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Resumen.-Para evaluar la respuesta metabólica del coral simbiótico Pocillopora capitata a la reducción del pH del agua de mar en un sistema in vitro, 112 ramas de P. capitata se obtuvieron de la comunidad de corales La Boquita (LB) sin exhibir algún daño aparente de blanqueamiento. Se evaluaron 2 tratamientos de pH: a) 7,85/7,95 pH (Tratamiento C 1 ), b) 7,60/7,70 (Tratamiento C 2 ) y 8,00/8,40 pH tratamiento de control (CC). Las ramas de coral fueron asignadas aleatoriamente a unidades experimentales (n= 38 por tratamiento). Las muestras fueron tomadas en 2 tiempos para el análisis bi oquímico y para evaluar cualitativamente los aspectos microestructurales por microscopía electrónica de barrido: tiempo inicial, muestra tomada en 12 h (T 1 ); tiempo final, muestras del último día de la exposición (T f , día 7 del experimento). A diferencia del tejido simbionte, el análisis bioquímico del tejido del coral reveló que P. capitata muestra una respuesta inmediata reflejada en los coeficientes de ARN/ADN y proteína/ADN, así como en las concentraciones de ARN y proteína, particularmente en el tratamiento de C 2 en las horas iniciales del experimento. El análisis microestructural cualitativo identificó principalmente efectos en el tratamiento C 2 , que fue influenciado por la presencia de disgregaciones micro-superficiales en las regiones terminales de las fibras esqueléticas. Palabras clave: Pocillopora capitata, coral, ARN/ADN, Proteina/ADN, fibras esqueléticas, estrésAbstract.-To evaluate the metabolic response of the symbiotic coral Pocillopora capitata to reduced seawater pH in an in vitro system, 112 branches of P. capitata with no apparent damage from bleaching were collected from the La Boquita (LB) coral community. Two pH treatments were evaluated: a) pH 7.85/7.95 (Treatment C 1 ), b) 7.60/7.70 (Treatment C 2 ), and 8.00/ 8.40 pH control treatment (CC). The coral branches were randomly assigned to experimental units (n= 38 per treatment). Samples were taken at 2 separate times for biochemical analysis and qualitative assessment of microstructural aspects with scanning electron microscopy: initial time, sample taken at 12 h (T 1 ); end time, samples from the final day of exposure (T f , day 7 of the experiment). Unlike the symbiont tissue, the biochemical analysis of the host tissue revealed that P. capitata displayed an immediate response as reflected in the RNA/DNA and protein/DNA ratios as well as in the concentrations of RNA and protein, particularly in the initial hours of the experiment in treatment C 2 . Qualitative microstructural analysis primarily identified effects in treatment C 2 which was influenced by the presence of micro surface detachments in the terminal regions of the skeletal fibers.

The greatest threat scleractinian corals face today is accelerated climate change. Assuming that most scleractinians are incapable of genetic adaptation to rapid global changes, the alternative response would be phenotypic plasticity, which is classically described as acclimatization. With the purpose of establishing a baseline for the study of acclimatization in corals of the Pacific coast of Mexico, we assessed the molecular and physiological response of 36 colonies of 3 Pocillopora morphospecies (Pocillopora cf. capitata, Pocillopora cf. damicornis, and Pocillopora cf. verrucosa) located at 2 sites (east and west) on Carrizales Reef. Our results show higher incidence of light and chlorophyll concentrations in seawater samples from the west side, suggesting the presence of at least 2 microenvironments with more and less light in the reef. In response, coral morphospecies from the west side showed higher gene expression and significant differences in pigment concentrations, endosymbiont densities, and metabolic markers (RNA, DNA, and proteins). Given the present concern about the future of coral reefs, we consider that the present study could be used as a baseline for the study of the physiological and molecular plasticity of Pocillopora corals in Mexican waters, so conservation strategies could be developed for key morphospecies in coral reefs on the Pacific coast of Mexico.