Abstract
AbstractExtremes in seasonal environmental conditions can significantly impact the health and physiological functioning of reef corals, underscoring the need for knowledge of seasonally specific baselines from which to monitor and forecast impending stress. Increases above summertime means in seawater temperature, sunlight intensity, turbidity, or sedimentation may reduce coral immunocompetency and increase disease and bleaching susceptibility. We analyzed temporal patterns in innate immunity parameters over nine time points throughout one year to establish baseline levels from which anomalies might be detected for representative species from three major reef‐building coral families (Acroporidae, Faviidae, and Poritidae). Temporal patterns in both phenoloxidase activity and expression of green fluorescent protein‐like proteins varied among the three families, as did overall constitutive levels. For example, Porites cylindrica had 2.8‐fold higher yearly average levels of phenoloxidase activity than Acropora millepora, which had the lowest levels. In contrast, mean fluorescence was lowest in Acropora millepora and highest in Echinopora mammiformis. Relationships between the potential physical drivers (seasonal variation in seawater temperature, rainfall, salinity) and temporal patterns in these parameters also differed among the three species. For example, phenoloxidase activity was positively correlated with seawater temperature in A. millepora, but negatively correlated in both E. mammiformis and P. cylindrica. Distinctions in constitutive levels and temporal patterns in these parameters among species suggest that corals from these three families have evolved different strategies for investing resources into innate immune parameters. Such differences highlight the need for species‐specific baselines and long‐term assessments to accurately predict coral reef trajectories in rapidly changing environments.
Highlights
Global declines in coral reef ecosystem function is a critical concern, both for vertebrates and invertebrates dependent on reefs for food and shelter, and for the millions of people who draw extensively on them for food, coastal protection, tourism income, and cultural values (Burke et al 2011)
As a competent immune system is integral to maintaining an organism’s health, parameters associated with the coral innate immune system, such as activity of the prophenoloxidase system and expression of green fluorescent protein- like (GFP-like) proteins, have been suggested as potential indicators of stress based on their detectable responses to the variations in local environmental conditions (D’Angelo et al 2008, Palmer et al 2010, Roth and Deheyn 2013)
Patterns in the ratios of PO to tpPO activities among species indicate that A. millepora stores the greatest proportion of its total potential phenoloxidase activity in the inactive proPO zymogen form and P. cylindrica the least
Summary
Global declines in coral reef ecosystem function is a critical concern, both for vertebrates and invertebrates dependent on reefs for food and shelter, and for the millions of people who draw extensively on them for food, coastal protection, tourism income, and cultural values (Burke et al 2011). As a competent immune system is integral to maintaining an organism’s health, parameters associated with the coral innate immune system, such as activity of the prophenoloxidase (proPO) system and expression of green fluorescent protein- like (GFP-like) proteins, have been suggested as potential indicators of stress based on their detectable responses to the variations in local environmental conditions (D’Angelo et al 2008, Palmer et al 2010, Roth and Deheyn 2013) Both parameters vary in response to warm seawater temperature anomalies, which are known to significantly affect the health of the coral holobiont. Warm seawater temperatures and changes in salinity and agricultural pollutants have all been shown to compromise the functioning of the innate immune systems of a range of marine invertebrates, thereby increasing disease susceptibility and mortality (Tseng and Chen 2004, Ellis et al 2011, Lin et al 2012). Short-term studies are beginning to explore how environmental stressors affect the proPO-activating system and GFP- like protein expression, an understanding of what constitutes seasonal baselines in healthy levels is needed to explore these parameters as potential indicators of immune-c ompromising environmental conditions
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