Abstract
Subtropical coral assemblages are threatened by similar extreme thermal stress events to their tropical counterparts. Yet, the mid- and long-term thermal stress responses of corals in subtropical environments remain largely unquantified, limiting our capacity to predict their future viability. The annual survival, growth and recruitment of 311 individual corals within the Solitary Islands Marine Park (Australia) was recorded over a 3-year period (2016-2018), including the 2015/2016 thermal stress event. These data were used to parameterise integral projection models quantifying the effect of thermal stress within a subtropical coral assemblage. Stochastic simulations were also applied to evaluate the implications of recurrent thermal stress scenarios predicted by four different Representative Concentration Pathways. We report differential shifts in population growth rates (λ) among coral populations during both stress and non-stress periods, confirming contrasting bleaching responses among taxa. However, even during non-stress periods, the observed dynamics for all taxa were unable to maintain current community composition, highlighting the need for external recruitment sources to support the community structure. Across all coral taxa, projected stochastic growth rates (λs ) were found to be lowest under higher emissions scenarios. Correspondingly, predicted increases in recurrent thermal stress regimes may accelerate the loss of coral coverage, species diversity and structural complexity within subtropical regions. We suggest that these trends are primarily due to the susceptibility of subtropical specialists and endemic species, such as Pocillopora aliciae, to thermal stress. Similarly, the viability of many tropical coral populations at higher latitudes is highly dependent on the persistence of up-current tropical systems. As such, the inherent dynamics of subtropical coral populations appear unable to support their future persistence under unprecedented thermal disturbance scenarios.
Highlights
Climate change and anthropogenic disturbance are reshaping the structure of biological communities and modifying the global distribution of abiotic regimes (Newman, 2019; Pecl et al, 2017)
The greatest effect occurred in P. aliciae, with scenarios of heightened carbon emissions resulting in a severe reduction in λs
We demonstrate that despite prior exposure to variable abiotic environments, and a slow pace of thermal stress increase, subtropical coral assemblages will likely be subject to substantial degradation by future recurrent thermal stress events
Summary
Climate change and anthropogenic disturbance are reshaping the structure of biological communities and modifying the global distribution of abiotic regimes (Newman, 2019; Pecl et al, 2017). Despite comprehensive evidence of climate stress impacting reefs (Hughes et al, 2019; Hughes, Kerry, et al, 2018), we lack the mechanistic understanding to predict how changing environments will affect global coral population dynamics (Edmunds & Riegl, 2020) It is crucial we define the link between environmental conditions and population performance, and identify drivers enhancing the resilience of corals to future e nvironmental shifts (Benton et al, 2006; Darling & Côté, 2018). The genus-specific collapse and recovery responses of subtropical corals and their drivers, following thermal stress events, remain largely unknown (Kim et al, 2019) This limited perspective regarding the future viability and condition of subtropical coral communities around the globe is hindering our capacity to predict their future and manage them effectively. | Journal of Animal Ecolo gy 3 conducted stochastic projections to investigate the effects of future thermal stress patterns, predicted by the different representative concentration pathways (RCPs), on the long-term condition of a subtropical coral assemblage
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