Reef-building corals farm and feed on their photosynthetic symbionts

Coral reefs are highly diverse ecosystems that thrive in nutrient-poor waters, a phenomenon frequently referred to as the Darwin paradox1. The energy demand of coral animal hosts can often be fully met by the excess production of carbon-rich photosynthates by their algal symbionts2,3. However, the understanding of mechanisms that enable corals to acquire the vital nutrients nitrogen and phosphorus from their symbionts is incomplete4-9. Here we show, through a series of long-term experiments, that the uptake of dissolved inorganic nitrogen and phosphorus by the symbionts alone is sufficient to sustain rapid coral growth. Next, considering the nitrogen and phosphorus budgets of host and symbionts, we identify that these nutrients are gathered through symbiont 'farming' and are translocated to the host by digestion of excess symbiont cells. Finally, we use a large-scale natural experiment in which seabirds fertilize some reefs but not others, to show that the efficient utilization of dissolved inorganic nutrients by symbiotic corals established in our laboratory experiments has the potential to enhance coral growth in the wild at the ecosystem level. Feeding on symbionts enables coral animals to tap into an important nutrient pool and helps to explain the evolutionary and ecological success of symbiotic corals in nutrient-limited waters.

Light pollution alters the skeletal morphology of coral juveniles and impairs their light capture capacity

Urbanization and infrastructure development have changed the night-time light regime of many coastal marine habitats. Consequently, Artificial Light at Night (ALAN) is becoming a global ecological concern, particularly in nearshore coral reef ecosystems. However, the effects of ALAN on coral architecture and their optical properties are unexplored. Here, we conducted a long-term ex situ experiment (30 months from settlement) on juvenile Stylophora pistillata corals grown under ALAN conditions using light-emitting diodes (LEDs) and fluorescent lamps, mimicking light-polluted habitats. We found that corals exposed to ALAN exhibited altered skeletal morphology that subsequently resulted in reduced light capture capacity, while also gaining better structural and optical modifications to increased light levels than their ambient-light counterparts. Additionally, light-polluted corals developed a more porous skeleton compared to the control corals. We suggest that ALAN induces light stress in corals, leading to a decrease in the solar energy available for photosynthesis during daytime illumination.

Assessment of storm impact on coral reef structural complexity

Extreme weather events are increasing in frequency and magnitude. Consequently, it is important to understand their effects and remediation. Resilience reflects the ability of an ecosystem to absorb change, which is important for understanding ecological dynamics and trajectories. To describe the impact of a powerful storm on coral reef structural complexity, we used novel computational tools and detailed 3D reconstructions captured at three time points over three years. Our data-set Reefs4D of 21 co-registered image-based models enabled us to calculate the differences at seven sites over time and is released with the paper. We employed six geometrical metrics, two of which are new algorithms for calculating fractal dimension of reefs in full 3D. We conducted a multivariate analysis to reveal which sites were affected the most and their relative recovery. We also explored the changes in fractal dimension per size category using our cube-counting algorithm. Three metrics showed a significant difference between time points, i.e., decline and subsequent recovery in structural complexity. The multivariate analysis and the results per size category showed a similar trend. Coral reef resilience has been the subject of seminal studies in ecology. We add important information to the discussion by focusing on 3D structure through image-based modeling. The full picture shows resilience in structural complexity, suggesting that the reef has not gone through a catastrophic phase shift. Our novel analysis framework is widely transferable and useful for research, monitoring, and management.

Morpho-functional traits of the coral Stylophora pistillata enhance light capture for photosynthesis at mesophotic depths

The morphological architecture of photosynthetic corals modulates the light capture and functioning of the coral-algal symbiosis on shallow-water corals. Since corals can thrive on mesophotic reefs under extreme light-limited conditions, we hypothesized that microskeletal coral features enhance light capture under low-light environments. Utilizing micro-computed tomography scanning, we conducted a novel comprehensive three-dimensional (3D) assessment of the small-scale skeleton morphology of the depth-generalist coral Stylophora pistillata collected from shallow (4–5 m) and mesophotic (45–50 m) depths. We detected a high phenotypic diversity between depths, resulting in two distinct morphotypes, with calyx diameter, theca height, and corallite marginal spacing contributing to most of the variation between depths. To determine whether such depth-specific morphotypes affect coral light capture and photosynthesis on the corallite scale, we developed 3D simulations of light propagation and photosynthesis. We found that microstructural features of corallites from mesophotic corals provide a greater ability to use solar energy under light-limited conditions; while corals associated with shallow morphotypes avoided excess light through self-shading skeletal architectures. The results from our study suggest that skeleton morphology plays a key role in coral photoadaptation to light-limited environments.

Micro-computed tomography scanning and 3D light simulation models reveals distinct morphotypes of the coral species Stylophora pistillata depending on depth, and suggest that coral skeletal micromorphology plays a key role in coral photoadaptation.

Emerging 3D technologies for future reformation of coral reefs: Enhancing biodiversity using biomimetic structures based on designs by nature

The rapid decline of vulnerable coral reefs has increased the necessity of exploring interdisciplinary methods for reef restoration. Examining how to upgrade these tools may uncover options to better support or increase biodiversity of coral reefs. As many of the issues facing reef restoration today deal with the scalability and effectiveness of restoration efforts, there is an urgency to invest in technology that can help reach ecosystem-scale. Here, we provide an overview on the evolution to current state of artificial reefs as a reef reformation tool and discuss a blueprint with which to guide the next generation of biomimetic artificial habitats for ecosystem support. Currently, existing artificial structures have difficulty replicating the 3D complexity of coral habitats and scaling them to larger areas can be problematic in terms of production and design. We introduce a novel customizable 3D interface for producing scalable, biomimetic artificial structures, utilizing real data collected from coral ecosystems. This interface employs 3D technologies, 3D imaging and 3D printing, to extract core reef characteristics, which can be translated and digitized into a 3D printed artificial reef. The advantages of 3D printing lie in providing customized tools by which to integrate the vital details of natural reefs, such as rugosity and complexity, into a sustainable manufacturing process. This methodology can offer economic solutions for developing both small and large-scale biomimetic structures for a variety of restoration situations, that closely resemble the coral reefs they intend to support.

