Studying anthropogenic climate change in the Mediterranean Sea beyond instrumental data: the temperate coral Cladocora caespitosa as bioindicator and archive of environmental and ecological changes
Final Report Abstract
The main objective of this project was to develop the Mediterranean reef-builder coral Cladocora caespitosa as an archive of environmental and ecological information to study and contextualize climate change impacts in the Mediterranean Sea. The main innovation in this project is related to using the same organism as living bioindicator of climate change impacts and as an archive of past environmental conditions and ecological processes. With the support of using the longest coral monitoring and local temperature data series existing in the Mediterranean Sea (developed by PI D.K. Kersting), which in addition offer a unique calibration set. Different approaches were used to obtain information to reconstruct environmental and ecological variables. From X-rays and CT-scans to reconstruct growth rates, skeletal stress markers and recovery structures, to geochemical analyses (stable isotopes and trace elements) to reconstruct environmental and ecological conditions. The reanalysis of the long-term data series on coral mortality and local water temperature showed how the association between positive thermal anomalies and coral mortality has persisted throughout the series, from 2002 to 2019. In relation to these mortalities, this project, together with the information obtained from the long-term coral monitoring in the Columbretes Islands (NW Mediterranean Sea), has allowed to discover a new survival and recovery strategy in extant corals. This process, called rejuvenescence, was only known from Paleozoic corals and our findings show its triggering causes and ecological role in front of climate change. This discovery opens new lines of research in paleoecology, the evolution of corals, and the responses of corals to climatic changes. High resolution sampling of C. caespitosa skeletons using classical methods (drilling) to undertake stable isotopes analyses was unfeasible because of the slow growth rates of this coral. To overcome this problem, we developed a new methodology that allowed sampling the skeleton in intervals of 50 µm, significantly increasing sampling resolution of classical methods. In addition, this methodology is transferable to slow-growing corals with fragile skeletons (incl. fossils) and to other calcareous organisms (e.g., bivalves). Applying this method, we achieved at least fortnightly resolution in δ18O and δ13C, which showed seasonal cycles associated to temperature and photosynthetic activity, respectively, both in extant and fossil corallites. Trace elements were sampled by laser ablation and seasonal cycles were found in Li/Ca, Ba/Ca, Sr/Ca, Mg/Ca and U/Ca, as well both in extant and fossil corallites. Intra and inter-colony variability in stable isotopes and trace elements was assessed for the first time in this coral species and we developed composite records to overcome errors associated to reconstructions using single corallites.
Publications
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(2019) Living evidence of a fossil survival strategy raises hope for warming-affected corals. Science Advances 5:eaax2950
Kersting DK, Linares C
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Ecology, paleontology and geochemistry meet to assess climate change in the Mediterranean Sea. 5th Young Earth Scientists Congress. Berlin, 2019
Kersting DK
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Interdisciplinary long-term monitoring of a “living fossil”. 1st Meeting of the Iberial Ecological Society. Barcelona, 2019
Kersting DK, Linares C, Brachert T, Hathorne EC, Leinfelder R, Montagna P, Pretus JLl, Reuning L, Spreter P, Zinke J
