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Cañón de Creus - June Campaign - CSIC
For the INDEMARES-2 campaign in the Cañón de Creus, the priority has been to explore the areas to the south of the canyon between the coast and the area farthest away from the canyon. This campaign was carried out with the García del Cid Oceanographic Boat from 7 to 16 June.
One of the biggest difficulties in the study of the seabeds of the shelf is the localisation of the representative communities, above all because with the currently available means it would be practically impossible to prospect the entire area. If we do not start with prior information to know where and how the different communities are distributed, the oceanographic campaigns could be a failure. Having at least good bathymetric information and the geomorphologic characterisation of the marine bed will allow us to get a prior overview of the bottoms.
For example, using echosound techniques we can obtain a very rough image of the type of bottoms. With this, we can design the biological samplings and calculate the time required for carrying them out. Our objective is to obtain a cartography of the habitats for the entire area partly based on direct observations and also making inferences on the sedimentary bottoms that with the same slope and an even surface will be home to the same type of communities. In the same way on the bars, projections, mountains or small plateaus the domination of the same biological communities is to be expected.
Our campaign started with the bathymetric and geomorphologic characterisation of the southern area of the canyon we had no information on. As can be seen in the picture, there are a series of areas with small localised projections on a plateau measuring some 20 metres in height.
Trawlers usually concentrate in the surrounding areas of these rocky areas from the edge of the continental shelf, as the sea bed communities attract shoals of fish with commercial interest that find food and refuge there.
The first evidence of the wealth of these seabeds comes from the work of researchers who studied the organisms recovered on board caught up in the nets.
In this campaign, we were able to visit the boundary area between the wall of the canyon and the continental shelf and we saw bottoms where the communities that make up the Phakelia ventilabrum sponge that might be relicts can be seen in this area of the Mediterranean.
Using specific cartographic techniques for the bottom, at a greater depth and associated to the high area of the Cap de Creus canyon, we found some alterations on the bottom in the shape of a small bar or hills. The possible importance of this area gave rise to one of the immersions of the JAGO submarine. During the immersion, we saw that these hills look like serpulid polychaete reefs that normally grow on the coast line. It could be said that they are subfossil reefs (in the fossilisation process) as the calcareous structure is made up by tubes of dead polychaete and their holes and spaces filled by sediment and other organic remains. The sample we collected from this “reef” to be studied in our laboratory can be seen in the pictures.
During the last decade, we have been able to confirm the role of the deep coral communities as important habitats for many species, as they provide them with refuge in their larva and youth phases. In previous campaigns, we took samples of zooplankton with nets that move very near to the bottom, so much so than in many cases they even collected sediments when they touched the substrate. We have taken samples of larva phases of some fish and crustaceans, which are not frequent in open waters and other species such as hake larva (Merluccius merluccius) that are usually very rare in plankton samples. This finding set out the need for us being certain that what we were really studying with this methodology was the populations or communities of zooplankton associated to the coral colonise or rocky structures (as cavities) situated on the wall of the canyon wall, and that the samples we recovered on board had not been contaminated on crossing the 400 mm of the water column, The only possibility we had of being sure that the samples we wanted to study came from the same walls or coral communities was to collect them on site with suction pumps associated to the JAGO submarine and that we could have an absolute control of the process and the certainty of knowing how and where they were collected.
As far as we know, samples have been collected on site on a wall of a submarine canyon in the Mediterranean for the first time. In a first inspection of the samples collected, we have been able to establish that the amount of plankton collected by the pump is much higher in the stations where we knew there were colonies of Madrepora oculata. We were also able to establish that the samples with a lower concentration of plankton corresponded to locations where there no coral colonies, in block or terrace areas in the high part of the canyon wall.
Studies carried out in the laboratories of the Sea Science Institute of Barcelona on the growth of deep coral have shown that they grow much faster than thought and, even, at rates comparable to some tropical coral species. These colonies, that are so important for the recovery of stocks of species of fish with commercial interest, could be recovered in decades and not in centuries or longer as feared.
During this campaign, we have started a new series of experiments, this time on a gorgonian species. It is a species of the Eunicella genus that develops in some populations in the middle area of the continental shelf with a certain density. The populations are grouped in small shoals or groups separated by areas trawled by all types of fishing methods. Among these nuclei of just 10 to 20 metres in diameter, there are small colonies, recruits that are apparently in charge of recovering the gorgonian meadows. To know their growth and reproduction potential we collected colonies that will be studied after acclimatisation in the aquariums.
With the same objective as the Eunicella colonies, we also collected some individuals from the Leptometra falangium crinoid. This species, like the gorgonian, forms meadows considered the preferred areas for the recruitment of certain species, up to the point of being considered a critical habitat for the fishing resources of the Mediterranean, and constitute points of high diversity and are subject to protection in some areas of the Mediterranean. These crinoids that usually get caught up in trawling nets are then thrown back into the sea under the suspicion that they do not die or are easily recovered. Our team is going to investigate if this supposition is true. To do so, specimens collected in the middle area of the shelf with a seabed trawling sledge have been installed in the ICM's aquariums. What we can say is that, after a few weeks, the different individuals although adapting to the conditions of the aquarium did not show any signs of recovery. However, after two months some individuals showed a start of growth of their arms broken when they were collected, which could give us some hope for the conservation of this essential habitat.
