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新污染物对珊瑚共生体碳代谢关键过程影响的研究进展
Research progress on the effects of emerging contaminants on key carbon metabolic processes of coral holobionts
南海是我国重要的珊瑚礁分布区,也是新污染物输入和累积的高风险海域。近年来,新污染物(emerging contaminants, ECs,主要包括持久性有机污染物、内分泌干扰物、抗生素及微塑料等)已在南海及其沿岸海域普遍检出,并对珊瑚礁生态系统构成潜在威胁。然而,对于ECs如何通过干扰珊瑚共生体的关键生理过程,进而改变其碳循环功能,仍缺乏系统性认识。本文系统综述了南海ECs污染现状,重点评述了其对珊瑚共生体光合作用、呼吸作用、钙化过程及微生物过程等关键碳循环环节的影响。综合现有研究发现,ECs可通过抑制虫黄藻光合固碳、增强异养呼吸、干扰钙化及改变微生物群落结构与代谢功能,削弱珊瑚共生体的碳汇功能,甚至在特定条件下促使其由碳汇向碳源转变。总体来看,ECs对珊瑚共生体碳代谢的影响具有多过程耦合性和功能累积效应,可能对珊瑚礁碳汇功能及其潜在蓝碳属性的长期稳定性产生不利影响。本文在总结现有认识的基础上,进一步提出未来研究中亟需关注的方向,如ECs长期暴露效应、多过程耦合机制及其对珊瑚礁碳汇功能的综合影响,为南海珊瑚礁生态保护与碳汇功能维持提供科学参考。
The South China Sea is one of the most important coral reef regions in China and also represents a high-risk area for the input and accumulation of emerging contaminants (ECs). In recent years, numerous studies have reported the widespread occurrence of ECs, including persistent organic pollutants, endocrine-disrupting chemicals, antibiotics, and microplastics, in the South China Sea and its adjacent coastal waters, posing potential threats to coral reef ecosystems. However, a comprehensive understanding of how ECs alter coral holobiont carbon cycling functions through their effects on key physiological processes remains limited. This review systematically summarizes the current status of ECs pollution in the South China Sea and critically evaluates their impacts on key carbon cycling processes in coral holobionts, including photosynthesis, respiration, calcification, and microbially mediated processes. Available evidence indicates that ECs can suppress photosynthetic carbon fixation by symbiotic dinoflagellates, enhance heterotrophic respiration, disrupt calcification, and alter microbial community structure and metabolic functions, thereby weakening the carbon sink capacity of coral holobionts and under certain conditions, promoting a shift from a carbon sink to a carbon source. Overall, the impacts of ECs on carbon metabolism in coral holobionts exhibit process coupling and cumulative functional effects, which may compromise the long-term stability of coral reef carbon sink functions and their potential relevance in the blue carbon framework. Based on the synthesis of current knowledge, this review further highlights critical research priorities, such as the long-term consequences of ECs exposure, multi-process coupling mechanisms, and their integrated impacts on coral reef carbon sink functions, providing a scientific basis for coral reef conservation, carbon sink assessment, and related marine management in the South China Sea.
珊瑚共生体 / 虫黄藻 / 新污染物 / 光合作用 / 呼吸作用 / 钙化作用 / 碳代谢 / 碳循环
coral holobiont / zooxanthellae / emerging contaminants / photosynthesis / respiration / calcification / carbon metabolism / carbon cycle
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The commonly observed high diversity of trees in tropical rain forests and corals on tropical reefs is a nonequilibrium state which, if not disturbed further, will progress toward a low-diversity equilibrium community. This may not happen if gradual changes in climate favor different species. If equilibrium is reached, a lesser degree of diversity may be sustained by niche diversification or by a compensatory mortality that favors inferior competitors. However, tropical forests and reefs are subject to severe disturbances often enough that equilibrium may never be attained.
