Nutrient Enrichment Predominantly Affects Low Diversity Microbiomes in a Marine Trophic Symbiosis between Algal Farming Fish and Corals

While studies show that nutrient pollution shifts reef trophic interactions between fish, macroalgae, and corals, we know less about how the microbiomes associated with these organisms react to such disturbances. To investigate how microbiome dynamics are affected during nutrient pollution, we exposed replicate Porites lobata corals colonized by the fish Stegastes nigricans, which farm an algal matrix on the coral, to a pulse of nutrient enrichment over a two-month period and examined the microbiome of each partner using 16S amplicon analysis. We found 51 amplicon sequence variants (ASVs) shared among the three hosts. Coral microbiomes had the lowest diversity with over 98% of the microbiome dominated by a single genus, Endozoicomonas. Fish and algal matrix microbiomes were ~20 to 70× more diverse and had higher evenness compared to the corals. The addition of nutrients significantly increased species richness and community variability between samples of coral microbiomes but not the fish or algal matrix microbiomes, demonstrating that coral microbiomes are less resistant to nutrient pollution than their trophic partners. Furthermore, the 51 common ASVs within the 3 hosts indicate microbes that may be shared or transmitted between these closely associated organisms, including Vibrionaceae bacteria, many of which can be pathogenic to corals.

Bioerosión interna en corales masivos asociados a las comunidades arrecifales del Pacífico nororiental tropical: Efecto de factores intrínsecos y extrínsecos

El desarrollo y el mantenimiento de los arrecifes coralinos depende del balance entre la producción (acreción) y la remoción (erosión) del CaCO3 generado principalmente por corales hermatípicos. El material calcáreo puede ser removido del esqueleto de coral por agentes físicos, químicos o biológicos, y este último es el de mayor influencia. Pese a su importancia, pocos estudios han estimado la tasa de bioerosión en comunidades coralinas de la costa mexicana del Pacífico. En este estudio se determinó el volumen y el porcentaje de CaCO3 removido vía erosión biológica en los principales corales masivos, Pavona gigantea, Porites lobata y Porites panamensis, distribuidos en el Parque Nacional Islas Marietas y el Parque Nacional Isla Isabel (México). Además, se evaluó el efecto de factores intrínsecos (morfología, sexo y edad de las colonias) y extrínsecos (localidad y profundidad) en la bioerosión. Se utilizó la técnica de peso boyante para calcular parámetros de remoción interna y densidad de CaCO3. A nivel de especie, P. gigantea presentó valores de volumen de bioerosión de 71.31 ± 32.35 cm3 (27.28 ± 18.05% de bioerosión interna); Po. lobata, 26.60 ± 4.87 cm3 (16.87 ± 16.31%); y Po. panamensis, 29.6 ± 14.61 cm3 (31.127 ± 29.43%). A nivel de género, Pavona presentó los valores más altos en bioerosión y densidad del esqueleto (1.61 g·cm–3). Con relación a la morfología, la bioerosión fue mayor en colonias masivas, pero considerando la edad, fue superior en colonias más longevas (10–26 años). A nivel de localidad, en el Parque Nacional Islas Marietas se presentaron los valores más altos de volumen y porcentaje de bioerosión. La evidencia sugiere que los arrecifes de coral de la costa central mexicana del Pacífico están experimentando una alta tasa de erosión no conspicua causada por bioerosionadores endolíticos y varía en función de factores intrínsecos y extrínsecos. Si este efecto continúa incrementando, podría poner en riesgo el mantenimiento a largo plazo de las comunidades coralinas, lo que modificaría el balance de los flujos de carbonato y la funcionalidad del ecosistema arrecifal.

Trace Metals Content in Annually-Banded Scleractinian Coral ‘Porites Lobata’ Across the Northern Persian Gulf

Concentration of trace metals in skeleton growth bands of dominant scleractinian coral ‘Porites lobata’ were investigated in Kharg and Hebourabi islands across the northern Persian Gulf. The highest average concentration of elements were as Sr> Mg> Zn> Ba> Cu> U> Ni> Mn> Cr> Co> Pb> V> Cd in Kharg Island respectively and as Sr> Mg> Ba> Cu> U> Ni> Zn> Mn> Cr> Co> V> Pb> Cd in Hendourabi Island. Except for Cr, the concentrations of other trace metals in Kharg Island were higher than those of Hendourabi Island. The coefficient of variation percentage (CV%) for Cr, Mn, Zn, Ba and Pb in Kharg Island and for Cu and Ba in Hendourabi Island was more than 50%. Results of PCA analyses revealed that the trace metals Kharg Island was defined by three principal components including the first component (Mn, V, Pb, Zn, Ni and half of Mg, Cr and Co) corresponding to the past regional military conflicts and oil pollution, second component (Sr, U and Mg) corresponding to SST changes, and the third component (Cr and Co) corresponding to other factors. Results of PCA analyses revealed that trace metals in Hendourabi Island was defined by two principal components including first component (Co, Ni, Cr, Mn and half of Ba) corresponding to annual precipitation changes and the second component (U, Zn and Ba) corresponding to coastal constructions.