Coral fluorescence: a prey-lure in deep habitats

Fluorescence is highly prevalent in reef-building corals, nevertheless its biological role is still under ongoing debate. This feature of corals was previously suggested to primarily screen harmful radiation or facilitate coral photosynthesis. In mesophotic coral ecosystems (MCEs; 30-150 m depth) corals experience a limited, blue-shifted light environment. Consequently, in contrast to their shallow conspecifics, they might not be able to rely on photosynthates from their photosymbionts as their main energy source. Here, we experimentally test an alternative hypothesis for coral fluorescence: a prey-lure mechanism for plankton. We show that plankton exhibit preferential swimming towards green fluorescent cues and that compared to other morphs, higher predation rates are recorded in a green fluorescing morph of the mesophotic coral Euphyllia paradivisa. The evidence provided here - that plankton are actively attracted to fluorescent signals - indicates the significant role of fluorescence in amplifying the nutritional sink adjacent to coral reefs.

Soft coral reproductive phenology along a depth gradient: Can "going deeper" provide a viable refuge?

Many species across a wide range of taxa and habitats display phenological shifts and differences in response to both environmental gradients and climate change. Moreover, the wide‐scale decline of numerous ecosystems is leading to increasing efforts to identify zones that might serve as natural refuges from various disturbances, including ocean warming. One such refuge was suggested to be that of the deep coral reefs, but whether depth can provide coral populations with a viable and reproductive refuge remains unclear. Given the global coral‐reef degradation and the key role that corals play as ecosystem engineers, their reproductive ecology has been widely studied. A particular knowledge gap nonetheless exists regarding coral reproductive phenology along a depth gradient. Filling in this gap may uncover the environmental cues that regulate coral reproduction, leading to better predictions of population connectivity, and their possible responses to climate change and other environmental changes. Here, using long‐term in situ observations of the soft coral Rhytisma fulvum's reproductive activity along its entire depth range (0–45 m), we examined the relationship among several environmental factors and the coral's reproductive phenology and activity over five successive annual breeding seasons. Compared with the shallow depths, a lower number of reproducing colonies was found in habitats deeper than 30 m, highlighting possible constraints on coral reproduction at the deeper end of their range. Our results further revealed that an increase in seawater temperature over 1–2‐day intervals during the breeding season correlated with the onset of reproductive activity along the depth gradient, leading to different reproductive periodicities in different depths. These differences suggest that differential temperature regimes and reproductive timing across depth may create intraspecific temporal reproductive segregation, possibly reducing connectivity among populations along a depth gradient. Moreover, we found high variability among years in both the timing of breeding activities and in the level of reproductive synchrony among corals from different depths. Overall, our study questions whether depth can provide a long‐term and viable refuge for corals in the face of global environmental changes.

Biogeography, reproductive biology and phylogenetic divergence within the Fungiidae (mushroom corals)

While the escalating impacts of climate change and other anthropogenic pressures on coral reefs are well documented at the coral community level, studies of species-specific trends are less common, owing mostly to the difficulties and uncertainties in delineating coral species. It has also become clear that traditional coral taxonomy based largely on skeletal macromorphology has underestimated the diversity of many coral families. Here, we use targeted enrichment methods to sequence 2476 ultraconserved elements (UCEs) and exonic loci to investigate the relationship between populations of Fungia fungites from Okinawa, Japan, where this species reproduces by brooding (i.e., internal fertilization), and Papua New Guinea and Australia, where it reproduces by broadcast-spawning (i.e., external fertilization). Moreover, we analyzed the relationships between populations of additional fungiid species (Herpolitha limax and Ctenactis spp.) that reproduce only by broadcast-spawning. Our phylogenetic and species delimitation analyses reveal strong biogeographic structuring in both F. fungites and Herpolitha limax, consistent with cryptic speciation in Okinawa in both species and additionally for H. limax in the Red Sea. By combining UCE/exon data and mitochondrial sequences captured in off-target reads, we reinforce earlier findings that Ctenactis, a genus consisting of three nominal morphospecies, is not a natural group. Our results highlight the need for taxonomic and systematic re-evaluations of some species and genera within the family Fungiidae. This work demonstrates that sequence data generated by the application of targeted capture methods can provide objective criteria by which we can test phylogenetic hypotheses based on morphological and/or life history traits.

An Indo-Pacific coral spawning database

The discovery of multi-species synchronous spawning of scleractinian corals on the Great Barrier Reef in the 1980s stimulated an extraordinary effort to document spawning times in other parts of the globe. Unfortunately, most of these data remain unpublished which limits our understanding of regional and global reproductive patterns. The Coral Spawning Database (CSD) collates much of these disparate data into a single place. The CSD includes 6178 observations (3085 of which were unpublished) of the time or day of spawning for over 300 scleractinian species in 61 genera from 101 sites in the Indo-Pacific. The goal of the CSD is to provide open access to coral spawning data to accelerate our understanding of coral reproductive biology and to provide a baseline against which to evaluate any future changes in reproductive phenology.

