Combined effects of climate change and the herbicide diuron on the coral Acropora millepora

Mitigation of Vibrio coralliilyticus-induced coral bleaching through bacterial dysbiosis prevention by Ruegeria profundi

Vibrio species are prevalent in ocean ecosystems, particularly Vibrio coralliilyticus, and pose a threat to corals and other marine organisms under global warming conditions. While microbiota manipulation is considered for coral disease management, understanding the role of commensal bacteria in stress resilience remains limited. Here, a single bacterial species (Ruegeria profundi) rather than a consortium of native was used to combat pathogenic V. coralliilyticus and protect corals from bleaching. R. profundi showed therapeutic activity in vivo, preventing a significant reduction in bacterial diversity in bleached corals. Notably, the structure of the bacterial community differed significantly among all the groups. In addition, compared with the bleached corals caused by V. coralliilyticus, the network analysis revealed that complex interactions and positive correlations in the bacterial community of the R. profundi protected non-bleached corals, indicating R. profundi's role in fostering synergistic associations. Many genera of bacteria significantly increased in abundance during V. coralliilyticus infection, including Vibrio, Alteromonas, Amphritea, and Nautella, contributing to the pathogenicity of the bacterial community. However, R. profundi effectively countered the proliferation of these genera, promoting potential probiotic Endozoicomonas and other taxa, while reducing the abundance of betaine lipids and the type VI section system of the bacterial community. These changes ultimately influenced the interactive relationships among symbionts and demonstrated that probiotic R. profundi intervention can modulate coral-associated bacterial community, alleviate pathogenic-induced dysbiosis, and preserve coral health. These findings elucidated the relationship between the behavior of the coral-associated bacterial community and the occurrence of pathological coral bleaching.IMPORTANCEChanges in the global climate and marine environment can influence coral host and pathogen repartition which refers to an increased likelihood of pathogen infection in hosts. The risk of Vibrio coralliilyticus-induced coral disease is significantly heightened, primarily due to its thermos-dependent expression of virulent and populations. This study investigates how coral-associated bacterial communities respond to bleaching induced by V. coralliilyticus. Our findings demonstrate that Ruegeria profundi exhibits clear evidence of defense against pathogenic bacterial infection, contributing to the maintenance of host health and symbiont homeostasis. This observation suggests that bacterial pathogens could cause dysbiosis in coral holobionts. Probiotic bacteria display an essential capability in restructuring and manipulating coral-associated bacterial communities. This restructuring effectively reduces bacterial community virulence and enhances the pathogenic resistance of holobionts. The study provides valuable insights into the correlation between the health status of corals and how coral-associated bacterial communities may respond to both pathogens and probiotics.

Environmental Concentrations of Herbicide Prometryn Render Stress-Tolerant Corals Susceptible to Ocean Warming

Global warming has caused the degradation of coral reefs around the world. While stress-tolerant corals have demonstrated the ability to acclimatize to ocean warming, it remains unclear whether they can sustain their thermal resilience when superimposed with other coastal environmental stressors. We report the combined impacts of a photosystem II (PSII) herbicide, prometryn, and ocean warming on the stress-tolerant coral Galaxea fascicularis through physiological and omics analyses. The results demonstrate that the heat-stress-induced inhibition of photosynthetic efficiency in G. fascicularis is exacerbated in the presence of prometryn. Transcriptomics and metabolomics analyses indicate that the prometryn exposure may overwhelm the photosystem repair mechanism in stress-tolerant corals, thereby compromising their capacity for thermal acclimation. Moreover, prometryn might amplify the adverse effects of heat stress on key energy and nutrient metabolism pathways and induce a stronger response to oxidative stress in stress-tolerant corals. The findings indicate that the presence of prometryn at environmentally relevant concentrations would render corals more susceptible to heat stress and exacerbate the breakdown of coral Symbiodiniaceae symbiosis. The present study provides valuable insights into the necessity of prioritizing PSII herbicide pollution reduction in coral reef protection efforts while mitigating the effects of climate change.

Evaluating the effects of climate change and chemical, physical, and biological stressors on nearshore coral reefs: A case study in the Great Barrier Reef, Australia