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Global species richness, whether estimated by taxon, habitat, or ecosystem, is a key biodiversity metric. Yet, despite the global importance of biodiversity and increasing threats to it (e.g., we are no better able to estimate global species richness now than we were six decades ago. Estimates of global species richness remain highly uncertain and are often logically inconsistent. They are also difficult to validate because estimation of global species richness requires extrapolation beyond the number of species known. Given that somewhere between 3% and >96% of species on Earth may remain undiscovered, depending on the methods used and the taxa considered, such extrapolations, especially from small percentages of known species, are likely to be highly uncertain. An alternative approach is to estimate all species, the known and unknown, directly. Using expert taxonomic knowledge of the species already described and named, those already discovered but not yet described and named, and those still awaiting discovery, we estimate there to be 830,000 (95% credible limits: 550,000-1,330,000) multi-cellular species on coral reefs worldwide, excluding fungi. Uncertainty surrounding this estimate and its components were often strongly skewed toward larger values, indicating that many more species on coral reefs is more plausible than many fewer. The uncertainties revealed here should guide future research toward achieving convergence in global species richness estimates for coral reefs and other ecosystems via adaptive learning protocols whereby such estimates can be tested and improved, and their uncertainties reduced, as new knowledge is acquired.Copyright © 2015 Elsevier Ltd. All rights reserved.
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Land-based sources of pollution have been identified as significant stressors linked to the widespread declines of coral cover in coastal reef ecosystems over the last 30 years. Metal contaminants, although noted as a concern, have not been closely monitored in these sensitive ecosystems, nor have their potential impacts on coral-algal symbioses been characterized. In this study, three species of laboratory-reared scleractinian corals, Acropora cervicornis, Pocillopora damicornis, and Montastraea faveolata each containing different algal symbionts (Symbiodinium A3, C1 and D1a, respectively) were exposed to copper (ranging from 2 to 20microg/L) for 5 weeks. At the end of the exposure period, copper had accumulated in the endosymbiotic dinoflagellate ("zooxanthellae") and animal tissue of A. cervicornis and the animal tissue of M. faveolata; however, no copper accumulation was detected in the zooxanthellae or animal tissue of P. damicornis. The three coral species exhibited significantly different sensitivities to copper, with effects occurring in A. cervicornis and P. damicornis at copper concentrations as low as 4microg/L. Copper exposure affected zooxanthellae photosynthesis in A. cervicornis and P. damicornis, and carbonic anhydrase was significantly decreased in A. cervicornis and M. faveolata. Likewise, significant decreases in skeletal growth were observed in A. cervicornis and P. damicornis after copper exposure. Based on preliminary results, no changes in Symbiodinium communities were apparent in response to increasing copper concentration. These results indicate that the relationships between physiological/toxicological endpoints and copper accumulation between coral species differ, suggesting different mechanisms of toxicity and/or susceptibility. This may be driven, in part, by differences in the algal symbiont communities of the coral species in question.
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Manmade antibiotics are emerging organic pollutants widely detected in the marine environment. In this study, 14 out of 19 target antibiotics were detected in corals collected from coastal and offshore regions in the South China Sea. The average total antibiotic concentrations (∑ABs) in the two regions were similar: 28 ng/g for coastal corals and 31 ng/g for offshore corals, based on dry tissue weight (dw). Fluoroquinolones (FQs) were predominant antibiotics in the coastal corals (mean ∑FQs: 18 ng/g dw), while sulfonamides (SAs) predominated in the offshore corals (mean ∑SAs: 23 ng/g dw). However, corals living in coastal regions tend to excrete more mucus than corals in offshore habitat. We found 53% by average of ∑ABs in the mucus of the coastal corals; while in offshore corals, most antibiotics (88% by average) were accumulated in the tissues. In addition, the tissue-mucus mass distribution differs among individual antibiotics. Sulfonamides were mainly accumulated in tissues while fluoroquinolones were present mainly in mucus. The results of this study suggest that mucus played an important role in the bioaccumulation of antibiotics by corals. It may resist the bioaccumulation of antibiotics by coral tissue, especially for the coastal corals. Additionally, corals were compared with other marine biotas in the study area and found to be more bioaccumulative towards antibiotics.Copyright © 2019 Elsevier Ltd. All rights reserved.
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The reported toxicity of oxybenzone-based sunscreens to corals has raised concerns about the impacts of ecotourist-shed sunscreens on corals already weakened by global stressors. However, oxybenzone's toxicity mechanism(s) are not understood, hampering development of safer sunscreens. We found that oxybenzone caused high mortality of a sea anemone under simulated sunlight including ultraviolet (UV) radiation (290 to 370 nanometers). Although oxybenzone itself protected against UV-induced photo-oxidation, both the anemone and a mushroom coral formed oxybenzone-glucoside conjugates that were strong photo-oxidants. Algal symbionts sequestered these conjugates, and mortality correlated with conjugate concentrations in animal cytoplasm. Higher mortality in anemones that lacked symbionts suggests an enhanced risk from oxybenzone to corals bleached by rising temperatures. Because many commercial sunscreens contain structurally related chemicals, understanding metabolite phototoxicity should facilitate the development of coral-safe products.
