Experimental Techniques to Assess Coral Physiology in situ Under Global and Local Stressors: Current Approaches and Novel Insights

Abstract

Coral reefs are declining worldwide due to global changes in the marine environment. The increasing frequency of massive bleaching events in the tropics is highlighting the need to better understand the stages of coral physiological responses to extreme conditions. Moreover, like many other coastal regions, coral reef ecosystems are facing additional localized anthropogenic stressors such as nutrient loading, increased turbidity, and coastal development. Different strategies have been developed to measure the health status of a damaged reef, ranging from the resolution of individual polyps to the entire coral community, but techniques for measuring coral physiology in situ are not yet widely implemented. For instance, while there are many studies of the coral holobiont response in single or limited-number multiple stressor experiments, they provide only partial insights into metabolic performance under more complex and temporally and spatially variable natural conditions. Here, we discuss the current status of coral reefs and their global and local stressors in the context of experimental techniques that measure core processes in coral metabolism (respiration, photosynthesis, and biocalcification) in situ, and their role in indicating the health status of colonies and communities. We highlight the need to improve the capability of in situ studies in order to better understand the resilience and stress response of corals under multiple global and local scale stressors.

Irradiance driven trophic plasticity in the coral Madracis pharensis from the Eastern Mediterranean

“…Examining coral photophysiology in situ primarily relies on instantaneous measurements such as maximum quantum yield which is commonly used as a proxy for photosynthetic efficiency 28 . However, the coral host itself can also attain nutrients via heterotrophy and thus the photosynthate produced by endosymbiotic Symbiodiniacaea is not the only available source of nutrients 29 .…”

Variability in Symbiont Chlorophyll of Hawaiian Corals from Field and Airborne Spectroscopy

“…Field-based monitoring of coral color is usually relegated to qualitative approaches such Remote Sens. 2024, 16, 732 2 of 14 as diver-based color cards [13,14]. This works well for determining major changes in symbiont presence, such as during coral bleaching surveys [15].…”

“…This works well for determining major changes in symbiont presence, such as during coral bleaching surveys [15]. However, despite efforts to standardize such visual colorimetric methods, there remains a need for increasingly quantitative, physiologically based approaches to support reef research and conservation applications [16]. This is particularly pressing at the ecosystem level, where the full range of coral responses to external stresses occur but are rarely quantified [17].…”

Nutrition of Corals and Their Trophic Plasticity under Future Environmental Conditions

“…However, in the era of Anthropocene, coral reefs are among the habitats on Earth that are suffering the most and are dramatically degrading, since a multitude of factors are plaguing these marine ecosystems. Abiotic factors such as abnormally elevated or reduced temperatures, ocean acidification, high ultraviolet radiations, and fluctuation in salinity are increasing the occurrence of coral bleaching events [14][15][16][17][18]. Additionally, industrial pollution, coastal development, and excessive nutrient input, as well as biotic stressors such as predation outbreaks, epizootic diseases, and bioerosion are leading to further coral reef degradation around the world [19][20][21][22].…”