In vitro cell-toxicity screening as an alternative animal model for coral toxicology: effects of heat stress, sulfide, rotenone, cyanide, and cuprous oxide on cell viability and mitochondrial function

Fine-scale geographic risk assessment of oxybenzone sunscreen pollution within Hanauma Bay using hydrodynamic characterization and modeling

Hanauma Bay's coral reef system is threatened by sunscreen pollution. Understanding the hydrodynamic nature of the bay is crucial for understanding the transport and fate of pollutants within the bay. This study conducted a comprehensive hydrodynamic analysis, revealing significant aspects of current patterns and their influence on sunscreen pollutant behavior. The analysis demonstrated the formation of flows that drive currents parallel to the shoreline, resulting in increased pollutant retention time over sensitive reef areas. Direct flushing currents were identified as playing a role in reducing pollution buildup. Particle dynamics analysis highlighted the importance of considering temporal dynamics and their implications for pollutant pathways, particularly through the swash zone during high tide phases. The study identified primary current patterns near the reef area and emphasized the circular behavior within the water body, affecting corals' susceptibility to bleaching in the southwestern part of Hanauma bay. To understand where oxybenzone concentrations were a threat to wildlife, we created a geographic model that integrated ecological risk assessment with hydrodynamic behavior in a given system, which we designate the Risk Quotient Plume - the geographic area where the concentration is above the threat level for a chemical. The study found high oxybenzone concentrations throughout the bay, threatening coral, fish, and algae populations. Oxybenzone's distribution indicated a serious threat to the entire back reef habitat and a hinderance to coral restoration efforts. The study also emphasizes the need to consider the hydrodynamic behavior of pollutants and their interaction with microplastics in the bay. Overall, the findings provide insights into hydrodynamics and pollutant dispersion in Hanauma Bay, supporting effective pollution management and conservation strategies.

Harnessing the Power of Model Organisms To Unravel Microbial Functions in the Coral Holobiont

Stony corals build the framework of coral reefs, ecosystems of immense ecological and economic importance. The existence of these ecosystems is threatened by climate change and other anthropogenic stressors that manifest in microbial dysbiosis such as coral bleaching and disease, often leading to coral mortality. Despite a significant amount of research, the mechanisms ultimately underlying these destructive phenomena, and what could prevent or mitigate them, remain to be resolved. This is mostly due to practical challenges in experimentation on corals and the highly complex nature of the coral holobiont that also includes bacteria, archaea, protists, and viruses. While the overall importance of these partners is well recognized, their specific contributions to holobiont functioning and their interspecific dynamics remain largely unexplored. Here, we review the potential of adopting model organisms as more tractable systems to address these knowledge gaps. We draw on parallels from the broader biological and biomedical fields to guide the establishment, implementation, and integration of new and emerging model organisms with the aim of addressing the specific needs of coral research. We evaluate the cnidarian models Hydra, Aiptasia, Cassiopea, and Astrangia poculata; review the fast-evolving field of coral tissue and cell cultures; and propose a framework for the establishment of "true" tropical reef-building coral models. Based on this assessment, we also suggest future research to address key aspects limiting our ability to understand and hence improve the response of reef-building corals to future ocean conditions.

Impact of intestinal microbiota on metabolic toxicity and potential detoxification of amygdalin

Amygdalin (Amy) is metabolized into cyanide in vivo, which may lead to fatal poisoning after oral administration. The defense mechanisms against toxic cyanide have not yet been adequately studied. In this study, comparative toxicokinetics study of Amy was performed in normal and pseudo germ-free rats. The efficiency of cyanide release was significant higher in normal group when given a single oral dose of 440 mg/kg (50% median lethal dose). Thiocyanate, the detoxification metabolite, was firstly detected in feces, caecum, and intestinal microbiota incubation enzymic system. The results suggest intestinal microbiota is involved in bidirectional regulation of toxicity and detoxification of Amy. We further identified the species related to cyanogenesis of Amy with metagenomic sequencing, such as Bifidobacterium pseudolongum, Marvinbryantia formatexigens, and Bacteroides fragilis. Functional analysis of microbiota reveals the detoxification potential of intestinal microbiota for cyanide. Sulfurtransferase superfamily, such as rhodanese, considered as main detoxification enzymes for cyanide, are largely found in Coriobacteriaceae bacterium, Butyricicoccus porcorum, Akkermansia muciniphila, etc. Besides, cyanoamino acid metabolism pathway dominated by Escherichia coli may contribute to the detoxification metabolism of cyanide. In summary, intestinal microbiota may be the first line of defense against the toxicity induced by Amy.

