Biology subjects

Gates, R. D.

Publications and source records attributed to Gates, R. D..

4 recordsLinked to original sources

bioRxiv2018

Spatial variation in the biochemical and isotopic composition of corals during bleaching and recovery

Ocean warming and the increased prevalence of coral bleaching events threaten coral reefs. However, the biology of corals during and following bleaching events under field conditions is poorly understood. We examined bleaching and post-bleaching recovery in Montipora capitata and Porites compressa corals that either bleached or did not bleach during a 2014 bleaching event at three reef locations in K[a]ne ohe Bay, O ahu. We measured changes in chlorophylls, biomass, and nutritional plasticity using stable isotopes ({delta}13C, {delta}15N). Coral traits showed significant variation among bleaching conditions, reef sites, time periods, and their interactions. Bleached colonies of both species had lower chlorophyll and total biomass. While M. capitata chlorophyll and biomass recovered three months later, P. compressa chlorophyll recovery was location-dependent and total biomass of previously bleached colonies remained low. Biomass energy reserves were not affected by bleaching, instead M. capitata proteins and P. compressa biomass energy declined over time, and P. compressa lipid biomass was site-specific. Stable isotope analyses of host and symbiont tissues did not indicate increased heterotrophic nutrition in bleached colonies of either species, during or after thermal stress. Instead, mass balance calculations revealed variance in {delta}13C values was best explained by augmented biomass composition, whereas {delta}15N values reflected spatial and temporal variability in nitrogen sources in addition to bleaching effects on symbiont nitrogen demand. These results emphasize total biomass quantity may change substantially during bleaching and recovery. Consequently, there is a need to consider the influence of biomass composition in the interpretation of isotopic values in corals.

physiology↗

bioRxiv2018

High-frequency temperature variability mirrors fixed differences in thermal limits of the massive coral Porites lobata (Dana, 1846)

Spatial heterogeneity in environmental characteristics can drive adaptive differentiation when contrasting environments exert divergent selection pressures. This environmental and genetic heterogeneity can substantially influence population and community resilience to disturbance events. Here, we investigated corals from the highly variable back reef habitats of Ofu Island in American Samoa that thrive in thermal conditions known to elicit widespread bleaching and mortality elsewhere. To investigate the hypothesis that thermal variability is the driving force shaping previously observed differences in coral tolerance limits in Ofu, specimens of the common Indo-Pacific coral Porites lobata (Dana, 1846) from locations with differing levels of thermal variability were acclimated to low and high thermal variation in controlled common garden experimental aquaria. Overall, there was minimal effect of the acclimation exposure. Corals native to the site with the highest level of daily variability grew fastest, regardless of acclimation treatment. When exposed to lethal thermal stress, corals native to both variable sites contained elevated levels of heat shock proteins and maintained photosynthetic performance for 1-2 days longer than corals from the stable environment. Despite being separated by < 5 km, there was significant genetic differentiation among coral colonies (FST = 0.206, p < 0.0001; nuclear ribosomal DNA), while Symbiodinium phylotypes were all ITS2-type C15. Our study demonstrates consistent signatures of adaptation in growth and stress resistance in corals from naturally thermally variable habitats, emphasizing that existing genetic diversity of corals is an important asset in strategies to protect and manage coral reef ecosystems in the face of global change.\n\nSummary StatementCorals native to highly variable habitats demonstrate greater thermal tolerance than corals from less variable habitats after 36-days of acclimation to thermally stable or variable common garden treatments.

evolutionary biology↗

bioRxiv2018

Nurtured by nature: Considering the role of environmental and parental legacies in coral ecological performance

The persistence of reef building corals is threatened by human-induced environmental change. Maintaining coral reefs into the future requires not only the survival of adults, but also the influx of recruits to promote genetic diversity and retain cover following adult mortality. Few studies examine the linkages among multiple life stages of corals, despite a growing knowledge of carryover effects in other systems. We provide a novel test of coral parental preconditioning to ocean acidification (OA) to better understand impacts on the processes of offspring recruitment and growth. Coral planulation was tracked for three months following adult exposure to high pCO2 and offspring from the second month were reciprocally exposed to ambient and high pCO2. Offspring of parents exposed to high pCO2 had greater settlement and survivorship immediately following release, retained survivorship benefits during one and six months of continued exposure, and further displayed growth benefits to at least one month post release. Enhanced performance of offspring from parents exposed to high conditions was maintained despite the survivorship in both treatments declining in continued exposure to OA. Preconditioning of the adults while they brood their larvae may provide a form of hormetic conditioning, or environmental priming that elicits stimulatory effects. Defining mechanisms of positive carryover effects, or positive trans-generational plasticity, is critical to better understanding ecological and evolutionary dynamics of corals under regimes of increasing environmental disturbance. Considering parental and environmental legacies in ecological and evolutionary projections may better account for coral reef response to the chronic stress regimes characteristic of climate change.

physiology↗

bioRxiv2017

A Dynamic Bioenergetic Model For Coral-Symbiodinium Symbioses And Coral Bleaching As An Alternate Stable State

Coral reef ecosystems owe their ecological success-and vulnerability to climate change-to the symbiotic metabolism of corals and Symbiodinium spp. The urgency to understand and predict the stability and breakdown of these symbioses (i.e., coral bleaching) demands the development and application of theoretical tools. Here, we develop a dynamic bioenergetic model of coral-Symbiodinium symbioses that demonstrates realistic steady-state patterns in coral growth and symbiont abundance across gradients of light, nutrients, and feeding. Furthermore, by including a mechanistic treatment of photo-oxidative stress, the model displays dynamics of bleaching and recovery that can be explained as transitions between alternate stable states. These dynamics reveal that healthy and bleached states correspond broadly to nitrogen- and carbon-limitation in the system, with transitions between them occurring as integrated responses to multiple environmental factors. Indeed, a suite of complex emergent behaviors reproduced by the model (e.g., bleaching is exacerbated by nutrients and attenuated by feeding) suggests it captures many important attributes of the system; meanwhile, its modular framework and open source R code are designed to facilitate further problem-specific development. We see significant potential for this modeling framework to generate testable hypotheses and predict integrated, mechanistic responses of corals to environmental change, with important implications for understanding the performance and maintenance of symbiotic systems.

systems biology↗