Facultative lifestyle drives diversity of coral algal symbionts.

The photosynthetic symbionts of corals sustain biodiverse reefs in nutrient-poor, tropical waters. Recent genomic data illuminate the evolution of coral symbionts under genome size constraints and suggest that retention of the facultative lifestyle, widespread among these algae, confers a selective advantage when compared with a strict symbiotic existence. We posit that the coral symbiosis is analogous to a 'bioreactor' that selects winner genotypes and allows them to rise to high numbers in a sheltered habitat prior to release by the coral host. Our observations lead to a novel hypothesis, the 'stepping-stone model', which predicts that local adaptation under both the symbiotic and free-living stages, in a stepwise fashion, accelerates coral alga diversity and the origin of endemic strains and species.

Coral diversity matches marine park zonation but not economic value of coral reef sites at St. Eustatius, eastern Caribbean.

Stony corals play a key role in the marine biodiversity of many tropical coastal areas as suppliers of substrate, food and shelter for other reef organisms. Therefore, it is remarkable that coral diversity usually does not play a role in the planning of protected areas in coral reef areas. In the present study we examine how stony coral diversity patterns relate to marine park zonation and the economic value of reefs around St. Eustatius, a small island in the eastern Caribbean, with fisheries and tourism as important sources of income. The marine park contains two no-take reserves. A biodiversity survey was performed at 39 sites, 24 inside the reserves and 15 outside; 22 had a maximum depth >18 m and 17 were shallower. Data on economic value per site were obtained from the literature. Corals were photographed for the verification of identifications made in the field. Coral species richness (n = 49) was highest in the no-take reserves and species composition was mainly affected by maximum depth. No distinct relation is observed between coral diversity and fishery value or total economic value. Based on the outcome of this study we suggest that in future designs of marine park zonation in reef areas, coral diversity should be taken into consideration. This is best served by including reef areas with a continuous depth gradient from shallow flats to deep slopes.

The Skeleton and Biomineralization Mechanism as Part of the Innate Immune System of Stony Corals.

Stony corals are among the most important calcifiers in the marine ecosystem as they form the coral reefs. Coral reefs have huge ecological importance as they constitute the most diverse marine ecosystem, providing a home to roughly a quarter of all marine species. In recent years, many studies have shed light on the mechanisms underlying the biomineralization processes in corals, as characterizing the calicoblast cell layer and genes involved in the formation of the calcium carbonate skeleton. In addition, considerable advancements have been made in the research field of coral immunity as characterizing genes involved in the immune response to pathogens and stressors, and the revealing of specialized immune cells, including their gene expression profile and phagocytosis capabilities. Yet, these two fields of corals research have never been integrated. Here, we discuss how the coral skeleton plays a role as the first line of defense. We integrate the knowledge from both fields and highlight genes and proteins that are related to biomineralization and might be involved in the innate immune response and help the coral deal with pathogens that penetrate its skeleton. In many organisms, the immune system has been tied to calcification. In humans, immune factors enhance ectopic calcification which causes severe diseases. Further investigation of coral immune genes which are involved in skeleton defense as well as in biomineralization might shed light on our understanding of the correlation and the interaction of both processes as well as reveal novel comprehension of how immune factors enhance calcification.

Evolution of Protein-Mediated Biomineralization in Scleractinian Corals.

While recent strides have been made in understanding the biological process by which stony corals calcify, much remains to be revealed, including the ubiquity across taxa of specific biomolecules involved. Several proteins associated with this process have been identified through proteomic profiling of the skeletal organic matrix (SOM) extracted from three scleractinian species. However, the evolutionary history of this putative "biomineralization toolkit," including the appearance of these proteins' throughout metazoan evolution, remains to be resolved. Here we used a phylogenetic approach to examine the evolution of the known scleractinians' SOM proteins across the Metazoa. Our analysis reveals an evolutionary process dominated by the co-option of genes that originated before the cnidarian diversification. Each one of the three species appears to express a unique set of the more ancient genes, representing the independent co-option of SOM proteins, as well as a substantial proportion of proteins that evolved independently. In addition, in some instances, the different species expressed multiple orthologous proteins sharing the same evolutionary history. Furthermore, the non-random clustering of multiple SOM proteins within scleractinian-specific branches suggests the conservation of protein function between distinct species for what we posit is part of the scleractinian "core biomineralization toolkit." This "core set" contains proteins that are likely fundamental to the scleractinian biomineralization mechanism. From this analysis, we infer that the scleractinians' ability to calcify was achieved primarily through multiple lineage-specific protein expansions, which resulted in a new functional role that was not present in the parent gene.

Apoptosis in gonadal somatic cells of scleractinian corals: implications of structural adjustments for gamete production and release.