Population dynamics and growth rates of free-living mushroom corals (Scleractinia: Fungiidae) in the sediment-stressed reefs of Singapore

The reefs of Singapore provide an excellent opportunity to study the population dynamics and growth rates of free-living mushroom corals (Fungiidae) under sediment-stressed conditions. Transect surveys at four study sites revealed a total of 11 free-living mushroom coral species-the same 11 species as those found by local studies since the 1980s. The abundance of the four most common species ranged from 1.0 to 68.3 Ind. per 100m², while their population size-structure showed a common pattern of a higher proportion of small-sized corals than large-sized ones (i.e. positively skewed size-structure), although very few individuals of the smallest-size classes were recorded for any of the four species. A more positively skewed size-structure for each of the four most common species was observed at the reef slope (5-6m depth) than at the reef crest (2-3m depth), possibly due to a slower growth rate caused by light reduction with depth. All the mushroom corals studied exhibited a decline in growth rate with increasing size and weight, indicating determinate growth. Growth rate of each of the four most common species was similar among the study sites, despite variation in environmental conditions. Our results demonstrate species richness stability over the past three decades, suggesting that these free-living mushroom coral assemblages comprise species that are well-adapted to the chronic high sedimentation characteristic of Singapore's reefs. However, if the paucity of individuals of the smallest-size classes reflects poor recruitment and/or early mortality, there may be some cause for concern. Our robust baseline data can contribute to a long-term monitoring strategy for determination of changes in mushroom coral population dynamics.

Reciprocal-transplantation between shallow and mesophotic stony corals

Most studies to date on the various life-history aspects of scleractinian corals (e.g. reproduction, connectivity, and physiology) have focused on their innate habitats. However, comprehensive data on the ability of both shallow and mesophotic corals to contend in the coming decades with the different environmental conditions they may encounter due to new habitats or environmental changes (e.g. eutrophication), are scarce. Long-term cross-transplantation experiments assessing the potential responses and acclimatization ability of corals are thus needed in order to expand our knowledge. Here we examined the survivorship and changes in the photobiological acclimatization of corals following their cross-transplantation between two different depths (5-10 m and 45 m) and two sites characterized by different abiotic conditions (i.e. light, nutrient, and sedimentation regime). This year-long in-situ experiment was performed on five depth-generalist coral species. Depth of origin and the species' particular morphology were found to be the strongest predictors of survivorship. Physiological responses occurred mainly among those corals that had been translocated from deep-to-shallow water, and were expressed in a significant reduction in chlorophyll-a concentration and algal density, as well as changes in photosynthetic parameters (e.g. minimal/maximal saturating points, E_k and E_m, and rETR_max). Our study contributes to a better assessment of the physiological and ecological consequences of corals under acute and long-term environmental perturbations and their endurance abilities. Furthermore, it contributes to the information necessary for effective management intervention aimed at supporting the possible acclimation or rehabilitation of coral species.

The Complexity of the Holobiont in the Red Sea Coral Euphyllia paradivisa under Heat Stress

The recognition of the microbiota complexity and their role in the evolution of their host is leading to the popularization of the holobiont concept. However, the coral holobiont (host and its microbiota) is still enigmatic and unclear. Here, we explore the complex relations between different holobiont members of a mesophotic coral Euphyllia paradivisa. We subjected two lines of the coral-with photosymbionts, and without photosymbionts (apo-symbiotic)-to increasing temperatures and to antibiotics. The different symbiotic states were characterized using transcriptomics, microbiology and physiology techniques. The bacterial community's composition is dominated by bacteroidetes, alphaproteobacteria, and gammaproteobacteria, but is dependent upon the symbiont state, colony, temperature treatment, and antibiotic exposure. Overall, the most important parameter determining the response was whether the coral was a symbiont/apo-symbiotic, while the colony and bacterial composition were secondary factors. Enrichment Gene Ontology analysis of coral host's differentially expressed genes demonstrated the cellular differences between symbiotic and apo-symbiotic samples. Our results demonstrate the significance of each component of the holobiont consortium and imply a coherent link between them, which dramatically impacts the molecular and cellular processes of the coral host, which possibly affect its fitness, particularly under environmental stress.

Effects of Light Pollution on the Early Life Stages of the Most Abundant Northern Red Sea Coral

The growth in human population along coastal areas is exposing marine environments to increasing anthropogenic light sources. Despite the potential effects of this modern phenomenon, very few studies have examined its implications for corals. Here, we present a long-term study of coral early life stages under light pollution conditions at night. Coral larvae were collected from Stylophora pistillata colonies, and then settled and grown under experimental conditions of two different common city lighting methods (fluorescent or LED). Effects of the artificial lighting on the coral settlement success, survivorship, growth rate, photosynthetic efficiency, and calcification rate were examined over a period of one year. The control exhibited ~30% higher settlement success compared to the two light treatments, while under the light treatments corals showed higher survivorship, growth, and calcification rates. In addition, an indication of damage to the photosynthetic system was found in the light-polluted corals, which was reflected in their photosynthesis efficiency parameters: i.e., lower maximum light utilization coefficient (α), lower maximum potential photosynthetic rate (P_max), and lower photosynthetic maximal quantum yield (F_v/F_m). Our findings provide evidence of the potential adverse effects of artificial lighting methods on the natural environment of coral reefs. We conclude that the use of the LED lighting method has high interference potential for the early life stages of corals.

Breakdown in spawning synchrony: A silent threat to coral persistence

The impacts of human and natural disturbances on coral reefs are typically quantified through visible damage (e.g., reduced coral coverage as a result of bleaching events), but changes in environmental conditions may also cause damage in less visible ways. Despite the current paradigm, which suggests consistent, highly synchronized spawning events, corals that reproduce by broadcast spawning are particularly vulnerable because their reproductive phenology is governed by environmental cues. Here, we quantify coral spawning intensity during four annual reproductive seasons, alongside laboratory analyses at the polyp, colony, and population levels, and we demonstrate that, compared with historical data, several species from the Red Sea have lost their reproductive synchrony. Ultimately, such a synchrony breakdown reduces the probability of successful fertilization, leading to a dearth of new recruits, which may drive aging populations to extinction.

