• Energy Research

Stress-tolerant coral species, such as Platygyra spp., are considered to be well adapted to survive in marginal reefs, but their physiological response to short term exposure to abnormally high temperature and lowered salinity remains poorly understood. Using non-invasive techniques to quantitatively assess the health of Platygyra carnosa (e.g. respiration, photosynthesis, biocalcification and whiteness), we identified the plasticity of its energetics and physiological limits. Although these indicators suggest that it can survive to increasing temperature (25-32 °C), its overall energetics were seriously diminished at temperatures >30 °C. In contrast, it was well adapted to hyposaline waters (31-21 psu) but with reduced biocalcification, indicating short term adaptation for expected future changes in salinity driven by increased amounts and intensities of precipitation. Our findings provide useful insights to the effect of these climate drivers on P. carnosa metabolism and thus better forecast changes in their health status under future climate change scenarios.

Marine sediments are part of the hydrological cycle and the ultimate storage compartment of land-derived organic matter, including pollutants. Since relevant microbially-driven processes occurring at benthic level may affect the quality of the overall aquatic system, the necessity for incorporating information about microbial communities functioning for ecosystem modelling is arising. The aim of this field study was to explore the links occurring between sediment contamination patterns by three selected class of organic pollutants (Polycyclic Aromatic Hydrocarbons, PAHs, Nonylphenols, NPs, Bisphenol A, BPA) and major microbial properties (Prokaryotic Biomass, PB; total living biomass, C-ATP; Prokaryotic C Production rate, PCP; Community Respiration rate, CR) across a gradient of anthropogenic pollution. Sediments were sampled from 34 sites selected along 700 km of the western coastline of the Adriatic Sea. Organic contamination was moderate (PAHs <830 ng g-1; NPs <350 ng g-1; BPA <38 ng g-1) and decreased southward. The amount of PAHs-associated carbon (C-PAHs) increased significantly with sediment organic carbon (OC), along with microbial functional rates. The negative relation between PCP/CR ratio and OC indicated the shift toward oxidative processes in response to organic pollution and potential toxicity, estimated as Toxic Equivalents (TEQs). Our outcomes showed that sediment organic contamination and benthic microbial processes can be intimately linked, with potential repercussions on CO2 emission rates and C-cycling within the detritus-based trophic web.

Scleractinian corals obtain metabolic energy from their endosymbiotic autotrophic microalgae, and from remineralization of organic matter by bacteria and viruses, along with the heterotrophic food sources. The mutualistic symbiosis is generally stable but can be disrupted when environmental conditions surrounding the corals, such as increasing seawater temperature, become unfavorable to sustain each component of the holobiont. In this connection, the effects of global stressors such as climate change, and local stressors such as pollution, and their combination, are posing serious threats to the metabolic resistance of corals. However, some more resilient coral species have developed specific mechanisms to cope with fluctuating environmental conditions according to the trophic strategy (autotrophy, heterotrophy, or mixotrophy), and by modulating their energy expenditure. In this chapter, the role of nutrition in the coral symbiosis as the energetic budget for metabolic performance will be discussed, with a focus on the role of acquisition of nutrients through feeding, regulation of energy reserves (lipids, proteins, and carbohydrates), and adaptation capability in the natural environment, including the expression of heat-shock proteins (Hsps). Future environmental conditions under a combination of global changes and local impacts will also be discussed, with the aim of identifying the trophic niches of corals and geographical areas as possible refugia.