Mesophotic coral ecosystems of French Polynesia are hotspots of alpha and beta generic diversity for scleractinian assemblages

Aim: Revealing how diversity varies across the depth gradient is key for understanding the role of mesophotic coral ecosystems in the functioning of coral reefs. We quantitatively examined how alpha and beta generic diversity of scleractinian coral assemblages vary across a wide depth gradient for coral reefs. Location: Sixteen sites in eight islands of three archipelagos in French Polynesia. Methods: We studied generic diversity patterns of scleractinian corals, as derived from the analysis of photo-quadrats, across the seafloor from shallow to lower mesophotic depths (6–120 m) and on a wide geographic scale. Our sampling considered quantitative coral cover to explore the patterns of alpha and beta components of diversity across depth and horizontal space. Results: We show that in French Polynesia, mesophotic coral ecosystems host higher alpha and beta generic diversity than shallow reefs despite decreasing coral cover with depth. The variation of coral genus richness across the depth gradient is mainly driven by a mid-domain effect with a peak at 40 m depth. At the same time, we found that the differences in coral genera across islands (spatial beta-diversity) increased steadily along the depth gradient. Main conclusions: Our findings report the first quantitative results of coral cover and diversity from mesophotic coral ecosystems in French Polynesia and also present one of the few existing studies to examine the broad breadth of the mesophotic depth gradient. We demonstrate that mesophotic depths can host unexpectedly high generic richness of scleractinian coral assemblages. At the same time, we showed that increasing depth increases the differences in generic diversity composition across islands, whereas shallow reefs are similar in between. While a single island could conserve shallow regional biodiversity, mesophotic depths containing the richest diversity require site-specific measures, suggesting that considering these mesophotic depths in conservation is necessary to maintain regional diversity

First report of bioaccumulation and bioconcentration of aliphatic hydrocarbons (AHs) and persistent organic pollutants (PAHs, PCBs and PCNs) and their effects on alcyonacea and scleractinian corals and their endosymbiotic algae from the Persian Gulf, Iran

The coral reefs of the Persian Gulf are the most diverse systems of life in the marine environment of the Middle East. Unfortunately, they are highly threatened by local and global stressors, particularly oil pollutants. This is the first quantitative and qualitative study aimed at assessing the concentration and sources of n-alkanes and POPs (PAHs, PCBs and PCNs) in coral tissues, symbiotic algae (zooxanthellae), reef sediments and seawaters in coral reefs of Lark and Kharg in the Persian Gulf, Iran. This work was conducted on eight species of six genera and three families of hard corals and one family of soft coral. A significant variation in the concentration of Σ30n-alkanes and POPs (Σ40PAHs, Σ22PCBs and 20PCNs) was found in the decreasing order: zooxanthellae > coral tissue > skeleton > reef sediment > seawater. The bioaccumulation of these compounds was 2-times higher in ahermatypic than in hermatypic corals, among which significant variations were observed in both sites. In Kharg, Porites lutea had the highest mean concentration of Σ30n-alkanes and Σ40PAHs in soft tissue, whereas the lowest values were in Platygyra daedalea. A contrasting trend was documented for Σ22PCBs and 20PCNs, with the highest level reported in soft tissue of P. daedalea and the lowest in P. lutea at Kharg. Compositional pattern of AHs and PAHs demonstrated the predominance of LMW-PAHs and n-alkanes. In skeleton and reef sediments, tetra, penta and tri-CBs were the most abundant PCBs congeners followed by di-CB > hexa-CB > hepta-CB > octa-CB,whiletri-CB > di-CB > tetra-CB > penta-CB > hexa-CB > hepta-CB > octa-CB was observed for soft tissue, zooxanthellae and seawater. The results of RAD test indicated significantly negative correlation between total concentration of these compounds with zooxanthellae density, the chlorophyll-a and C2 in corals at both reefs. This is the first report on levels, health assessment and source apportionments of POPs in zooxanthellae and a first step in the implementation of specific coral reef management measures