Apoptosis is an evolutionarily conserved process of programmed cell death. Here, we show structural changes in the gonads caused by apoptosis during gametogenesis in the scleractinian coral, Euphyllia ancora. Anatomical and histological analyses revealed that from the non-spawning to the spawning season, testes and ovaries increased in size due to active proliferation, differentiation and development of germ cells. Additionally, the thickness and cell density of the gonadal somatic layer decreased significantly as the spawning season approached. Further analyses demonstrated that the changes in the gonadal somatic layer were caused by apoptosis in a subpopulation of gonadal somatic cells. The occurrence of apoptosis in the gonadal somatic layer was also confirmed in other scleractinian corals. Our findings suggest that decreases in thickness and cell density of the gonadal somatic layer are structural adjustments facilitating oocyte and spermary (male germ cell cluster) enlargement and subsequent gamete release from the gonads. In animal reproduction, apoptosis in germ cells is an important process that controls the number and quality of gametes. However, apoptosis in gonadal somatic cells has rarely been reported among metazoans. Thus, our data provide evidence for a unique use of apoptosis in animal reproduction.

Testicular somatic cells in the stony coral Euphyllia ancora express an endogenous green fluorescent protein.

In a variety of organisms, adult gonads contain several specialized somatic cells that regulate and support the development of germline cells. In stony corals, the characteristics and functions of gonadal somatic cells remain largely unknown. No molecular markers are currently available that allow for the identification and enrichment of gonadal somatic cells in corals. Here, we showed that the testicular somatic cells of a stony coral, Euphyllia ancora, express an endogenous green fluorescent protein (GFP). Fluorescence microscopy showed that, in contrast to the endogenous expression of the red fluorescent protein of E. ancora ovaries that we have previously reported, the testes displayed a distinct green fluorescence. Molecular identification and spectrum characterization demonstrated that E. ancora testes expressed a GFP (named EaGFP) that is a homolog of the GFP from the jellyfish Aequorea victoria and that possesses an excitation maximum of 506 nm and an emission maximum of 514 nm. Immunohistochemical analyses revealed that the testicular somatic cells, but not the germ cells, expressed EaGFP. EaGFP was enclosed within one or a few granules in the cytoplasm of testicular somatic cells, and the granule number decreased as spermatogenesis proceeded. We also showed that testicular somatic cells could be enriched by using endogenous GFP as an indicator. The present study not only revealed one of the unique cellular characteristics of coral testicular cells but also established a technical basis for more in-depth investigations of the function of testicular somatic cells in spermatogenesis in future studies.

Pollution and coral damage caused by derelict fishing gear on coral reefs around Koh Tao, Gulf of Thailand.

Most lost fishing gear is made of non-biodegradable plastics that may sink to the sea floor or drift around in currents. It may remain unnoticed until it shows up on coral reefs, beaches and in other coastal habitats. Stony corals have fragile skeletons and soft tissues that can easily become damaged when they get in contact with lost fishing gear. During a dive survey around Koh Tao, a small island in the Gulf of Thailand, the impact of lost fishing gear (nets, ropes, cages, lines) was studied on corals representing six different growth forms: branching, encrusting, foliaceous, free-living, laminar, and massive. Most gear (>95%) contained plastic. Besides absence of damage (ND), three categories of coral damage were assessed: fresh tissue loss (FTL), tissue loss with algal growth (TLAG), and fragmentation (FR). The position of the corals in relation to the fishing gear was recorded as either growing underneath (Un) or on top (On), whereas corals adjacent to the gear (Ad) were used as controls. Nets formed the dominant type of lost gear, followed by ropes, lines and cages, respectively. Branching corals were most commonly found in contact with the gear and also around it. Tubastraea micranthus was the most commonly encountered coral species, either Un, On, or Ad. Corals underneath gear showed most damage, which predominantly consisted of tissue loss. Fragmentation was less common than expected, which may be related to the low fragility of T. micranthus as dominant branching species. Even if nets serve as substrate for corals, it is recommended to remove them from reefs, where they form a major component of the plastic pollution and cause damage to corals and other reef organisms.

The physiological response of the deep-sea coral Solenosmilia variabilis to ocean acidification.