Response of fluorescence morphs of the mesophotic coral Euphyllia paradivisa to ultra-violet radiation

Euphyllia paradivisa is a strictly mesophotic coral in the reefs of Eilat that displays a striking color polymorphism, attributed to fluorescent proteins (FPs). FPs, which are used as visual markers in biomedical research, have been suggested to serve as photoprotectors or as facilitators of photosynthesis in corals due to their ability to transform light. Solar radiation that penetrates the sea includes, among others, both vital photosynthetic active radiation (PAR) and ultra-violet radiation (UVR). Both types, at high intensities, are known to have negative effects on corals, ranging from cellular damage to changes in community structure. In the present study, fluorescence morphs of E. paradivisa were used to investigate UVR response in a mesophotic organism and to examine the phenomenon of fluorescence polymorphism. E. paradivisa, although able to survive in high-light environments, displayed several physiological and behavioral responses that indicated severe light and UVR stress. We suggest that high PAR and UVR are potential drivers behind the absence of this coral from shallow reefs. Moreover, we found no significant differences between the different fluorescence morphs' responses and no evidence of either photoprotection or photosynthesis enhancement. We therefore suggest that FPs in mesophotic corals might have a different biological role than that previously hypothesized for shallow corals.

Photoacclimation and induction of light-enhanced calcification in the mesophotic coral Euphyllia paradivisa

Corals and their photosymbionts experience inherent changes in light along depth gradients, leading them to have evolved several well-investigated photoacclimation strategies. As coral calcification is influenced by light (a process described as LEC-'light-enhanced calcification'), studies have sought to determine the link between photosynthesis and calcification, but many puzzling aspects still persist. Here, we examine the physiology of Euphyllia paradivisa, a coral species found at a wide range of depths but that is strictly mesophotic in the Red Sea; and also examines the coupling between photosynthesis and LEC by investigating the response of the coral under several controlled light regimes during a long-term experiment. E. paradivisa specimens were collected from 40 to 50 m depth and incubated under three light conditions for a period of 1 year: full-spectrum shallow-water light (approx. 3 m, e.g. shallow-light treatment); blue deep-water light (approx. 40 m, e.g. mesophotic-light treatment) or total darkness (e.g. dark treatment). Net photosynthesis remained similar in the shallow-light-treated corals compared to the mesophotic-light-treated corals, under both low and high light. However, calcification increased dramatically with increasing light intensity in the shallow-light-treated corals, suggesting a decoupling between these processes. Photoacclimation to shallow-water conditions was indicated by enhanced respiration, a higher density of zooxanthellae per polyp and lower chlorophyll a content per cell. The dark-treated corals became completely bleached but did not lower their metabolism below that of the mesophotic-light-treated corals. No Symbiodinium clade shift was found following the year-long light treatments. We conclude that E. paradivisa, and its original symbiont clade, can adapt to various light conditions by controlling its metabolic rate and growth energy investment, and consequently induce LEC.

Can mesophotic reefs replenish shallow reefs? Reduced coral reproductive performance casts a doubt

Mesophotic coral ecosystems (i.e., deep coral reefs at 30-120 m depth) appear to be thriving while many shallow reefs in the world are declining. Amid efforts to understand and manage their decline, it was suggested that mesophotic reefs might serve as natural refuges and a possible source of propagules for the shallow reefs. However, our knowledge of how reproductive performance of corals alters with depth is sparse. Here, we present a comprehensive study of the reproductive phenology, fecundity, and abundance of seven reef-building conspecific corals in shallow and mesophotic habitats. Significant differences were found in the synchrony and timing of gametogenesis and spawning between shallow and mesophotic coral populations. Thus, mesophotic populations exhibited delayed or protracted spawning events, which led to spawning of the mesophotic colonies in large proportions at times where the shallow ones had long been depleted of reproductive material. All species investigated demonstrated a substantial reduction in fecundity and/or oocyte sizes at mesophotic depths (40-60 m). Two species (Seriatopora hystrix and Galaxea fascicularis) displayed a reduction in both fecundity and oocyte size at mesophotic depths. Turbinaria reniformis had only reduced fecundity and Acropora squarrosa and Acropora valida only reduced oocyte size. In Montipora verrucosa, reduced fecundity was found during one annual reproductive season while, in the following year, only reduced oocyte size was found. In contrast, reduced oocyte size in mesophotic populations of Acropora squarrosa was consistent along three studied years. One species, Acropora pharaonis, was found to be infertile at mesophotic depths along two studied years. This indicates that reproductive performance decreases with depth; and that although some species are capable of reproducing at mesophotic depths, their contribution to the replenishment of shallow reefs may be inconsequential. Reduced reproductive performance with depth, combined with the possible narrower tolerance to environmental factors, further suggests that mesophotic corals may in fact be more vulnerable than previously conceived. Furthermore, we posit that the observed temporal segregation in reproduction could lead to assortative mating, and this, in turn, may facilitate adaptive divergence across depth.

Reproductive strategies of the coral Turbinaria reniformis in the northern Gulf of Aqaba (Red Sea)

Here we describe for the first time the reproductive biology of the scleractinian coral Turbinaria reniformis studied during three years at the coral reefs of Eilat and Aqaba. We also investigated the possibility of sex change in individually tagged colonies followed over a period of 12 years. T. reniformis was found to be a stable gonochorist (no detected sex change) that reproduces by broadcast spawning 5-6 nights after the full moon of June and July. Spawning was highly synchronized between individuals in the field and in the lab. Reproduction of T. reniformis is temporally isolated from the times at which most other corals reproduce in Eilat. Its relatively long reproductive cycle compared to other hermaphroditic corals may be due to the high reproductive effort associated with the production of eggs by gonochoristic females. Sex ratio in both the Aqaba and Eilat coral populations deviated significantly from a 1:1 ratio. The larger number of males than of females may provide a compensation for sperm limitation due to its dilution in the water column. We posit that such sex allocation would facilitate adaptation within gonochoristic species by increasing fertilization success in low density populations, constituting a phenomenon possibly regulated by chemical communication.