Evaluation of fluorescence-based viability stains in cells dissociated from scleractinian coral Pocillopora damicornis

The application of established cell viability assays such as the commonly used trypan blue staining method to coral cells is not straightforward due to different culture parameters and different cellular features specific to mammalian cells compared to marine invertebrates. Using Pocillopora damicornis as a model, we characterized the autofluorescence and tested different fluorescent dye pair combinations to identify alternative viability indicators. The cytotoxicity of different representative molecules, namely small organic molecules, proteins and nanoparticles (NP), was measured after 24 h of exposure using the fluorescent dye pair Hoechst 33342 and SYTOX orange. Our results show that this dye pair can be distinctly measured in the presence of fluorescent proteins plus chlorophyll. P. damicornis cells exposed for 24 h to Triton-X100, insulin or titanium dioxide (TiO₂) NPs, respectively, at concentrations ranging from 0.5 to 100 µg/mL, revealed a LC50 of 0.46 µg/mL for Triton-X100, 6.21 µg/mL for TiO₂ NPs and 33.9 µg/mL for insulin. This work presents the approach used to customize dye pairs for membrane integrity-based cell viability assays considering the species- and genotype-specific autofluorescence of scleractinian corals, namely: endogenous fluorescence characterization followed by the selection of dyes that do not overlap with endogenous signals.

Cryopreservation and Cryobanking of Cells from 100 Coral Species

When coral species become extinct, their genetic resources cannot be recovered. Coral cryobanks can be employed to preserve coral samples and thereby maintain the availability of the samples and increase their potential to be restocked. In this study, we developed a procedure to determine coral species-specific requirements for cryobank freezing through determining suitable cryoprotective agents (CPAs), CPA concentrations, equilibration times, holding durations, viability rates, and cell amounts for banked coral cells, and we established the first ever coral cell cryobank. Coral cells, including supporting and gland cells, epidermal nematocysts, Symbiodiniaceae and symbiotic endoderm cells (SEC) were found from the extracted protocol. Approximately half of the corals from the experimental corals consisted of spindle and cluster cells. Gastrodermal nematocysts were the least common. The overall concentration of Symbiodiniaceae in the coral cells was 8.6%. Freezing using DMSO as a CPA was suitable for approximately half of the corals, and for the other half of species, successful cell cryopreservation was achieved using MeOH and EG. EG and DMSO had similar suitabilities for Acanthastrea, Euphyllia, Favites, Lobophyllia, Pavona, Seriatopora, and Turbinaria, as did EG and MeOH for Acropora, Echinopyllia, and Sinularia and MeOH and DMSO for Platygyra after freezing. At least 14 straws from each species of coral were cryobanked in this study, totaling more than 1884 straws (0.5 mL) with an average concentration of 6.4 × 10⁶ per mL. The results of this study may serve as a framework for cryobanks worldwide and contribute to the long-term conservation of coral reefs.

Oxybenzone contamination from sunscreen pollution and its ecological threat to Hanauma Bay, Oahu, Hawaii, U.S.A

Hanauma Bay is a 101-acre bay created by the partial collapse of a volcanic cone and once supported a vibrant coral reef system. It is the most popular swimming area in the Hawaiian Islands and has been reported to have averaged between 2.8 and 3.5 million visitors a year between the 1980s and the 2010s, with visitors averaging between 3000-4000 a day and peaking around 10,000-13,000 per day. Concentrations of oxybenzone and other common UV filters were measured in subsurface water samples and in sands from the beach-shower areas in Hanauma Bay. Results demonstrate that beach showers also can be a source of sunscreen environmental contamination. Hydrodynamic modeling indicates that oxybenzone contamination within Hanauma Bay's waters could be retained between 14 and 50 h from a single release event period. Focusing on only oxybenzone, two different Hazard and Risk Assessment analyses were conducted to determine the danger of oxybenzone to Hanauma Bay's coral reef system. Results indicate that oxybenzone contamination poses a significant threat to the wildlife of Hanauma Bay. To recover Hanauma Bay's natural resources to a healthy condition and to satisfactorily conserve its coral reef and sea grass habitats, effective tourism management policies need to be implemented that mitigate the threat of sunscreen pollution.

Development of an in vitro tissue culture system for hammer coral (Fimbriaphyllia ancora) ovaries

In vitro gonad culture systems have proven useful to investigate intrinsic mechanisms of sexual reproduction in animals. Here we describe development of an in vitro culture method for coral ovaries. Mesenterial tissues containing both ovaries and mesenterial filaments were microscopically isolated from the scleractinian coral, Fimbriaphyllia ancora, and culture conditions were optimized. M199 diluted 10× (10% M199, pH 8.1) and supplemented with 25 mM HEPES and the antibiotics, ampicillin, penicillin and streptomycin, supported oocyte survival and maintained the structural integrity of ovaries during short-term culture (~ 6 days). Addition of a commercial antibiotic-antimycotic solution (Anti-Anti) and fetal bovine serum adversely affected ovary maintenance and caused tissue disintegration. Characterization of cultured ovaries showed that there is no difference in cell proliferation of ovarian somatic cells between culture Days 1 and 6. Moreover, the presence of oogonia and expression of a major yolk protein, vitellogenin, were confirmed in ovaries cultured for 6 days. This system will be useful for studying effects of a wide range of substances on coral oogenesis.