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Benzophenone-2 (BP-2) is an additive to personal-care products and commercial solutions that protects against the damaging effects of ultraviolet light. BP-2 is an "emerging contaminant of concern" that is often released as a pollutant through municipal and boat/ship wastewater discharges and landfill leachates, as well as through residential septic fields and unmanaged cesspits. Although BP-2 may be a contaminant on coral reefs, its environmental toxicity to reefs is unknown. This poses a potential management issue, since BP-2 is a known endocrine disruptor as well as a weak genotoxicant. We examined the effects of BP-2 on the larval form (planula) of the coral, Stylophora pistillata, as well as its toxicity to in vitro coral cells. BP-2 is a photo-toxicant; adverse effects are exacerbated in the light versus in darkness. Whether in darkness or light, BP-2 induced coral planulae to transform from a motile planktonic state to a deformed, sessile condition. Planulae exhibited an increasing rate of coral bleaching in response to increasing concentrations of BP-2. BP-2 is a genotoxicant to corals, exhibiting a strong positive relationship between DNA-AP lesions and increasing BP-2 concentrations. BP-2 exposure in the light induced extensive necrosis in both the epidermis and gastro dermis. In contrast, BP-2 exposure in darkness induced autophagy and autophagic cell death.The LC50 of BP-2 in the light for an 8 and 24 hour exposure was 120 parts per million (ppm) and 165 parts per billion (ppb), respectively. The LC50s for BP-2 in darkness for the same time points were 144 parts per million and 548 parts per billion [corrected].
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Benzophenone-3 (BP-3; oxybenzone) is an ingredient in sunscreen lotions and personal-care products that protects against the damaging effects of ultraviolet light. Oxybenzone is an emerging contaminant of concern in marine environments—produced by swimmers and municipal, residential, and boat/ship wastewater discharges. We examined the effects of oxybenzone on the larval form (planula) of the coral Stylophora pistillata, as well as its toxicity in vitro to coral cells from this and six other coral species. Oxybenzone is a photo-toxicant; adverse effects are exacerbated in the light. Whether in darkness or light, oxybenzone transformed planulae from a motile state to a deformed, sessile condition. Planulae exhibited an increasing rate of coral bleaching in response to increasing concentrations of oxybenzone. Oxybenzone is a genotoxicant to corals, exhibiting a positive relationship between DNA-AP lesions and increasing oxybenzone concentrations. Oxybenzone is a skeletal endocrine disruptor; it induced ossification of the planula, encasing the entire planula in its own skeleton. The LC50 of planulae exposed to oxybenzone in the light for an 8- and 24-h exposure was 3.1 mg/L and 139 µg/L, respectively. The LC50s for oxybenzone in darkness for the same time points were 16.8 mg/L and 779 µg/L. Deformity EC20 levels (24 h) of planulae exposed to oxybenzone were 6.5 µg/L in the light and 10 µg/L in darkness. Coral cell LC50s (4 h, in the light) for 7 different coral species ranges from 8 to 340 µg/L, whereas LC20s (4 h, in the light) for the same species ranges from 0.062 to 8 µg/L. Coral reef contamination of oxybenzone in the U.S. Virgin Islands ranged from 75 µg/L to 1.4 mg/L, whereas Hawaiian sites were contaminated between 0.8 and 19.2 µg/L. Oxybenzone poses a hazard to coral reef conservation and threatens the resiliency of coral reefs to climate change.
