On-board Diary: To the Columbretes Islands
Author: Ricardo Aguilar
Date: July 19, 2006
After leaving Torredembarra at night, we saw various ships pass by us at sunrise, including cruise ships, cargo ships, etc. Further away, more or less two miles away, we saw a trawler. When we reached the area, we saw dozens of dead fish on the surface, mainly bogues (Boops boops), most probably the frequent leftovers of these trawlers. We have collected some with the fish net in order to identify and examine them. Many of them had suffered some injury, while others were completely destroyed.
Luckily, a few minutes later, our luck changed and we were paid a visit by a group of dolphins, who came to cheer us up. In this case, they were bottlenosed dolphins (Tursiops truncatus), approximately 12 of them, and they were jumping and hitting the water with their tail fins. It seemed as if they were feeding!
And now, we see Columbretes ahead. We send a message to the Natural Reserve and proceed to anchor off Isla Grossa. After speaking with the guards and explaining our plans, we set sail for Isla Horadada, less than two miles away.
During our stay here, we must be very careful to avoid making noise; it is mating season for the Eleonora's hawk (Falco eleonorae) and we have already seen more than a dozen of them. An estimated 40 mating pairs are nesting in Columbretes this year. Other marine birds like the Audouin's gulls (Larus audouinii), the yellow-legged gulls (Larus cachinanns), the Cory's shearwaters (Calonectric diomedea), shags (Phalacrocorax aristotelis), etc., are also to be found on these islands.
We concentrate on the north-eastern coast of Horadada Island on our first dive. We must be very careful as we dive into the water: there are plenty of jellyfish! (Pelagia noctiluca). It is not a plague, but even so, there are many of them. At 14 meters depth, we spot a large layer of brown algae, especially Dictyopteris membranacea, that covers a large extension of the ocean bottom. Many other brown algae are also visible, like Sargassum vulgare, Zonaria tournefortii, Dictiota dichotoma, etc. In the rocky areas, it is the green algae, Halimeda tuna, that abounds. And where the waves break, we find Cystoseira amentacea, which is another brown algae that should be a priority in terms of protection due to the habitats it creates.
Among the "forests" of Dictyopteris, we find many mollusc spawns, mainly nudibranchs (those sea slugs without shells, with gills on their dorsal surface, but coloured in magnificent hues), but also marine shells (buccinidae and muricidae). We also spot a few large nudibranchs like the Platydoris argo. Further on ahead, a group of ornate wrasse or green fish (Thalassoma pavo) seems to be having a feast among spawns of damselfish (Chromis chromis). And later, large and spectacular banks of young damselfish, displaying those intense and imposing tonalities of blue.
In the afternoon, we concentrate on the Cymodocea nodosa prairies. This plant, one of Posidonia's "little sisters," constitutes important and interesting marine forests. Among them, we find giant pen shells (Pinna nobilis) that look like huge mussels stuck in the sand, young octopus (Octopus vulgaris), spawns of squids (Loligo sp.), and many fish, such as rainbow wrasse (Coris julis), peacock wrasse (Symphodus tinca), painted combers (Serranus scriba), etc. And again rhodolites of Lithothamnium and an incipient maerl which beings here.
The Columbretes are volcanic islands, arising from an eruption which occurred one million years ago, and as such are quite young. This fact is especially apparent in its marine ecosystem. It seems as if the typical Mediterranean colonies have not wholly established themselves here, or they have not been well distributed. There is still no sign of Posidonia oceanica, and there are only prairies of some other marine plants; Cymodocea nodosa. The maerl, which is an interesting habitat made up of calcareous red algae that looks like ramified coral, blends with these prairies in some areas and shallow places, less than 20 meters deep, we have seen some rhodolites of Lithothamnium among colonies of Dictyopteris, when normally these algae are located deeper than 30-40 meters. It is almost as if the "hormones" of this young ecosystem have not settled yet.
It is also interesting to see the large artillery pieces camouflaged among the hills of the island, reminiscent of the military past of this area. Luckily for us today, that is history.
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