Coral Reefs最新文献

Ocean acidification (OA) and ocean warming (OW) affect the calcification of corals, and intraspecific variations in response to these stressors in the population level need to be clarified for better future predictions. Using Acropora digitifera as our subject, we examined the intraspecific variability in calcification and maximum quantum yield (F_v/F_m) of photosystem II of symbiotic zooxanthella in responses to OA, OW, and OA + OW. Samples were taken from two different sites: Sesoko Station (warmer) and Sesoko South (cooler) in Okinawa, Japan. Calcification rates varied between the two sites, and noticeable differences were observed only among coral colonies from the Sesoko South site, specifically under control and OA treatments. Furthermore, F_v/F_m showed no variation between the sites due to those stresses. Hence, the calcification rates among A. digitifera colonies varied by habitat, and we found within-site variation only in the lower temperature location, Sesoko South. We observed diminished variation in response among colonies in the warmer site. The adapting to diverse environmental conditions and responding to changes such as seawater pCO₂ and temperature, may lead to differences in sensitivity between the two populations to OA, OW, and OA + OW. These intraspecific variation could arise from factors like acclimatizations, the influence of specific genotypes, or phenotypic plasticity of the colonies.

A key goal of coral restoration is to re-establish self-sustaining coral populations and ensure resilience to future stressors, which requires that genetic diversity is maximised. However, coral genetic and genotypic (clonal) diversity is variable across reef sites via success of sexual recruitment, and cryptic species diversity can complicate breeding efforts. Assessing genotypic and genetic diversity of colonies to be used in restoration is therefore critical to avoid founder, inbreeding or outbreeding effects. Considering recent efforts to upscale coral propagation on the Great Barrier Reef (GBR), we examined species, population and clonal structure of a commonly out-planted tabular Acropora species—Acropora hyacinthus (Dana, 1864). A total of 189 colonies were sampled from six reef systems throughout the northern-central GBR and genotyped using an Acropora-specific Affymetrix microarray, which resulted in 1387 variant sites that passed quality control. Cryptic species were readily resolved and all sampled A. hyacinthus colonies represented unique genotypes within sites at three reefs. At reefs that contained multi-ramet genets (clonal genotypes), the mean and maximum between-ramet distances were 0.68 and 1.99 m, respectively. Therefore, sampling colonies > 2 m apart increases the likelihood these colonies represent distinct genets. Such a sampling design therefore maximises genotypic diversity when sourcing colonies for propagation and out-planting. Based on these variant sites, we found no between-reef genetic divergence based on locality. Furthermore, through unintentional sampling of non-target tabular Acroporid species, we show how this genotyping method may be used for resolving taxonomic uncertainty as well as population dynamics.

Antipathes galapagensis, Deichmann (Smithson Misc Collect 9:1–18, 1941), has been the object of intensive fishing in the Eastern Tropical Pacific due to its large and arborescent colonies and dense forests. Despite its importance as a habitat-forming species, little information exists about its basic biology. Thus, the objective of this study is to describe its reproductive cycle. Samplings were performed in Espiritu Santo Archipelago (La Paz Bay, Gulf of California, Mexico) over 22 months. Histological analyses were conducted on 197 coral samples collected to assess their reproductive strategy from 2018 to 2019. For the first time, male and female gametogenic development stages are described for the species, determining the mean diameter and size range of oocytes and spermatocysts for each gametogenesis sub-stage. The black coral A. galapagensis is an external spawner, adopting a partial spawning strategy, showing evidence of sequential hermaphroditism, and this latter representing the first documentation for the order Antipatharia. The estimated colony sexual maturity height is 102 and 93 cm for females and males, respectively. Gametogenesis begins in June and reaches the reproductive peak in September–October, where the highest frequency is observed of mature females and males and partial spawning. The reproductive cycle shows a correlation with seawater surface temperature increase in the study area, which reaches its maximum from September–October. The results provide the first knowledge contribution to the species biology, essential for its protection and conservation management.