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Plastic waste can promote microbial colonization by pathogens implicated in outbreaks of disease in the ocean. We assessed the influence of plastic waste on disease risk in 124,000 reef-building corals from 159 reefs in the Asia-Pacific region. The likelihood of disease increases from 4% to 89% when corals are in contact with plastic. Structurally complex corals are eight times more likely to be affected by plastic, suggesting that microhabitats for reef-associated organisms and valuable fisheries will be disproportionately affected. Plastic levels on coral reefs correspond to estimates of terrestrial mismanaged plastic waste entering the ocean. We estimate that 11.1 billion plastic items are entangled on coral reefs across the Asia-Pacific and project this number to increase 40% by 2025. Plastic waste management is critical for reducing diseases that threaten ecosystem health and human livelihoods.Copyright © 2018, The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
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Scleractinian corals have been observed to be capable of accumulating microplastics from reef environments; however, the tolerant mechanism is poorly known. Here, we examined the response of Porites pukoensis to microplastic pollution by analyzing algal symbiont density, energetic metabolism, and caspase3 activities (representing the apoptosis level) in the coral–Symbiodiniaceae association. The environments of three fringing reef regions along the south coast of Sanya City, Hainan Province of China, were polluted by microplastics (for example, microplastic concentrations in the seawater ranged from 3.3 to 46.6 particles L–1), resulting in microplastic accumulation in P. pukoensis (0.4–2.4 particles cm–2). The accumulation of microplastics was negatively correlated to algal symbiont density in the corals but not to caspase3 activities in the two symbiotic partners, demonstrating that P. pukoensis could tolerate accumulated microplastics despite the decrease of algal symbiont density. Furthermore, results from the carbon stable isotope and cellular energy allocation assay indicated that P. pukoensis obtained energy availability (mainly as lipid reserves) using the switch between heterotrophy and autotrophy to maintain energy balance and cope with accumulated microplastics. Collectively, P. pukoensis achieved tolerance to microplastic pollution by maintaining energy availability, which was largely attributed to its high heterotrophic plasticity.
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The productivity of coral reefs in oligotrophic tropical waters is sustained by an efficient uptake and recycling of nutrients. In reef-building corals, the engineers of these ecosystems, this nutrient recycling is facilitated by a constant exchange of nutrients between the animal host and endosymbiotic photosynthetic dinoflagellates (zooxanthellae), bacteria, and other microbes. Due to the complex interactions in this so-called coral holobiont, it has proven difficult to understand the environmental limitations of productivity in corals. Among others, the micronutrient iron has been proposed to limit primary productivity due to its essential role in photosynthesis and bacterial processes. Here, we tested the effect of iron enrichment on the physiology of the coral from the central Red Sea during a 12-day experiment. Contrary to previous reports, we did not see an increase in zooxanthellae population density or gross photosynthesis. Conversely, respiration rates were significantly increased, and microbial nitrogen fixation was significantly decreased. Taken together, our data suggest that iron is not a limiting factor of primary productivity in Red Sea corals. Rather, increased metabolic demands in response to iron enrichment, as evidenced by increased respiration rates, may reduce carbon (i.e., energy) availability in the coral holobiont, resulting in reduced microbial nitrogen fixation. This decrease in nitrogen supply in turn may exacerbate the limitation of other nutrients, creating a negative feedback loop. Thereby, our results highlight that the effects of iron enrichment appear to be strongly dependent on local environmental conditions and ultimately may depend on the availability of other nutrients.
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In situ field investigations coupled with coral culture experiments were carried out in the coral reef waters of the eastern coast of Shenzhen, Da’ao Bay (DAB), Dalu Bay (DLB), and Yangmeikeng Sea Area (YMKSA) to study the dynamics of the carbon dioxide (CO2) system in seawater and its controlling factors. The results indicated that the CO2 parameters were highly variable over a range of spatiotemporal scales, forced by various physical and biochemical processes. Comprehensively, DAB acted as a sink for atmospheric CO2 with exchange flux of –1.51 ± 0.31 to 0.27 ± 0.50 mmol C m−2 d−1, while DLB and YMKSA acted as a CO2 source with exchange fluxes of –0.42 ± 0.36 to 1.69 ± 0.74 mmol C m−2 d−1 and –0.58 ± 0.48 to 1.69 ± 0.41 mmol C m−2 d−1, respectively. The biological process and mixing effect could be the most important factor for the seasonal variation in total alkalinity (TA). In terms of dissolved inorganic carbon (DIC), in addition to biological process and mixing, its seasonal variation was affected by air–sea exchange and coral metabolism to some extent. Different from the former, the other CO2 parameters, total scale pH (pHT), partial pressure of CO2 (pCO2), and aragonite saturation state (ΩA), were mainly controlled by a combination of the temperature change, biochemical processes, air–sea exchange, and coral metabolism, while water mixing has little effect on them. In addition, our results indicated that coral communities could significantly increase the DIC/TA ratio by reducing the TA concentration and increasing the DIC in the reef waters, which may promote the acidification of local seawater and need attention.
