Coral reefs are among the richest ecosystems on earth in terms of biodiversity and productivity, yet are at high risk of habitat degradation and species extinction from climate change and other anthropogenic influences. Resilience refers to the maintenance of key physiological and ecological functions following disturbances, which can be studied from the scale of individual organisms, populations, to entire ecosystems. Ecological factors that can negatively impact coral reefs include increased water temperatures, increased water acidification, overfishing, nutrient pollution, sedimentation, and impacts of climate variability such as the El Niño-Southern Oscillation. On the individual organism and population scale, resilience occurs through eco-physiological plasticity and/or gene expression and regulation during stress, and the capacity for resilience varies greatly across species and populations. Mechanisms related to resilience at this scale include response traits to environmental changes, population growth rates, and genetic diversity that can measured at both short-term and long-term responses to environmental shifts. Other ecosystem attributes that contribute to resilience includes connectivity, temporal and spatial variability, and functional redundancy. Oceanographic parameters, including water currents at small, meso-, and large scales, tidal force, upwelling, and seasonal rainfall patterns influence marine habitats that may impact the resilience of local organisms. These abiotic parameters can alter nutrient availability, stratification, irradiance levels, the degree of larval retention or dispersal, productivity, and numerous other ecological factors. The high temporal and spatial variability of oceanographic patterns often means that locations must be studied over several years before assumptions can be made regarding resilience of coral reef ecosystems. Our ability to understand resilience is enhanced with modern technology, including oceanographic sensing instrumentation and molecular genetics. Many reef-building corals and other reef organisms host endosymbiotic algae, a particular topic of interest among coral reef researchers. This host-symbiont relationship creates a complex of nutrient cycling and is recognized to impact resilience on the individual organism and population scale. Advances in molecular genetics and instrumentation such as flow cytometers have helped researchers understand these relationships in recent years. With documentation of worldwide coral reef habitat degradation spanning decades, competitive research grants continue to fund studies across both tropical and temperate reef ecosystems, and the number of coral reef-related research projects increases. Thus, we expect that the research presented in this session will highlight advancements in our understanding of resilience in coral reef ecosystems across many scales. This includes the species, population, and community levels, as well as across spatial and temporal variation.
Lead Organizer: Star Dressler, University of Guam (dresslerc@gotritons.uog.edu)
Co-organizers:
Atsushi Fujimura, University of Guam (fujimuraa@triton.uog.edu)
Presentations
06:30 PM
Microbiota as symbionts of the coral Tubastrea aurea in four contrasting environments of Taiwan (6265)
Primary Presenter: Jiang-Shiou Hwang, National Taiwan Ocean University (jshwang@mail.ntou.edu.tw)
Very little is known about microbiota associated with the azooxanthellate scleratinan coral Tubastrea aurea, native to the Indo-Pacific region. Symbiotic microbiota of T. aurea were studied at four particular marine water habitats of Taiwan including hydrothermal vents (HV), the coastal waters next to an abandoned copper mine(CM), nuclear power plants (NPP) and a site next to conservation zone (CZ). . DNA sequencing of the bacterial barcoding gene 16S rRNA full-length (~1.5 kbp) was applied to reveal the biodiversity of the coral-associated microbiome in response to above contrasting environments. Bacterial communities from coral samples significantly varied between extremely polluted and normal habitats. The chemoheterotrophic bacterial genus Endozoicomonas dominated the tissue samples from HV and CM sites, while phototrophic cyanobacteria belonging to Synechococcus dominated the NPP and CZ sites. The results revealed that the bacterial communities associated with T. aurea vary in their structural and functional profiles to support host adaptations towards extreme environmental conditions, which can be added to their physiological strategies in dispersion success, range expansion and invasiveness. The present study represents a pilot approach in Taiwan and provides information for several as yet unanswered questions that will be pursued by in situ transplantalation experiments of individual corals in the future.
