Mass mortality events of the coral Balanophyllia europaea (Scleractinia, Dendrophylliidae) in the Mljet National Park (eastern Adriatic Sea) caused by sea temperature anomalies
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Recurrent climate-induced mass mortalities of marine animals have been recorded in the Mediterranean Sea over the past 15 years. These mortality outbreaks have been associated with positive thermal anomalies. In this study, we assessed long-term (from 2003 to 2013) responses of the temperate coral Balanophyllia europaea to increasing seawater temperatures in the Mljet National Park in the Adriatic Sea (Northern Mediterranean Sea) and described the relationship between recurrent mortality events and sea temperature regimes in the southern Adriatic Sea. Our results indicate that polyp bleaching and tissue necrosis caused the observed mortality. The first observations of B. europaea mortality within the study area in the Mljet NP were in early September 2003. The Mediterranean area experienced high temperatures and hydrographic stability over a period of several weeks throughout that summer, which resulted in a mass mortality event. In the Mljet National Park, the highest impact of mass mortality started during the exceptionally hot summer of 2012, representing one of the most severe mass mortality events ever observed in the Adriatic Sea. In 2012, sea temperatures at a 5 m depth during the summer period (from June to September) ranged from 24.44 to 30.16 °C in the Mljet NP. The northern sites in the Mljet NP were highly impacted, with up to 80 % of B. europaea specimens affected by necrosis, while the southern sites displayed the highest impact, with 90–100 % of affected individuals. Without any coral adaptation to warming and under the present climate-warming trend, new mass mortality events may occur in the near future, possibly causing a major coral biodiversity crisis in the Mediterranean Sea.
KeywordsSea temperature anomaly Balanophyllia europaea Mass mortality Climate change Adriatic Sea
The authors wish to thank Dr. Dušan Zavodnik from the Rovinj Research Centre and Dr. Helmut Zibrowius from Centre d’Océanologie de Marseille (France) for their helpful suggestions and support. Special thanks go to Dr. Hrvoje Mihanović from the Hydrographic Institute of the Republic of Croatia (HHI) for help with sea temperature data. We also thank the staff of Mljet National Park for fieldwork support and laboratory help.
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