Rocky shores

This article describes the habitat of the rocky shores. It is one of the habitat sub-categories within the section dealing with biodiversity of marine habitats and ecosystems. It gives an overview about the biota that lives there, the problems and adaptations the habitat is facing with and the importance of it in the marine environment.

Introduction

A rocky shore is an intertidal area that consists of solid rocks. It is often a biologically rich environment and can include many different habitat types like steep rocky cliffs, platforms, rock pools and boulder fields. Because of the continuously action of the tides, it is characterized by erosional features. Together with the wind, sunlight and other physical factors it creates a complex environment. Organisms that live in this area experience daily fluctuations in their environment. For this reason, they must be able to tolerate extreme changes in temperature, salinity, moisture and wave action to survive.

Rocky shore of the Costa Vicentina

Formation

Sufficient loose or unconsolidated material and a suitable coastal environment to allow the sediments to accumulate are key features in the formation of beaches. The sediments can be terrigenous (land-derived), transported by rivers and streams or through erosion of coastal cliffs. In tropical regions or places with a lack of land-derived material, sediments may be biogenous and consists of broken corals or shells. Beaches on volcanic islands may be black and consists of broken lava and volcanic minerals. Rocky shores are usually steeper than sandy shores. These differences are the result of the different permeability of the sediments and the balance between waves that retreat and come up. Rocky shores have a high permeability and much of the upcoming wave percolates into the bottom. This reduces the outwash of sediment toward the sea. For this reason, coarse sediment can accumulate on the beach and can be transported further on the beach by stronger waves.

Zonation

Each region on the coast has a specific group of organisms that form distinct horizontal bands or zones on the rocks. The appearance of dominant species in these zones is called vertical zonation. It is a nearly universal feature of the intertidal zone.

Supratidal zone

When the tide retreats, the upper regions become exposed to air. The organisms that live in this region are facing problems like gas exchange, desiccation, temperature changes and feeding. This upper region is called the supratidal or splash zone. It is only covered during storms and extremely high tides and is moistened by the spray of the breaking waves. Organisms are exposed to the drying heat of the sun in the summer and to extreme low temperatures in the winter. Because of these severe conditions, only a few resistant organisms live here. Common organisms are lichens. They are composed of fungi and microscopic algae living together and sharing food and energy to grow. The fungi trap moisture for both themselves and their algal symbiont. The algae on the other hand produce nutrients by photosynthesis. Green algae and cyanobacteria can also be found on the rocks of the North Atlantic coasts. They are capable of surviving on the moisture of the sea spray from waves. During the winter, they are found lower on the intertidal rocks. The algae growing higher on the rocks gradually die when the air temperature changes. At the lower edge of the splash zone, rough snails (periwinkles) graze on various types of algae. These snails are well adapted to life out of the water by trapping water in their mantle cavity or hiding in cracks of rocks. Other common animals are isopods, barnacles, limpets,…