The adverse weather conditions we suffered on some days during the campaign forced us to focus our prospecting activities on the area of the shelf parallel to the southern face of the Cap de Creus. An immersion was carried out with two objectives. Firstly, it is one of the areas we have less information on, above all due to having encountered difficulties like the ones above on previous occasions. Secondly, due to the possibility of the areas where fishermen most regularly throw their nets being areas of special interest for our research, which would correspond to the abundance of species of commercial interest. Having the skill of Jurgen Schauer, the JAGO submarine’s pilot and of Covadonga Orejas, our most experienced argonaut who currently works in the Santander IEO and who regularly takes part in the campaigns, ensured the total success of the exploration in the area. During the prospecting we observed that the area coincides with an area of rock bars colonised by sponges and gorgonians, that very affected by the nets that touch the bottom when they are thrown. During the immersion, we avoided the fishing nets but we saw other abandoned ones that were in some of its sections lying on the bottom. A surprising and also deplorable scene was observing how the abandoned nets acted as a lethal trap for fish and crustaceans.
During one of the last immersions with the JAGO submarine, we observed a phenomenon that although not strange in the Mediterranean is very difficult to see as it is apparently motivated by peculiar temporary situations.
This was large agglomerations of ofiuras, with specifically the Ophiotrix fragilis species. We were able to establish the presence of a large concentration of these organisms some 100 metres deep down in the middle area of the continental shelf to the south of the Cap de Creus canyon. The weather conditions during these days of the campaign, with strong south- easterly winds, occasionally changing to northerly winds, favoured the transport and suspension of a very high concentration of particles in the water. Both the abundance of particles and the surprising concentration of ofiuras are yet another example of the high productivity of the area, which definitively has a bearing on the high biodiversity of both species and habitats.
Currently, the use of submarine robots, manned submarines and direct visual and photographic observation systems are radically changing this situation. A huge progress is worth mentioning, as destroying the seabed to study it is not necessary any more; we do not have to drag tools along the bottom to collect organisms that will be identified and studied in the laboratory. On the other hand, the study of the images collected with the submarine vehicles, added to the selective collection of some specimens and samples allows knowing the distribution and structure of species and populations and getting an objective and real perspective of the distribution of the organisms.
Throughout the different campaigns, we have observed how species of fish or crustaceans travel around the shelf looking for protection, places to reproduce or a greater availability of food. In the last campaign, we even saw a singular case as was the detection of a community of shelf coraligenic where the most coastal species coexist such as the zoantharia Parazoanthus axinellae (picture on the right) among other medium depth species such as the Madrepora oculata coral colonies. We also saw how the fish find refuge in the sessile species that configure three dimensional substrates on the platform. As it is easy to understand, when these structures and communities of the platform are destroyed by trawling, the connectivity between the coastal area and the semi-deep communities of the platform and the continental slope is seriously damaged.
Studies such as those being carried out in the Cap de Creus require multidisciplinary oceanographic campaigns and previous experience that allows making the most of efforts and work. The study also includes coastal campaigns, treatment of historical data, acquisition of information from different sources on bathymetry, hydrography, biological data, etc. The campaigns require the combination of different study techniques: probes for bathymetry, water column sampling devices and systems, indirect sampling equipment such as nets and dredges and to make it even more complicated, all of the necessary logistics for the JAGO submarine to work with the maximum guarantees of safety and profitability.
The most complicated moment is when we have to put the submarine into the water. Each of these operations requires the collaboration of at least 8 of the technicians and scientists on board and 6 members of the crew. It sometimes requires the help of all the available personnel. During the immersion which may take hours (3 hours on average), the boat has to follow the submarine on the surface and be in constant contact with the pilot.
It is evident that we cannot carry out any other activity until the submarine has been recovered. Then, when it is on deck, the submarine needs around four hours to recharge its batteries and fill the compressed air tanks before programming a new immersion. If the submarine has collected specimens for in vivo study in the ICM’s aquariums, this is the moment to take them to the maintenance aquariums installed in the boat's laboratory, controlled at all times by the staff trained for maintaining and taking care of the organisms until the end of the campaign.
With the studies carried out in both the framework of the INDEMARES project and other previous studies, we can confirm that the coastal strip and the shelf of the Cap de Creus area has one of the highest levels of biological diversity in the Mediterranean. The general causes of this phenomenon of high diversity have been known for some time and are related to both high biological production, with a continued and intense hydrodynamism, to seasonal mixing of surface and deep waters and a big variety of geomorphologic structures on the seabed that provide a great diversity of habitats.
The new habitats associated to the concentration of species that have been discovered and studied during the last campaign, after prospecting new areas we had not worked on before, corroborate both the diversity of habitats and species in the area.
The study that is being carried out in the sphere of the INDEMARES project the extraordinary collaboration of several of the leading experts in Mediterranean biodiversity. Leading scientists such as Iosune Uriz, Mikel Zabala, Pablo J. López, Ana Sabatés, Rafael Sardá, Montserrat Ramón, Pere Abelló and Teresa Madurell, guarantee the outcome of the identifications of the samples and an objective and exhaustive approximation of the area’s biodiversity.