Decadal stability of coral reef benthic communities on Palmyra Atoll, central Pacific, through two bleaching events

Abstract

The prevalence of coral bleaching due to thermal stress has been increasing on coral reefs worldwide. While many studies have documented how corals respond to warming, fewer have focused on benthic community responses over longer time periods or on the response of non-coral taxa (e.g., crustose coralline algae, macroalgae, or turf). Here, we quantify spatial and temporal changes in benthic community composition over a decade using image analysis of permanent photoquadrats on Palmyra Atoll in the central Pacific Ocean. Eighty permanent plots were photographed annually between 2009 and 2018 on both the wave-exposed fore reef (FR, 10 m depth, n = 4 sites) and the wave-sheltered reef terrace (RT, 5 m depth, n = 4 sites) habitats. The El Niño events of 2009–2010 and 2015–2016 resulted in acute thermal stress and coral bleaching was observed at both reef habitats during these events. Across 10 yr and two bleaching events, the benthic community structure on Palmyra shows evidence of long-term stability. Communities on the RT exhibited minimal change in percent cover of the dominant functional groups, while the FR had greater variability and minor declines in hard coral cover. There was also spatial variation in the trajectory of each site through time. Coral cover decreased at some sites 1 yr following both bleaching events and was replaced by different algal groups depending on the site, yet returned to pre-bleaching levels within 2 yr. Overall, our data reveal the resilience of calcifier-dominated coral reef communities on Palmyra Atoll that have persisted over the last decade despite two bleaching events, demonstrating the capacity for these reefs to recover from and/or withstand disturbances in the absence of local stressors.

Coral adaptive capacity insufficient to halt global transition of coral reefs into net erosion under climate change

“…Given the near-term threat to coral reefs, there is increasing attention to active management interventions which can help coral reefs and the services they provide persist in the face of climate change (Hoegh-Guldberg et al, 2018). For example, climate-smart marine-protected area design can focus on locations which may be more resilient to heat stress due to frequent exposure to heat stress (Beyer et al, 2018;Khen et al, 2022) The results of this study indicate that efforts to restore coral reefs by propagating heat-tolerant taxa, species or populations should also select those with high rates of NCCP and morphologies favouring reef accretion. Otherwise, active restoration efforts may be unsuccessful at maintaining positive NCCP and key ecosystem services like wave attenuation and habitat provision.…”

“…Given the near‐term threat to coral reefs, there is increasing attention to active management interventions which can help coral reefs and the services they provide persist in the face of climate change (Hoegh‐Guldberg et al, 2018). For example, climate‐smart marine‐protected area design can focus on locations which may be more resilient to heat stress due to frequent exposure to heat stress (Beyer et al, 2018; Khen et al, 2022), local meteorological or oceanographic conditions (Gonzalez‐Espinosa & Donner, 2021; Storlazzi et al, 2020), or presence of sufficient coral cover (e.g. Darling et al, 2019).…”

Ocean currents magnify upwelling and deliver nutritional subsidies to reef-building corals during El Niño heatwaves

“…A central challenge in coral reef science is disentangling how natural physical drivers and anthropogenic drivers interact across scales and background conditions to influence differences in ecosystem response to bleaching (47). While many reefs are showing signs of rapid change and reorganization following repeated mass bleaching, some like Palmyra appear to positively deviate from the global trend (39,48). Our results underscore the need to consider the connected roles of regional and local oceanographic processes in driving on-reef biological mechanisms that may underpin such DCH provides an integrated upwelling metric that accounts for both the magnitude and duration of cold pulses such that a cold pulse that reduces temperature by 2°C and lasts for 2 hour is equal to 4 DCHs.…”