2.2 The rocky coast

The rocky coast has a step-shaped profile of different heights with the presence of promontories where rocks, coves, small sandy beaches or cobblestones alternate.
Often, among the rocks, the “tidal pools” are formed, which are periodically subject to flood and dewatering; despite temperature fluctuations, salinity, oxygen and pH, these environments are colonized by organisms which are adapted to these conditions.

Fig1_SES2.2 Tidal pool.
By Alvesgaspar – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=6107283

Inside tidal pool (FIG.1_SES2.2), often there are shrimps that spend time peeling the algae cleaning them up with small residues of organic debris; hermit crabs, crustaceans with a soft abdomen that use the shell of a gastropod to complete their body protection. There are also the fishes, as butterfly blenny (FIG.2_SES2.2); its body is covered by a layer of burr that allows it to retain moisture and stay out of the water. This fish lost the swim bladder, because always live on the bottom and has developed filiform ventral fins under the throat, which allow it to advance to the bottom and to anchor itself to it during storm surges.

Fig2_SES2.2 Butterfly blennius. By Nicola Bombardini – Fondazione Cetacea

A curious green algae, sometimes present in tidal pool, is the Acetabularia acetabulum (FIG.3 and 4_SES2.2); it has an umbrella shape, but its color is not green but white, due to calcium fouling. This organism is made up of a single cell; during the winter only the stem remains, while the umbrella begins to develop in spring.

Fig3_SES2.2 Draw of Acetabularia acetabulum
By Ernst Haeckel – Kunstformen der Natur (1904), plate 64: Siphoneae,
Public Domain, https://commons.wikimedia.org/w/index.php?curid=9872722
Fig4_SES2.2 Acetabularia acetabulum
By Albert Kok – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=9867004