Abstract
The IPCC predicted that ocean surface temperature will rise of 0.6-2.0 °C by 2100. Ocean warming is expected to produce strong impacts on marine ecosystems such as coral reefs, affecting their physiological events including reproductive processes. To date, relatively few studies have examined the effects of climate change on the reproductive success of temperate corals and even less in the azooxanthellate ones. This study examined the reproductive output of the azooxanthellate Mediterranean coral Caryophyllia inornata along a wide latitudinal gradient of seawater temperature and solar radiation. A total of 260 samples, collected from five populations along the Western Italian coast, have been analyzed through histological techniques. The intriguing aspects characterizing all populations of C. inornata along the latitudinal gradient are a strong male-biased sex ratio and the presence of embryos in all stages of development throughout the year in females, males and sexually inactive individuals. This peculiarity could suggest a mixed strategy of sexual and asexual reproduction in this species as has been observed for some anemones of the genus Actinia. Fecundity and spermary abundance (i.e., the number of reproductive elements per body volume unit), gonadal index (i.e., the percentage of body volume occupied by the germ cells) and fertility (i.e., the number of embryos per body volume unit) in females, males and sexually inactive individuals were unrelated to solar radiation and temperature along the latitudinal gradient. Only gamete diameters were influenced by environmental parameters but without a clear trend, suggesting that C. inornata is tolerant to increased solar radiation and temperature. The lack of zooxanthellae could make this species less dependent on these environmental parameters, as previously hypothesized for another azooxanthellate species, Leptopsammia pruvoti, investigated along the same gradient.
Highlights
Climate change is today one of the most serious threats to the biodiversity of our planet
Climatic models predict a greater influence of the global warming in the temperate areas than tropical ones (IPCC, 2014)
The present study examined the azooxanthellate solitary coral Caryophyllia inornata, which is widely distributed in the eastern and western Mediterranean Sea (Zibrowius, 1980), extending to the northeast of the Atlantic coast (Cairns, 1999) and from the Canary Islands to the southern coasts of England (Zibrowius, 1980)
Summary
Climate change is today one of the most serious threats to the biodiversity of our planet. According to the Intergovernmental Panel on Climate Change (IPCC), ocean warming is severely impacting marine ecosystems, which are among the most ecologically and socio-economically vital on the planet (Harley et al, 2006). Climatic models predict a greater influence of the global warming in the temperate areas than tropical ones (IPCC, 2014). The warming rates of the Mediterranean Sea are three times higher than those of the oceans (IPCC, 2014). These traits make the Mediterranean Sea one of the most emblematic natural model for studying the interactions between marine life and environmental changes (Feely et al, 2004; Lejeusne et al, 2010)
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