An understanding of the combined effects of climate change (CC) and other anthropogenic stressors, such as chemical exposures, is essential for improving ecological risk assessments of vulnerable ecosystems. In the Great Barrier Reef, coral reefs are under increasingly severe duress from increasing ocean temperatures, acidification, and cyclone intensities associated with CC. In addition to these stressors, inshore reef systems, such as the Mackay-Whitsunday coastal zone, are being impacted by other anthropogenic stressors, including chemical, nutrient, and sediment exposures related to more intense rainfall events that increase the catchment runoff of contaminated waters. To illustrate an approach for incorporating CC into ecological risk assessment frameworks, we developed an adverse outcome pathway network to conceptually delineate the effects of climate variables and photosystem II herbicide (diuron) exposures on scleractinian corals. This informed the development of a Bayesian network (BN) to quantitatively compare the effects of historical (1975-2005) and future projected climate on inshore hard coral bleaching, mortality, and cover. This BN demonstrated how risk may be predicted for multiple physical and biological stressors, including temperature, ocean acidification, cyclones, sediments, macroalgae competition, and crown of thorns starfish predation, as well as chemical stressors such as nitrogen and herbicides. Climate scenarios included an ensemble of 16 downscaled models encompassing current and future conditions based on multiple emission scenarios for two 30-year periods. It was found that both climate-related and catchment-related stressors pose a risk to these inshore reef systems, with projected increases in coral bleaching and coral mortality under all future climate scenarios. This modeling exercise can support the identification of risk drivers for the prioritization of management interventions to build future resilient reefs. Integr Environ Assess Manag 2024;20:401-418. © 2023 Norwegian Institute for Water Research and The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Acute Toxicity Assays with Adult Coral Fragments: A Method for Standardization

Coral reefs are globally declining due to various anthropogenic stressors. Amongst those, chemical pollutants, such as pesticides from agricultural runoff, sewage or an overabundance of personal care products in coastal waters due to intense tourism, may be considered as a local stressor for reef-building corals. The extent to which such chemicals exhibit toxic effects towards corals at environmentally relevant concentrations is currently controversially discussed and existing studies are often based on varying and sometimes deficient test methods. To address this uncertainty, we adapted available methods into a reliable and comprehensive acute coral toxicity test method for the reef-building coral Montipora digitata. The toxicities of the four substances benzophenone-3 (BP-3), Diuron (DCMU), copper (Cu2+ as CuCl2, positive control) and dimethylformamide (DMF, solvent) were assessed in a 96 h semi-static test design. Endpoints such as maximum quantum yield, bleaching, tissue loss and mortality were evaluated with respect to their suitability for regulatory purposes. Overall, the endpoints bleaching and mortality yielded sensitive and robust results for the four tested substances. As the test method follows the principles of internationally standardized testing methods (ISO, OECD), it can be considered suitable for further validation and standardization. Once validated, a standardized test method will help to obtain reproducible toxicity results useful for marine hazard and risk assessment and regulatory decision making.

Interactions between quorum sensing/quorum quenching and virulence genes may affect coral health by regulating symbiotic bacterial community

Quorum sensing (QS) and quorum quenching (QQ) are two antagonistic processes that may regulate the composition, function and structure of bacterial community. In coral holobiont, autoinducers signaling mediate the communication pathways between interspecies and intraspecies bacteria, which regulate the expression of the virulence factors that can damage host health. However, under environmental stressors, the interaction between the QS/QQ gene and virulence factors and their role in the bacterial communities and coral bleaching is still not fully clear. To address this question, here, metagenomics method was used to examine the profile of QS/QQ and virulence genes from a deeply sequenced microbial database, obtained from three bleached and non-bleached corals species. The prediction of bacterial genes of bleached samples involved in functional metabolic pathways were remarkably decreased, and the bacterial community structure on bleached samples was significantly different compared to non-bleached samples. The distribution and significant difference in QS/QQ and virulence genes were also carried out. We found that Proteobacteria was dominant bacteria among all samples, and AI-1 system is widespread within this group of bacteria. The identified specific genes consistently exhibited a trend of increased pathogenicity in bleached corals relative to non-bleached corals. The abundance of pathogenicity-associated QS genes, including bapA, pfoA and dgcB genes, were significantly increased in bleached corals and can encode the protein of biofilm formation and the membrane damaging toxins promoting pathogenic adhesion and infection. Similarly, the virulence genes, such as superoxide dismutase (Mn-SOD gene), metalloproteinase (yme1, yydH and zmpB), glycosidases (malE, malF, malG, and malK) and LodAB (lodB) genes significantly increased. Conversely, QQ genes that inhibit QS activity and virulence factors to defense the pathogens, including blpA, lsrK, amiE, aprE and gmuG showed a significant decrease in bleached groups. Furthermore, the significant correlations were found among virulence, QS/QQ genes, and coral associated bacterial community, and the virulence genes interact with key QS/QQ genes, directly or indirectly influence symbiotic bacterial communities homeostasis, thereby impacting coral health. It suggested that the functional and structural divergence in the symbiont bacteria may be partially attribute to the interplay, involving interactions among the host, bacterial communication signal systems, and bacterial virulence factors. In conclusion, these data helped to reveal the characteristic behavior of coral symbiotic bacteria, and facilitated a better understanding of bleaching mechanism from a chemical ecological perspective.