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.

Spectral Diversity and Regulation of Coral Fluorescence in a Mesophotic Reef Habitat in the Red Sea

The phenomenon of coral fluorescence in mesophotic reefs, although well described for shallow waters, remains largely unstudied. We found that representatives of many scleractinian species are brightly fluorescent at depths of 50–60 m at the Interuniversity Institute for Marine Sciences (IUI) reef in Eilat, Israel. Some of these fluorescent species have distribution maxima at mesophotic depths (40–100 m). Several individuals from these depths displayed yellow or orange-red fluorescence, the latter being essentially absent in corals from the shallowest parts of this reef. We demonstrate experimentally that in some cases the production of fluorescent pigments is independent of the exposure to light; while in others, the fluorescence signature is altered or lost when the animals are kept in darkness. Furthermore, we show that green-to-red photoconversion of fluorescent pigments mediated by short-wavelength light can occur also at depths where ultraviolet wavelengths are absent from the underwater light field. Intraspecific colour polymorphisms regarding the colour of the tissue fluorescence, common among shallow water corals, were also observed for mesophotic species. Our results suggest that fluorescent pigments in mesophotic reefs fulfil a distinct biological function and offer promising application potential for coral-reef monitoring and biomedical imaging.

Modeling the Impact of White-Plague Coral Disease in Climate Change Scenarios

Coral reefs are in global decline, with coral diseases increasing both in prevalence and in space, a situation that is expected only to worsen as future thermal stressors increase. Through intense surveillance, we have collected a unique and highly resolved dataset from the coral reef of Eilat (Israel, Red Sea), that documents the spatiotemporal dynamics of a White Plague Disease (WPD) outbreak over the course of a full season. Based on modern statistical methodologies, we develop a novel spatial epidemiological model that uses a maximum-likelihood procedure to fit the data and assess the transmission pattern of WPD. We link the model to sea surface temperature (SST) and test the possible effect of increasing temperatures on disease dynamics. Our results reveal that the likelihood of a susceptible coral to become infected is governed both by SST and by its spatial location relative to nearby infected corals. The model shows that the magnitude of WPD epidemics strongly depends on demographic circumstances; under one extreme, when recruitment is free-space regulated and coral density remains relatively constant, even an increase of only 0.5°C in SST can cause epidemics to double in magnitude. In reality, however, the spatial nature of transmission can effectively protect the community, restricting the magnitude of annual epidemics. This is because the probability of susceptible corals to become infected is negatively associated with coral density. Based on our findings, we expect that infectious diseases having a significant spatial component, such as Red-Sea WPD, will never lead to a complete destruction of the coral community under increased thermal stress. However, this also implies that signs of recovery of local coral communities may be misleading; indicative more of spatial dynamics than true rehabilitation of these communities. In contrast to earlier generic models, our approach captures dynamics of WPD both in space and time, accounting for the highly seasonal nature of annual WPD outbreaks.

Coral reefs are deteriorating at alarming rates, with coral disease outbreaks increasing in prevalence and in space. Anomalously high ocean temperatures are thought to significantly contribute to this problem. We collected a unique and highly resolved dataset of a White Plague Disease (WPD) outbreak from the coral reef of Eilat (Israel, Red Sea). By fitting a novel epidemiological model to the data, we characterize the dynamics of WPD, and study the possible effects of future increasing sea-surface temperatures (SST) on disease dynamics. In contrast to earlier studies, our approach captures the dynamics of coral disease both in space and time, and accounts for the highly seasonal nature of the annual outbreaks. We also apply a novel combination of spatiotemporal statistics and null hypothesis approaches to study the disease progression. Model forecasts into the future show that for some scenarios even an increase of only 0.5°C in SST can cause epidemics to double in magnitude. Since the probability of infection is found to be negatively associated with coral density, this implies that the spatial nature of disease transmission can both enhance and restrict the magnitude of annual epidemics. The results have implications for designing management policies appropriate for coral reef conservation.

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.

Heat-stress and light-stress induce different cellular pathologies in the symbiotic dinoflagellate during coral bleaching

Coral bleaching is a significant contributor to the worldwide degradation of coral reefs and is indicative of the termination of symbiosis between the coral host and its symbiotic algae (dinoflagellate; Symbiodinium sp. complex), usually by expulsion or xenophagy (symbiophagy) of its dinoflagellates. Herein, we provide evidence that during the earliest stages of environmentally induced bleaching, heat stress and light stress generate distinctly different pathomorphological changes in the chloroplasts, while a combined heat- and light-stress exposure induces both pathomorphologies; suggesting that these stressors act on the dinoflagellate by different mechanisms. Within the first 48 hours of a heat stress (32°C) under low-light conditions, heat stress induced decomposition of thylakoid structures before observation of extensive oxidative damage; thus it is the disorganization of the thylakoids that creates the conditions allowing photo-oxidative-stress. Conversely, during the first 48 hours of a light stress (2007 µmoles m⁻² s⁻¹ PAR) at 25°C, condensation or fusion of multiple thylakoid lamellae occurred coincidently with levels of oxidative damage products, implying that photo-oxidative stress causes the structural membrane damage within the chloroplasts. Exposure to combined heat- and light-stresses induced both pathomorphologies, confirming that these stressors acted on the dinoflagellate via different mechanisms. Within 72 hours of exposure to heat and/or light stresses, homeostatic processes (e.g., heat-shock protein and anti-oxidant enzyme response) were evident in the remaining intact dinoflagellates, regardless of the initiating stressor. Understanding the sequence of events during bleaching when triggered by different environmental stressors is important for predicting both severity and consequences of coral bleaching.

