Early trajectories of benthic coral reef communities following the 2015/16 coral bleaching event at remote Aldabra Atoll, Seychelles

Abstract

Documenting post-bleaching trajectories of coral reef communities is crucial to understand their resilience to climate change. We investigated reef community changes following the 2015/16 bleaching event at Aldabra Atoll, where direct human impact is minimal. We combined benthic data collected pre- (2014) and post-bleaching (2016–2019) at 12 sites across three locations (lagoon, 2 m depth; seaward west and east, 5 and 15 m depth) with water temperature measurements. While seaward reefs experienced relative hard coral reductions of 51–62%, lagoonal coral loss was lower (− 34%), probably due to three-fold higher daily water temperature variability there. Between 2016 and 2019, hard coral cover did not change on deep reefs which remained dominated by turf algae and Halimeda, but absolute cover on shallow reefs increased annually by 1.3% (east), 2.3% (west) and 3.0% (lagoon), reaching, respectively, 54%, 68% and 93% of the pre-bleaching cover in 2019. Full recovery at the shallow seaward locations may take at least five more years, but remains uncertain for the deeper reefs. The expected increase in frequency and severity of coral bleaching events is likely to make even rapid recovery as observed in Aldabra’s lagoon too slow to prevent long-term reef degradation, even at remote sites.

First insights into coral recruit and juvenile abundances at remote Aldabra Atoll, Seychelles

“…For the purposes of this study, the 2 m and 5 m depths are referred to as ‘shallow’ and 15 m as ‘deep’. The division of the seaward reef sites into ‘west’ and ‘east’ is based on the different wind and wave exposure on either side of Aldabra and the differing benthic community compositions [ 34 ]. Although both locations are subject to strong currents, the north-west and west of Aldabra are relatively sheltered throughout most of the year, while the north-east, east and south-east are more exposed to strong winds and high wave energy [ 36 ].…”

“…Its marine ecosystem has therefore been protected from commercial fishing pressure for almost 40 years, there is no coastal development, and human-driven nutrient inputs are absent. Nevertheless, coral bleaching events have caused high coral mortality at Aldabra in 1998/1999 (38–66% mortality at 10–20 m water depth [ 32 ]) and in 2015/2016 (34–62% mortality at 2–15 m water depth [ 33 , 34 ]). Furthermore, while the reefs at 2–5 m water depth recovered 54–93% of their pre-bleaching (2015/2016) coral cover by 2019, no recovery was observed at 15 m water depth [ 34 ].…”

Coral bleaching occurrence along the Egyptian coast of the Red Sea during the summer heat stress period, 2020

“…In contrast, the recorded bleaching pattern provides filed evidence on the buffering properties of the northern region to the heat stress and underpins the potential role of this region as a natural coral refuge (Osman et al, 2018). In the light of the knowledge that the severity of bleaching can affect the structure of the reef and delay its recovery rate (Berumen et al, 2019;Koester et al, 2020), our study underlines that the frequency of the heat stress episodes may threaten corals over the time and can drive acute effects on the Egyptian reefs, especially at the southern coast.…”

Vulnerability of fishery-based livelihoods to climate variability and change in a tropical island: insights from small-scale fishers in Seychelles

“…Bleaching was particularly severe in the Indian Ocean, with post-bleaching levels of mortality reaching as much as 90% in parts of eastern Africa and the Maldives and 50-90% over extensive areas of shallow reefs in the Seychelles, Comoros, Madagascar and Chagos [83]. The Seychelles suffered another coral bleaching event in 2016 and the resilience of coral is much better in areas with minimal human activities [84]. Aside from ocean warming and its effect on the fishery sector, climate change manifesting through global warming thereby resulting in sea level rise [85,86].…”