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September 19, 2006

Cape Blanc

BY: Ricardo Aguilar



We wake up early to find the impressive cliffs of Cap Blanc in front of us. There are vestiges of a large fossil coral reef here that existed in this area of the Mediterranean during the Miocene. More than 5 million years after, we are here to see how these sea floors have evolved. We will use the transection method in order to learn the distributions of the different ecosystems and species between the cliff and the depths of 100 meters. For this, we will work with both the divers in the shallower areas and the robot in the deeper areas.

Various landslides on the cliff have filled the sea floor with large blocks of rock which have become home to many species. Small solitary corals, sponges, algae, etc., the invasive algae Lophocladia lallemandi and further on, a prairie of Posidonia oceanica begins. At 35 meters depth, the sea floors change and spread out over the sand and detritous we see another invasive algae Caulerpa racemosa, spreading out extensively, while the local algae Arthrocladia villosa forms small colonies on the hillocks. Strangely enough, many white gorgonias (Eunicella singularis) can be found in this substrate. We also spot some Mediterranean madrepora reefs (Cladocora caespitosa), many of which are quite large. At 50 meters depth, the sand is becoming more and more fine. We can now see many types of red algae such as Osmundaria volubilis or Phyllopora crispa, and finally this area becomes home to the carrion-eaters and detrivores, especially star-fish and hermit crabs. It is not strange to find other species as well, such as scallops (Pecten jacobeus), brown combers (Serranus hepatus) and crabs belonging to the Inachus family. We also spot many bryozoans, some living atop the hermit crab’s shells, and even a seven-armed star-fish (Luidia ciliaris). And something even stranger; a solitary rock coral, the Caryophillia smithi, on a sea floor such as this, made up of fine sediment. Each dive brings us some surprises.