Delayed coral recovery in a warming ocean

Abstract

Climate change threatens coral reefs across the world. Intense bleaching has caused dramatic coral mortality in many tropical regions in recent decades, but less obvious chronic effects of temperature and other stressors can be equally threatening to the long-term persistence of diverse coral-dominated reef systems. Coral reefs persist if coral recovery rates equal or exceed average rates of mortality. While mortality from acute destructive events is often obvious and easy to measure, estimating recovery rates and investigating the factors that influence them requires long-term commitment. Coastal development is increasing in many regions, and sea surface temperatures are also rising. The resulting chronic stresses have predictable, adverse effects on coral recovery, but the lack of consistent long-term data sets has prevented measurement of how much coral recovery rates are actually changing. Using long-term monitoring data from 47 reefs spread over 10 degrees of latitude on Australia's Great Barrier Reef (GBR), we used a modified Gompertz equation to estimate coral recovery rates following disturbance. We compared coral recovery rates in two periods: 7 years before and 7 years after an acute and widespread heat stress event on the GBR in 2002. From 2003 to 2009, there were few acute disturbances in the region, allowing us to attribute the observed shortfall in coral recovery rates to residual effects of acute heat stress plus other chronic stressors. Compared with the period before 2002, the recovery of fast-growing Acroporidae and of "Other" slower growing hard corals slowed after 2002, doubling the time taken for modest levels of recovery. If this persists, recovery times will be increasing at a time when acute disturbances are predicted to become more frequent and intense. Our study supports the need for management actions to protect reefs from locally generated stresses, as well as urgent global action to mitigate climate change.

Spatial resilience of the Great Barrier Reef under cumulative disturbance impacts

“…Tropical cyclones were the strongest driver of coral cover on the GBR over the last 22 years, which stems from a combination of greater effect size and frequency compared to CoTS outbreaks or bleaching. Only a broad‐scale and high‐resolution approach such as ours that explicitly maps spatial variation across individual reefs could reveal these spatiotemporal patterns, because most of the cyclone impacts occurred within unmonitored reef sections (e.g., Figure S2) that were not considered in previous studies (De'ath et al, ; Osborne et al, ). The stronger effect size of cyclones likely reflects that cyclones typically alter habitat structural complexity immediately, unlike other disturbances that can leave coral skeletons intact (Osborne et al, ).…”

Demographic Mechanisms of Reef Coral Species Winnowing from Communities under Increased Environmental Stress

“…The principle of species winnowing by environmental disturbances is compatible with concepts like "winners and losers" in response to bleaching (Loya et al, 2001;vanWoesik et al, 2011). Concomitant changes in community structure are not merely theoretical expectations but have already been observed in PAG and elsewhere (Kayanne et al, 2002;Purkis and Riegl, 2005;McClanahan et al, 2011;Edmunds et al, 2014;Harii et al, 2014;McClanahan, 2014, among many others) and it has been shown that coral recovery is delayed in a warming ocean (Osborne et al, 2017). Our study demonstrates the primary mechanisms causing delayed recovery, namely reduced population fertility due to tissue death resulting in fewer, and smaller coral colonies (Figure 6B).…”

“…Temperature and photosynthetically active irradiation are key determinants of coral distribution and many future climate projections suggest physiologically unsustainable changes (Sheppard, 2003;Donner et al, 2005;vanHooidonk et al, 2013;Cacciapaglia and vanWoesik, 2015). This may alter geographic distributions of many coral species through increased frequency and severity of mortality (Jackson, 2001;Sheppard, 2003;Donner et al, 2005;Cacciapaglia and vanWoesik, 2015;Hughes et al, 2017a,b), retarded regeneration (Osborne et al, 2017), or range extension (Precht and Aronson, 2004;Yamano et al, 2011). Dramatic changes in community patterns have already been observed Hughes et al, 2017a).…”

Rethinking coral reef functional futures

“…These events are often overwhelming local management and environmental variability to cause mass coral mortality at unprecedented scales (Hughes, Kerry, et al, ) and reconfiguring entire reef assemblages (Hughes, Kerry, et al, ; Stuart‐Smith, Brown, Ceccarelli, & Edgar, ). Despite the potential for recovery between bleaching events (Gilmour, Smith, Heyward, Baird, & Pratchett, ; Graham, Jennings, MacNeil, Mouillot, & Wilson, ; Sheppard, Harris, & Sheppard, ), global climate change model projections predict a continued diminishing return time of coral bleaching events in the coming decades (van Hooidonk et al, ) that will severely challenge the capacity for reef recovery (Osborne et al, ). It is unequivocal that coral reefs have entered the Anthropocene (Hughes, Barnes, et al, ; Norström et al, ), an epoch where humans are the dominant force of planetary change.…”