Effects of Ocean Acidification on Coral Endolithic Bacterial Communities in Isopora palifera and Porites lobata

Endolithic microbes in coral reefs may act as a nutrient source for their coral hosts. Increasing atmospheric CO2 concentrations are causing ocean acidification (OA), which may affect marine organisms and ecosystems, especially calcifying organisms such as reef-building corals. However, knowledge of how OA affects marine microbes remains limited, and little research has been done on how coral endolithic communities respond to shifting environmental baselines. In this study, the endolithic communities of two common shallow water coral species, Isopora palifera and Porites lobata, were examined to investigate the microbial community dynamics under OA treatments. The colonies were placed in an environment with a partial pressure of carbon dioxide (pCO2) of 1,000 or 400 ppm (control) for 2 months. Several I. palifera colonies bleached and died at 1,000 ppm pCO2, but the P. lobata colonies remained unaffected. Inversely, the endolithic community in P. lobata skeletons showed significant changes after OA treatment, whereas no significant dynamics were observed among the I. palifera endoliths. Our findings suggest that the skeletal structures of different coral species may play a key role in corals host and endoliths under future high-OA scenarios.

The putative endemic Mexican reef coral Porites baueri Squires 1959 (Scleractinia: Poritidae) is a synonym of the widespread coral Porites lobata Dana 1846

Morphological analysis and microscopic observations of the Porites baueri holotype and specimens of other Porites species from different sites of the Mexican Pacific, allowed confirmation that Porites baueri is subjective synonym of Porites lobata. The holotype of Porites baueri was collected in the Marías Islands in 1957, and described as a new species by Squires in 1959. Since then, this species was considered as endemic, which is due to the lack of other specimens or a review of the taxonomic characters until now. The Mexican Pacific marine fauna loses a valid reef coral species, currently at 34, but gains in taxonomic clarity by ending almost 60 years of controversy.

Genetic Variation in Response to Global Warming in a Coral Reef Species, Porites lobata

Climate change due to global warming is one of the worst environmental disasters in the world, which affects all ecosystems and has led to increasing degradation of coral reefs. The increase of sea surface temperature is inversely related to the resistance of corals and is directly associated with their bleaching. High temperature disrupts the symbiotic relationship between coral and algal symbiont and results in coral bleaching. To evaluate the adaptation of corals to heat stress, in this study, we investigated the thermal stress effect on the expression of genes involved in programmed cell death (PCD), cysteinyl aspartate proteases 3 (will be mentioned as Caspas3 hereafter) and anti-apoptotic pathway, B-cell lymphoma 2 (will be mentioned as Bcl2 hereafter) in Porites lobata (Dana, 1846). Corals were incubated at 25°C for 2 weeks (adaptation period) and then exposed to 34°C (heat shock) for 24 and 48 hours. Then, the expression of genes was measured using real-time PCR. The results revealed that both genes were up-regulated at 24 hours after heat induction. Bcl-2 expression (anti-apoptotic gene) was induced at 24 hours and was down-regulated at 48 hours. In contrast, Caspase3 (apoptotic gene) continued to be expressed up to 48 hours. These results might indicate that coral cells are headed towards bleaching and death with increased temperature. The results of this study, regarding the observed expression patterns, can clarify the response of different genes to a thermal stress in coral reefs. The exposure of corals to acute conditions with high temperatures presented the behavior of the desired genes in the studied conditions.

“Jardinería” para la restauración coralina en el Golfo Dulce, Costa Rica: Una prueba práctica

Introducción: Los corales del Golfo Dulce del Pacífico Sur de Costa Rica están desapareciendo debido a la contaminación y sedimentación por origen antrópico. Objetivo: Desarrollar una guardería de corales en Punta Encanto con el fin de establecer su viabilidad y replicarlo en otras partes del Pacífico costarricense, el estudio se realizó entre diciembre del 2014 y mayo del 2016. Metodología: Construimos una estructura de jardinería que colocamos a media columna de agua, utilizamos fragmentos de oportunidad de las especies de coral Porites lobata, Psammocora stellata y Pavona varians que colocamos en galletas de cemento y de esta forma realizamos una medición de su crecimiento en cm3 y tomamos además muestras de agua para su análisis físico químico. Resultados: Determinamos que la especie Psammocora stellata fue la de mostró mejor crecimiento, la menor concentración de nutrientes tuvo lugar a media columna de agua, los silicatos fueron los más abundantes en todo el periodo del estudio. En general, podemos decir que los niveles concentración en nutrientes son normales respecto a los reportados en otros estudios similares. La alta concentración salina y de fosfato afectó negativamente el crecimiento en todas las especies evaluadas. Conclusión: El estudio demostró la factibilidad de realizar jardinerías de coral en el Golfo Dulce como una técnica de restauración ecológica.

Genetic structure is stronger across human-impacted habitats than among islands in the coral Porites lobata

We examined genetic structure in the lobe coral Porites lobata among pairs of highly variable and high-stress nearshore sites and adjacent less variable and less impacted offshore sites on the islands of Oahu and Maui, Hawaii. Using an analysis of molecular variance framework, we tested whether populations were more structured by geographic distance or environmental extremes. The genetic patterns we observed followed isolation by environment, where nearshore and adjacent offshore populations showed significant genetic structure at both locations (AMOVA FST = 0.04∼0.19, P < 0.001), but no significant isolation by distance between islands. Strikingly, corals from the two nearshore sites with higher levels of environmental stressors on different islands over 100 km apart with similar environmentally stressful conditions were genetically closer (FST = 0.0, P = 0.73) than those within a single location less than 2 km apart (FST = 0.04∼0.08, P < 0.01). In contrast, a third site with a less impacted nearshore site (i.e., less pronounced environmental gradient) showed no significant structure from the offshore comparison. Our results show much stronger support for environment than distance separating these populations. Our finding suggests that ecological boundaries from human impacts may play a role in forming genetic structure in the coastal environment, and that genetic divergence in the absence of geographical barriers to gene flow might be explained by selective pressure across contrasting habitats.