Response diversity in corals: hidden differences in bleaching mortality among cryptic Pocillopora species

Abstract

Variation among functionally similar species in their response to environmental stress buffers ecosystems from changing states. Functionally similar species may often be cryptic species representing evolutionarily distinct genetic lineages that are morphologically indistinguishable. However, the extent to which cryptic species differ in their response to stress, and could therefore provide a source of response diversity, remains unclear because they are often not identified or are assumed to be ecologically equivalent. Here, we uncover differences in the bleaching response between sympatric cryptic species of the common Indo-Pacific coral, Pocillopora. In April 2019, prolonged ocean heating occurred at Moorea, French Polynesia. 72% of pocilloporid colonies bleached after 22 days of severe heating (>8 C-days) at 10 m depth on the north shore fore reef. °C olony mortality ranged from 11% to 42% around the island four months after heating subsided. The majority (86%) of pocilloporids that died from bleaching belonged to a single haplotype, despite twelve haplotypes, representing at least five species, being sampled. Mitochondrial (open reading frame) sequence variation was greater between the haplotypes that experienced mortality versus haplotypes that all survived than it was between nominal species that all survived. Colonies >30 cm in diameter were identified as the haplotype experiencing the most mortality, and in 1125 colonies that were not genetically identified, bleaching and mortality increased with colony size. Mortality did not increase with colony size within the haplotype suffering the highest mortality, suggesting that sizedependent bleaching and mortality at the genus level was caused instead by differences among cryptic species. The relative abundance of haplotypes shifted between February and August, driven by declines in the same common haplotype for which mortality was estimated directly, at sites where heat accumulation was greatest, and where larger colony sizes occurred. The identification of morphologically indistinguishable species that differ in their response to thermal stress, but share a similar ecological function in terms of maintaining a coral-dominated state, has important consequences for uncovering response diversity that drives resilience, especially in systems with low or declining functional diversity.

Scaling the effects of ocean acidification on coral growth and coral–coral competition on coral community recovery

“…Indeed, sensitivity analysis suggest that coral recruitment can strongly affect projected coral cover, with a 20% decline in recruitment resulted in a~15% decline in coral cover after 7 years. Lastly, the frequency and severity of bleaching events will almost certainly increase as ocean warming continues (Heron et al, 2016), further challenging the capacity of the coral community to maintain its resilience, possibly as has occurred following severe bleaching in 2019 (Burgess et al, 2021). Despite the aforementioned limitations of the present study, the outcome of this modelling effort provides an important advance towards understanding the impacts of OA on corals at a reef-scale.…”

“…has often been considered sensitive to acute disturbances (Gleason, 1993;Darling et al, 2012), Pocillopora spp. appears to be a diverse genus (i.e., consisting of at least six species including P. verrucosa and P. meandrina (Edmunds et al, 2016b;Burgess et al, 2021) that has overcome acute disturbances through high rates of recruitment in the 2-3 years following cessation of the COTs outbreak and cyclone Oli (Bramanti & Edmunds, 2016). High recruitment of Pocillopora on the fore reef of Moorea has resulted in a rate of increase in coral cover that exceeds that of any Indo-Pacific fore reef sites to date (Graham, Nash & Kool, 2011).…”

“…By 2016, coral cover at the same site had reached 66 ± 3%, with Acropora, Pocillopora, Porites, and Montipora, contributing >97% of the cover. Our model, therefore, focused on: Pocillopora, which in this location includes at least P. verrucosa, P. meandrina, P. eydouxi, P. effuses, and several unnamed haplotypes (Edmunds et al, 2016b;Burgess et al, 2021); Acropora spp. which includes at least 15 species (Bosserelle et al, 2014); Montipora spp.…”

Deep Heat: A Comparison of Water Temperature, Anemone Bleaching, Anemonefish Density and Reproduction between Shallow and Mesophotic Reefs

“…Despite lower temperatures in mesophotic zones compared to those in shallow reefs, extreme temperatures in 2019 that induced a massive coral and anemone bleaching event in the shallow waters of Moorea lagoon [55] also resulted in extreme temperatures on mesophotic reefs and induced anemone bleaching at 50 m. The water temperatures in 2019 linearly regress in a similar manner to water temperatures in the other years (2011-2020), but temperatures in the hottest months of 2019 extend the regression line above the bleaching threshold at both depths (Figure 3). The strong positive temperature anomalies (>1 • C difference) during the warm season, exceeded the critical value at which anemones started to become bleached, both in the lagoon and at the deep sites.…”

“…The year 2019 was exceptionally warm in French Polynesia, and a severe coral bleaching event was observed in Moorea where 72% of pocilloporid coral colonies bleached at 10 m and mortality ranged from 11 % to 42 % four months after the warming event [55]. On 8 April 2019, water temperatures reached 30.42 • C at 8 m, 1.62 • C higher than the average in non-bleaching years (Figure 2 and blue triangles in Figure 3).…”