Ocean acidification results from the ocean’s absorption of roughly 30% of anthropogenic CO2, which chemically reacts with seawater to lower its pH. Since the Industrial Revolution, the ocean’s surface waters have experienced a 40% increase in acidity, altering the delicate chemical balance essential to the formation of calcium carbonate, the mineral basis of coral skeletons. The decreased availability of carbonate ions is theorized to undermine coral calcification, potentially leading to fragile skeletal structures that jeopardize reef stability. However, existing empirical data from laboratory and field experiments have produced mixed signals regarding the degree of acidification impact on coral growth and skeleton density.

Employing Raman spectroscopy—a sophisticated analytical method that utilizes laser light to elucidate molecular structure—the study analyzed the chemical composition and microstructural integrity of two historical coral skeleton samples, aged approximately 200 and 115 years respectively. These specimens, sourced from the Great Barrier Reef and the Coral Sea, were scrutinized for evidence of changes in their crystalline calcium carbonate matrix under conditions of progressive ocean acidification. Raman spectroscopy provided unprecedented resolution into molecular ordering, detecting subtle variations in mineral impurities that influence skeletal robustness.

The principal investigator, Jessica Hankins, a doctoral candidate in Geological Sciences, identified that despite the increase in ocean acidity over two centuries, the coral specimens maintained their ability to regulate the chemistry of their calcifying fluid—a semi-isolated microenvironment situated between the growing skeleton and overlying soft tissues. This regulation effectively sustains supersaturation conditions favoring calcium carbonate precipitation, thus enabling continuous skeletal growth. Intriguingly, while conditions conducive to rapid calcification corresponded with heightened molecular disorder due to the incorporation of extraneous ions, the corals prioritized growth rates, suggesting an evolved flexibility in their biomineralization pathways.

The study’s findings challenge conventional assumptions that ocean acidification invariably compromises coral skeletal density. Instead, they unveil a nuanced biological response where corals manipulate internal geochemical processes to mitigate external environmental stressors. This insight prompts a reassessment of coral resilience thresholds and indicates that the calcifying fluid functions as a critical buffer zone, mediating mineral ion transport and facilitating skeletal construction despite declining oceanic carbonate availability.

Nonetheless, the molecular mechanisms underlying this regulatory capacity remain not fully characterized. Hankins emphasizes that the complexity of coral physiological responses demands more comprehensive investigations across diverse species and geographic locales to ascertain the generality and limits of this adaptation. The temporal scope of such resilience also calls for longitudinal monitoring to evaluate whether prolonged acidification will eventually overwhelm these compensatory processes.

Beyond the chemical challenge posed by acidifying oceans, coral reefs endure multiplicative stress from rising sea surface temperatures, anthropogenic pollution, and unsustainable fishing, all contributing to widespread coral bleaching events. Bleaching is characterized by the expulsion of symbiotic algae essential for coral metabolism, debilitating reef vitality. Alarmingly, between 2023 and mid-2024, mass coral bleaching afflicted at least 62 countries and territories, highlighting the precarious state of reef ecosystems globally.

Coral reefs are keystone ecosystems, underpinning marine biodiversity hotspots, providing nursery habitats for vital fish populations, and shielding coastlines from erosion and severe weather impacts. The integrity of the calcified reef framework is paramount; any decline in skeletal density or morphological complexity can cascade into ecological instability, threatening myriad species reliant on coral habitats.

This research contributes a hopeful dimension to coral reef conservation narratives by demonstrating intrinsic biological responses that may afford the reefs a degree of buffering against ocean acidification. However, scientists caution against complacency, recognizing that such resilience is not a panacea. Multifaceted environmental pressures persist, and effective global mitigation of climate change remains imperative to safeguard these ecosystems for future generations.

Moreover, Hankins’ work underscores the interconnectedness of global ecosystems; transformations in ocean chemistry reverberate beyond marine boundaries, influencing planetary health at large. As she articulates, even regions distant from the sea, such as Colorado, are entwined in the ocean’s fate, emphasizing the universal stakes of coral reef preservation efforts.

In summary, this pioneering study leverages cutting-edge Raman spectroscopic techniques to reveal that coral skeleton biomineralization exhibits adaptive regulation in the face of rising ocean acidity. While this discovery instills cautious optimism, it simultaneously calls for expanded research and concerted conservation strategies to fully elucidate and harness coral resilience amid accelerating environmental change.

Subject of Research: Coral resilience to ocean acidification and biomineralization mechanisms under changing ocean chemistry

Article Title: Corals Show Adaptive Regulation of Skeletal Calcification Amid Two Centuries of Ocean Acidification

News Publication Date: August 27, 2024

Web References: DOI: 10.1126/sciadv.adr0264

Image Credits: Jessica Hankins

Keywords: Coral reefs, ocean acidification, biomineralization, Raman spectroscopy, calcifying fluid, calcium carbonate, skeletal formation, climate change, coral resilience, marine ecosystems

Traditional methods for studying coral bleaching and photosynthesis have largely relied on destructive sampling or low-resolution techniques that fail to capture the fine-scale physiological dynamics of coral-algal symbiosis. However, BUMP employs pulse amplitude modulated (PAM) light measurement techniques integrated within a diver-operable microscope system. This approach enables researchers to quantify photosynthetic efficiency and visualize fluorescence emitted by individual symbiotic microalgae residing within coral tissues, all while maintaining the structural and functional integrity of the living reefs. This is especially crucial, considering that coral bleaching—a stress response characterized by loss of symbiotic algae—remains a poorly understood phenomenon due to the challenges in accessing and monitoring processes at the micro-scale in situ.