06:30 PM
DIFFERENTIAL MICROBIOME RESPONSE TO ANTIBIOTIC CHALLENGES IN TWO CARRIBEAN STAGHORN CORAL GENOTYPES (5933)
Primary Presenter: Sunni Patton, Oregon State University (pattonsu@oregonstate.edu)
Caribbean acroporid corals, such as Acropora cervicornis, are essential for maintaining productive reef ecosystems, yet are facing widespread decline due to disease and anthropogenic threats. For this reason, many restoration initiatives in the Caribbean target A. cervicornis as it is fast growing and provides invaluable resources as an ecosystem engineer. Despite these efforts, many environmental threats can lead to dysbiotic microbiome shifts that compromise the success of outplants and native colonies, thereby leading to disease. In some cases, antibiotics are used to mitigate coral disease, yet few studies have investigated how these antibiotics affect apparently healthy coral, or how antibiotic-induced microbiome alterations will impact the coral’s ability to respond to future perturbations. To address this unknown, we conducted an aquaria-based experiment to investigate how two A. cervicornis genotypes with vastly different microbiome structures and varying predisposition to disease respond to antibiotic challenges. Throughout a five-day antibiotic exposure, we collected coral tissue samples for 16S rRNA sequencing and microscopy, as well as water samples for bacterial counts to comprehensively identify genotypic, antibiotic-specific, and dose-dependent microbiome responses. The results from this work provide fundamental information regarding how healthy corals respond to antibiotics, and constitute the basis for subsequent experimentation to reveal microbial mechanisms of coral resilience, recovery, or susceptibility to sequential environmental stressors.
06:30 PM
Assessing the potential for mesophotic coral reefs to ensure the survival of shallow coral reefs (6676)
Primary Presenter: Colin Scherpereel, UCLouvain (colin.scherpereel@uclouvain.be)
Mesophotic coral ecosystems (MCEs), located at depths greater than 30m, are one of the last lifeboats for coral reefs worldwide. Being partly sheltered from global warming, they could fare better than shallower coral reefs in the next decades and help repopulate them through larval exchanges. The United States Virgin Islands (USVI) are home to some of World’s richest and best documented MCEs. However, these islands are highly threatened by the spread of the stony coral tissue loss disease (SCTLD). The transmission of the SCTLD is likely to be supported by the dispersal of fine sediments transported by the same ocean currents responsible for larval exchanges. As connectivity can be a double-edged sword, it is therefore particularly challenging to identify which reefs are best suited to protection/restoration efforts. Here, we aim to assess the contribution of USVI MCEs to the resilience of the entire coral ecosystem. More specifically, we simulate the dispersal of larvae and disease agents thanks to a Lagrangian transport model coupled with a three- dimensional unstructured-mesh hydrodynamic model to deal with the USVI’s deep and steep bathymetry. We then identify the best larvae exporters and weakest disease importers in the connectivity networks by deriving conservation metrics based on graph theory algorithms. We consider different species with various susceptibilities to SCTLD and various larval traits in order to account for the USVI’s coral diversity. This allows us to highlight the MCEs with the most positive impact on the entire coral ecosystem and that should therefore be protected/restored in priority. In addition, we give a quantitative estimate of MCEs’ contribution to shallow larval recruitment and inform on the potential of the SCTLD to reach mesophotic reefs and spread among them.