Stem cells of aquatic invertebrates as an advanced tool for assessing ecotoxicological impacts

Environmental stressors are assessed through methods that quantify their impacts on a wide range of metrics including species density, growth rates, reproduction, behaviour and physiology, as on host-pathogen interactions and immunocompetence. Environmental stress may induce additional sublethal effects, like mutations and epigenetic signatures affecting offspring via germline mediated transgenerational inheritance, shaping phenotypic plasticity, increasing disease susceptibility, tissue pathologies, changes in social behaviour and biological invasions. The growing diversity of pollutants released into aquatic environments requires the development of a reliable, standardised and 3R (replacement, reduction and refinement of animals in research) compliant in vitro toolbox. The tools have to be in line with REACH regulation 1907/2006/EC, aiming to improve strategies for potential ecotoxicological risks assessment and monitoring of chemicals threatening human health and aquatic environments. Aquatic invertebrates' adult stem cells (ASCs) are numerous and can be pluripotent, as illustrated by high regeneration ability documented in many of these taxa. This is of further importance as in many aquatic invertebrate taxa, ASCs are able to differentiate into germ cells. Here we propose that ASCs from key aquatic invertebrates may be harnessed for applicable and standardised new tests in ecotoxicology. As part of this approach, a battery of modern techniques and endpoints are proposed to be tested for their ability to correctly identify environmental stresses posed by emerging contaminants in aquatic environments. Consequently, we briefly describe the current status of the available toxicity testing and biota-based monitoring strategies in aquatic environmental ecotoxicology and highlight some of the associated open issues such as replicability, consistency and reliability in the outcomes, for understanding and assessing the impacts of various chemicals on organisms and on the entire aquatic environment. Following this, we describe the benefits of aquatic invertebrate ASC-based tools for better addressing ecotoxicological questions, along with the current obstacles and possible overhaul approaches.

Applying model approaches in non-model systems: A review and case study on coral cell culture

Model systems approaches search for commonality in patterns underlying biological diversity and complexity led by common evolutionary paths. The success of the approach does not rest on the species chosen but on the scalability of the model and methods used to develop the model and engage research. Fine-tuning approaches to improve coral cell cultures will provide a robust platform for studying symbiosis breakdown, the calcification mechanism and its disruption, protein interactions, micronutrient transport/exchange, and the toxicity of nanoparticles, among other key biological aspects, with the added advantage of minimizing the ethical conundrum of repeated testing on ecologically threatened organisms. The work presented here aimed to lay the foundation towards development of effective methods to sort and culture reef-building coral cells with the ultimate goal of obtaining immortal cell lines for the study of bleaching, disease and toxicity at the cellular and polyp levels. To achieve this objective, the team conducted a thorough review and tested the available methods (i.e. cell dissociation, isolation, sorting, attachment and proliferation). The most effective and reproducible techniques were combined to consolidate culture methods and generate uncontaminated coral cell cultures for ~7 days (10 days maximum). The tests were conducted on scleractinian corals Pocillopora acuta of the same genotype to harmonize results and reduce variation linked to genetic diversity. The development of cell separation and identification methods in conjunction with further investigations into coral cell-type specific metabolic requirements will allow us to tailor growth media for optimized monocultures as a tool for studying essential reef-building coral traits such as symbiosis, wound healing and calcification at multiple scales.

A Critical Review of Organic Ultraviolet Filter Exposure, Hazard, and Risk to Corals

There has been a rapid increase in public, political, and scientific interest regarding the impact of organic ultraviolet (UV) filters to coral reefs. Such filters are found in sunscreens and other consumer products and enter the aquatic environment via direct (i.e., recreational activities, effluents) or indirect (i.e., land runoff) pathways. This review summarizes the current state of the science regarding the concentration of organic UV filters in seawater and sediment near coral reef ecosystems and in coral tissues, toxicological data from early and adult life stages of coral species, and preliminary environmental risk characterizations. Up to 14 different organic UV filters in seawater near coral reefs have been reported across 12 studies, with the majority of concentrations in the nanograms per liter range. Nine papers report toxicological findings from no response to a variety of biological effects occurring in the micrograms per liter to milligrams per liter range, in part given the wide variations in experimental design and coral species and/or life stage used. This review presents key findings; scientific data gaps; flaws in assumptions, practice, and inference; and a number of recommendations for future studies to assess the environmental risk of organic UV filters to coral reef ecosystems. Environ Toxicol Chem 2021;40:967-988. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Novel methods to establish whole-body primary cell cultures for the cnidarians Nematostella vectensis and Pocillopora damicornis

Cnidarians are emerging model organisms for cell and molecular biology research. However, successful cell culture development has been challenging due to incomplete tissue dissociation and contamination. In this report, we developed and tested several different methodologies to culture primary cells from all tissues of two species of Cnidaria: Nematostella vectensis and Pocillopora damicornis. In over 170 replicated cell cultures, we demonstrate that physical dissociation was the most successful method for viable and diverse N. vectensis cells while antibiotic-assisted dissociation was most successful for viable and diverse P. damicornis cells. We also demonstrate that a rigorous antibiotic pretreatment results in less initial contamination in cell cultures. Primary cultures of both species averaged 12–13 days of viability, showed proliferation, and maintained high cell diversity including cnidocytes, nematosomes, putative gastrodermal, and epidermal cells. Overall, this work will contribute a needed tool for furthering functional cell biology experiments in Cnidaria.

