Abstract
Cladocora caespitosa is the only Mediterranean scleractinian similar to tropical reef-building corals. While this species is part of the recent fossil history of the Mediterranean Sea, it is currently considered endangered due to its decline during the last decades. Environmental factors affecting the distribution and persistence of extensive bank reefs of this endemic species across its whole geographic range are poorly understood. In this study, we examined the environmental response of C. caespitosa and its main types of assemblages using ecological niche modeling and ordination analysis. We also predicted other suitable areas for the occurrence of the species and assessed the conservation effectiveness of Mediterranean marine protected areas (MPAs) for this coral. We found that phosphate concentration and wave height were factors affecting both the occurrence of this versatile species and the distribution of its extensive bioconstructions in the Mediterranean Sea. A set of factors (diffuse attenuation coefficient, calcite and nitrate concentrations, mean wave height, sea surface temperature, and shape of the coast) likely act as environmental barriers preventing the species from expansion to the Atlantic Ocean and the Black Sea. Uncertainties in our large-scale statistical results and departures from previous physiological and ecological studies are also discussed under an integrative perspective. This study reveals that Mediterranean MPAs encompass eight of the ten banks and 16 of the 21 beds of C. caespitosa. Preservation of water clarity by avoiding phosphate discharges may improve the protection of this emblematic species.
Highlights
The Mediterranean Sea is considered a hotspot of biodiversity shaped by geological events, climatic changes and its narrow connection with the Atlantic Ocean (Boudouresque 2004; Templado 2014)
We examined the relationship between environmental parameters and the occurrence of C. caespitosa and that of its main types of assemblages using Ecological Niche Modelling (ENM) and ordination analysis
We found generalized linear models (GLMs) obtained a lower Akaike’s Information Criterion (AIC = 16) and fitted our data better (D2 = 100%) than quadratic and cubic smoothing splines used by generalized additive models (GAMs) (AIC = 68)
Summary
The Mediterranean Sea is considered a hotspot of biodiversity shaped by geological events, climatic changes and its narrow connection with the Atlantic Ocean (Boudouresque 2004; Templado 2014). Extensive coral reef systems developed in the Mediterranean during warm geologic periods (Dabrio et al 1981; Pomar 1991), but at the end of the Miocene the Mediterranean coral fauna underwent a drastic modification that led to the disappearance of almost all zooxanthellate corals and the well-established shallowwater coral reefs (Vertino et al 2014). The colonial zooxanthellate scleractinian Cladocora caespitosa is the only coral that can be considered as a remnant of the ancient Mediterranean reefs. C. caespitosa is, physiologically and morphologically, like the typical tropical reef-building corals in being zooxanthellate, colonial, and able to form extensive bioherms that may fuse in reef-like structures (Schuhmacher and Zibrowius 1985; Kružić et al 2008a)
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