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The conservation status of 845 zooxanthellate reef-building coral species was assessed by using International Union for Conservation of Nature Red List Criteria. Of the 704 species that could be assigned conservation status, 32.8% are in categories with elevated risk of extinction. Declines in abundance are associated with bleaching and diseases driven by elevated sea surface temperatures, with extinction risk further exacerbated by local-scale anthropogenic disturbances. The proportion of corals threatened with extinction has increased dramatically in recent decades and exceeds that of most terrestrial groups. The Caribbean has the largest proportion of corals in high extinction risk categories, whereas the Coral Triangle (western Pacific) has the highest proportion of species in all categories of elevated extinction risk. Our results emphasize the widespread plight of coral reefs and the urgent need to enact conservation measures.
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Synthetic estrogens such as ethinylestradiol (EE2) are persistent micropollutants that are not effectively removed from wastewater by conventional treatments. These contaminants are released into waterbodies, where they disrupt endocrine systems of organisms and cause harmful effects such as feminization, infertility, reproduction problems and genital malformations. The consequences of this pollution for key marine ecosystems such as coral reefs and their associated microbiomes are underexplored. We evaluated the effects of EE2 concentrations of 100 ng L and 100 µg L on the coral metaorganism Mussismilia harttii. The results indicated no effects on visible bleaching or F/F ratios in the corals during a 17-day microcosm experiment. However, next-generation sequencing of 16S rDNA revealed a statistically significant effect of high EE2 concentrations on OTU richness, and shifts in specific microbial groups after treatments with or without EE2. These groups might be bioindicators of early shifts in the metaorganism composition caused by EE2 contamination.
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In light of the rapid expansion of the marine aquaculture industry, there has been widespread and irregular usage of aquatic drugs to combat biological diseases, which significantly impact the neighboring aquatic ecosystems. This study delves into the impact of the antibiotic aquatic drug known as doxycycline hydrochloride (DOX) on offshore soft corals, providing valuable data for the responsible use and management of aquatic drugs. In this investigation, we subjected Sarcophyton trocheliophorum to acute exposure to varying concentrations of DOX (0, 1, 5, and 10 mg L−1). We meticulously assessed critical parameters and observed alterations in protein levels, superoxide dismutase (SOD) activity, catalase (CAT) activity, lipid peroxidation (LPO), malondialdehyde (MDA) levels, Acid phosphatase (ACP) activity, alkaline phosphatase (AKP) activity, glutathione (GSH) concentration, glutathione S-transferase (GST) activity, glutathione Peroxidase (GSH-Px) activity, zooxanthellae density, and chlorophyll content. Our findings reveal that in the presence of DOX-induced environmental stress, there is a significant increase in LPO, MDA, chlorophyll, carotenoid levels, and the activities of ACP, GST, and GSH-Px in soft corals. Simultaneously, there is a noteworthy decrease in zooxanthellae density. Additionally, the protein concentration and SOD activity in soft corals experience substantial reduction when exposed to 5 mg L−1 DOX. Notably, CAT activity varies significantly in environments with 1 and 10 mg L−1 DOX. Moreover, these conditions exhibit a discernible influence on AKP activity, GSH content, and chlorophyll levels. These findings suggest that DOX exposure carries the potential for toxicity in aquaculture settings, affecting protein synthesis in soft corals and influencing oxidative stress, lipid peroxidation, immunity, and detoxification processes within these organisms. There is also a risk of compromising the coral defense system, potentially leading to coral bleaching. Furthermore, this study underscores the significant impact on photosynthesis, growth, and the metabolic dynamics of the coral-zooxanthellae symbiotic system. Consequently, our research offers vital insights into the mortality and bleaching effects of aquatic drugs on marine corals, offering a foundation for the prudent use and management of such substances.