Sulfur-Containing Carotenoids from A Marine Coral Symbiont Erythrobacter flavus Strain KJ5

Erythrobacter flavus strain KJ5 (formerly called Erythrobacter sp. strain KJ5) is a yellowish marine bacterium that was isolated from a hard coral Acropora nasuta in the Karimunjawa Islands, Indonesia. The complete genome sequence of the bacterium has been reported recently. In this study, we examined the carotenoid composition of this bacterium using high-performance liquid chromatography coupled with ESI-MS/MS. We found that the bacterium produced sulfur-containing carotenoids, i.e., caloxanthin sulfate and nostoxanthin sulfate, as the most abundant carotenoids. A new carotenoid zeaxanthin sulfate was detected based on its ESI-MS/MS spectrum. The unique presence of sulfated carotenoids found among the currently known species of the Erythrobacter genus were discussed.

Colorimetric method for determining viability of sea urchin sperm applied in toxicity tests

The aim of this study was to improve the methodological procedure for the evaluation of sea urchin (Lytechinus variegatus) sperm sensitivity in MTT (3-(4,5-dimethylthiazol-2yl)-2,5 diphenyltetrazolium bromide) enzyme reduction assays with the formation of formazan (purple color) in the interior of viable cells. Assays were carried out with the reference toxicants sodium dodecyl sulfate (SDS), copper, zinc, cadmium and ammonium, using a sperm solution previously activated in sea water and a sperm solution prepared in sea water containing 400 μg L^-1 verapamil, which enabled activation of the sperm to occur only when exposed to the toxicants. The assays performed with sperm in verapamil presented similar sensitivity to that shown in the fertilization tests with copper, zinc and SDS, while the assays carried out with the pre-activated sperm solution presented greater resistance to the action of the toxicants. It appears that the action of verapamil involves an intracellular effect on the distribution of Ca²⁺ ions and that the toxicants used prevent the metabolic reactivation of the sperm.

Exploring coral microbiome assemblages in the South China Sea

Coral reefs are significant ecosystems. The ecological success of coral reefs relies on not only coral-algal symbiosis but also coral-microbial partnership. However, microbiome assemblages in the South China Sea corals remain largely unexplored. Here, we compared the microbiome assemblages of reef-building corals Galaxea (G. fascicularis) and Montipora (M. venosa, M. peltiformis, M. monasteriata) collected from five different locations in the South China Sea using massively-parallel sequencing of 16S rRNA gene and multivariate analysis. The results indicated that microbiome assemblages for each coral species were unique regardless of location and were different from the corresponding seawater. Host type appeared to drive the coral microbiome assemblages rather than location and seawater. Network analysis was employed to explore coral microbiome co-occurrence patterns, which revealed 61 and 80 co-occurring microbial species assembling the Galaxea and Montipora microbiomes, respectively. Most of these co-occurring microbial species were commonly found in corals and were inferred to play potential roles in host nutrient metabolism; carbon, nitrogen, sulfur cycles; host detoxification; and climate change. These findings suggest that the co-occurring microbial species explored might be essential to maintain the critical coral-microbial partnership. The present study provides new insights into coral microbiome assemblages in the South China Sea.

Metagenomic analysis reveals a green sulfur bacterium as a potential coral symbiont

Coral reefs are ecologically significant habitats. Coral-algal symbiosis confers ecological success on coral reefs and coral-microbial symbiosis is also vital to coral reefs. However, current understanding of coral-microbial symbiosis on a genomic scale is largely unknown. Here we report a potential microbial symbiont in corals revealed by metagenomics-based genomic study. Microbial cells in coral were enriched for metagenomic analysis and a high-quality draft genome of “Candidatus Prosthecochloris korallensis” was recovered by metagenome assembly and genome binning. Phylogenetic analysis shows “Ca. P. korallensis” belongs to the Prosthecochloris clade and is clustered with two Prosthecochloris clones derived from Caribbean corals. Genomic analysis reveals “Ca. P. korallensis” has potentially important ecological functions including anoxygenic photosynthesis, carbon fixation via the reductive tricarboxylic acid (rTCA) cycle, nitrogen fixation, and sulfur oxidization. Core metabolic pathway analysis suggests “Ca. P. korallensis” is a green sulfur bacterium capable of photoautotrophy or mixotrophy. Potential host-microbial interaction reveals a symbiotic relationship: “Ca. P. korallensis” might provide organic and nitrogenous nutrients to its host and detoxify sulfide for the host; the host might provide “Ca. P. korallensis” with an anaerobic environment for survival, carbon dioxide and acetate for growth, and hydrogen sulfide as an electron donor for photosynthesis.

