- Francois O Seneca, Stephen R. Palumbi (2015) The role of transcriptome resilience in resistance of corals to bleaching. Molecular Ecology, 24: 1467-1484
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ONGOING RESEARCH PROJECTS
Land-based Pollution Effects on Coral Health
With increasing human population, continued agriculture and urban development is inevitable. But, it is becoming increasingly apparent that human activities need to simultaneously strive for sustainability in order to preserve the integrity of the planet’s climate and the natural resources of its ecosystems. As the reality widespread environmental degradation and its consequences is slowly infiltrating public awareness, broad-scale cultural and political change is slow. However, local management and conservation initiatives can take meaningful actions more rapidly to alleviate anthropogenic stress at smaller scales.
Corals are the foundation taxa of coral reef ecosystems and are sensitive to water quality. Thus, land-based pollution can have devastating effects on the health of corals and their reliant reef ecosystems. Local initiatives can be excellent strategies for addressing such issues, however in order to be effective, management decisions must be based on sound science. To address land-based pollution on coral reefs, pollutant stress and threat thresholds for corals are urgently needed but currently unknown. Such scientific basic knowledge is critical to implement best management practices with a true potential for the sustainability of the resources at stake.
Thus, I am currently studying the dynamics of the stress response in corals exposed to varying land-based pollutants with the goal to provide thresholds of minimum sublethal and maximum pollutant exposures for several species of local Hawaiian corals. This information will be used by coral reef managers and stakeholders to implement local plans to mitigate land-based pollution damage to corals and reefs.
Research Collaborator: Professor Robert Richmond, Kewalo Marine Laboratory, University of Hawaii.
Coral Adaptation to Global Climate Change
Reef-building corals are currently in decline. It is predicted that worldwide coral populations will experience devastating mass mortality within 50 – 100 years if they do not possess the capacity to adapt or acclimatize to the environmental changes expected from ongoing global climate change.
Meanwhile, some existing coral populations inhabit harsh environments and may be already adapted to challenging environmental conditions. Therefore, there is an urgent need to determine whether these populations deserve conservation priority as promising sources for recolonization of degraded reefs. I am currently studying the resilience of such potential refugia in American Samoa, where I have conducted reciprocal transplantation and transcriptomic experiments on corals living at extreme temperatures.
The outcomes of this research are essential to successful management of climate change effects on coral reef ecosystems and designating such valuable populations as conservation priorities.
Research Collaborators: Professor Stephen Palumbi, Hopkins Marine Station, Stanford University. Dr Daniel Barshis, Old Dominion University, Virginia.
The Role of Apoptosis during Coral Bleaching and Recovery
Apoptosis is one of several mechanisms by which cnidarians are known to lose algal symbionts in response to stress stimuli. A recent study suggested that caspase-dependent apoptosis pathways underpin the bleaching response in corals, and proposed a model for coral resistance to thermal bleaching that involves the down-regulation of caspase (Tchernov et al. 2011).
In order to evaluate the generality of caspase-mediated bleaching to the coral thermal stress response, I have tested the prevalence of this phenomenon across multiple species and stress regimes.
Research Collaborator: Professor Stephen Palumbi, Hopkins Marine Station, Stanford University.
Coral Molecular Stress Responses in a Changing Climate
Global climate change has an undeniably detrimental effect on the coral reef ecosystem. Coral mortality due to various stressors and most significantly mass bleaching plays a primary role. Understanding why corals are dying can help predict the future of the whole reef ecosystem, and also the potential of acclimatization, adaptation and recovery.
I have characterized the molecular stress response in corals during a natural bleaching event. My results shed light on the different biological processes involved in coral bleaching and highlight new genes as promising candidates for the understanding of coral biology.
Research Collaborators: Professor David Miller, James Cook University Townsville. Dr Madeleine van Oppen, Australian Institute of Marine Science.
Anthropogenic Pollution Effects on Coral Larvae
In addition to global climate change, anthropogenic pollution impacts corals at different life history stages. For example, exposure to chemicals from runoff in agricultural areas can influence the physiological performance of coral larvae, having serious implications for settlement and survival success.
I have studied the effects of agricultural chemicals on the transcriptome of coral larvae with the goal to complement previous physiological observations at the organismal level.
Research Collaborators: Dr. Andrew Negri, Australian Institute of Marine Science.
Molecular Aspects of the Coral-Symbiodinium Symbiosis
As a result of my doctoral work on coral bleaching and molecular stress, I was inspired to understand the underlying molecular implications of harboring photosynthetic algae in animal tissue. I have conducted a study that compares the heat shock/ oxidative stress response, innate immune response and the molecular signals of symbiosis establishment in thermally challenged coral larvae with and without algal symbionts.
