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1. Grazers and predators mediate the post-settlement bottleneck in Caribbean octocoral forests

   https://doi.org/10.3389/fmars.2024.1361137  

   Wells, Christopher D; Benz, Joseph; Tonra, Kaitlyn J; Anderson, Emily R; Lasker, Howard R (August 2024, Frontiers in Marine Science)

   In the Caribbean, reef-building scleractinian corals have declined precipitously and octocorals have emerged as one of their main successors. The success of octocorals and the formation of octocoral forests has been attributed to their continuing recruitment to reef habitats, as well as tolerance to pollution, reduced direct competition with scleractinians, and resistance and resilience to climatic events. Benthic grazers on coral reefs can facilitate the growth and recruitment of corals by reducing the abundance of competitive algal turfs and macroalgae. However, grazing can also hinder corals through sublethal damage to coral tissue and predation of recruits. We assessed the effects of grazing by fishes and the sea urchinDiadema antillarumas well as predation by mesofauna on octocoral recruitment through a series of manipulativein situandex situexperiments. Exposure to fish and urchin grazing significantly reduced the post-settlement survival of octocoral recruits, while turf-associated mesofauna did not significantly affect recruitment. We also found a positive relationship between octocoral recruitment and the abundance of turf algae, which may reflect the deleterious effect of grazing on both turf algae and octocoral recruits. These data suggest that grazers and predators mediate the bottleneck characteristic of recruitment, primarily through their effect on post-settlement survival. Thus, the declines in the abundance of grazing fishes and urchins throughout the Caribbean may have contributed to the increase in Caribbean octocoral abundance, concurrent with the loss of scleractinians. 

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2. Niche breadth and divergence in sympatric cryptic coral species ( Pocillopora spp.) across habitats within reefs and among algal symbionts

   https://doi.org/10.1111/eva.13762  

   Burgess, Scott C; Turner, Alyssa M; Johnston, Erika C (August 2024, Evolutionary Applications)

   Abstract While the presence of morphologically cryptic species is increasingly recognized, we still lack a useful understanding of what causes and maintains co‐occurring cryptic species and its consequences for the ecology, evolution, and conservation of communities. We sampled 724Pocilloporacorals from five habitat zones (the fringing reef, back reef, and fore reef at 5, 10, and 20 m) at four sites around the island of Moorea, French Polynesia. Using validated genetic markers, we identified six sympatric species ofPocillopora, most of which cannot be reliably identified based on morphology:P. meandrina(42.9%),P. tuahiniensis(25.1%),P. verrucosa(12.2%),P. acuta(10.4%),P. grandis(7.73%), andP.cf.effusa(2.76%). For 423 colonies (58% of the genetically identified hosts), we also usedpsbA^ncror ITS2 markers to identify symbiont species (Symbiodiniaceae). The relative abundance ofPocilloporaspecies differed across habitats within the reef. Sister taxaP. verrucosaandP. tuahiniensishad similar niche breadths and hosted the same specialist symbiont species (mostlyCladocopium pacificum) but the former was more common in the back reef and the latter more common deeper on the fore reef. In contrast, sister taxaP. meandrinaandP. grandishad the highest niche breadths and overlaps and tended to host the same specialist symbiont species (mostlyC. latusorum).Pocillopora acutahad the narrowest niche breadth and hosted the generalist, and more thermally tolerant,Durusdinium gynnii. Overall, there was a positive correlation between reef habitat niche breadth and symbiont niche breadth—Pocilloporaspecies with a broader habitat niche also had a broader symbiont niche. Our results show how fine‐scale variation within reefs plays an important role in the generation and coexistence of cryptic species. The results also have important implications for how niche differences affect community resilience, and for the success of coral restoration practices, in ways not previously appreciated. 

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3. Remnant hollowed out dead coral skeleton branches defer coral community recovery

   https://doi.org/10.1371/journal.pone.0339527  

   Scafidi, Kathryn C; Fouke, Kyle W; Sivaguru, Mayandi; Fouke, Bruce W; Edmunds, Peter J (March 2026, PLOS One)

   Tavakoli-Kolour, Parviz (Ed.)