Landfill leachate sludge use as soil additive prior and after electrocoagulation treatment: A cytological assessment using CHO-k1 cells

Electrocoagulation has recently attracted attention as a potential technique for treating toxic effluents due to its versatility and environmental compatibility, generating a residue chemically suitable to be used as a soil additive. In the present study, landfill leachate sludge hazardous effects were investigated prior and after electrocoagulation process using in vitro assays with the mammalian cells CHO-k1. An integrated strategy for risk assessment was used to correctly estimate the possible adverse landfill leachate sludge effects on human health and ecosystem. Electrocoagulation process proved to be an effective treatment due to possibility to improve effluent adverse characteristics and produce sludge with potential to be used as soil additive. Despite low cytoxicity, the residue presented genotoxic and mutagenic effects, indicating a capacity to induce genetic damages, probably due to induction of polyploidization process in cells. The observed effects demand an improvement of waste management methods for reduce negative risks of landfill leachate sludge application.

Toxicopathological Effects of the Sunscreen UV Filter, Oxybenzone (Benzophenone-3), on Coral Planulae and Cultured Primary Cells and Its Environmental Contamination in Hawaii and the U.S. Virgin Islands

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.

The deep-sea glass sponge Lophophysema eversa harbours potential symbionts responsible for the nutrient conversions of carbon, nitrogen and sulfur

Glass sponge (Hexactinellida, Porifera) is a special lineage because of its unique tissue organization and skeleton material. Structure and physiology of glass sponge have been extensively studied. However, our knowledge of the glass sponge-associated microbial community and of the interaction with the host is rather limited. Here, we performed genomic studies on the microbial community in the glass sponge Lophophysema eversa in seamount. The microbial community was dominated by an ammonia-oxidizing archaeum (AOA), a nitrite-oxidizing bacterium (NOB) and a sulfur-oxidizing bacterium (SOB), all of which were autotrophs. Genomic analysis on the AOA, NOB and SOB in the sponge revealed specific functional features of sponge-associated microorganisms in comparison with the closely related free-living relatives, including chemotaxis, phage defence, vitamin biosynthesis and nutrient uptake among others, which are related to ecological functions. The three autotrophs play essential roles in the cycles of carbon, nitrogen and sulfur in the microenvironment inside the sponge body, and they are considered to play symbiotic roles in the host as scavengers of toxic ammonia, nitrite and sulfide. Our study extends knowledge regarding the metabolism and the evolution of chemolithotrophs inside the invertebrate body.

Responses of the sea anemone, Exaiptasia pallida, to ocean acidification conditions and copper exposure

Ocean acidification (OA) is a growing concern due to its deleterious effects on aquatic organisms. Additionally, the combined effects of OA and other local stressors like metal pollution are largely unknown. In this study, we examined physiological effects in the sea anemone, Exaiptasia pallida after exposure to the global stressor carbon dioxide (CO2), as well as the local stressor copper (Cu) over 7 days. Cu accumulated in the tissues of E. pallida in a concentration-dependent manner. At some time points, sea anemones exposed to 1000 ppm CO2 had higher tissue Cu concentrations than those exposed to 400 ppm CO2 at the same Cu exposure concentrations. In general, the activities of all anti-oxidant enzymes measured (catalase, CAT; glutathione peroxidase, GPx, glutathione reductase, GR) increased with exposure to increasing Cu concentrations. Significant differences in GR, CAT and to some degree GPx activity, were observed due to increasing CO2 exposure in control treatments. Sea anemones exposed to Cu in combination with higher CO2 generally had higher anti-oxidant enzyme activities than those exposed to the same concentration of Cu and lower CO2. Activity of the enzyme, carbonic anhydrase (CA), involved in acid-base balance, was significantly decreased with increasing Cu exposure. At the two lowest Cu concentrations, the extent of CA inhibition was lessened with increasing CO2 concentration. These results provide insight into toxic mechanisms of both Cu and CO2 exposure to the sensitive cnidarian E. pallida and have implications for environmental exposure of multiple contaminants.