Several forms of calcifying scleractinian corals provide important habitat complexity in the deep-sea and are consistently associated with a high biodiversity of fish and other invertebrates. How these corals may respond to the future predicted environmental conditions of ocean acidification is poorly understood, but any detrimental effects on these marine calcifiers will have wider impacts on the ecosystem. Colonies of Solenosmilia variabilis, a protected deep-sea coral commonly occurring throughout the New Zealand region, were collected during a cruise in March 2014 from the Louisville Seamount Chain. Over a 12-month period, samples were maintained in temperature controlled (∼3.5 °C) continuous flow-through tanks at a seawater pH that reflects the region's current conditions (7.88) and an end-of-century scenario (7.65). Impacts on coral growth and the intensity of colour saturation (as a proxy for the coenenchyme tissue that covers the coral exoskeleton and links the coral polyps) were measured bimonthly. In addition, respiration rate was measured after a mid-term (six months) and long-term (12 months) exposure period. Growth rates were highly variable, ranging from 0.53 to 3.068 mm year-1 and showed no detectable difference between the treatment and control colonies. Respiration rates also varied independently of pH and ranged from 0.065 to 1.756 µmol O2 g protein-1 h-1. A significant change in colour was observed in the treatment group over time, indicating a loss of coenenchyme. This loss was greatest after 10 months at 5.28% and could indicate a reallocation of energy with physiological processes (e.g.  growth and respiration) being maintained at the expense of coenenchyme production. This research illustrates important first steps to assessing and understanding the sensitivity of deep-sea corals to ocean acidification.

Reclutamiento de corales pétreos en arrecifes coralinos a diferentes distancias de fuentes de contaminación en La Habana, Cuba / Stony coral recruitment in coral reefs at different distances from pollution sources in Habana, Cuba

The effect of pollution on coral recruitment has been insufficiently studied. This research deals with coral recruitment in coastal areas and aimed to determine the variations of density and dominant species of corals recruits in sites at different distances from pollution sources. The composition and structure of stony coral (scleractinian and milleporids) recruit associations were characterized in the fringing reef of Western Havana, Cuba. This reef is influenced by urban pollution from the Almendares River and a sewage outlet located at its mouth. Four sites were sampled on the upper fore reef escarpment at 10m deep every three months between July 2007 and May 2008. A 25cm side quadrat was used to determine the density and taxonomic composition of recruits smaller than 3cm in diameter. Sampling units were placed following a random-systematic pattern. The mean density of recruits was determined both at assemble and species level. Bifactoral ANOVA tests were applied to compare mean densities at both sampling sites and dates. Student-Newman-Keuls test was applied to compare pairs of means. Cluster and nMDS analyses were applied to evaluate between site similarities. The predominant species was Siderastrea siderea followed by S. radians and Porites astreoides. Recruit densities were similar among La Puntilla, Calle 16 and Acuario sites. Lower densities were always found in Malecón. Significant differences in mean stony recruit densities were found both between sites and sampling dates. The statistic analysis did not show significant spatial-temporal interactions. Malecón, the most polluted site, showed the lowest recruit density and the greater presence of species considered as indicators of organic pollution, sedimentation and abrasion. The density of recruit species was higher in October 2007 and lower in May 2008, and it was apparently influenced by reproduction and cold front seasons, respectively. The higher dominance and abundance of S. siderea, S. radians and P. astreoides recruits were apparently due to their high reproductive potential and resistance to disturbances. The identity of dominant species was apparently related to distance from major pollution sources. We highly recommended the replication of this research in other areas of the greater Caribbean region to test the generality of present results and to compare among areas. Future research should take into account the influence of other environmental factors, along with an appraisal of recruit species tolerance to these factors, to better ponder the effect of urban pollution on recruitment. Areas with well assessed pollution regimes are recommended for research.