The taxonomy and phylogeny of Echinometra (Camarodonta: Echinometridae) from the red sea and western Indian Ocean

The number of valid species in the genus Echinometra (Echinodermata, Echinoidea) and their associated identification keys have been debated in the scientific literature for more than 180 years. As the phylogeny and dispersal patterns of these species have been widely used as a prominent model for marine speciation, new insights into their taxonomy have the potential to deepen our understanding of marine speciation processes. In this study we examine Echinometra taxonomy, combining morphology and molecular tools. We present the taxonomy and phylogeny of Red Sea and western Indian Ocean Echinometra. The currently available morphological keys were found to be limited in their ability to delineate all species within this genus. Nonetheless, morphological similarities between the Red Sea and western Indian Ocean populations were high, and delimited them from the other species. These latter populations together formed a monophyletic clade, genetically distant from any of the other Echinometra species by more than 3%. Combining both traditional taxonomy and molecular evidence, we found that these populations were neither Echinometra mathaei nor E. oblonga, as previously considered. The morphological discrepancies of these populations, and their genetic divergence from the other Echinometra species, suggest that they should be considered as a new Echinometra species.

Bacterial consortium of Millepora dichotoma exhibiting unusual multifocal lesion event in the Gulf of Eilat, Red Sea

Colonies of the hydrocoral Millepora dichotoma along the Gulf of Eilat are exhibiting unusual tissue lesions in the form of white spots. The emergence and rapid establishment of these multifocal tissue lesions was the first of its kind reported in this region. A characterization of this morphological anomaly revealed bleached tissues with a significant presence of bacteria in the tissue lesion area. To ascertain possible differences in microbial biota between the lesion area and non-affected tissues, we characterized the bacterial diversity in the two areas of these hydrocorals. Both culture-independent (molecular) and culture-dependent assays showed a shift in bacterial community structure between the healthy and affected tissues. Several 16S rRNA gene sequences retrieved from the affected tissues matched sequences of bacterial clones belonging to Alphaproteobacteria and Bacteroidetes members previously associated with various diseases in scleractinian corals.

Reproductive characteristics and steroid levels in the scleractinian coral Oculina patagonica inhabiting contaminated sites along the Israeli Mediterranean coast

In this study we compared reproductive characteristics and steroid hormone levels in the non-indigenous scleractinian coral, Oculina patagonica, inhabiting contaminated vs. uncontaminated reference sites along the Israeli Mediterranean coast. Our results indicate significantly higher steroid levels in both seawater and coral tissue samples from contaminated sites as compared to reference sites, suggesting that corals tend to accumulate steroids from the surrounding waters. Despite their higher steroid levels, corals from the contaminated sites showed reproductive potential comparable to those of the reference sites. Interestingly, a clear distinction could be seen between corals exposed to pollution for long vs. short durations, with the latter showing a failure to complete gametogenesis. This suggests that reproduction in O. patagonica is susceptible to acute rather than chronic stress. The involvement of adjustment/adaptation processes may explain this species tolerance, and may reflect the ability of O. patagonica to successfully invade new areas in the Mediterranean Sea.

A novel method for coral explant culture and micropropagation

We describe here a method for the micropropagation of coral that creates progeny from tissue explants derived from a single polyp or colonial corals. Coral tissue explants of various sizes (0.5-2.5 mm in diameter) were manually microdissected from the solitary coral Fungia granulosa. Explants could be maintained in an undeveloped state or induced to develop into polyps by manipulating environmental parameters such as light and temperature regimes, as well as substrate type. Fully developed polyps were able to be maintained for a long-term in a closed sea water system. Further, we demonstrate that mature explants are also amenable to this technique with the micropropagation of second-generation explants and their development into mature polyps. We thereby experimentally have established coral clonal lines that maintain their ability to differentiate without the need for chemical induction or genetic manipulation. The versatility of this method is also demonstrated through its application to two other coral species, the colonial corals Oculina patigonica and Favia favus.

Global human footprint on the linkage between biodiversity and ecosystem functioning in reef fishes

Difficulties in scaling up theoretical and experimental results have raised controversy over the consequences of biodiversity loss for the functioning of natural ecosystems. Using a global survey of reef fish assemblages, we show that in contrast to previous theoretical and experimental studies, ecosystem functioning (as measured by standing biomass) scales in a non-saturating manner with biodiversity (as measured by species and functional richness) in this ecosystem. Our field study also shows a significant and negative interaction between human population density and biodiversity on ecosystem functioning (i.e., for the same human density there were larger reductions in standing biomass at more diverse reefs). Human effects were found to be related to fishing, coastal development, and land use stressors, and currently affect over 75% of the world's coral reefs. Our results indicate that the consequences of biodiversity loss in coral reefs have been considerably underestimated based on existing knowledge and that reef fish assemblages, particularly the most diverse, are greatly vulnerable to the expansion and intensity of anthropogenic stressors in coastal areas.

Coral community reproductive patterns: red sea versus the great barrier reef

In contrast to many corals of the Great Barrier Reef, Australia, which are synchronous multispecific spawners, the abundant coral species in the northern Red Sea, Israel, exhibit temporal reproductive isolation. Spawning dates of 12 of the 13 Red Sea species followed lunar periodicity and were consistent throughout 3 years of study. Spawning periods of all species occurred in different seasons, different months, or different lunar phases within the same month. The high abundance of the corals studied at Eilat may be due in part to the advantages gained through not having overlapping spawning periods and settlement times.

