Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 14, 817-826, 2017
http://www.biogeosciences.net/14/817/2017/
doi:10.5194/bg-14-817-2017
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
24 Feb 2017
Coral mortality induced by the 2015–2016 El-Niño in Indonesia: the effect of rapid sea level fall
Eghbert Elvan Ampou1,2,3, Ofri Johan4, Christophe E. Menkes5, Fernando Niño3, Florence Birol3, Sylvain Ouillon3, and Serge Andréfouët1,2 1UMR9220 ENTROPIE, Institut de Recherche pour le Développement, Université de la Réunion, CNRS, B.P.A5, 98848, Noumea, New Caledonia
2Institute for Marine Research and Observation, SEACORM/INDESO center, Jl. Baru Perancak, Negara-Jembrana, Bali 82251, Indonesia
3Laboratoire d'Etudes en Géophysique et Océanographie Spatiales, Université de Toulouse, CNRS, IRD, CNES, UPS, 14 avenue Edouard-Belin, 31400 Toulouse, France
4Research and Development Institute for Ornamental Fish Culture, Jl. Perikanan No. 13, Pancoran Mas, Kota Depok, Jawa Barat 16436, Indonesia
5Laboratoire d'Océanographie et du Climat: Expérimentations et Approches Numériques, Sorbonne Universités, UPMC Université Paris 06, IPSL, UMR CNRS/IRD/MNHN, B.P.A5-98848, Noumea, New Caledonia
Abstract. The 2015–2016 El-Niño and related ocean warming has generated significant coral bleaching and mortality worldwide. In Indonesia, the first signs of bleaching were reported in April 2016. However, this El Niño has impacted Indonesian coral reefs since 2015 through a different process than temperature-induced bleaching. In September 2015, altimetry data show that sea level was at its lowest in the past 12 years, affecting corals living in the bathymetric range exposed to unusual emersion. In March 2016, Bunaken Island (North Sulawesi) displayed up to 85 % mortality on reef flats dominated by Porites, Heliopora and Goniastrea corals with differential mortality rates by coral genus. Almost all reef flats showed evidence of mortality, representing 30 % of Bunaken reefs. For reef flat communities which were living at a depth close to the pre-El Niño mean low sea level, the fall induced substantial mortality likely by higher daily aerial exposure, at least during low tide periods. Altimetry data were used to map sea level fall throughout Indonesia, suggesting that similar mortality could be widespread for shallow reef flat communities, which accounts for a vast percent of the total extent of coral reefs in Indonesia. The altimetry historical records also suggest that such an event was not unique in the past two decades, therefore rapid sea level fall could be more important in the dynamics and resilience of Indonesian reef flat communities than previously thought. The clear link between mortality and sea level fall also calls for a refinement of the hierarchy of El Niño impacts and their consequences on coral reefs.

Citation: Ampou, E. E., Johan, O., Menkes, C. E., Niño, F., Birol, F., Ouillon, S., and Andréfouët, S.: Coral mortality induced by the 2015–2016 El-Niño in Indonesia: the effect of rapid sea level fall, Biogeosciences, 14, 817-826, doi:10.5194/bg-14-817-2017, 2017.
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The 2015–2016 El Niño was the strongest on record and has generated significant coral bleaching and mortality worldwide. In Indonesia, first signs of bleaching were reported in April 2016. However, we show that this El Niño has impacted Indonesian reefs since 2015 through a different process than temperature-induced bleaching. Another El Niño-induced process, sea level fall, is responsible for significant coral mortality on North Sulawesi shallow reefs, and probably throughout Indonesia.
The 2015–2016 El Niño was the strongest on record and has generated significant coral bleaching...
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