Unravelling the role of zooxanthellae in the uptake and depuration of an essential metal in Exaiptasia pallida; an experiment using a model cnidarian

Coral skeletons record historical trace metal levels in the environment, however, the use of coral skeletal records for biomonitoring studies mostly fail to consider the influence of metal regulation by the living components of coral and subsequent incorporation into the skeleton. This study presents Exaiptasia pallida as a representative of the living components of coral and shows metal partitioning between the tissue and zooxanthellae after chronic exposure to Zn. A strong tendency for preferential accumulation in the zooxanthellae occurred after 32 days exposure and Zn concentrations in tissue and zooxanthellae were 123.3±0.7 mg kg(-1) and 294.9±8.5 respectively. This study shows zooxanthellae density plays an important role in controlling Zn loading in whole anemones and must be considered when investigating metal uptake and loading in zooxanthellate organisms. Further studies that investigate links between aragonite deposition rates and zooxanthellae density and incorporation pathways of metals into skeleton are warranted.

Comparative effects of dissolved copper and copper oxide nanoparticle exposure to the sea anemone, Exaiptasia pallida

Increasing use of metal oxide nanoparticles (NP) by various industries has resulted in substantial output of these NP into aquatic systems. At elevated concentrations, NP may interact with and potentially affect aquatic organisms. Environmental implications of increased NP use are largely unknown, particularly in marine systems. This research investigated and compared the effects of copper oxide (CuO) NP and dissolved copper, as copper chloride (CuCl2), on the sea anemone, Exaiptasia pallida. Sea anemones were collected over 21 days and tissue copper accumulation and activities of the enzymes: catalase, glutathione peroxidase, glutathione reductase, and carbonic anhydrase were quantified. The size and shape of CuO NP were observed using a ecanning electron microscope (SEM) and the presence of copper was confirmed by using Oxford energy dispersive spectroscopy systems (EDS/EDX). E. pallida accumulated copper in their tissues in a concentration- and time-dependent manner, with the animals exposed to CuCl2 accumulating higher tissue copper burdens than those exposed to CuO NP. As a consequence of increased copper exposure, as CuO NP or CuCl2, anemones increased activities of all of the antioxidant enzymes measured to some degree, and decreased the activity of carbonic anhydrase. Anemones exposed to CuO NP generally had higher anti-oxidant enzyme activities than those exposed to the same concentrations of CuCl2. This study is useful in discerning differences between CuO NP and dissolved copper exposure and the findings have implications for exposure of aquatic organisms to NP in the environment.

Effects of Cd, Co, Cu, Ni and Zn on asexual reproduction and early development of the tropical sea anemone Aiptasia pulchella

Currently few studies present sub-lethal toxicity data for tropical marine species, and there are no routine toxicity tests using marine cnidarians. The symbiotic sea anemone Aiptasia pulchella has been identified as a useful species for ecotoxicological risk assessment, and would provide a tropical marine cnidarian representative. Chronic sub-lethal toxicity tests assessing the effects of 28-day trace metal exposure on asexual reproduction in A. pulchella were investigated, and concentration-dependant reductions in the number of offspring that were produced were evident for all metal exposures. Metal concentration estimates causing 50% reductions in the numbers of asexually-reproduced juveniles after 28-day exposures (28-day effect concentrations 50%: EC50s) were 14 µg/L for copper, 63 µg/L for zinc, 107 µg/L for cobalt, 145 µg/L for cadmium, and 369 µg/L for nickel. Slightly higher 28-day EC50s of 16 µg/L for copper, 192 µg/L for zinc, 172 µg/L for cobalt, 185 µg/L for cadmium, and 404 µg/L for nickel exposures and were estimated based on reductions in the total number of live developed and undeveloped offspring. These sensitive and chronic sub-lethal toxicity estimates help fill the knowledge gap related to metal effects on cnidarians over longer exposure periods, and this newly-developed bioassay may provide a much needed tool for ecotoxicological risk assessment relevant to tropical marine environments.

Toxicological effects of the sunscreen UV filter, benzophenone-2, on planulae and in vitro cells of the coral, Stylophora pistillata

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].

The possible role of cyanobacterial filaments in coral black band disease pathology

Black band disease (BBD), characterized by a black mat or line that migrates across a coral colony leaving behind it a bare skeleton, is a persistent disease affecting massive corals worldwide. Previous microscopic and molecular examination of this disease in faviid corals from the Gulf of Eilat revealed a number of possible pathogens with the most prominent being a cyanobacterium identified as Pseudoscillatoria coralii. We examined diseased coral colonies using histopathological and molecular methods in order to further assess the possible role of this cyanobacterium, its mode of entry, and pathological effects on the coral host tissues. Affected areas of colonies with BBD were sampled for examination using both light and transmission electron microscopies. Results showed that this dominant cyanobacterium was found on the coral surface, at the coral-skeletal interface, and invading the polyp tissues and gastrovascular cavity. Although tissues surrounding the invasive cyanobacterial filaments did not show gross morphological alterations, microscopic examination revealed that the coral cells surrounding the lesion were dissociated, necrotic, and highly vacuolated. No amoebocytes were evident in the mesoglea of affected tissues suggesting a possible repression of the coral immune response. Morphological and molecular similarity of the previously isolated BBD-associated cyanobacterium P. coralii to the current samples strengthens the premise that this species is involved in the disease in this coral. These results indicate that the cyanobacteria may play a pivotal role in this disease and that the mode of entry may be via ingestion, penetrating the coral via the gastrodermis, as well as through the skeletal-tissue interface.