Diversity partitioning of stony corals across multiple spatial scales around Zanzibar Island, Tanzania

BACKGROUND

The coral reefs of Zanzibar Island (Unguja, Tanzania) encompass a considerable proportion of the global coral-reef diversity and are representative of the western Indian Ocean region. Unfortunately, these reefs have been recently subjected to local and regional disturbances. The objectives of this study were to determine whether there are potentially non-random processes forcing the observed coral diversity patterns, and highlight where and at which spatial scales these processes might be most influential.

METHODOLOGY/PRINCIPAL FINDINGS

A hierarchical (nested) sampling design was employed across three spatial scales, ranging from transects (

CONCLUSIONS/SIGNIFICANCE

The non-random outcome of the partitioning analyses helped to identify the among-sites scale (i.e., 10's of kilometers) and the within-transects scale (i.e., a few meters; especially at Changuu) as spatial boundaries within which to examine the processes that may interact and disproportionately differentiate coral diversity. In light of coral community compositions and diversity patterns we strongly recommend that Bawe be declared a MPA.

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Key Words Collapse

MESH Headings

• Animals
• Anthozoa/genetics
• Anthozoa/physiology
• Biodiversity
• Coral Reefs
• Ecology
• Ecosystem
• Geography
• Indian Ocean
• Population Density
• Tanzania

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Affiliation(s)

Assaf Zvuloni Department of Zoology, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel.
Robert van Woesik
Yossi Loya

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Stramenopile microorganisms associated with the massive coral Favia sp

The surfaces of massive corals of the genus Favia from Eilat, Red Sea, and from Heron Island, Great Barrier Reef, are covered by a layer of eukaryotic microorganisms. These microorganisms are embedded in the coral mucus and tissue. In the Gulf of Eilat, the prevalence of corals covered by patches of eukaryotic microorganisms was positively correlated with a decrease in water temperatures (from 25-28 degrees C in the summer to 20-23 degrees C in winter). Comparisons carried out using transmission and scanning electron microscopy showed morphological similarities between the microorganisms from the two geographically distant reefs. The microorganisms found on and in the tissues were approximately 5-15 microm in diameter, surrounded by scales in their cell wall, contained a nucleus, and included unique auto-florescent coccoid bodies of approximately 1 mum. Such morphological characters suggested that these microorganisms are stramenopile protists and in particular thraustochytrids. Molecular analysis, carried out using specific primers for stramenopile 18S rRNA genes, revealed that 90% (111/123) of the clones in the gene libraries were from the Thraustochytriidae. The dominant genera in this family were Aplanochytrium sp., Thraustochytrium sp., and Labyrinthuloides sp. Ten stramenopile strains were isolated and cultured from the corals. Some strains showed > or =97% similarity to clones derived from libraries of mucus-associated microorganisms retrieved directly from these corals. Fatty acid characterization of one of the prevalent strains revealed a high percentage of polyunsaturated fatty acids, including omega-3. The possible association of these stramenopiles in the coral holobiont appeared to be a positive one.

Tunicate mitogenomics and phylogenetics: peculiarities of the Herdmania momus mitochondrial genome and support for the new chordate phylogeny

Background

Tunicates represent a key metazoan group as the sister-group of vertebrates within chordates. The six complete mitochondrial genomes available so far for tunicates have revealed distinctive features. Extensive gene rearrangements and particularly high evolutionary rates have been evidenced with regard to other chordates. This peculiar evolutionary dynamics has hampered the reconstruction of tunicate phylogenetic relationships within chordates based on mitogenomic data.

Results

In order to further understand the atypical evolutionary dynamics of the mitochondrial genome of tunicates, we determined the complete sequence of the solitary ascidian Herdmania momus. This genome from a stolidobranch ascidian presents the typical tunicate gene content with 13 protein-coding genes, 2 rRNAs and 24 tRNAs which are all encoded on the same strand. However, it also presents a novel gene arrangement, highlighting the extreme plasticity of gene order observed in tunicate mitochondrial genomes. Probabilistic phylogenetic inferences were conducted on the concatenation of the 13 mitochondrial protein-coding genes from representatives of major metazoan phyla. We show that whereas standard homogeneous amino acid models support an artefactual sister position of tunicates relative to all other bilaterians, the CAT and CAT+BP site- and time-heterogeneous mixture models place tunicates as the sister-group of vertebrates within monophyletic chordates. Moreover, the reference phylogeny indicates that tunicate mitochondrial genomes have experienced a drastic acceleration in their evolutionary rate that equally affects protein-coding and ribosomal-RNA genes.

Conclusion

This is the first mitogenomic study supporting the new chordate phylogeny revealed by recent phylogenomic analyses. It illustrates the beneficial effects of an increased taxon sampling coupled with the use of more realistic amino acid substitution models for the reconstruction of animal phylogeny.

Pseudoscillatoria coralii gen. nov., sp. nov., a cyanobacterium associated with coral black band disease (BBD)

Black band disease (BBD) is a widespread coral disease which mainly infects massive framework-building corals. BBD is believed to be caused by a consortium of microorganisms and may not result from the actions of a primary pathogen. The BBD microbial community is dominated, in terms of biomass, by filamentous cyanobacteria. Here we describe a cyanobacterial strain, designated BgP10_4S(T), cultured from a BBD-affected Favia sp. 25 degreesoal from the northern Red Sea (Gulf of Eilat, Israel). This dark-green pigmented cyanobacterium showed optimal growth at salinities of 5.0 to 5.5% (w/v), pH of 7 to 8 and cultivation temperatures of 25 0C. Morphological examination revealed cylindrical, unbranched trichomes with tapering and blunt cells at the ends which leave a thin mucilaginous trail as they glide. No sheath was evident under these conditions. Inclusion bodies and straight thylakoids were clearly discerned by transmission electron microscopy. Pigment analysis revealed absorption spectra for phycocyanin, carotenoid and chlorophyll a. The sequence of the 16S rRNA gene in this cyanobac(t)erium isolate showed high similarity (99%) to cyanobacterial sequences retrieved from BBD-affected corals from different geographical sites (i.e. the Caribbean Sea, Palau and the Red Sea). The BgP10_4ST strain is observed to be a persisten(t) component of the BBD mat of Faviid corals and may thus be an important agent in the disease etiology. On the basis (of its morphological, physiological and phylogenetic distinctiveness, strain BgP10_4ST represents a novel genus and species of Subsection III (formerly Oscillatoriales), for which the name Pseudoscillatoria coralii gen. nov., sp. nov. is proposed.

