September 18, 2006
Taking advantage of the fact that we are close to Mondragó Cove, the divers are going to film the sea bottom and, more importantly, the caves and rock walls. An unfamiliar yet highly important habitat for the coastal area can be found here, it is a "troittoir" or "ledge," known in the Balearic Islands as "tenasses." It is a mass of calcareous red algae (normally of the Litophyllum species, but sometimes also Neogoniolithon) which forms a small ledge just where the waves break, making an immensely interesting biological community.
The majority of the trottoirs we have seen before were quite discoloured on the top, but this one is bright burgundy red. We were not disappointed by this area, apart from being incredibly beautiful, the fauna and associated flora are quite important. The structure is colonised by a multitude of sponges, corals, bryozoans, hydrozoans and molluscs. And many other species, apart from these. On the underside of the trottoir there are more concentrations red algae, such as the Corallina elongata and the Galaxaura oblongata. It is a true spectacle to see.
We will work with the robot in the afternoon. This time we will visit sea floors at greater depths, more than 100 meters.
The first thing we find is a detritious bottom and then the sediment begins to thin out until it becomes almost muddy. In some areas, there is a large concentration of hundreds of Leptometra phalangium crinoids. They form a veritable "forest" where all the animals are placed facing the currents with their arms outstretched in order to capture the plankton that floats in the water. Amongst these, we spot a few red lance-urchins (Stylocidaris affinis) and tube anemones (Cerianthus sp.).
Surprise! we find an area of tree corals (Dendrophyllia cornigera) at approximately 140 meters depth. The specimens we see are large and spectacularly shaped. The yellow-coloured polyps are bright and vivid.
Night is falling and we decide to finish our work, but before we do, we spot some catsharks (Scyliorhinus canicula) and a thornback ray (Raja clavata) probably getting ready to begin its nightly rounds.