06:30 PM
Exploring mechanisms of heat and cold tolerance in Galápagos Pocillopora communities (6992)
Primary Presenter: Katrina Giambertone, CSU Monterey Bay and Moss Landing Marine Laboratories (kgiambertone@csumb.edu)
Mass coral bleaching and mortality events jeopardize the persistence of coral reefs worldwide. Galápagos corals experience a wide range of temperatures and inhabit marginal conditions compared to other tropical reefs. The stress tolerance of corals remaining after recent warm- and cold-water bleaching events in the archipelago may be the product of adaptation and acclimatization. In the spring of 2019, we investigated thermal tolerance differences in Pocillopora sp., a widespread reef-building coral in the Indo-Pacific found throughout the Galápagos. We unexpectedly found that corals from northern sites–which experience warmer and less variable annual average temperatures–were more resilient than those from central and southern sites, having both greater heat and cold tolerances. In this study, we sequenced the mitochondrial open reading frame (ORF) to determine Pocillopora haplotype, amplified actin using quantitative PCR to determine symbiont type, and used RNAseq to explore gene expression patterns in our samples. We aim to understand how these variables correlate with heat and cold tolerance. Preliminary results suggest that the thermally-tolerant symbiont Durisdinium is absent from most central and southern sites and a thermally tolerant Pocillopora ORF haplotype (type 1) exists in far northern and most central southeastern communities, possibly explaining differences in thermal tolerance across regions. Our results can provide insight into the adaptive potential of reefs worldwide as they endure warm and cold stress events.
06:30 PM
EFFECT OF WATER FLOW ON TEMPERATURE-INDUCED CORAL BLEACHING (6327)
Primary Presenter: Atsushi Fujimura, University of Guam (fujimuraa@triton.uog.edu)
Studies in the last few decades have shown that bleaching of various coral species are mitigated by high water flow. One of the well-supported theories behind is enhancement of mass transfer by water current. High flow causes a thinning of the momentum boundary layer as well as the diffusive boundary layer that facilitates gas flux between the coral and the environment, thus efflux of harmful reactive oxygen species (ROS) from coral tissues increases. However, no study has directly measured ROS in the boundary layer under the water current. I have measured concentrations of hydrogen peroxide, a common ROS, within a few mm above the coral surface under heat stress in a laboratory flume. As expected, under high temperature condition, concentrations of hydrogen peroxide over the corals and bleaching severity in a high-flow condition were lower than those in a low flow. The result supports the theory that the mass transfer of ROS controls degrees of coral bleaching. Also, there was interspecific variability: <em>Acropora tenuis</em> bleached more harshly than <em>Galaxea fascicularis</em> which produced less hydrogen peroxide and may be more heat tolerant. Moreover, it is known that cold temperature can also cause bleaching. Coral bleaching was tested under cold temperature in a similar experimental setup. The outcome is more complex as it did not clearly show ROS productions or expected bleaching responses. Possible reasons will be discussed. Exploring bleaching mechanisms under different temperature/flow regimes will help coral reef management and conservation efforts.
06:30 PM
Assessing the heterotrophic abilities of two scleractinian corals during thermal stress as a strategy of resilience (4768)
Primary Presenter: Star Dressler, University of Guam (dresslerc@gotritons.uog.edu)
Corals that host endosymbiotic dinoflagellates maintain the majority of their metabolisms through photoautotrophy, and the coral host can additionally feed heterotrophically. These feeding modes can be regulated by some corals, and an increase of heterotrophic feeding during thermal stress can increase resilience of the coral holobiont. This two part laboratory-based study examines the degree of heterotrophic plasticity of two scleractinian corals, Acropora azurea and Pocillopora damicornis, at normal water temperatures and elevated temperatures. A. azurea has a higher predicted bleaching susceptibility compared to P. damicornis, and the two species may regulate their heterotrophic capacities to differing degrees with increased water temperatures. The heterotrophic capacities for A. azurea are not currently known, while P. damicornis is recognized to rely on heterotrophy to maintain metabolic functions. One controlled experiment examines the clearance rates that each coral species removes natural planktonic assemblages in water from Pago Bay, Guam. This research provides the opportunity to assess the size-fractionated planktonic community structure in a nearshore reef environment, which is poorly understood throughout Micronesia. In an additional controlled experiment, each coral species will be fed with isotopically enriched Artemia nauplii and assessed for the contribution of photoautotrophy and heterotrophy to the holobiont through carbon-13 and nitrogen-15 stable isotope analysis of coral tissue and endosymbionts.
SS115P Resilience in Coral Reef Ecosystems
Description
Time: 6:30 PM
Date: 8/6/2023
Room: Mezzanine