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The impact of low-density polyethylene (LDPE) microplastics (<100 μm; P100-A P100-B, P100-C, 100-200 μm; P200, 200-500 μm; P500) on Acropora formosa was investigated. This study investigated the bleaching and necrosis extent of A. formosa caused by LDPE contamination via laboratory assay. The staghorn coral ingested the microplastics, resulting in bleaching and necrosis that concomitantly occurred with the release of zooxanthellae. P100-A experimentation was the worst case, showing bleaching by day 2 (10.8 ± 2.2%) and continued bleaching to 93.6% ± 2.0 by day 14 followed by 5.9 ± 2.5% necrosis. The overall results confirmed that the LDPE concentration impacts coral health. We highlighted that microplastics have been ingested and partially egested. Their presence showed either a direct or indirect impact on coral polyps via direct interaction or through photosynthesis perturbation due to microplastics that cover the coral surface.Copyright © 2019 Elsevier Ltd. All rights reserved.
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| [70] |
Severe, global-scale thermal stress events like those of 1998 and 2016, are becoming more frequent and intense, potentially compromising the future of coral reefs. Here we report the effects of the 1998 bleaching event on coral calcification as well as the composition of the calcifying fluid (cf) from which corals precipitate their calcium carbonate skeletons. This was investigated by using the Sr/Ca, Li/Mg (temperature), and boron isotopes (delta B-11) and B/Ca (carbonate chemistry) proxies in a Porites sp. coral. Following the summer of 1998 the coral exhibited a prolonged period (similar to 18 months) of reduced calcification (similar to 60%) and a breakdown in the seasonality of the geochemical proxies. However, the maintenance of elevated dissolved inorganic carbon (DICcf; > x2 seawater) and pH(cf) (> 8.3 compared to seawater similar to 8.0) even during severe stress of 1998 indicate that a minimum threshold of high aragonite saturation state (Omega(cf)) of similar to 14 (similar to x4 seawater), is an essential pre-requisite for coral calcification. However, despite maintaining elevated levels of Omega(cf) even under severe stress, coral growth is still impaired. We attribute this to reductions in either the effective active volume of calcification and/or DICcf as bleaching compromises the photosynthetically fixed carbon pool available to the coral.
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| [71] |
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| [72] |
Experimental and field evidence support the assumption that global warming and ocean acidification is decreasing rates of calcification in the oceans. Local measurements of coral growth rates in reefs from various locations have suggested a decline of similar to 6-10% per decade since the late 1990's. Here, by measuring open water strontium-to-alkalinity ratios along the Red Sea, we show that the net contribution of hermatypic corals to the CaCO3 budget of the southern and central Red Sea declined by similar to 100% between 1998 and 2015 and remained low between 2015 and 2018. Measured differences in total alkalinity of the Red Sea surface water indicate a 26 +/- 16% decline in total CaCO3 deposition rates along the basin. These findings suggest that coral reefs of the southern Red Sea are under severe stress and demonstrate the strength of geochemical measurements as cost-effective indicators for calcification trends on regional scales.
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| [73] |
Tropical coral reefs cover ca. 0.1% of the Earth’s surface but host an outstanding biodiversity and provide important ecosystem services to millions of people living nearby. However, they are currently threatened by both local (e.g. nutrient enrichment and chemical pollution of coastal reefs, arising from poor land management, agriculture and industry) and global stressors (mainly seawater warming and acidification, i.e. climate change). Global and local stressors interact together in different ways, but the presence of one stressor often reduces the tolerance to additional stress. While global stressors cannot be halted by local actions, local stressors can be reduced through ecosystem management, therefore minimizing the impact of climate change on reefs. To inform decision-makers, we propose here to systematically map the evidence of impacts of chemicals arising from anthropogenic activities on tropical reef-building corals, which are the main engineer species of reef ecosystems. We aim to identify the combinations of chemical and coral responses that have attracted the most attention and for which evidence can be further summarized in a systematic review that will give practical information to decision-makers.
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| [74] |
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| [75] |
Microplastics have been detected on beaches and in the ocean from surface habitats to the deep-sea. Microplastics can be mistaken for food items by marine organisms, posing a potential risk for bioaccumulation and biomagnification in the food chain. Our understanding of microplastic pollution effects on ecosystem and physiological processes of coral reefs is still limited. This study contributes to the understanding of effects of microplastic pollution on skeletal precipitation of hermatypic corals. In a five month aquarium-based experiment, specimens of four tropical species were temporarily exposed to high concentrations (ca. 0.5 g L-1) of polyethylene terephthalate (PET) microplastic particles (< 500 μm). The coral specimens all survived this treatment and show skeletal growth. The skeletal material produced during the experiment, however, incorporated plastic particles and plastic fibres in the aragonitic structure. Long-term consequences of such inclusions on skeletal properties such as stability are yet unknown.