BUMP’s design represents an engineering masterpiece. Developed by the Jaffe Lab for Underwater Imaging at Scripps Oceanography, the microscope is both compact and user-friendly, incorporating a high-magnification lens array paired with focused LED excitation sources and sensitive fluorescence detectors. The entire system is controlled via a waterproof touchscreen interface and powered by an onboard battery pack, enabling divers to transport and deploy the device at the seafloor without relying on heavy, ship-based instrumentation. This portability empowers marine scientists to conduct non-invasive, real-time assessments of coral health across diverse reef ecosystems globally.

The microscope detects and maps the red fluorescence originating from chlorophyll within the photosynthetic microalgae, which serve as symbionts and vital energy sources for corals. By measuring the intensity of this fluorescence through PAM techniques, BUMP provides a quantitative index of photosynthetic efficiency at micron-scale resolution—an ability never before achieved in natural underwater environments. Additionally, the system captures cyan and green fluorescence emitted by specialized proteins produced by the corals themselves, shedding light on their physiological state and potential adaptive responses to environmental stressors.

Testing of this device spanned multiple iconic reef locations, including Hawaii, the Red Sea, and Palmyra Atoll. In partnership with the Smith Lab, the researchers calibrated and validated BUMP’s sensitivity and accuracy, ensuring that measurements are robust and representative of natural conditions. Lead author Or Ben-Zvi, a marine biologist, reported surprising observations during in-field deployments, such as dynamic changes in coral polyp volume and complex behaviors reminiscent of “kissing” or “fighting” between adjacent polyps. These behavioral insights, combined with photosynthetic data, provide new dimensions in understanding coral ecology and response mechanisms.

BUMP not only reveals the microstructure of coral tissue but also permits the non-invasive tracking of photosynthetic performance in real time. This is particularly critical given the accelerating frequency and severity of marine heatwaves, which trigger coral bleaching and widespread reef degradation. Through early detection of subtle declines in algal photosynthetic function, the microscope offers a potential warning system that could inform timely conservation interventions before irreversible damage occurs. This capability aligns closely with ecological management goals amid the climate crisis.

Beyond coral research, BUMP holds tremendous promise for investigating other photosynthetic marine organisms at micro-scales. For instance, researchers are already leveraging this technology to study the initial life stages of giant kelp, a keystone species along the California coast. Understanding photosynthetic efficiency and growth dynamics in these species under changing ocean conditions will provide broader insights into marine ecosystem health and productivity.

The development of BUMP underscores the vital role of federal funding and scientific innovation in addressing pressing environmental challenges. Instrumentation such as this not only enhances our fundamental knowledge of marine biology but also equips the scientific community with tools essential for developing informed strategies to protect vulnerable habitats. Researchers emphasize that continued investment in technology is indispensable for unraveling complex physiological mysteries—such as why corals bleach—and for crafting responsive mitigation efforts.

Scripps Oceanography’s interdisciplinary collaboration between engineers, marine biologists, and oceanographers that culminated in BUMP illustrates the power of converging expertise to confront multifaceted scientific problems. By merging cutting-edge microscopy, optical physics, and ecological fieldwork, this project sets a new standard for in situ marine imaging. The capacity to visualize interactions between coral hosts and their algal symbionts at unprecedented spatial and temporal resolution fundamentally transforms our approach to marine conservation science.

As coral reef ecosystems globally face existential threats from warming oceans, acidification, and human disturbance, innovative tools like BUMP provide a beacon of hope. The knowledge it generates will help shape effective policies and restoration practices by illuminating the mechanisms underlying coral health and resilience. Its ability to non-invasively monitor the delicate balance of coral-algal relationships promises advances in how researchers and conservationists assess and respond to environmental stressors on reef systems worldwide.

In summary, the Benthic Underwater Microscope Imaging PAM (BUMP) emerges as a transformative technology in marine science, enabling direct, real-time visualization and quantification of photosynthetic processes deep within live coral tissues. It represents a monumental technological breakthrough, fostering new understanding of coral physiology at microscopic scales and offering a vital tool to help protect these keystone ecosystems amid mounting global change pressures. The research published by UC San Diego scientists ushers in a new era for oceanographic imaging and coral reef conservation.

Subject of Research: Animals

Article Title: The Benthic Underwater Microscope Imaging PAM (BUMP): A Non-invasive Tool for In Situ Assessment of Microstructure and Photosynthetic Efficiency

News Publication Date: 3-Jul-2025

Web References:
https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/2041-210X.70078
https://jaffeweb.ucsd.edu/
https://seaweedecologylab.ucsd.edu/

References:
Ben-Zvi, O., Jaffe, J., Roberts, P., Deheyn, D., Lertvilai, P., Ratelle, D., Smith, J., Snyder, J., & Wangpraseurt, D. (2025). The Benthic Underwater Microscope Imaging PAM (BUMP): A Non-invasive Tool for In Situ Assessment of Microstructure and Photosynthetic Efficiency. Methods in Ecology and Evolution. DOI: 10.1111/2041-210x.70078

Image Credits: Or Ben-Zvi

Keywords: Reef building corals; Coral bleaching; Coral reefs; Marine photosynthesis; Microbiology; Microalgae; Fluorescence microscopy; Research methods; Observational studies; Imaging