Individual and combined effects of herbicide prometryn and nitrate enrichment at environmentally relevant concentrations on photosynthesis, oxidative stress, and endosymbiont community diversity of coral Acropora hyacinthus

Nitrogen pollution and pesticides such as photosystem II (PSII) inhibitor herbicides have several detrimental impacts on coral reefs, including breakdown of the symbiosis between host corals and photosynthetic symbionts. Although nitrogen and PSII herbicide pollution separately cause coral bleaching, the combined effects of these stressors at environmentally relevant concentrations on corals have not been assessed. Here, we report the combined effects of nitrate enrichment and PSII herbicide (prometryn) exposure on photosynthesis, oxidative status and endosymbiont community diversity of the reef-building coral Acropora hyacinthus. Coral fragments were exposed in a mesocosm system to nitrate enrichment (9 μmol/L) and two prometryn concentrations (1 and 5 μg/L). The results showed that sustained prometryn exposure in combination with nitrate enrichment stress had significant detrimental impacts on photosynthetic apparatus [the maximum quantum efficiency of photosystem II (Fv/Fm), nonphotochemical quenching (NPQ) and oxidative status in the short term. Nevertheless, the adaptive mechanism of corals allowed the normal physiological state to be recovered following 1 μg/L prometryn and 9 μmol/L nitrate enrichment individual exposure. Moreover, exposure for 9 days was insufficient to trigger a shift in Symbiodiniaceae community. Most importantly, the negative impact of exposure to the combined environmental concentrations of 1 μg/L prometryn and 9 μmol/L nitrate enrichment was found to be significantly greater on the Fv/Fm, quantum yield of non-regulated energy dissipation [Y(NO)], NPQ, and oxidative status of corals compared to the impact of individual stressors. Our results show that interactions between prometryn stress and nitrate enrichment have a synergistic impact on the photosynthetic and oxidative stress responses of corals. This study provides valuable insights into combined effects of nitrate enrichment and PSII herbicides pollution for coral's physiology. Environmental concentrations of PSII herbicides may be more harmful to photosystems and antioxidant systems of corals under nitrate enrichment stress. Thus, future research and management of seawater quality stressors should consider combined impacts on corals rather than just the impacts of individual stressors alone.

Addressing chemical pollution in biodiversity research

Climate change, biodiversity loss, and chemical pollution are planetary-scale emergencies requiring urgent mitigation actions. As these "triple crises" are deeply interlinked, they need to be tackled in an integrative manner. However, while climate change and biodiversity are often studied together, chemical pollution as a global change factor contributing to worldwide biodiversity loss has received much less attention in biodiversity research so far. Here, we review evidence showing that the multifaceted effects of anthropogenic chemicals in the environment are posing a growing threat to biodiversity and ecosystems. Therefore, failure to account for pollution effects may significantly undermine the success of biodiversity protection efforts. We argue that progress in understanding and counteracting the negative impact of chemical pollution on biodiversity requires collective efforts of scientists from different disciplines, including but not limited to ecology, ecotoxicology, and environmental chemistry. Importantly, recent developments in these fields have now enabled comprehensive studies that could efficiently address the manifold interactions between chemicals and ecosystems. Based on their experience with intricate studies of biodiversity, ecologists are well equipped to embrace the additional challenge of chemical complexity through interdisciplinary collaborations. This offers a unique opportunity to jointly advance a seminal frontier in pollution ecology and facilitate the development of innovative solutions for environmental protection.

Adaptive Responses of the Sea Anemone Heteractis crispa to the Interaction of Acidification and Global Warming

Ocean acidification and warming are two of the most important threats to the existence of marine organisms and are predicted to co-occur in oceans. The present work evaluated the effects of acidification (AC: 24 ± 0.1 °C and 900 μatm CO2), warming (WC: 30 ± 0.1 °C and 450 μatm CO2), and their combination (CC: 30 ± 0.1 °C and 900 μatm CO2) on the sea anemone, Heteractis crispa, from the aspects of photosynthetic apparatus (maximum quantum yield of photosystem II (PS II), chlorophyll level, and Symbiodiniaceae density) and sterol metabolism (cholesterol content and total sterol content). In a 15-day experiment, acidification alone had no apparent effect on the photosynthetic apparatus, but did affect sterol levels. Upregulation of their chlorophyll level is an important strategy for symbionts to adapt to high partial pressure of CO2 (pCO2). However, after warming stress, the benefits of high pCO2 had little effect on stress tolerance in H. crispa. Indeed, thermal stress was the dominant driver of the deteriorating health of H. crispa. Cholesterol and total sterol contents were significantly affected by all three stress conditions, although there was no significant change in the AC group on day 3. Thus, cholesterol or sterol levels could be used as important indicators to evaluate the impact of climate change on cnidarians. Our findings suggest that H. crispa might be relatively insensitive to the impact of ocean acidification, whereas increased temperature in the future ocean might impair viability of H. crispa.