   Through repeated impacts of ecosystem disturbances, most coral reefs have transitioned to a degraded state with low living coral cover. Until recently, the reefs of Moorea, French Polynesia, have provided an exception to this trend as their coral communities have recovered from sequential disturbances over the last 50 years. Early in 2019, the north shore fore reef at 10-m depth had ~ 75% live coral cover, but was decimated by bleaching to leave 17% coral cover by August 2020 and many kilometers of reef dominated by dead-in-place colonies ofPocilloporaspp. By 2025, coral recovery had not begun because of the chronology of decay affecting deadPocilloporaskeletons. We combine ecological analyses of deadPocilloporacolonies with high-resolution microscopy of aragonite skeletal structure to better understand the fate of these dead branching corals. Bleaching in 2019 created a reef dominated by deadPocilloporacolonies that initially were resilient to breakage and removal. Dead corals were colonized by macroalgae, occupied by a unique assemblage of invertebrates, and deterred coral recruitment as evidenced by coral settlers on settlement tiles but not on dead skeletons. In 2022–2023, three years afterPocilloporacolonies were killed, their remnant hollowed-out branches were first detected. High-resolution microscopy indicates hollowing occurred through bioerosion of dead branches that were scaffolded by encrusting taxa and entrapped sediments. Over 2011–2019, coral communities in Moorea rapidly recovered from devastation, but recovery from the 2019 bleaching has been deferred by the retention of dead corals on reef surfaces, creating the opportunity for erosion to further hollow out and weaken dead coral branches. This study shows how the synergy of well-studied disturbances can create ecological surprises that at best defer community recovery, but at worst portend a different outcome of major disturbance events, preventing recovery of the original coral community. 

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4. Coral performance is comparable when transplanted to disparate reef sites despite divergent histories of reef decline and recovery

   https://doi.org/10.3354/meps14712  

   Clements, CS; Ladd, MC; Gallagher, JP; Hay, ME (November 2024, Marine Ecology Progress Series)

   As coral reefs degrade worldwide, researchers and managers need to determine whether corals can acclimatize to altered local conditions or whether their fixed phenotypes prevent coral persistence under these new environmental conditions. Fixed phenotypes could produce environmental mismatches that reduce population connectivity and exacerbate decline in the near-term, but a capacity for acclimatization could be harnessed in both passive and proactive coral restoration efforts. Here, we conducted a reciprocal transplant experiment in Mo‘orea, French Polynesia, to test how intraspecific performance of 2 common coral species (Acropora hyacinthusandPocillopora verrucosa) varied between a neighboring forereef and backreef that differed dramatically in trajectories of coral loss, resilience over decadal time scales, and cover of corals versus competing macroalgae. We also tested how corals responded to 2 common stressors—corallivory and macroalgal competition—and how this varied as a function of transplant location and the area of origin. Growth and survival of both coral species were affected by macroalgal competition, corallivory, transplant location, or some combination thereof, but we found limited evidence that the habitat of origin significantly impacted intraspecific performance. These results suggest that acclimatization capacity may outweigh local adaptation for these common reef-building species and could be leveraged to facilitate coral restoration. 

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5. How fishes and invertebrates impact coral resilience

   Stier, Adrian C; Osenberg, Craig W (July 2024, Current biology)

   Increasingly intense and frequent ocean heatwaves are causing widespread coral mortality. These heatwaves are just one of the many stressors — among for instance ocean acidifi cation, nutrient pollution and destructive fi shing practices — that have caused widespread decline of coral reefs over the past century. This destruction of reefs threatens the remarkable biodiversity of organisms that depend upon coral reefs. However, recent research suggests that many of the fi shes and invertebrates that inhabit coral reefs may play an underappreciated role in infl uencing the resistance and recovery of corals to stressors, especially those caused by global climate change such as ocean heatwaves. Unraveling the threads that link these coral inhabitants to the corals’ response to stressors has the potential to weave a more comprehensive model of resilience that integrates the plight of coral reefs with the breathtaking diversity of life they host. Here, we aim to elucidate the critical roles that coral-associated fishes and invertebrates play in mediating coral resilience to environmental stressors. By integrating recent research findings, we aim to showcase how these often-overlooked organisms influence coral resilience in the face of climate change. 

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