On-board Diary: In search of the Mediterranean madrepora.

Author: Carlos Minguell
Date: August 2, 2010

As the Oceana Ranger must remain in port for ROV repairs (this afternoon the specialist in charge of it arrives), Ricardo has decided that we divers should spend the day on an unusual search: locating and documenting some Mediterranean madrepora Cladocora caespitosa colonies that were filmed briefly during an Oceana Ranger expedition in 2006. This coral is on the decline in the Mediterranean and its small colonies, of a size that does not usually exceed 20 cm in diameter. It is found spread out on shallow seabeds of our coasts. The peculiarity of the coral filmed by the ROV in 2006 is specifically their size because they formed small reefs measuring around 1 m in diameter. The difficulty of the search lies in that apparently, these reefs occupy a very small area and are at a depth of 36 m on a bed of sand and loose rocks. This makes it hard to locate them in spite of having approximate coordinates.

To maximize the area covered, we decided to descend to a depth that would enable us to locate the colonies (some 7 or 8 meters above the bottom) and from there make zigzag, descending to the bottom only when we saw something interesting. That is how we did it, though I immediately realized that we would have to go a little closer to the bottom than we had expected: a slight thermocline in some areas prevented me from clearly making out the seabed’s differentiated dark spots that always turned out to be rocks covered with calcareous algae and other benthonic organisms. The trip went on for 23 minutes and neither of the 2 pairs of divers managed to find the slightest trace of madrepora. The dive was more than interesting because the flat bottom was inhabited by a good number of species that we do not usually see on our dives: irregular sea urchins, comb sea stars, ascidians Aplidium sp., … although I could not amuse myself photographing them as I was concentrated on the search for coral. The upcoming days will be devoted to ROV submersions. However, we may have a second chance when we return to Majorca.