Biology subjects

Ferrara, E. F.

Publications and source records attributed to Ferrara, E. F..

3 recordsLinked to original sources

bioRxiv2025

Establishment of menthol bleaching protocols for six stony coral species

The mutualistic symbiosis between stony corals and unicellular algae of the family Symbiodiniaceae forms the base of coral reef ecosystems. However, anthropogenic stressors, such as rising seawater temperatures, cause a breakdown of the coral-algal symbiosis, so-called coral bleaching, which leads to mass mortalities and a rapid loss of coral reefs. To functionally disassemble the coral-algal symbiosis, corals have been artificially rendered aposymbiotic using temperature stress, DCMU, or menthol. As menthol has proven to be an efficient and gentle bleaching agent, we tested four menthol treatments with six commonly investigated stony coral species. The overarching aim was to establish a broadly efficient bleaching protocol as a guide for future investigations. Menthol-induced bleaching was traced with chlorophyll fluorescence and tissue color analyses over time and confirmed as final symbiont cell density two weeks after the last day of menthol treatment. Here we found that the coral species varied greatly in their menthol bleaching tolerance, underlining the importance of establishing bespoke bleaching approaches. Acropora muricata and Stylophora pistillata were efficiently bleached within two days of menthol exposure with symbiont cell reductions of 94 % to 98 %. For Galaxea fascicularis, Montipora digitata and Porites cylindrica, six days of menthol exposure proved most successful in reducing symbiont density by 92 to 97 %. While these coral species suffered no mortality, fragments of Pocillopora verrucosa died or suffered severe necrosis in most of the protocols, making the tested menthol treatments unsuitable for this species. We demonstrate that repeated menthol treatment at low concentrations renders most coral species aposymbiotic within few days without visual or physiological damage. Our study, therefore, provides a guideline for efficient and customized application of menthol bleaching treatments for future coral symbiosis research.

systems biology↗

bioRxiv2024

RGB color indices as proxy for symbiont cell density and chlorophyll content during coral bleaching

Coral bleaching, the breakdown of the symbiosis between the coral host and endosymbiotic microalgae, is the main cause of widespread coral reef degradation. Current methods for assessing coral health based on visual appearance, such as the use of color reference cards, are limited by subjective human color perception and low resolution. Digital photography with RGB (Red, Green, Blue) color channel analyses offers a fast, non-invasive, and standardized alternative to estimate physiological parameters. However, the link between coral color and physiological parameters during bleaching may vary depending on the type of stressor. While such approaches are extensively used in plant studies, their application in estimating Symbiodiniaceae cell density and chlorophyll content in corals requires further attention. In this study, we analyzed the correlation between Symbiodiniaceae cell density and chlorophyll content across three coral species (Acropora muricata, Pocillopora verrucosa, and Stylophora pistillata) with 19 color indices derived from the RGB channels currently established as predictors of chlorophyll content in plants. Corals were exposed to three bleaching conditions (acute short-term and chronic long-term heat stress and menthol bleaching) to identify the best color indices for assessing coral health through image analysis. We found that the Red index had the strongest linear correlation with symbiont cell density and chlorophyll content across species (R2 up to 0.97), so that relative changes in this color index can be directly interpreted as corresponding changes in tissue parameters. To train a model that predicts symbiont densities of a distinct sample set using the Red index, we found 10 to 12 samples to be sufficient to achieve an accuracy of > 95 % of the models trained on the full datasets. This research contributes to improved image analysis as a reliable and non-invasive tool for monitoring, by providing guidelines for a systematic use of RGB data to interpret coral health.

ecology↗

bioRxiv2024

Thermal preconditioning modulates coral physiology and heat tolerance: A multi-species perspective

Global warming threatens reef-building corals by challenging their natural adaptive capacity. Therefore, interventions such as stress hardening by thermal preconditioning could become crucial for their survival. Stress-hardening approaches recognize that organisms living in thermally variable environments are better able to withstand marine heat waves. However, a systematic assessment of preconditioning effects on the baseline physiology and thermal tolerance across coral species is lacking. We assessed the changes of thermal tolerance in six stony coral species (Galaxea fascicularis, Porites rus, Acropora muricata, Montipora digitata, and Stylophora pistillata) in three thermal preconditioning treatments of stable-high 29 {degrees}C and variable-high 29 {degrees}C with a daily oscillation of {+/-} 1.5 {degrees}C, compared to corals in stable-ambient 26 {degrees}C. We quantified changes in photosynthetic efficiency and coral bleaching intensity before and after a short-term heat stress assay and up to 30 days later. Stress-hardening success after preconditioning was observed in nearly all preconditioned corals, but the increases in thermal tolerance were species-specific. The greatest increase was recorded in G. fascicularis and A. muricata, with stress responses reduced by over 80 %. In contrast, preconditioning regimes had minor effects on stress tolerance of S. pistillata, making it least receptive to this intervention. After 30 days, most stress-hardened species demonstrated higher survival and recovery rates than their conspecifics from the stable-ambient regime. Notably, both preconditioning regimes affected baseline physiology, especially in the branching species, as indicated by minor tissue paling and decreased photosynthetic efficiency. We conclude that implementing thermal stress hardening protocols will require careful consideration of the species-specific receptiveness and evaluation of the potential trade-offs that can be inflicted with the post-conditioning shifts in physiological baselines.

ecology↗