Cellular pathology and histopathology of hypo-salinity exposure on the coral Stylophora pistillata

Coral reefs can experience extreme salinity changes, particularly hypo-salinity, as a result of storms, heavy rainy seasons (e.g., monsoons), and coastal runoff. Field and laboratory observations have documented that corals exposed to hypo-saline conditions can undergo extensive bleaching and mortality. There is controversy in the literature as to whether hypo-saline conditions induce a pathological response in corals, and if there is a relationship between decreasing salinity treatment and pathological responses. To test the hypothesis that hypo-salinity exposure does not have a pathological effect on coral, we used histological and cellular diagnostic methods to characterize the pathology in hypo-salinity-exposed corals. Colonies of Stylophora pistillata were exposed to five salinity concentrations [39 parts per thousand (ppt), 32 ppt, 28 ppt, 24 ppt, and 20 ppt] that may realistically occur on a reef. Histological examination indicated an increasing severity of pathomorphologies associated with decreasing salinity, including increased tissue swelling, degradation and loss of zooxanthellae, and tissue necrosis. Pulse-amplitude modulated chlorophyll fluorimetry kinetics demonstrated a decreasing photosynthetic efficiency with decreasing salinity conditions. Cytochrome P450 levels were affected by even slight changes in salinity concentration suggesting that detoxification pathways, as well as several endocrine pathways, may be adversely affected. Finally, these studies demonstrated that hypo-saline conditions can induce an oxidative-stress response in both the host and in its algal symbiont, and in so doing, may synergistically increase oxidative-stress burdens. As with other types of environmental stresses, exposure to hypo-saline conditions may have long-term consequences on coral physiology.

An updated 18S rRNA phylogeny of tunicates based on mixture and secondary structure models

BACKGROUND

Tunicates have been recently revealed to be the closest living relatives of vertebrates. Yet, with more than 2500 described species, details of their evolutionary history are still obscure. From a molecular point of view, tunicate phylogenetic relationships have been mostly studied based on analyses of 18S rRNA sequences, which indicate several major clades at odds with the traditional class-level arrangements. Nonetheless, substantial uncertainty remains about the phylogenetic relationships and taxonomic status of key groups such as the Aplousobranchia, Appendicularia, and Thaliacea.

RESULTS

Thirty new complete 18S rRNA sequences were acquired from previously unsampled tunicate species, with special focus on groups presenting high evolutionary rate. The updated 18S rRNA dataset has been aligned with respect to the constraint on homology imposed by the rRNA secondary structure. A probabilistic framework of phylogenetic reconstruction was adopted to accommodate the particular evolutionary dynamics of this ribosomal marker. Detailed Bayesian analyses were conducted under the non-parametric CAT mixture model accounting for site-specific heterogeneity of the evolutionary process, and under RNA-specific doublet models accommodating the occurrence of compensatory substitutions in stem regions. Our results support the division of tunicates into three major clades: 1) Phlebobranchia + Thaliacea + Aplousobranchia, 2) Appendicularia, and 3) Stolidobranchia, but the position of Appendicularia could not be firmly resolved. Our study additionally reveals that most Aplousobranchia evolve at extremely high rates involving changes in secondary structure of their 18S rRNA, with the exception of the family Clavelinidae, which appears to be slowly evolving. This extreme rate heterogeneity precluded resolving with certainty the exact phylogenetic placement of Aplousobranchia. Finally, the best fitting secondary-structure and CAT-mixture models suggest a sister-group relationship between Salpida and Pyrosomatida within Thaliacea.

CONCLUSION

An updated phylogenetic framework for tunicates is provided based on phylogenetic analyses using the most realistic evolutionary models currently available for ribosomal molecules and an unprecedented taxonomic sampling. Detailed analyses of the 18S rRNA gene allowed a clear definition of the major tunicate groups and revealed contrasting evolutionary dynamics among major lineages. The resolving power of this gene nevertheless appears limited within the clades composed of Phlebobranchia + Thaliacea + Aplousobranchia and Pyuridae + Styelidae, which were delineated as spots of low resolution. These limitations underline the need to develop new nuclear markers in order to further resolve the phylogeny of this keystone group in chordate evolution.

Active nematocyst isolation via nudibranchs

Cnidarian venoms are potentially valuable tools for biomedical research and drug development. They are contained within nematocysts, the stinging organelles of cnidarians. Several methods exist for the isolation of nematocysts from cnidarian tissues; most are tedious and target nematocysts from specific tissues. We have discovered that the isolated active nematocyst complement (cnidome) of several sea anemone (Cnidaria: Anthozoa) species is readily accessible. These nematocysts are isolated, concentrated, and released to the aqueous environment as a by-product of aeolid nudibranch Spurilla neapolitana cultures. S. neapolitana feed on venomous sea anemones laden with stinging nematocysts. The ingested stinging organelles of several sea anemone species are effectively excreted in the nudibranch feces. We succeeded in purifying the active organelles and inducing their discharge. Thus, our current study presents the attractive possibility of using nudibranchs to produce nematocysts for the investigation of novel marine compounds.