Mud and sand. That is what we are looking for. The sea floors made up of fine sediment are usually forgotten by marine conservationists and considered “dispensable” when discussing underwater sewage pipeline installations, high-impact fishing methods or any other activity that is considered necessary but damaging. These marine “deserts” are not as popular as rocky sea floors, walls covered in gorgonias and sponges, marine prairies or other ecosystems that are more pleasing to the eye.
Although these sea floors are visually less attractive, this does not mean they are not vital, and much less, that they do not harbour life. But that life is usually found underneath the substrate and not on top of it. And it is only an night when its inhabitants are visible or show themselves in all their splendour: Sea Urchins, starfish, crustaceans, molluscs, tube anemones, etc.
Some of these sea floors are to be found in front of the city of Burriana, in the province of Castellon. After having tested the composition of the sea floor by taking samples with the dredger, we begin the diving work. We will do two dives here, one during the day and one at night. During the morning dive, the sea floor is reticent to show us its hidden treasures. It is made up of a very fine sediment on top of which some strange looking algae live. Small prairies of two types of Caulerpa are abundant, one of which is an invader, Caulerpa racemosa, introduced in the Mediterranean a few years ago and now present in large extensions. As far as fauna is concerned, a few hermit crabs (Dardanus calidus), sea cucumbers (Holothuria tubulosa), green tuskshells (Antalis taphrium), cockles (Cerastoderma edule), etc…
At night, we approach an area where the muddy sea floors begin to turn into sea floors full of detritus with small groups of Posidonia and some rocks. This combination of habitats may give us the opportunity to observe more diverse species. And this is precisely what happens, because it is in the darkness of the seabed that life explodes and activity begins. There is also a few dozing fish to be seen, like the peacock wrasse (Symphodus tinca), but the rest seem to be having a party: Octopus hunting cuttlefish, tube anemones eating zooplankton, a cuttlefish trying to trap a small fish, starfish searching for molluscs and a multitude of crustaceans, so antisocial during the day, and yet so spectacular like the sponge crab (Dromia sp.), named after the sponge it carries on its back; or the harlequin shrimp (Gnathophyllum elegans) with its chubby body covered in yellow spots. The “desert” is full of life.
On the surface, we pick up some samples of water in order to carefully study the tiny species of zooplankton that has whirled up around our boat thanks to our spotlights. It is comprised mainly of worms, fish and crab larvae, but we also find a tiny seahorse, measuring only one centimetre, which we quickly return to the sea.