Severe coral bleaching of Siderastrea stellata at the only atoll in the South Atlantic driven by sequential Marine Heatwaves

Abstract

Threatened by global warming and extreme climatic events, such as El Niño Southern Oscillation (ENSO) and Marine Heatwaves (MHW), coral reefs worldwide faced the worst bleaching and mortality event between 2014 and 2017, induced by the 2015/2016 ENSO. We evaluated the impacts of ENSO and MHW episodes on bleaching and mortality frequencies of Siderastrea stellata at Rocas Atoll, Southwestern Atlantic, using visual censuses conducted in 2016, 2017 and 2019. Bleaching rate varied significantly along the sampling period (11.71% in 2016, 1.52% in 2017, and 88% in 2019), but mortality was always less than 4%. Bleaching events in Atlantic reefs have been constantly associated with ENSO, until these recent events of the last two years. We suggest that MHW were probably the primary driver of the observed bleaching, especially in 2019, when much higher bleaching rates were observed than in ENSO periods. Although Southwestern Atlantic massive corals are considered more resistant to thermal stress than reefs corals worldwide, the strong events registered since 2019 highlight the need for continuous monitoring to better understand coral bleaching dynamics and improve predictions on the effects of global change in the region.

bnormal average increase in sea surface temperature may promote the first documented mortality event of a marine sponge in the Southeastern Brazil

“…However, an exceptional average increase of 2 °C in the SST since 2015 at Ilha Grande Bay (SE Brazil) and the species death are facts. Also, this year had extreme heat waves episodes that severely impacted Brazilian fauna in both Northeast (Duarte et al 2020;Gaspar et al 2021) and Southeast regions (Santos et al 2021). In contrast to the survival of sponge assemblages after ENSO (Kelmo et al 2013), Gaspar et al (2021) suggests a higher impact on corals when ENSO and longer heat waves occur sequentially.…”

“…South Atlantic marine ecosystems have been documented as less impacted than Indo-Pacific and Caribbean ones in relation to thermal stress events (Baird and Marshall 2002;Perry et al 2013;Kelmo et al 2013;DeCarlo et al 2017;Hughes et al 2018;Mies et al 2020). However, the impact of climate changes within Brazilian ZEE is poorly understood, with only local evidence of severe impacts on marine biota (Coutinho et al 2016;Teixeira et al 2019Teixeira et al , 2021Duarte et al 2020;Gaspar et al 2021). At Rio de Janeiro state, for example, Carvalho (2019) observed a persistent increase in air temperature overtaking 40 °C at Marambaia barrier island from September to February (austral spring and summer) in the XXI century, Skinner (2018a, b) have detected 33 ºC for SST with sensor in situ, in two sites of Ilha Grande Bay (IGB), from 2012 to Coutinho et al (2016) documented SST overtaking the daily range of 30 °C at Arraial do Cabo (RJ), a coastal city with historical predominance of cold waters, due to the influence of a strong upwelling during spring and summer months (Valentin 2001).…”

“…The year of 2019 was exceptionally hot in Brazil causing an unprecedented mass mortality event on the major reef building hydrocoral Millepora alcicornis (Linnaeus, 1758) at the biggest coral reef of the South Atlantic, Abrolhos (Duarte et al 2020), on the endemic coral species Siderastrea stellata Verrill, 1868 in the Rocas Atoll (Gaspar et al 2021), and bleaching on cnidarians in Rio de Janeiro, Southeast Brazil (Santos et al 2021). This heat wave throughout the year may also have caused a population decline and the first documented mortality event on the marine sponge species Desmapsamma anchorata (Carter, 1882) in the Southwestern Atlantic, Rio de Janeiro, IGB (Figure 1).…”

A Functional Perspective for Reef Benthic Communities: Temporal Trends in the Only Atoll in Southern Atlantic

“…In this context, a long-term ecological research can help to ful ll gaps of knowledge in understanding reef communities' spatiotemporal patterns in the Brazilian oceanic islands. All four Brazilian oceanic island are Marine Protected Areas, nevertheless, some are already impacted by over shing, tourism (Giglio et al 2018) and by coral bleaching events associated to thermal anomalies (Ferreira et al 2013;Gaspar et al 2021). These phenomena jeopardize reef biodiversity, and ecosystem functions and services (Hughes et al 2018a;.…”

“…carbonate accretion), and hence cause erosions in FRic and even smaller FEnt values. Indeed, a strong bleaching event has stricken Rocas Atoll bioconstructors recently(Gaspar et al 2021). Therefore, reef communities are expected to show changes in the next years.…”