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International audience; Environmental Vibrio strains represent a major threat in aquaculture, but the understanding of their virulence mechanisms heavily relies on the transposition of knowledge from human-pathogen vibrios. Here, the genetic bases of the virulence of Vibrio harveyi ORM4 towards the European abalone Haliotis tuberculata were characterized. We demonstrated that luxO, encoding a major regulator of the quorum sensing system, is crucial for the virulence of this strain, and that its deletion leads to a decrease in swimming motility, biofilm formation, and exopolysaccharide production. Furthermore, the biofilm formation by V. harveyi ORM4 was increased by abalone serum, which required LuxO. The absence of LuxO in V. harveyi ORM4 yielded opposite phenotypes compared with other Vibrio species including V. campbellii (still frequently named V. harveyi). In addition, we report a full type III secretion system (T3SS) gene cluster in the V. harveyi ORM4 genome. LuxO was shown to negatively regulate the promoter activity of exsA, encoding the major regulator of the T3SS genes, and the deletion of exsA abolished the virulence of V. harveyi ORM4. These results unveil virulence mechanisms set up by this environmentally important bacterial pathogen and pave the way for a better molecular understanding of the regulation of its pathogenicity.

Coral bleaching events due to elevated temperatures are increasing in both frequency and magnitude worldwide. Mass bleaching was recorded at five sites in the northern Persian Gulf during August and September 2012. Based on available seawater temperature data from field, satellite and previous studies, we suggest that the coral bleaching threshold temperature in the northern Persian Gulf is between 33.5 and 34°C, which is about 1.5 to 2.5°C lower than that in the southern part. To assess the bleaching effects, coral genera counted during 60-minute dives were categorized into four groups including healthy, slightly bleached (< 50% bleached tissue), mostly bleached ( > 50% bleached tissue) and fully bleached colonies. The anomalously high sea surface temperature resulted in massive coral bleaching (~84% coral colonies affected). Acropora spp. colonies, which are known as the most vulnerable corals to thermal stress, were less affected by the bleaching than massive corals, such as Porites, which are among the most thermo-tolerant corals. Turbid waters, suggested as coral refugia against global warming, did not protect corals in this study since most affected corals were found in the most turbid waters. The 2012 bleaching in the northern Persian Gulf was relatively strong from the viewpoint of coral bleaching severity. Long-term monitoring is needed to understand the actual consequences of the bleaching event on the coral reefs and communities., Los eventos de blanqueamiento de corales están aumentando en frecuencia y magnitud debido al aumento de la temperatura en los océanos. En este trabajo se describe un evento de blanqueamiento masivo observado en seis localidades del norte del Golfo Pérsico entre Agosto y Septiembre de 2012. Los datos de temperatura disponibles, medidas in situ y observaciones de satélites de la temperatura de la superficie del mar, sugieren que la temperatura umbral que desencadena el blanqueo de coral en el norte del Golfo Pérsico corresponde a una temperatura de entre 33,5-34°C que es una temperatura entre 1.5 a 2.5°C inferior a la observada en las zonas más meridionales del Golfo Persico (35-36°C). Para la evaluación de los efectos de blanqueo sobre las comunidades de coral, se realizaron transectos de 60 minutos entre 0 y 6 m de profundidad. Durante las inmersiones cada colonia de coral se identificó a nivel de género y su estado se asignó a una de las siguientes categorías: no afectada, ligeramente afectada ( < 50% del tejido blanqueado), severamente afectada ( > 50% del tejido blanqueado) y colonias totalmente afectadas (100% del tejido blanqueado). El análisis de los datos de temperatura permitió identificar una anomalía térmica durante el periodo de blanqueamiento que afectó a un 84% de las colonias censadas. Contrariamente a otros eventos de blanqueamiento analizados, las colonias de Acropora spp., que se encuentran entre las especies más vulnerables al estrés térmico, fueron menos afectadas que las especies de corales masivos como Porites spp. que normalmente presentan una gran resistencia al estrés térmico. Igualmente a pesar que la turbidez de las aguas ha sido señalada como un factor protector en el contexto del calentamiento global, en nuestro estudio observamos que las zonas más afectadas por el blanqueamiento presentaban las tasas de turbidez más elevadas. En conclusión el evento de blanqueamiento de 2012 observado en el norte del Golfo Pérsico afectó severamente a las comunidades de coral. El seguimiento a largo plazo de las comunidades de coral se presenta como una necesidad para comprender las consecuencias de los eventos de blanqueamiento.

Little information is available on coral diseases in the Persian Gulf; however, in the recent years, reports of coral diseases increased in particular from Iranian side of the Persian Gulf. In this paper we report a White Mat Disease resulting in mass mortality of Porites colonies at Hormuz Island. This outbreak infected 96% of all Porites colonies and killed 58±30% (mean ± SD) of all Porites tissues.

Refugia can facilitate the persistence of biodiversity under changing environmental conditions, such as anthropogenic climate change, and therefore constitute the best chance of survival for many coral species in the wild. Despite an increasing amount of literature, the concept of coral reef refugia remains poorly defined; so that climate change refugia have been confused with other phenomena, including temporal refuges, pristine habitats and physiological processes such as adaptation and acclimatization. We propose six criteria that determine the capacity of refugia to facilitate species persistence, including long-term buffering, protection from multiple climatic stressors, accessibility, microclimatic heterogeneity, size, and low exposure to non-climate disturbances. Any effective, high-capacity coral reef refugium should be characterized by long-term buffering of environmental conditions (for several decades) and multi-stressor buffering (provision of suitable environmental conditions with respect to climatic change, particularly ocean warming and acidification). Although not always essential, the remaining criteria are important for quantifying the capacity of potential refugia.