Oxidative stress-the production and accumulation of reduced oxygen intermediates such as superoxide radicals, singlet oxygen, hydrogen peroxide, and hydroxyl radicals-can damage lipids, proteins, and ...DNA. Many disease processes of clinical interest and the aging process involve oxidative stress in their underlying etiology. The production of reactive oxygen species is also prevalent in the world's oceans, and oxidative stress is an important component of the stress response in marine organisms exposed to a variety of insults as a result of changes in environmental conditions such as thermal stress, exposure to ultraviolet radiation, or exposure to pollution. As in the clinical setting, reactive oxygen species are also important signal transduction molecules and mediators of damage in cellular processes, such as apoptosis and cell necrosis, for marine organisms. This review brings together the voluminous literature on the biochemistry and physiology of oxidative stress from the clinical and plant physiology disciplines with the fast-increasing interest in oxidative stress in marine environments.
Historically, the response of marine invertebrates to their environment, and environmentally induced stress, has included some measurement of their physiology or metabolism. Eventually, this approach ...developed into comparative energetics and the construction of energetic budgets. More recently, coral reefs, and scleractinian corals in particular, have suffered significant declines due to climate change-related environmental stress. In addition to a number of physiological, biophysical and molecular measurements to assess “coral health,” there has been increased use of energetic approaches that have included the measurement of specific biochemical constituents (i.e., lipid concentrations) as a proxy for energy available to assess the potential outcomes of environmental stress on corals. In reading these studies, there appears to be some confusion between energy budgets and carbon budgets. Additionally, many assumptions regarding proximate biochemical composition, metabolic fuel preferences and metabolic quotients have been made, all of which are essential to construct accurate energy budgets and to convert elemental composition (i.e., carbon) to energy equivalents. Additionally, models of energetics such as the metabolic theory of ecology or dynamic energy budgets are being applied to coral physiology and include several assumptions that are not appropriate for scleractinian corals. As we assess the independent and interactive effects of multiple stressors on corals, efforts to construct quantitative energetic budgets should be a priority component of realistic multifactor experiments that would then improve the use of models as predictors of outcomes related to the effects of environmental change on corals.
The evolutionary success and continued survival of reef-building corals under increasing environmental change will, in part, be determined by the composition of their endosymbiotic dinoflagellate ...communities (
Symbiodinium
sp.). Recent research suggests that differences in the phylotype composition of
Symbiodinium
in the same host can lead to different outcomes for the host when exposed to similar environmental conditions. One explanation for these observations is that symbioses between corals and
Symbiodinium
represent a continuum of interaction states that encompass mutualisms and parasitisms consistent with current evolutionary theory developed for other symbiotic systems. Here, we discuss the evidence supporting the existence of a parasitic to mutualistic continuum in
Symbiodinium
interactions and propose that a consideration of the evolutionary ecology of these associations will advance our understanding of how environmental change will influence the ecological outcomes in these important symbioses. We advocate that a robust taxonomic structure for
Symbiodinium
sp. and empirical studies on sexual reproduction in
Symbiodinium
, the stability of interaction states among
Symbiodinium
symbioses spatially and temporally and how interaction states change as the environment changes will generate data for models that accurately forecast how climate change will influence the persistence of corals and the reefs they structure.
The role of both host and dinoflagellate symbionts was investigated in the response of reef-building corals to thermal stress in the light. Replicate coral nubbins of
Stylophora pistillata and
...Porites cylindrica from the GBR were exposed to either 28 °C (control) or 32 °C for 5 days before being returned to an ambient reef temperature (28 °C).
S. pistillata was found to contain either
Symbiodinium genotype C1 or C8a, while
P. cylindrica had type C15 based on ITS genotyping. Analysis of the quantum yield of photosystem (PS) II fluorescence of the symbionts in
P. cylindrica showed that light-induced excitation pressure on the C15
Symbiodinium was significantly less, and the steady state quantum yield of PSII fluorescence at noon (
ΔF/Fm′) greater, than that measured in C1/C8a
Symbiodinium sp. from
S. pistillata. Immunoblots of the PS II D1 protein were significantly lower in
Symbiodinium from
S. pistillata compared to those in
P. cylindrica after exposure to thermal stress. The biochemical markers, heat-stress protein (HSP) 70 and superoxide dismutase (SOD), were significantly greater in
P. cylindrica before the experiment, and both species of coral increased their biosynthesis of HSP 70 and SOD when exposed to thermal stress. Concentrations of MAAs, glycerol, and lipids were not significantly affected by thermal stress in these experiments, but DNA damage was greater in heat-stressed
S. pistillata compared to
P. cylindrica. There was minimal coral mucus, which accounts for up to half of the total energy budget of a coral and provides the first layer of defense for invading microbes, produced by
S. pistillata after heat stress compared to
P. cylindrica. It is concluded that
P. cylindrica contains a heat resistant C15
Symbiodinium and critical host proteins are present at higher concentrations than observed for
S. pistillata, the combination of which provides greater protection from bleaching conditions of high temperature in the light.
Mesophotic coral ecosystems (MCEs), occurring at depths of 30 to over 150
m, represents the deep continuum of adjacent shallow coral reefs about which little is known. These reefs are most developed, ...and most frequently studied, in areas where light penetration is high and photosymbiotic reef-builders (corals) can persist as common members of the benthic community. The upper mesophotic zone typically extends to 60
m and comprises communities that are generally similar to those found in shallow reef systems. Below 60
m, the lower mesophotic zone is dominated by sponges and algae that are uncommon or absent from shallower areas, and a fish fauna that is largely specialized to these intermediate depths. It is likely that these ecosystems are much more widespread and important than was previously recognized. MCEs have the potential to function as refugia for shallow reefs because many disturbances in the upper 30
m may leave MCEs largely intact. Ontogenetic movement and spawning migrations by reef fishes provide an important ecological component to connectivity between shallow and mesophotic reefs and may represent the effective range of larval dispersal. However, there is currently limited information on genetic connectivity between deep and shallow coral reef populations, and this is a critical gap in understanding the role of MCEs in coral reef resilience. Here we review the connectivity and trophic relationships between the shallow and mesophotic coral reefs, the potential role of MCEs as refugia, and the effects of a new biological invader that exposes critical gaps in our understanding of the stability of these ecosystems.
