Biology subjects

Hancock, J. R.

Publications and source records attributed to Hancock, J. R..

4 recordsLinked to original sources

bioRxiv2025

Proactive Coral Reef Restoration Using Thermally Tolerant Corals in Hawaii

Effective conservation of degraded ecosystems requires mitigation of the original cause of decline, but this step can be difficult in the context of global climate change. On coral reefs, persistent environmental stress which causes coral bleaching may be addressed by using coral restoration stock which is naturally more resilient, often termed "proactive restoration" in terrestrial management. To explore the feasibility and consequences of this approach, we outplanted 391 colonies of 7 species of reef-building coral designated as thermally tolerant or thermally sensitive during stress testing and monitored them for 2 years using photogrammetry to evaluate tradeoffs and return-on-effort. We found no growth, complexity or effort tradeoffs when using thermally tolerant corals, but tolerant corals had lower survivorship during our monitoring period, driven primarily by one genus. These data illustrate nuanced tradeoffs and consequences to proactive reef restoration and suggest that the potential benefits of this approach may only be fully realized during future coral bleaching events.

ecology↗

bioRxiv2025

Positive associations between growth and thermal tolerance in the reef-building coral Montipora capitata

Relationships between ecologically important traits are increasingly important for the future of coral reefs, which are declining globally due to a variety of stressors. Corals that resist and recover from bleaching will be selected under future climates, which may negatively or positively impact a range of associated traits important for the structure and function of contemporary and future reefs. Using standardized assays, we investigated growth under ambient conditions, bleaching resistance and recovery after bleaching in a model population of 60 Montipora capitata colonies harboring diverse symbiont communities. We found significantly higher trait variance within Durusdinium-dominated colonies, highlighting the interaction of host and symbiont. We also show that symbiont community impacted thermal tolerance and survivorship during the thermal stress assay, but not recovery or growth. There was also a positive relationship between thermal tolerance and change in surface area and thermal tolerance and recovery from equivalent amounts of stress. These results demonstrate limited tradeoffs to thermal tolerance and suggest that bleaching tolerant corals in this model system are suited to recover from stress and maintain high growth rates under ambient conditions, providing insight into the adaptive capacity of thermally tolerant corals in the Anthropocene.

ecology↗

bioRxiv2022

Fine-scale variability in coral bleaching and mortality during a marine heatwave

Coral bleaching and mortality can show significant spatial and taxonomic heterogeneity at local scales, highlighting the need to understand the fine-scale drivers and impacts of thermal stress. In this study, we used structure-from-motion photogrammetry to track coral bleaching, mortality, and changes in community composition during the 2019 marine heatwave in K[a]ne ohe Bay, Hawai i. We surveyed 30 shallow reef patches every 3 weeks for the duration of the bleaching event (August-December) and one year after, resulting in a total of 210 large-area, high-resolution photomosaics that enabled us to follow the fate of thousands of coral colonies through time. We also measured environmental variables such as temperature, sedimentation, depth, and wave velocity at each of these sites, and extracted estimates of habitat complexity (rugosity R and fractal dimension D) from digital elevation models to better understand their effects on patterns of bleaching and mortality. We found that up to 80% of corals experienced moderate to severe bleaching in this period, with peak bleaching occurring in October when heat stress (DHW) reached its maximum. Mortality continued to accumulate as bleaching levels dropped, driving large declines in more heat-susceptible species (77% loss of Pocillopora cover) and moderate declines in heat-tolerant species (19% and 23% for Porites compressa and Montipora capitata, respectively). Declines in live coral were accompanied by a rapid increase in algal cover across the survey sites. Spatial differences in bleaching were significantly linked to habitat complexity and coral species composition, with reefs that were dominated by Pocillopora experiencing the most severe bleaching. Mortality was also influenced by species composition, fractal dimension, and site-level differences in thermal stress. Our results show that spatial heterogeneity in the impacts of bleaching are driven by a mix of environmental variation, habitat complexity, and differences in assemblage composition.

ecology↗

bioRxiv2020

Bleaching resistant corals retain heat tolerance following acclimatization to environmentally distinct reefs

Urgent action is needed to prevent the demise of coral reefs as the climate crisis leads to an increasingly warmer and more acidic ocean. Propagating climate change resistant corals to restore degraded reefs is one promising strategy; however, empirical evidence is needed to determine if resistance is retained following transplantation within or beyond a corals natal reef. Here we assessed the performance of bleaching-resistant individuals of two coral species following reciprocal transplantation between environmentally distinct reefs (low vs high diel variability) to determine if stress resistance is retained following transplantation. Critically, transplantation to either environment had no influence on coral bleaching resistance, indicating that this trait was relatively fixed and is thus a useful metric for selecting corals for reef restoration within their native range. In contrast, growth was highly plastic, and native performance was not predictive of performance in the novel environment. Coral metabolism was also plastic, with cross transplants of both species matching the performance of native corals at both reefs within three months. Coral physiology (autotrophy, heterotrophy, and metabolism) and overall fitness (survival, growth, and reproduction) were higher at the reef with higher flow and fluctuations in diel pH and dissolved oxygen, and did not differ between native corals and cross-transplants. Conversely, cross-transplants at the low-variability reef had higher fitness than native corals, thus increasing overall fitness of the recipient population. This experiment was conducted during a non-bleaching year, which suggests that introduction of these bleaching-resistant individuals will provide even greater fitness benefits to recipient populations during bleaching years. In summary, this study demonstrates that propagating and transplanting bleaching-resistant corals can elevate the resistance of coral populations to ocean warming while simultaneously maintaining reef function as the climate crisis worsens.

ecology↗