Coral mortality induced by the 2015–2016 El-Niño in Indonesia: the effect of rapid sea level fall

Abstract

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.

Environmental Drivers of Variation in Bleaching Severity of Acropora Species during an Extreme Thermal Anomaly

“…The absence of a depth effect also demonstrates that abnormally low sea levels were not the cause of coral bleaching at our study location. Although low sea levels due to El Niño Southern Oscillation have been associated with a local coral mortality event in Indonesia (Ampou et al, 2017), a strong depth-dependent pattern of bleaching severity, with higher severity in the shallowest depths (i.e., <1 m depth), would be expected in areas where coral bleaching was caused by tidal emersion.…”

A comparison between the 2010 and 2016 El-Ninō induced coral bleaching in the Indonesian waters

“…Several scientific papers are also beginning to emerge [31,[33][34][35][36]. The longest and the most extensive bleaching event on record in 2015/16, that impacted some reefs of Indonesian waters, was reported by various organizations as in 2010 but so far only one paper was issued [6].…”

“…When corals are in a stressful condition due to sea temperature rise during El-Nino event, corals expel their symbiont, a single-cell micro algae genus Symbiodinium known as zooxanthellae, which lives in coral tissues [1,6,[8][9][10][11]. As a consequence, the variation and the beautiful color of corals become white, pale, or purple as the color of limestone, the skeleton of corals.…”

Pemutihan Karang Akibat Pemanasan Global Tahun 2016 Terhadap Ekosistem Terumbu Karang: Studi Kasus Di TWP Gili Matra (Gili Air, Gili Meno dan Gili Trawangan) Provinsi NTB

“…Genera Heliopora yang merupakan jenis karang ahermatipik juga mengalami pemutihan akibat pemanasan global dan merupakan salah satu ancaman genus ini selain dari penyakit [39]. Hasil penelitian [19] juga memperlihatkan genus Heliopora mengalami bleaching di Pulau Bunaken. e-0,6 , P<0,001) namun tidak berbeda signifikan (P>0,05) antar lokasi maupun antar pulau.…”

“…Pemutihan karang masal tercatat tahun 1982-1983 [16] selanjutnya tahun 1998 [17] dan 2010 [18]. El Nino yang terjadi tahun 2015-2016 menyebabkan kematian dan pemutihan karang yang signifikan di seluruh dunia [19] yang menyebabkan beberapa daerah di perairan Indonesia mengalami perubahan suhu permukaan laut seperti di Aceh, Karimunjawa, Lombok, Sulawesi, dan daerah lainnya [20] termasuk TWP Gili Matra di dalamnya.…”