ABSTRACT
Three decades ago, Acropora palmata was one of the main reef-building coral species throughout the Caribbean, forming an essential component of the structural complexity of shallow coral reef habitats. These colonies still provide microhabitats for settlement, food and shelter to many vertebrates and invertebrates. The recent decline of A. palmata has been followed by a significant loss in spatial heterogeneity and possibly in species diversity. Studies addressing whether dead and living stands of Acropora hold different fish and benthic assemblages are scarce. The status of Acropora colonies and their associated species were assessed in October 2012, at two reef zones of Cayo Sombrero, Venezuela. Visual censuses of fish abundance and the number of macrofaunal individuals were recorded for both live and dead zones. Living Acropora colonies had the lowest abundance (˂31%). In both zoned the fish community was dominated by damselfishes (˂53%) and wrasses (˂36%), the benthic macrofauna by peracarid crustaceans (˂40%) and polychaetes (˂38%). Fish and benthic communities were not correlated with the condition (live or dead) of the Acropora habitats; possibly branching structures provide the necessary shelter and protection no matter if they are dead or alive. More replication is necessary to test this unexpected result.
Hace tres décadas, Acropora palmata fue una de las principales especies de coral constructoras de arrecifes a lo largo del Caribe, formando un componente esencial de la complejidad estructural disponible en los hábitats arrecifales someros. Estas colonias todavía proveen microhábitats para el asentamiento, alimentación y refugio de muchas especies de vertebrados e invertebrados. El declive reciente de A. palmata ha sido precedido por una pérdida significativa de heterogeneidad espacial y se piensa que ésta reducción ha producido una disminución importante en la diversidad de especies. Los estudios señalan que las colonias muertas o vivas de Acropora que sostienen diferentes comunidades de bentos y de peces son escasas. El estado de las colonias de Acropora y sus especies asociadas fueron evaluadas en Octubre de 2012, en dos zonas arrecifales diferentes de Cayo Sombrero, Venezuela. Censos visuales de la abundancia de especies de peces y el número de individuos de la macrofauna fueron también registrados para ambas zonas, tanto vivas como muertas. Las colonias vivas presentaron la menor abundancia (˂31%). En ambos sitios la comunidad de peces fue dominada por los peces damiselas (˂53%) y lábridos (˂36%); la macrofauna bentónica por crustáceos peracáridos (˂40%) y poliquetos (˂38%). Las comunidades de peces y bentos no mostraron correlación con la condición (vivo o muerto) de los hábitats de Acropora; posiblemente las estructuras ramificadas proveen el refugio y protección necesario sin importar si están vivos o muertos. Una mayor replicación es necesaria para probar este resultado inesperado.
ABSTRACT
Coral diseases have been increasingly reported over the past few decades and are a major contributor to coral decline worldwide. The Caribbean, in particular, has been noted as a hotspot for coral disease, and the aptly named white syndromes have caused the decline of the dominant reef building corals throughout their range. White band disease (WBD) has been implicated in the dramatic loss of Acropora cervicornis and Acropora palmata since the 1970s, resulting in both species being listed as critically endangered on the International Union for Conservation of Nature Red list. The causal agent of WBD remains unknown, although recent studies based on challenge experiments with filtrate from infected hosts concluded that the disease is probably caused by bacteria. Here, we report an experiment using four different antibiotic treatments, targeting different members of the disease-associated microbial community. Two antibiotics, ampicillin and paromomycin, arrested the disease completely, and by comparing with community shifts brought about by treatments that did not arrest the disease, we have identified the likely candidate causal agent or agents of WBD. Our interpretation of the experimental treatments is that one or a combination of up to three specific bacterial types, detected consistently in diseased corals but not detectable in healthy corals, are likely causal agents of WBD. In addition, a histophagous ciliate (Philaster lucinda) identical to that found consistently in association with white syndrome in Indo-Pacific acroporas was also consistently detected in all WBD samples and absent in healthy coral. Treatment with metronidazole reduced it to below detection limits, but did not arrest the disease. However, the microscopic disease signs changed, suggesting a secondary role in disease causation for this ciliate. In future studies to identify a causal agent of WBD via tests of Henle-Koch's postulates, it will be vital to experimentally control for populations of the other potential pathogens identified in this study.
