Abstract
Cladocora caespitosa is the only reef-forming zooxanthellate scleractinian in the Mediterranean Sea. This endemic coral has suffered severe mortality events at different Mediterranean sites owing to anomalous summer heat waves related to global climate change. In this study, we assessed genetic structure and gene flow among four populations of this species in the Western Mediterranean Sea: Cape Palos (SE Spain), Cala Galdana (Balearic Islands), Columbretes Islands, and L’Ametlla (NE Spain). The results obtained from Bayesian approaches, F ST statistics, and Bayesian analysis of migration rates suggest certain levels of genetic differentiation driven by high levels of self-recruitment, a fact that is supported by egg-retention mechanisms. Conversely, genetic connectivity among distant populations, even if generally low, seems to be related to sporadic dispersal events through regional surface currents linked to the spawning period that occurs at the end of summer-beginning of autumn. These features, together with a certain isolation of the Columbretes Islands, could explain the regional genetic differentiation found among populations. These results help to better understand population structure and connectivity of the species and will serve as an approach for further studies on different aspects of the biology and ecology of C. caespitosa.
Highlights
The Mediterranean Sea is a semi-enclosed sea that has been characterized as a ‘‘miniature ocean’’ responding quickly to changes in temperature and increases in extreme events (Lejeusne et al 2009)
After removing identical genotypes from all populations, except Cape Palos were no identical genotypes were found, a total of 101 unique genotypes were considered for the analyses: 33 in Cala Galdana, in Columbretes Islands, in L’Ametlla and 13 from Cape Palos (Table 1)
Our results suggest that the studied populations are highly dependent on self-recruitment, likely enhanced by the eggretention mechanisms of this species (Kruzic et al 2008a), all of which is reflected in this species’ the distribution and recruitment patterns (Kersting and Linares 2012; Kersting et al 2014b)
Summary
The Mediterranean Sea is a semi-enclosed sea that has been characterized as a ‘‘miniature ocean’’ responding quickly to changes in temperature and increases in extreme events (Lejeusne et al 2009). The decrease of the geographical range of C. caespitosa reefs in the Mediterranean with respect to its fossil distribution prompted Augier (1982) to include this coral in a list of marine species under extinction risk. This regression is still in progress, enhanced by mortality events that the coral has suffered in recent decades together with other threats such as the presence of invasive algal species (Kruzic et al 2008b; Kersting et al 2014a)
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