Research Collaborators: Professor Bette Willis, James Cook University. Dr Madeleine van Oppen, Australian Institute of Marine Science.
Assay Development for Measurement of Gene Expression and Protein Activity in Symbiotic Organisms
Gene expression, genomic and proteomic technologies and methods are relatively new to the field of coral reef research and require considerable effort towards optimization and adjustment. I have a great interest in the application of molecular tools to marine ecology. And, I am constantly pursuing the improvement of methods I have developed and/ or used for gene/ protein expression and activity quantification in the coral holobiont, such as quantitative real time PCR, microarray, RNA-Seq, Gene Expression Analysis System (GeXP), Western blot hybridization, ELISA, and enzymatic assays.
I am currently a junior researcher in the Richmond Laboratory at the Kewalo Marine Station of the University of Hawaii where I investigate detoxification mechanisms in reef-building corals by examining gene expression, protein levels, enzymatic activity and physiological signs of stress.
Our work takes place on the Island of Oahu in Hawaii, where I am conducting toxicological experiments with corals living in areas affected by land-based pollution. These experiments aim to determine how corals from these populations survive exposure to pollutants and whether the corals show signs of adaptation to pollution exposure.
I am also investigating the role of the catalase enzymes during pollution stress by measuring catalase activity in several species with varying capacities for pollution resilience. In this study, I address the hypothesis that certain corals survive pollution exposures by regulating detoxifying enzymes, such as catalase, which remove the toxins and protect the coral from further cellular damage.
Increased knowledge of pollution stress response and resilience in corals is urgently needed as more local management strategies are planned with the goal to mitigate land-based pollution stress in coral reef ecosystems. In addition, detoxification mechanisms may play a similar role in the resilience of corals to climate change, providing invaluable information for reef managers and stakeholders alike.
On the cover: Coral bleaching, or the loss of vital photosynthetic algae from reef-building corals, is a devastating consequence of the warming of the oceans due to global climate change. For over 30 years, studies on the causes of bleaching have focused on damage occurring in the light thought to be due to photosynthetic production of reactive oxygen molecules. In this issue, Tolleter, Seneca, and colleagues (pages 1782–1786) show that light is not required for severe bleaching, and that heat alone can damage the coral photosynthetic apparatus. These findings reveal the presence of a light-independent pathway for coral bleaching and will help elucidate the cellular mechanisms of bleaching in corals. Photograph © François Seneca.
Ofu’s backreef system produces especially tough corals
On the island of Ofu in American Samoa, a small area of the coral-built lagoon covering a few hundreds square meters, is characterized by highly fluctuating physical conditions. During summer low tides and calm sunny conditions, restricted water flow in the lagoon leads to extreme water temperatures ( >34°C) in comparison to the surrounding reef areas.
The coupling of seasonal heat exposure and climate driven increases in temperature maxima would make this area of the lagoon inhospitable for most reef-building corals from other areas around the world.
Nonetheless, a diverse community of heat-resistant corals thrives in this area of the Ofu lagoon, which we refer to as the highly variable pool (HV; previously referred as pool 300 in Oliver & Palumbi 2011). In contrast, a neighboring pool, approximately 600 meters away from the HV pool, experiences less fluctuating conditions and is referred to as the moderately variable pool (MV; previously referred as pool 400 in Oliver & Palumbi 2011).
The relative resilience of coral individuals from the HV pool was demonstrated by exposing coral branches to short heat stress exposures that trigger a bleaching response in tank experiments. Oliver and Palumbi (2011) suggested that the dominant type D symbiont found in HV corals plays a critical role in the resilience of this subpopulation. However, after measuring the effect of heat exposure on the photochemical efficiency of symbiont D-associating corals from both pools, they suggested that pre-conditioning to highly variable environmental conditions also influences the performance of corals independently of their symbiont type.
With this in mind, we hypothesize that HV coral resilience is the result of a combination of three main factors: 1) the type of symbionts the corals associate with, 2) the conditioning from recurrent exposures to dramatic fluctuations in temperature, and 3) a genetic advantage selected for through recent selective sweeps. In order to investigate the role that each of these factors plays in the enhanced fitness of HV corals relative to more sensitive MV corals, we performed a reciprocal transplantation using Acropora surculosa colonies living in both pools. The initial proportion of symbiont types for each colony was determined using the sequencing data of PhD student Rachael Bay. After 17 months in the field, nubbins were subjected to a controlled heat stress experiment in tanks and sampled for bleaching state and transcriptomics.
The analysis is under way...
Adaptation & Acclimatization of Corals to Global Climate Change
Heat alone, in absence of light and consequently photosynthetically produced toxic oxygen radicals, can cause corals to bleach!
Check out our recent article published in Current Biology
Link to the paper: