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Model species

Cladocora caespitosa

Cladocora caespitosa has a slow growth rate and high longevity. It is the only Mediterranean endemic coral that can form major bioconstructions at a range of 5–20 metres of depth. These characteristics confer an extraordinary value to this species as a paleoclimatic proxy of the environmental fluctuations and perturbations that affected the Mediterranean in the past. Unfortunately, most of the largest formations of Cladocora have disappeared. Major formations only remain in some areas of the Mediterranean coast, such as Croatia or the Columbretes Islands. Nevertheless, individual colonies of C. Caespitosa can be found all along the Mediterranean coast. In recent years, this species has been significantly affected by recurring mass mortality events caused by episodes of water warming, and by the presence of invasive species such as Caulerpa racemosa or Lophocladia lallemandii. To guarantee the conservation of these exceptional populations, MedRecover is focusing its studies on understanding basic aspects of the biology and ecology of C. caespitosa, and on assessing the effect of impacts on their populations.

 

 

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Gorgonian species

MedRecover mainly works with three gorgonian species: red gorgonian Paramuricea clavata, white gorgonian Eunicella singularis and red coral Corallium rubrum. The distribution of these species is basically restricted to the Mediterranean, where they usually form dense populations that thrive at a range of 0–100 m depth. These species also contribute greatly to the aesthetic value of the Mediterranean sublittoral zone and attract high numbers of recreational divers. In recent years, gorgonian populations have suffered from the recurrent impact of strong disturbances, such as the direct and indirect effects of fisheries, invasive species, the presence of divers and mass mortality events associated with an unusual increase in water temperature. These disturbances have severe consequences on the viability of the populations, due to their longevity (they may be dozens to hundreds of year old) and slow population dynamics. MedRecover contributes to the conservation of these populations by studying their ecology, developing population viability models, analysing their genetic structure and investigating basic aspects of their biology.

 

 

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Cystoseira species

The Cystoseira genus (Fucales, Phaeophyceae) is formed by about 60 species, which are distributed worldwide. There are 30 species in the Mediterranean, 24 of which are endemic. These species characteristically display a perennial axis that is fixed to the substrate, from which branches grow seasonally. Due to their arboreal structure, they are considered key species in algae communities, since they provide high structural complexity (they form miniature forests). This enhances the diversity of associated species, where more than 160 taxons have been counted. Moreover, the different species of Cystoseira are adapted to a wide range of environmental conditions. They can be found in rough and calm areas, in shallow waters and at depths of over 50 metres.

Due to their perennial growth, these species and the communities that they form, particularly those adapted to deep and extreme environments are highly sensitive to changes. Physical disturbances caused by erosion or urchin overgrazing, competition with invasive species, or more diffused factors such as pollution, sedimentation and water turbidity, are all factors that can compromise the survival of these species. In fact, in areas affected by any of these disturbances, communities dominated by Cystoseira have disappeared and have been replaced by fast-growing and seasonal species, which provide less structure and diversity.

MedRecover is involved in long-term experiments on the effects of urchin overgrazing in communities dominated by Cystoseira balearica, which form dense shallow forests (10–15m). These involve experimental sea urchin eradications. Moreover, MedRecover participates in surveys of Cystoseira populations (C. spinosa and C. zosteroides) that thrive at 30–50m in several protected marine areas.

 

 

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Spiny lobster (Palinurus elephas)

The most emblematic species of all the large Mediterranean decapods is the European spiny lobster Palinurus elephas. This species, the most valuable commercial crustacean,  now shows clear signs of overexploitation. The actual fishery regulations seem not to be enough for maintaining the species as a marine resource. Therefore, it is urgent to promote management measures for its conservation. One of the main difficulties in its conservation is the lack of knowledge on several aspects of lobster ecology. Just a few years ago, MedRecover described the settlement processes and ecology of the juvenile phase, which was totally unknown. This opened up a field of study that enables us to understand the processes of dispersion, the connectivity between diverse populations and the influence of settlement variability on exploited populations. These studies, in conjunction with long-term surveys of lobster populations in various marine reserves in the western Mediterranean, provide key data for establishing recommendations to improve lobster management as a fishery resource. The adoption of these measures should favour conservation and contribute to the recovery of depleted populations.

 

 

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Benthic fishes

Over 700 fishes have been identified in the Mediterranean. About 60 of these species are endemic and over 100 are introduced species. The Mediterranean has been ancestrally fished. Intensive fishing has reduced the populations of many species, which are now overexploited or ecologically extinct. In particular fishing activities have led to the scarcity of large predators in extensive sectors of the coast. The predators that have been affected include groupers (Epinephelus spp.) and other highly prized species. Overfishing does not only affect the species that are directly exploited, it also produces secondary “cascade” effects, which cause changes at different trophic levels. For instance, the lack of fishes controlling sea urchin populations can transform algae forests into bald rocky areas with low algal coverage, the so-called sea urchin barrens.

MedRecover’s studies have highlighted that marine reserves can help to preserve the population of the most vulnerable species and to favour the repopulation of fishing areas.

 

 

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Sea-urchin Paracentrotus lividus

Sea urchins are considered the most important herbivorous species in temperate seas. In the western Mediterranean, Paracentrotus lividus is one the most common species and depending on their abundance, this herbivore is capable of determining the composition and dynamics of algal communities.Therefore is considered a key species for the functioning of rocky coastal ecosystems. In many Mediterranean areas, populations of this species have dramatically increased due to the decrease in the number of fish – their main predators – as a result of overfishing. An increase in urchin populations can lead to well-developed algal communities being transformed into overgrazed communities with very low diversity. On the other hand, sea urchins, as the main generalist herbivore in the NW Mediterranean may play a paramount role on seaweeds invasions by modifying the strength and direction of interactions between native and invasive algae. Thus, knowledge of urchin population dynamics is essential to the conservation of marine coastal ecosystems.

Nevertheless, other processes such as recruitment, post-settlement mortality, behaviour or infrequent disturbances such as diseases or storms can affect the abundance of this species. The combination of experimental studies with a survey of natural populations at suitable spatial and temporal scales gives us a better understanding of the population dynamics and the relative importance of each of these factors.

 

 

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