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| [76] |
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| [77] |
Biofouling is the growth of organisms on wet surfaces. Biofouling includes micro- (bacteria and unicellular algae) and macrofouling (mussels, barnacles, tube worms, bryozoans, etc.) and is a major problem for industries. However, the settlement and growth of some biofouling species, like oysters and corals, can be desirable. Thus, it is important to understand the process of biofouling in detail. Modern “omic” techniques, such as metabolomics, metagenomics, transcriptomics, and proteomics, provide unique opportunities to study biofouling organisms and communities and investigate their metabolites and environmental interactions. In this review, we analyze the recent publications that employ metagenomic, metabolomic, and proteomic techniques for the investigation of biofouling and biofouling organisms. Specific emphasis is given to metagenomics, proteomics and publications using combinations of different “omics” techniques. Finally, this review presents the future outlook for the use of “omics” techniques in marine biofouling studies. Like all trans-disciplinary research, environmental “omics” is in its infancy and will advance rapidly as researchers develop the necessary expertise, theory, and technology.
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| [78] |
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| [79] |
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| [80] |
The intensive use of sunscreen products has raised concerns regarding their environmental toxicity and the adverse impacts of ultraviolet (UV) filters on ecologically important coral communities. Prior metabolomic analyses on symbiotic coral Pocillopora damicornis exposed to the UV filter butyl methoxydibenzoylmethane (BM, avobenzone) revealed unidentified ions in the holobiont metabolome. In the present study, follow-up differential metabolomic analyses in BM-exposed P. damicornis detected 57 ions with significantly different relative concentrations in exposed corals. The results showed an accumulation of 17 BM derivatives produced through BM reduction and esterification. The major derivative identified C16:0-dihydroBM, which was synthesized and used as a standard to quantify BM derivatives in coral extracts. The results indicated that relative amounts of BM derivatives made up to 95% of the total BM (w/w) absorbed in coral tissue after 7 days of exposure. Among the remaining metabolites annotated, seven compounds significantly affected by BM exposure could be attributed to the coral dinoflagellate symbiont, indicating that BM exposure might impair the photosynthetic capacity of the holobiont. The present results suggest that the potential role of BM in coral bleaching in anthropogenic areas should be investigated and that BM derivatives should be considered in future assessments on the fate and effects of BM in the environment.
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| [81] |
During the past two decades, coral reefs have experienced extensive degradation worldwide. One etiology for this global degradation is a syndrome known as coral bleaching. Mass coral bleaching events are correlated with increased sea-surface temperatures, however, the cellular mechanism underlying this phenomenon is uncertain. To determine if oxidative stress plays a mechanistic role in the process of sea-surface temperature-related coral bleaching, we examined corals along a depth transect in the Florida Keys over a single season that was characterized by unusually high sea-surface temperatures. We observed strong positive correlations between accumulation of oxidative damage products and bleaching in corals over a year of sampling. High levels of antioxidant enzymes and small heat-shock proteins were negatively correlated with levels of oxidative damage products. Corals that experienced oxidative stress had higher chaperonin levels and protein turnover activity. Our results indicate that coral bleaching is tightly coupled to the antioxidant and cellular stress capacity of the symbiotic coral, supporting the mechanistic model that coral bleaching (zooxanthellae loss) may be a final strategy to defend corals from oxidative stress.
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| [82] |
Cnidarian bleaching is a breakdown in the mutualistic symbiosis between host Cnidarians, such as reef building corals, and their unicellular photosynthetic dinoflagellate symbionts. Bleaching is caused by a variety of environmental stressors, most notably elevated temperatures associated with global climate change in conjunction with high solar radiation, and it is a major contributor to coral death and reef degradation. This review examines the underlying cellular events that lead to symbiosis dysfunction and cause bleaching, emphasizing that, to date, we have only some pieces of a complex cellular jigsaw puzzle. Reactive oxygen species (ROS), generated by damage to both photosynthetic and mitochondrial membranes, is shown to play a central role in both injury to the partners and to inter-partner communication of a stress response. Evidence is presented that suggests that bleaching is a host innate immune response to a compromised symbiont, much like innate immune responses in other host–microbe interactions. Finally, the elimination or exit of the symbiont from host tissues is described through a variety of mechanisms including exocytosis, host cell detachment and host cell apoptosis.
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| [83] |
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