Settlement and post-settlement survival of Orbicella annularis and Orbicella faveolata (Scleractinia: Merulinidae) on substrates with coatings

Introduction: One of the main bottlenecks in restoration projects based on sexual reproduction is post-settlement survival, mainly due to competition for substrate with fleshy algae and predation. Therefore, substrates of different shapes and materials have been created and tested, seeking to optimize these processes with attractive surfaces for the larvae and structures where the recruits are protected from predation, and competition is reduced. Objective: To improve settlement and post-settlement survival of two important Caribbean reef-building corals, using different coatings on substrates. Methods: To determine whether substrate coatings properties are favourable to larval settlement in Orbicella annularis, and O. faveolata, collected in Puerto Morelos, Mexican Caribbean, we evaluated their settlement for three weeks on six coatings with a combination of properties. Each coating was designed to provide a combination of two out of three properties: 1) water repellence (hydrophobicity), 2) phosphorescence-based colour, and 3) mineral-enriched surface chemistry. In a separate experiment larvae settlement was tested using coatings with a single property. Finally, we determined the post-settlement survival of O. annularis and O. faveolata on the different coatings for seven weeks. Results: The combination of high hydrophobicity and light blue phosphorescent microparticles and high hydrophobicity and red-orange phosphorescent microparticles resulted in a higher settlement of O. annularis and O. faveolata when compared with other coatings (30.8 - 66.7 % higher). No significant differences were found in the number of larval settled when the water-repellence and the phosphorescence-based were evaluated independently. Post-settlement survival time on substrates was low, with a maximum of 34 days after settlement for O. annularis and 42 days for O. faveolata. Conclusions: In terms of the larval settlement, the combination of the coatings properties appears to play an essential role in the choice of microhabitat for both O. annularis and O. faveolata. But individually these properties did not generate an advantage in the larval settlement. Moreover, some chemical components associated with the coatings may be counterproductive to the survival of the polyps over time.

Introducción: Uno de los principales cuellos de botella en proyectos de restauración basada en reproducción sexual es la supervivencia de las larvas posterior al asentamiento, principalmente por la competencia por el sustrato con algas filamentosas y la depredación. Por ello, se han creado y analizado sustratos de diferentes formas y materiales, buscando optimizar estos procesos con superficies atrayentes para las larvas, y estructuras donde los reclutas se encuentran protegidos de la depredación y se disminuya la competencia. Objetivo: Mejorar el asentamiento y la supervivencia de dos importantes corales formadores de arrecifes del Caribe, utilizando diferentes recubrimientos en sustratos. Métodos: Para determinar si las propiedades de la superficie del sustrato son favorables para el asentamiento de larvas de Orbicella annularis y O. faveolata, recolectadas en Puerto Morelos, Caribe mexicano, evaluamos su asentamiento durante tres semanas en seis recubrimientos con una combinación de propiedades. Cada recubrimiento fue diseñado para proporcionar una combinación de dos de tres propiedades: 1) repelencia al agua (hidrofobicidad), 2) fosforescencia y 3) química superficial enriquecida con minerales. En un experimento separado se evaluó el asentamiento de larvas en sustratos con recubrimientos de una sola propiedad. Finalmente, se determinó la supervivencia posterior al asentamiento de O. annularis y O. faveolata sobre los diferentes recubrimientos durante siete semanas. Resultados: La combinación de alta hidrofobicidad y micropartículas fosforescentes azules y alta hidrofobicidad y micropartículas fosforescentes rojo-naranja dio como resultado un mayor asentamiento de O. annularis y O. faveolata en comparación con otros recubrimientos (30.8 - 66.7 % mayor). No se encontraron diferencias significativas en el número de larvas asentadas cuando se evaluaron de forma independiente la repelencia al agua y la fosforescencia. El tiempo de supervivencia posterior al asentamiento en los sustratos fue bajo, con un máximo de 34 días después del asentamiento para O. annularis y 42 días para O. faveolata. Conclusiones: En el asentamiento de larvas, la combinación de las propiedades del recubrimiento parece desempeñar un papel importante en la elección del microhábitat tanto para O. annularis como para O. faveolata. Pero de forma individual estas propiedades no generaron una ventaja en el asentamiento larvario. Además, algunos componentes químicos asociados con los recubrimientos pueden ser contraproducentes para la supervivencia de los pólipos a lo largo del tiempo.

Response of Millepora alcicornis (Milleporina: Milleporidae) to two bleaching events at Puerto Morelos reef, Mexican Caribbean

Two naturally occurring colonies of Millepora alcicornis were monitored during 1997 and 1998, both years in which this species bleached in the Mexican Caribbean. One colony (HL) was naturally exposed to a high light environment and another nearby colony (LL) was exposed to 5.9 times lower light levels due to shadowing by a pier. For 10 days in August 1997, seawater temperatures in the surrounding reef lagoon rose up to 1.5 degrees C above the 6-year August average. The HL colony bleached to white during this period, whereas, the LL colony remained dark-brown colored. The HL colony recovered its normal dark-brown coloration (reversible bleaching) within several weeks, during which time the seawater temperatures returned to average. The following year, for 10 days, seawater temperatures rose up to 3 degrees C above the 7-year August average and both colonies bleached to white and neither colony recovered (irreversible bleaching). Both colonies were rapidly overgrown by algae and hydroids and, as of June 2003, no recovery has taken place. Prior to the 1997 bleaching, experiments using solar radiation showed that the quantum yield of photosystem II charge separation of branches from HL and LL colonies were affected for several hours by exposure to ultraviolet radiation (UVR, 280 to 400 nm), but recovered by the same evening, suggesting that UVR does not have long-term effects on photochemistry in M. alcicornis. In situ effective quantum yield of photosystem II charge separation (deltaF/Fm') measurements before the 1998 bleaching event indicate that both colonies were healthy in terms of the physiological status of their endosymbionts. During and after the 1998 bleaching event, both colonies showed a reduction in deltaF/Fm' and consequently an increase in excitation pressure on photosystem II. The data suggest that temperature is not the only factor that causes bleaching and that solar radiation may play an important role in coral bleaching.