Abstract
Coral reefs, especially those located near-shore, are increasingly exposed to anthropogenic, eutrophic conditions that are often chronic. Yet, corals under unperturbed conditions may frequently receive natural and usually temporary nutrient supplementation through biological sources such as fishes. We compared physiological parameters indicative of long- and short-term coral health (day and night calcification, fragment surface area, productivity, energy reserves, and tissue stoichiometry) under continuous and temporary nutrient enrichment. The symbiotic coral Acropora intermedia was grown for 7 weeks under continuously elevated (press) levels of ammonium (14 µmol L−1) and phosphate (10 µmol L−1) as separate and combined treatments, to discern the individual and interactive nutrient effects. Another treatment exposed A. intermedia twice-daily to an ammonium and phosphate pulse of the same concentrations as the press treatments to simulate natural biotic supplementation. Press exposure to elevated ammonium or phosphate produced mixed effects on physiological responses, with little interaction between the nutrients in the combined treatment. Overall, corals under press exposure transitioned resources away from calcification. However, exposure to nutrient pulses often enhanced physiological responses. Our findings indicate that while continuous nutrient enrichment may pose a threat to coral health, episodic nutrient pulses that resemble natural nutrient supplementation may significantly benefit coral health and physiology.
Highlights
Coral reefs, especially those located near-shore, are increasingly exposed to anthropogenic, eutrophic conditions that are often chronic
The concentrations of inorganic nitrogen (N) and phosphorus (P) in coral reef waters are often amongst the lowest values recorded for aquatic s ystems[1, 2], yet many coral reefs are typified by substantially high rates of primary productivity[3]
Overall, GTA was governed by an interactive effect between levels of ammonium, and the time of day regardless of the level of phosphate
Summary
Especially those located near-shore, are increasingly exposed to anthropogenic, eutrophic conditions that are often chronic. Inorganic N and P are considered limiting factors for Symbiodiniaceae growth and photosynthesis[19,20,21] Addition of these nutrients to the surrounding seawater may lead to rapid nutrient uptake by the symbiont, C:N:P ratio shifts within the s ymbiont[22], increased symbiont photosynthesis, and organic carbon accumulation in both the host and the symbiont[23]. Corals naturally receive episodic pulses of nutrients several times higher than the background concentrations in the overlying waters, delivered to reefs by diurnal activities of fish and other aquatic organisms[36,37,38], as well as seabirds[39, 40] These nutrient influxes are dynamic and temporal, and usually reflect the diurnal migratory and feeding behaviour of fish[36,37,38]. Contrary to the negative effects of anthropogenic eutrophication on coral physiology, corals exposed to these temporary and natural nutrient pulses showed increased tissue thickness, CaCO3 accretion and skeletal expansion rates[38, 43, 44], provided that the reef is not yet in a degraded state[5, 45]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