El efecto de la contaminación sobre el reclutamiento ha sido insuficientemente estudiado. Este trabajo trata el tema del reclutamiento en sitios ubicados a diferentes distancias de dos importantes fuentes de contaminación. Se caracterizó la composición y estructura de las asociaciones de reclutas de corales pétreos (escleractinios y milepóridos) al oeste de la Ciudad de La Habana, Cuba. Esta área está influenciada por la contaminación urbana del río Almendares y del emisario submarino construido en su desembocadura. El objetivo de esta investigación fue determinar las variaciones en la densidad y predominio de las especies de reclutas, en sitios ubicados a diferentes distancias de fuentes de contaminación, en distintas épocas de un año. Se muestreó cada tres meses entre julio 2007- mayo 2008. Se escogieron cuatro sitios de muestreo cerca del borde superior del escarpe del arrecife frontal a 10m de profundidad. Se utilizó un marco cuadrado de 25cm de lado de forma aleatoria-sistémica para determinar la densidad y composición taxonómica de reclutas de corales pétreos (colonias menores de 3cm). Para comparar las densidades medias entre sitios y fechas de muestreo se aplicó un análisis de varianza bifactorial. Para comparar los pares de densidades medias se empleó la prueba de Student-Newman-Keuls. La aplicación de un análisis Clasificación Numérica Jerárquica Aglomerativa (Cluster Analysis) y uno de ordenamiento por Escalado Multidimensional no Métrico (nMDS) mostró una distribución en la que los sitios quedaron agrupados en función de sus distancias de las fuentes contaminantes. Predominó Siderastrea sidérea seguida por Siderastrea radians y Porites asteroides. Durante el año de muestreo, las densidades de reclutas fueron similares entre La Puntilla, Calle 16 y Acuario. Las menores densidades se observaron siempre en Malecón. Se encontraron diferencias significativas entre las densidades medias de los sitios, así como entre de las distintas fechas de muestreo. El análisis de variancia bifactorial no mostró interacción significativa espacio-tiemporal. Malecón, sitio más contaminado, presentó menor reclutamiento y mayor presencia de especies consideradas indicadoras de contaminación orgánica, sedimentación y abrasión. Las densidades fueron mayores en Octubre 2007 y menores en Mayo 2008, al parecer influenciados por las épocas de reproducción y la acción de los frentes fríos respectivamente. El mayor predominio y abundancia de reclutas de S. siderea, S. radians y P. astreoides parece responder a sus elevados potenciales reproductivos y altas resistencias a disturbios. La identidad de las especies dominantes estuvo relacionada aparentemente con las distancias de las principales fuentes de contaminación. Se recomienda replicar esta investigación en otros lugares de la región del Caribe para probar la generalidad de estos resultados. Estudios futuros debieran tener en cuenta la influencia de otros factores ambientales, junto con una valoración de la tolerancia de las especies de reclutas a estos factores, para ponderar mejor el efecto de la contaminación urbana sobre el reclutamiento.

Relationship between anthropogenic impacts and bleaching-associated tissue mortality of corals in Curaçao (Netherlands Antilles) / Relación entre los impactos antropogénicos y la mortalidad tisular asociada al blanqueamiento de corales en Curaçao (Antillas Holandesas)

Chronic anthropogenic impacts can have a negative effect on coral health and on coral energy budgets needed for regeneration of lesions. I therefore hypothesise that during massive bleaching events, the degree of corals showing bleaching-related tissue mortality is higher in areas subject to chronic anthropogenic impacts than in relatively pristine areas. In the present study, the degree of bleaching and bleaching-related tissue mortality was estimated for eight abundant coral species in Curaçao, at the onset of a massive Caribbean bleaching event in 1995, and three months afterwards. To study the possible effects of anthropogenic disturbances, the study was done at four unpolluted control sites, two polluted sites (sedimentation, sewage), and four sites at the mouth of lagoons with outflow of nutrient-rich, warm and turbid seawater. No pattern of an overall difference in bleaching between impacted and control sites was found for the degree of bleaching. However, the percentage of corals showing bleaching-related tissue mortality was higher at the impacted sites than at the control sites for the total number of corals and for corals with < 50% of their surface area bleached. Highest and most significant values of tissue mortality were found at a reef site experiencing chronic pollution by raw sewage. The data thus suggest that unfavourable conditions caused by anthropogenic influences, such as increased sedimentation, eutrophication and seawater temperature, have an additional negative effect on the tissue survival of coral colonies during bleaching episodes. Rev. Biol. Trop. 54 (Suppl. 3): 31-43. Epub 2007 Jan. 15.

Los impactos antropogénicos crónicos pueden tener efectos negativos en la salud y en las cantidades de energía necesarias para la regeneración de lesiones en los corales. Mi hipótesis fue que durante los casos de blanqueamiento masivo, el grado en que los corales muestren mortalidades de tejido relacionadas con el blanqueamiento, será mayor en áreas sujetas a impactos antropogénicos crónicos que en áreas relativamente prístinas. Estimé los grados de blanqueamiento y mortalidad tisular en ocho especies de coral abundantes en Curaçao, durante el comienzo de un de blanqueamiento masivo en el Caribe en 1995 y tres meses después. El estudio se realizó en cuatro sitios control no contaminados, dos sitios contaminados (sedimentación, aguas residuales), y cuatro sitios en la boca de lagunas con aguas tibias, ricas en nutrientes y turbias. En general, no se encontró ningún patrónx de diferencias en el grado de blanqueamiento entre sitios. Sin embargo, el porcentaje de corales que mostraron mortalidad tisular relacionada con el blanqueamiento fue mayor en los sitios impactados que en los controles, tanto en el número total de corales como en corales con <50% de su superficie blanquedada. Los valores más altos y más significativos de mortalidad tisular se encontraron en un arrecife que experimentaba contaminación crónica por aguas residuales crudas. La información sugiere que las condiciones desfavorables causadas por la influencia antropogénica, como el incremento en la sedimentación, eutrofización y la temperatura del agua, tienen un efecto negativo adicional en la supervivencia del tejido de las colonias de coral, durante el blanqueamiento.