Boat noise prevents soundscape-based habitat selection by coral planulae

Understanding the relationship between coral reef condition and recruitment potential is vital for the development of effective management strategies that maintain coral cover and biodiversity. Coral larvae (planulae) have been shown to use certain sensory cues to orient towards settlement habitats (e.g. the odour of live crustose coralline algae - CCA). However, the influence of auditory cues on coral recruitment, and any effect of anthropogenic noise on this process, remain largely unknown. Here, we determined the effect of protected reef (MPA), exploited reef (non-MPA) soundscapes, and a source of anthropogenic noise (boat) on the habitat preference for live CCA over dead CCA in the planula of two common Indo-Pacific coral species (Pocillopora damicornis and Acropora cytherea). Soundscapes from protected reefs significantly increased the phonotaxis of planulae of both species towards live CCA, especially when compared to boat noise. Boat noise playback prevented this preferential selection of live CCA as a settlement substrate. These results suggest that sources of anthropogenic noise such as motor boat can disrupt the settlement behaviours of coral planulae. Acoustic cues should be accounted for when developing management strategies aimed at maximizing larval recruitment to coral reefs

Unified Methods in Collecting, Preserving, and Archiving Coral Bleaching and Restoration Specimens to Increase Sample Utility and Interdisciplinary Collaboration

Coral reefs are declining worldwide primarily because of bleaching and subsequent mortality resulting from thermal stress. Currently, extensive efforts to engage in more holistic research and restoration endeavors have considerably expanded the techniques applied to examine coral samples. Despite such advances, coral bleaching and restoration studies are often conducted within a specific disciplinary focus, where specimens are collected, preserved, and archived in ways that are not always conducive to further downstream analyses by specialists in other disciplines. This approach may prevent the full utilization of unexpended specimens, leading to siloed research, duplicative efforts, unnecessary loss of additional corals to research endeavors, and overall increased costs. A recent US National Science Foundation-sponsored workshop set out to consolidate our collective knowledge across the disciplines of Omics, Physiology, and Microscopy and Imaging regarding the methods used for coral sample collection, preservation, and archiving. Here, we highlight knowledge gaps and propose some simple steps for collecting, preserving, and archiving coral-bleaching specimens that can increase the impact of individual coral bleaching and restoration studies, as well as foster additional analyses and future discoveries through collaboration. Rapid freezing of samples in liquid nitrogen or placing at −80 °C to −20 °C is optimal for most Omics and Physiology studies with a few exceptions; however, freezing samples removes the potential for many Microscopy and Imaging-based analyses due to the alteration of tissue integrity during freezing. For Microscopy and Imaging, samples are best stored in aldehydes. The use of sterile gloves and receptacles during collection supports the downstream analysis of host-associated bacterial and viral communities which are particularly germane to disease and restoration efforts. Across all disciplines, the use of aseptic techniques during collection, preservation, and archiving maximizes the research potential of coral specimens and allows for the greatest number of possible downstream analyses

Development of Gene Expression Markers of Acute Heat-Light Stress in Reef-Building Corals of the Genus Porites

Coral reefs are declining worldwide due to increased incidence of climate-induced coral bleaching, which will have widespread biodiversity and economic impacts. A simple method to measure the sub-bleaching level of heat-light stress experienced by corals would greatly inform reef management practices by making it possible to assess the distribution of bleaching risks among individual reef sites. Gene expression analysis based on quantitative PCR (qPCR) can be used as a diagnostic tool to determine coral condition in situ. We evaluated the expression of 13 candidate genes during heat-light stress in a common Caribbean coral Porites astreoides, and observed strong and consistent changes in gene expression in two independent experiments. Furthermore, we found that the apparent return to baseline expression levels during a recovery phase was rapid, despite visible signs of colony bleaching. We show that the response to acute heat-light stress in P. astreoides can be monitored by measuring the difference in expression of only two genes: Hsp16 and actin. We demonstrate that this assay discriminates between corals sampled from two field sites experiencing different temperatures. We also show that the assay is applicable to an Indo-Pacific congener, P. lobata, and therefore could potentially be used to diagnose acute heat-light stress on coral reefs worldwide