Effects of currently used marine antifouling paint biocides on green fluorescent proteins in Anemonia viridis

Some of the antifouling booster biocides affects the marine ecosystem negatively. The booster biocides that are resistant to degradation are accumulated in the sediment of the oceans. One of the sedentary organisms in the Mediterranean Sea is Anemonia viridis. This study aims at showing the toxicities of common biocides such as irgarol, seanine-211, zinc omadine, and acticide on the fluorescence by GFPs of A. viridis. The decreases in the fluorescence intensities of the GFP were measured within different booster biocide concentrations. The results show that fluorescent intensities of GFP proteins decrease more than 50% when they are exposed to different concentrations of irgarol, zinc omadine, acticide. In conclusion, ecosystem health should be prioritized when new antifouling paint compositions are proposed. From the results, it seems that A. viridis can be considered as a vulnerable organism and it is sensitive to booster biocides within self-polishing antifouling paint formulations.

Individual and combined effects of diuron and light reduction on marine microalgae

Coastal ecosystems such as those in the Great Barrier Reef (GBR) lagoon, are exposed to stressors in flood plumes including low light (caused by increased turbidity) and agricultural pesticides. Photosystem II (PSII)-inhibiting herbicides are the most frequently detected pesticides in the GBR lagoon, but it is not clear how their toxicity to phototrophic species depends on light availability. This study investigated the individual and combined effects of PSII-inhibiting herbicide, diuron, and reduced light intensity (as a proxy for increased turbidity) on the marine diatom, Phaeodactylum tricornutum. Effective quantum yield (EQY) and cell density were measured to calculate responses relative to the controls over 72-h, in tests with varying stressor intensities. Individually, diuron concentrations (0.1-3 μg l^-1) were not high enough to significantly reduce growth (cell density), but led to decreased EQY; while, low light generally led to increased EQY, but only reduced growth at the lowest tested light intensity (5 μmol photons m^-2 s^-1) after 48-hours. P. tricornutum was less affected by diuron when combined with low light scenarios, with increased EQY (up to 163% of the controls) that was likely due to increased electron transport per photon, despite lesser available photons at this low light intensity. In contrast, growth was completely inhibited relative to the controls when algae were simultaneously exposed to the highest stressor levels (3 μg l^-1 diuron and 5 μmol photons m^-2 s^-1). This study highlights the importance of measuring more than one biological response variable to capture the combined effects of multiple stressors. Management of water quality stressors should consider combined impacts rather than just the impacts of individual stressors alone. Reducing suspended sediment and diuron concentrations in marine waters can decrease harmful effects and bring synergistic benefits to water quality.

Physiological and transcriptomic analyses reveal the threat of herbicides glufosinate and glyphosate to the scleractinian coral Pocillopora damicornis

The amino acid metabolism-related herbicides glufosinate and glyphosate are used worldwide and have flowed into the oceans, threatening the marine organisms. In the present study, physiological activities and transcriptomic profiles of the scleractinian coral Pocillopora damicornis and symbiotic Symbiodiniaceae were determined during a 48 h-exposure to the two herbicides with the final concentration of 10 μmol L-1. Coral samples were collected at 0, 12, 24, and 48 h after exposure to determine symbiont density, chlorophyll content, as well as activities of superoxide dismutase (SOD), catalase (CAT), nitric oxide synthetase (NOS) and phenoloxidase (PO), and the caspase-3 levels, and the samples collected at 24 h were employed in the transcriptomic analysis. Specifically, the symbiont densities did not change significantly in response to the two herbicides, while the chlorophyll content increased significantly at 24 h post glufosinate exposure. SOD and CAT activities in the coral host increased significantly at 12 h after glufosinate and glyphosate exposure, while the activity of NOS in symbionts decreased significantly at 48 h after glufosinate exposure. Caspase-3 levels in the coral host declined significantly at 24 h after exposure to the two herbicides. In the transcriptomic analysis, glufosinate triggered the expression of genes related to the response to stimuli and immunoregulation in the coral host, and suppressed the expression of genes related to coral nitrogen-related metabolism, symbiont cell cycle, and response to nutrient levels. Furthermore, glyphosate activated the expression of genes involved in coral calcification and symbiont nutrient export and suppressed the expression of genes involved in coral meiosis and symbiont cell communication. These results suggest that although the coral-Symbiodiniaceae symbiosis is not disrupted, short-term glufosinate and glyphosate exposures alter several essential physiological processes including metabolism, calcification, and meiosis in the coral host, as well as the cell cycle and nutrient export in the symbiont. SUMMARY: Glufosinate and glyphosate herbicide exposures can disturb several essential physiological processes, including metabolism, calcification, and meiosis in the coral host as well as the cell cycle and nutrient export in the symbiont, threating the survival of scleractinian corals.