Scleractinian coral cell proliferation is reduced in primary culture of suspended multicellular aggregates compared to polyps

Cell cultures from reef-building scleractinian corals are being developed to study the response of these ecologically important organisms to environmental stress and diseases. Despite the importance of cell division to support propagation, cell proliferation in polyps and in vitro is under-investigated. In this study, suspended multicellular aggregates (tissue balls) were obtained after collagenase dissociation of Pocillopora damicornis coral, with varying yields between enzyme types and brands. Ultrastructure and cell type distribution were characterized in the tissue balls (TBs) compared to the polyp. Morphological evidence of cellular metabolic activity in their ciliated cortex and autophagy in their central mass suggests involvement of active tissue reorganization processes. DNA synthesis was evaluated in the forming multicellular aggregates and in the four cell layers of the polyp, using BrdU labeling of nuclei over a 24 h period. The distribution of BrdU-labeled coral cells was spatially heterogeneous and their proportion was very low in tissue balls (0.2 ± 0.1 %), indicating that suspended multicellular aggregate formation does not involve significant cell division. In polyps, DNA synthesis was significantly lower in the calicoderm (<1 %) compared to both oral and aboral gastroderm (about 10 %) and to the pseudostratified oral epithelium (15-25 % at tip of tentacle). DNA synthesis in the endosymbiotic dinoflagellates dropped in the forming tissue balls (2.7 ± 1.2 %) compared to the polyp (14 ± 3.4 %) where it was not different from the host gastroderm (10.3 ± 1.2 %). A transient (24 h) increase was observed in the cell-specific density of dinoflagellates in individually dissociated coral cell cultures. These results suggest disruption of coral cell proliferation processes upon establishment in primary culture.

Exposure to copper induces oxidative and stress responses and DNA damage in the coral Montastraea franksi

Copper is a common chemical contaminant in coastal environments, including coral reefs. Ecotoxicological studies have demonstrated that exposure to copper can cause stress and detrimental effects in both host cnidarian and algal symbionts. The objective of this study was to investigate the sublethal effects of copper on the reef-building coral Montastraea franksi, by identifying genes with altered expression in corals exposed to dissolved copper, and by measuring the extent of damage to DNA in response to copper exposure. Corals exposed to 30 μg L(-1) copper for 48 h experienced significant DNA damage and displayed changes in expression patterns of genes that are known to play role cellular and oxidative stress responses. Corals also experienced changes in gene expression of genes that are not already known to play roles in oxidative stress in corals. Our data suggest that these genes may either play roles directly in mediating a stress response, or may be genes acting downstream of the stress response. These include an ETS domain-containing transcription factor related to the ETS1 family of transcription factors, known in mammals to mediate development, disease, and stress response, and two genes that are associated with biomineralization: galaxin, a protein from the organic matrix of the coral skeleton, and a coral-specific gene SCRIP2.

Aiptasia pulchella: a tropical cnidarian representative for laboratory ecotoxicological research

An urgent need exists to identify suitable tropical marine species for use in the development of sensitive and reliable test methods for routine laboratory ecotoxicological testing. Corals are a group of organisms not represented in routine ecotoxicology due to inherent difficulties in laboratory husbandry, and sea anemones from the same phylum (cnidaria) may be useful proxies. Aiptasia pulchella is a tropical symbiotic sea anemone with a wide geographic range. It is well suited to laboratory conditions and has been used extensively in research. However, its suitability as a toxicity test species has not been investigated. Assessment of juvenile recruitment in laboratory and semi-outdoor conditions showed higher production in semi-outdoor conditions; however, laboratory rearing produced enough recruits to run routine toxicity tests. In investigations of the sensitivity of A. pulchella to contaminants, acute tests were conducted on 1- to 2-mm juveniles using copper. Lethal concentration, 50% (LC50) values at 96 h estimated from tests using five and 10 replicates ranged from 30 to 83 and 60 to 90 µg/L, respectively, and a 28-d LC50 of 26 µg/L was estimated. During the present study, sublethal endpoints were investigated; chronic assessment of inhibited asexual reproduction looks promising (12-d effective concentration, 50% [EC50] 15 µg/L) and should be assessed further. Aiptasia pulchella is a species worthy of investigation as a cnidarian representative, and will be an invaluable contribution to tropical marine ecotoxicologists.

