides. This implies that the conditions of temperature, humidity and solar radiation constantly change. That is the reason why organisms are well adapted.
HOW IS THE INTERTIDAL ZONE IN ROCKY SHORES AND WHO LIVE THERE?
Probably, this summer, if you went to the beach, you have seen that the area where the waves lap against the shore was inhabited by some organisms that practically disappeared when you put your head under the water. The reason is that on the rocky coasts, there is a clear zonation, in the same way that in the mountain there are different regions with increasing height due to a change in environmental conditions. Here we will focus on the Mediterranean.
The first is the supralittoral zone, which is located near the sea but above the maximum height of the tide, so that the salt water arrives only during the highest tides or storms. In this zone, the organisms that are present must resist the constant lack of water and only with the humidity and food that splashes and tides carry. Among these organisms there are cyanobacteria (bacteria that make photosynthesis) that give a black appearance (as Calothrix), lichens (Verrucaria), barnacles, gastropods (as Littorina) and isopods (Ligia).
Below, we find the mediolittoral zone, which occupies the area between the highest and lowest tide level. In areas where the tide is almost non-existent, as is the case of the Mediterranean, it corresponds to the area where the swinging waves take place. The species that live here need or tolerate immersion and almost continuous emersion. In hard substrates, this area can be subdivided into:
- Upper mediolittoral, when the immersion is less frequently. The typical organisms are barnacles, cyanobacteria and lichens, but also limpets (Patella), winkles like Littorina and Monodonta. Among seaweed, the most typical ones are Rissoella verruculosa, Ralfsia, Nemoderma, Enteromorpha, Blidingia…
- Lower mediolittoral, when the immersion is frequent. The most typical seaweed, but not the only one, is the calcareous red algae Lythophyllum tortuosum, which constitutes a bioconstructon called trottoir, with a balcony-like aspect. Limpets, winkles, chitons (Lepidochitona) are also present. Mediterranean mussels (Mytilus galloprovincialis) begin to appear.
Finally, we find the sublittoral zone, a totally marine zone that begins where the immersion is almost permanent and ends where algae with higher light requirements and seagrasses like Posidonia oceanica disappear. In the first meters of the zone we can find a high abundance in algae with high light requirements, which are replaced by algae with lower light requirements and animals.
- Ballesteros, E & Llobet, T (2015). Fauna i flora de la mar Mediterrània. Editoral Brau
- Castro, P & Huber, ME (2003). Marine biology. The McGraw Hill (4 ed)
- Ros, J (2001). Vora el mar broix. Problemàtica ambiental del litoral mediterrani. Editoral Empúries
- Smith, TM & Smith RL (2007). Ecología. Pearson Educación (7 ed).