► Mesophotic coral reef ecosystems can be divided into upper (<
60
m) lower zones (>
60
m). ► Mesophotic coral reefs can potentially act as refugia for a subset of the shallow coral reef community. ► The resilience of these deep reef habitats may depend on the degree of genetic connectivity with adjacent shallow reefs. ► Stability of mesophotic coral reefs can be variable in time and space.
Fundamental to holobiont biology is recognising how variation in microbial composition and function relates to host phenotypic variation. Sponges often exhibit considerable phenotypic plasticity and ...also harbour dense microbial communities that function to protect and nourish hosts. One of the most prominent sponge genera on Caribbean coral reefs is Agelas. Using a comprehensive set of morphological (growth form, spicule), chemical and molecular data on 13 recognised species of Agelas in the Caribbean basin, we were able to define only five species (=clades) and found that many morphospecies designations were incongruent with phylogenomic and population genetic analyses. Microbial communities were also strongly differentiated between phylogenetic species, showing little evidence of cryptic divergence and relatively low correlation with morphospecies assignment. Metagenomic analyses also showed strong correspondence to phylogenetic species, and to a lesser extent, geographical and morphological characters. Surprisingly, the variation in secondary metabolites produced by sponge holobionts was explained by geography and morphospecies assignment, in addition to phylogenetic species, and covaried significantly with a subset of microbial symbionts. Spicule characteristics were highly plastic, under greater impact from geographical location than phylogeny. Our results suggest that while phenotypic plasticity is rampant in Agelas, morphological differences within phylogenetic species affect functionally important ecological traits, including the composition of the symbiotic microbial communities and metabolomic profiles.
Elevated seawater temperatures have long been accepted as the principal stressor causing the loss of symbiotic algae in corals and other invertebrates with algal symbionts (i.e., "bleaching"). A ...secondary factor associated with coral bleaching is solar irradiance, both its visible (PAR: 400-700 nm) and ultraviolet (UVR: 290-400 nm) portions of the spectrum. Here we examined the synergistic role of solar radiation on thermally induced stress and subsequent bleaching in a common Caribbean coral, Montastraea faveolata. Active fluorescent measurements show that steady-state quantum yields of photosystem II (PSII) fluorescence in the zooxanthellae are markedly depressed when exposed to high solar radiation and elevated temperatures, and the concentration of D1 protein is significantly lower in high light when compared to low light treatments under the same thermal stress. Both photosynthetic pigments and mycosporine-like amino acids (MAAs) are also depressed after experimental exposure to high solar radiation and thermal stress. Host DNA damage is exacerbated under high light conditions and is correlated with the expression of the cell cycle gene p 53, a cellular gatekeeper that modulates the fate of damaged cells between DNA repair processes and apoptotic pathways. These markers of cellular stress in the host and zooxanthellae have in common their response to the enhanced production of reactive oxygen species during exposure to high irradiances of solar radiation and elevated temperatures. Taking these results and previously published data into consideration, we conclude that thermal stress during exposure to high irradiances of solar radiation, or irradiances higher than the current photoacclimatization state, causes damage to both photochemistry and carbon fixation at the same time in zooxanthellae, while DNA damage, apoptosis, or necrosis are occurring in the host tissues of symbiotic cnidarians.PUBLICATION ABSTRACT
Transcriptome and genome data from twenty stony coral species and a selection of reference bilaterians were studied to elucidate coral evolutionary history. We identified genes that encode the ...proteins responsible for the precipitation and aggregation of the aragonite skeleton on which the organisms live, and revealed a network of environmental sensors that coordinate responses of the host animals to temperature, light, and pH. Furthermore, we describe a variety of stress-related pathways, including apoptotic pathways that allow the host animals to detoxify reactive oxygen and nitrogen species that are generated by their intracellular photosynthetic symbionts, and determine the fate of corals under environmental stress. Some of these genes arose through horizontal gene transfer and comprise at least 0.2% of the animal gene inventory. Our analysis elucidates the evolutionary strategies that have allowed symbiotic corals to adapt and thrive for hundreds of millions of years.
Coral reef ecosystems are at the crossroads. While significant gaps still exist in our understanding of how “normal” reefs work, unprecedented changes in coral reef systems have forced the research ...community to change its focus from basic research to understand how one of the most diverse ecosystems in the world works to basic research with strong applied implications to alleviate damage, save, or restore coral reef ecosystems. A wide range of stressors on local, regional, and global spatial scales including over fishing, diseases, large-scale disturbance events, global climate change (e.g., ozone depletion, global warming), and over population have all contributed to declines in coral cover or phase shifts in community structure on time scales never observed before. Many of these changes are directly or indirectly related to anthropogenically induced changes in the global support network that affects all ecosystems. This review focuses on some recent advances in the experimental biology of coral reef ecosystems, and in particular scleractinian corals, at all levels of biological organization. Many of the areas of interest and techniques discussed reflect a progression of technological advances in biology and ecology but have found unique and timely application in the field of experimental coral reef biology. The review, by nature, will not be exhaustive and reflects the author's interests to a large degree. Because of the voluminous literature available, an attempt has been made to capture the essential elements and references for each topic discussed.
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