Preserving and using germplasm and dissociated embryonic cells for conserving Caribbean and Pacific coral

Coral reefs are experiencing unprecedented degradation due to human activities, and protecting specific reef habitats may not stop this decline, because the most serious threats are global (i.e., climate change), not local. However, ex situ preservation practices can provide safeguards for coral reef conservation. Specifically, modern advances in cryobiology and genome banking could secure existing species and genetic diversity until genotypes can be introduced into rehabilitated habitats. We assessed the feasibility of recovering viable sperm and embryonic cells post-thaw from two coral species, Acropora palmata and Fungia scutaria that have diffferent evolutionary histories, ecological niches and reproductive strategies. In vitro fertilization (IVF) of conspecific eggs using fresh (control) spermatozoa revealed high levels of fertilization (>90% in A. palmata; >84% in F. scutaria; P>0.05) that were unaffected by tested sperm concentrations. A solution of 10% dimethyl sulfoxide (DMSO) at cooling rates of 20 to 30°C/min most successfully cryopreserved both A. palmata and F. scutaria spermatozoa and allowed producing developing larvae in vitro. IVF success under these conditions was 65% in A. palmata and 53% in F. scutaria on particular nights; however, on subsequent nights, the same process resulted in little or no IVF success. Thus, the window for optimal freezing of high quality spermatozoa was short (∼5 h for one night each spawning cycle). Additionally, cryopreserved F. scutaria embryonic cells had∼50% post-thaw viability as measured by intact membranes. Thus, despite some differences between species, coral spermatozoa and embryonic cells are viable after low temperature (-196°C) storage, preservation and thawing. Based on these results, we have begun systematically banking coral spermatozoa and embryonic cells on a large-scale as a support approach for preserving existing bio- and genetic diversity found in reef systems.

Biogeochemical conditions determine virulence of black band disease in corals

The microenvironmental dynamics of the microbial mat of black band disease (BBD) and its less virulent precursor, cyanobacterial patch (CP), were extensively profiled using microsensors under different light intensities with respect to O(2), pH and H(2)S. BBD mats exhibited vertical stratification into an upper phototrophic and lower anoxic and sulphidic zone. At the progression front of BBD lesions, high sulphide levels up to 4977 μM were measured in darkness along with lower than ambient levels of pH (7.43±0.20). At the base of the coral-BBD microbial mat, conditions were hypoxic or anoxic depending on light intensity exposure. In contrast, CP mats did not exhibit strong microchemical stratification with mostly supersaturated oxygen conditions throughout the mats at all light intensities and with levels of pH generally higher than in BBD. Two of three replicate CP mats were devoid of sulphide, while the third replicate showed only low levels of sulphide (up to 42 μM) present in darkness and at intermediate light levels. The level of oxygenation and sulphide correlated well with lesion migration rates, that is virulence of the mats, which were greater in BBD than in CP. The results suggest that biogeochemical microgradients of BBD shaped by the complex microbial community, rather than a defined pathogen, are the major trigger for high virulence and the associated derived coral mortality of this disease.

Cytotoxicity assessment of four pharmaceutical compounds on the zebra mussel (Dreissena polymorpha) haemocytes, gill and digestive gland primary cell cultures

Pharmaceutical compounds are considered the new environmental pollutants but at present few studies have evaluated their ecotoxicity on aquatic invertebrates. This study was aimed to investigate the in vitro cytotoxicity of four common drugs, namely atenolol (ATL), carbamazepine (CBZ), diclofenac (DCF) and gemfibrozil (GEM), on three different cell typologies from the zebra mussel (Dreissena polymorpha): haemocytes, gill and digestive gland cells. Results obtained by the Trypan blue exclusion test revealed that exposure to increasing concentrations (0.001; 0.01; 0.1; 1 and 10 mg L(-1)) of CBZ, DCF and GEM were able to significantly decrease the viability of each cell type, while the MTT (3(4,5-dimethyl-2thiazholyl)-2,5-diphenyl-2H-tetrazolium bromide) reduction assay highlighted only a slight reduction of mitochondrial activity of gill and digestive gland cells. Overall, DCF was the most cytotoxic drug for zebra mussel cells, followed by GEM, CBZ, while ATL has not a noteworthy toxic potential. Our preliminary results lay the groundwork for further in vitro evaluations, which will allow a better definition of the potential toxicity of these drugs.

Molecular toxicology of corals: a review

Coral reefs worldwide have become increasingly affected by a phenomenon known as "coral bleaching," the loss of the symbiotic algae from the host corals. The underlying causes and mechanism(s) of coral bleaching are not well known, although several have been hypothesized. While coral bleaching has been a primary focus in recent years, corals respond differentially to numerous environmental stresses. The impacts of heat, hydrocarbons, salinity, sewage effluents, biocides, heavy metals, and ultraviolet light have been investigated in both laboratory experiments and field surveys among multiple coral species. Herein what is known regarding the biological impacts of such stresses on corals at the molecular level of organization is summarized. The objective is to focus attention at the early stages of biological effects in order to encourage and facilitate research that provide ways to understand how changes at the molecular level might elucidate processes likely occurring at the population level. This, in turn, should accelerate studies that may elucidate the cellular and physiological changes contributing to coral decline, rather than just document the continued global loss of coral diversity and abundance.