Savoirs locaux à propos des gorgones chez les travailleurs de la mer des îles de la Guadeloupe (Antilles françaises)

La Guadeloupe est soumise aux programmes régionaux en faveur de la conservation de la biodiversité pour sauvegarder les écosystèmes récifaux soumis à la surpêche. Les producteurs halieutiques doivent intégrer les mesures légales à travers leurs pratiques traditionnelles dont l’apprentissage repose encore beaucoup sur une transmission directe de savoirs concrets et utiles. Les gorgones, éléments structurels des paysages coralliens, sont des organismes emblématiques aux Antilles. L’enjeu se joue entre cultures et savoirs différents, dans un contexte socio-économique qui évolue vite. Les 14 pêcheurs et mareyeurs interrogés en 2012 ont une connaissance empirique des fonds marins coralliens qu’ils traduisent difficilement dans le langage scientifique. Les termes génériques caye, corail et récif, bien utilisés, renvoient à l’idée d’un monde dynamique et flou plutôt qu’à des taxons zoologiques. Ils désignent une entité composite, mais identifiable, mêlant vivant et inerte, indispensable aux poissons. Le rapport des pêcheurs au benthos est surtout tactile, lié à la manipulation des filets et nasses. Les contacts perçus comme désagréables inspirent une méfiance exacerbée par des croyances dont la connotation spirituelle est à corroborer. La place des gorgones, incertaine, est associée à la flore. Une classification populaire basée sur les échanges oraux est proposée. Si le lexique est pauvre et que décrire est un exercice difficile, les formes réticulées montrées sont bien reconnues. L‘assimilation des messages en faveur de la protection du benthos autre que les coraux est donc problématique. Les gorgones recouvrent cependant une double valeur d’usage. Elles sont indissociables à l’idée de bonne pêche et sont la source d’un savoir territorial exploitable pour le tourisme.The island of Guadeloupe has schemes promoting the preservation of biodiversity, to protect the reef ecosystems that have been subjected to overfishing. The fishing industry has to incorporate legal requirements into the traditional practices still largely passed on through practical apprenticeship. Gorgonian corals found in the coral reefs of Guadeloupe are the emblematic species of the French West Indies. There is a conflict between different cultures and knowledge in the context of a world fast-changing socio-economically. The fourteen fishermen and wholesale fish-merchants interviewed in 2012 have an empirical knowledge of the coral reefs but have some difficulties to translate it in a scientific language. The words cay, coral and coral reef, long in use, conjure up a soft-focus, dynamic image rather than a precise zoological classification. They describe a recognisable entity, the mixture of components, living and inert, essential to fish. The relationship of the fishermen to the creatures of the seafloor is above all tactile, from handling fishing nets and hoop nets. The disagreeable nature of handling leads to a mistrust reinforced by religious beliefs. The place of the Gorgonians within practical classifications is uncertain, but they are currently classified as plants. A popular classification based on the interviews is being suggested. Despite an inadequate vocabulary and difficulty in description, the reticulated forms shown are easy to recognise visually. Taking on board the messages promoting the protection of the seafloor (apart from the Scleractinian corals) is therefore difficult. The Gorgonian corals however have two usage values. They are essential for the well-being of the fish and nurture local knowledge useful for tourism

Hyposalinity stress compromises the fertilization of gametes more than the survival of coral larvae

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Thermal performance with depth: Comparison of a mesophotic scleractinian and an antipatharian species subjected to internal waves in Mo'orea, French Polynesia

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High resistance of Acropora coral gametes facing copper exposure

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