The projected degradation of subtropical coral assemblages by recurrent thermal stress

Abstract

1. 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. 2. 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. 3. 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. 4. Across all coral taxa, projected stochastic growth rates (λ s) 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. 5. 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 This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Linking population size structure, heat stress and bleaching responses in a subtropical endemic coral

“…3). The low density of P. aliciae at mid-shelf islands suggests that, although the populations may be viable, they rely heavily on sporadic recruitment from outside, likely nearby sources, congruent with the findings of Cant et al (2020). Thermal stress associations were observed, whereby suppressed recruitment processes occurred during periods of high heat stress and even moderate levels of heat stress (Fig.…”

“…These dynamics are influenced by speciesspecific life history strategies and differential responses to stress events. Using advanced quantitative techniques, such as integral projection models, future population trajectories can be determined from basic demographic information on vital rates (survival, growth, reproduction, recruitment) (Cant et al 2020;Capdevila et al 2020). Moreover, shortlived changes to vital rates can drive transient population dynamics with long-term impacts on population persistence (Capdevila et al 2020).…”

“…Nonetheless, episodes of coral bleaching at high-latitudes are becoming increasingly severe, with localised minor events in the 1980s and 1990s (Cook et al 1990;Celliers and Schleyer 2002;Schleyer et al 2008;Hongo and Yamano 2013) superseded by more destructive events in the 2010s (Dalton and Carroll 2011;Harrison et al 2011;Kim et al 2019). These bleaching and mortality events have long-term implications on coral reef composition (Dalton and Carroll 2011;Hongo and Yamano 2013), population dynamics, and demographic processes (Cant et al 2020).…”

“…Here we investigate the population dynamics of the subtropical endemic coral Pocillopora aliciae (Schmidt-Roach et al 2013) in a region of rapidly changing climate in subtropical eastern Australia over a 10-yr period (2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019) during which this species suffered severe bleaching and mortality in response to heat stress (Kim et al 2019;Cant et al 2020). Specifically, we address three questions: (1) How do survival, growth, and recruitment vary temporally, as indicated by population size-frequency distributions?…”

Different population trajectories of two reef‐building corals with similar life‐history traits

“…By using reproductive data from a former study, we made an assumption that the fecundity of the studied coral species has not changed through time. This might be a reasonable assumption, and the approach was adopted in previous demographic studies (Cant et al, 2020;Elahi et al, 2016;Precoda et al, 2018). However, fecundity may have changed through time.…”