Global coral reef degradation has precipitated phase shifts toward macroalgal-dominated communities. Despite the negative repercussions for reefscapes, higher abundances of primary producers have the potential to positively impact the physicochemical environment and mitigate negative impacts of ocean acidification (OA). In this study, we investigated the influence of macroalgal (cf. Sargassum vulgare) density on coral (Acropora millepora and A. hemprichii) calcification rates under current and future OA conditions. Corals were resistant to OA up to ~ 1100 µatm, with no changes in calcification rates. However, the presence of (low and high density) algae reduced calcification rates by ~ 41.8%, suggesting either a chemical defense response due to algal metabolites or potential physical impacts from shading or abrasion. Documented beneficial buffering effects of macroalgae in OA may also elicit negative impacts on coral calcification, suggesting further work is needed to elucidate how species interactions influence responses to projected climate change.

The ecological and evolutionary consequences of partner fidelity and flexibility among coral–dinoflagellate mutualisms are widely debated. Resident symbionts can modulate the resilience of their hosts to environmental stressors, which explains, in part, why host–symbiont combinations differ over broad geographic ranges and across physical–environmental gradients in light and temperature. Therefore, flexibility in these mutualisms may influence the longevity of coral populations and communities subjected to ocean warming. However, despite decades of research, basic knowledge about these mutualisms remains incomplete, hindering the development of predictive ecological theory. In particular, few studies have investigated the long-term composition of symbiont populations within individual colonies. To further examine the extent to which coral colonies have stable relationships with specific symbionts over multiple years, diverse coral taxa (Scleractinia) from a West Indo-Pacific fore reef (Palau) were tagged and sampled at various intervals—ranging from six months to several years—over nine years' time. Symbiont identity was examined using multiple genetic markers that resolved symbiont diversity to species and individual genotypes (i.e., clonal strains). Members of the genus Cladocopium (formerly Symbiodinium Clade C) were prevalent across the host community. Generally, corals with open modes of symbiont acquisition harbored a host–generalist symbiont, while corals with vertical symbiont transmission were associated with co-evolved host-specific symbionts. Consistent with previous colony monitoring studies, symbiont populations in a majority of colonies were dominated by one species and one strain (based on multilocus genotyping) over multiple years. Thus, the distribution of symbiont diversity at the genus, species and clone level, comprising specific and stable partner combinations, scale predictably to reef habitat, host taxon, and individual colony. Recognizing these fundamental ecological patterns establishes a more comprehensive understanding of the population and community structure of these mutualisms.

Caribbean coral reefs are currently facing a rapid decline caused by a plethora of threats including disease outbreaks. Octocorals appear to be unaffected by the majority of diseases impacting scleractinian corals, including stony coral tissue loss disease (SCTLD) that emerged in 2014 and resulted in a mass mortality of scleractinian coral populations inhabiting Florida, the USA, and Caribbean reefs. Although the Caribbean Sea is considered a disease hot spot, few investigations into the mechanism(s) responsible for the resistance of octocorals have been conducted. In response, the capacity for octocoral-derived extracts and natural products to inhibit strains of Vibrio coralliilyticus, pathogenic bacteria that can cause bleaching and disease in stony corals and can co-occur in SCTLD infections, was explored. Extracts obtained from each of the four octocoral species studied demonstrated antimicrobial activity against V. coralliilyticus. Bioassay-guided fractionations of crude extracts from Antillogorgia americana were employed to identify the antimicrobial compounds, revealing the presence of secosterols in the most bioactive fractions. These results suggest that octocoral species may utilize chemical defenses to protect themselves against infection by strains of a known coral pathogen and contribute to the body of knowledge regarding the success of octocorals on Caribbean reefs.

Hydrodynamic processes are a major driver for marine systems, linking marine organisms with their environment. However, a lack of hydrodynamic data at an ecologically relevant spatial resolution has stymied our understanding of reef function, as exemplified by Lizard Island on the Great Barrier Reef. To address this gap, 23 to 27 Marotte HS current meters were deployed over three periods, collecting 15 months of current velocity data. Combining these data with wind and tide datasets, we provide a preliminary description of the circulation in the Lizard Island lagoon, examining wind and tide influence, and flushing time. During south-easterly trade winds, flood tides flow through the Lagoon Entrance, while wind-induced waves cross the Bird-South crest, driving a north-westerly flow through Loomis Channel and across the western lagoon. Ebb tides flow east–south-east through the Lagoon Entrance and south-west through the Palfrey-South channel. Tides contribute a mean of 20.4% to the overall current speed, particularly in deeper sites with less reef interference, while shallow sites were more influenced by wind. Lizard Island lagoon flushing times ranged from a few hours to 10 days; longer during periods with low wind speeds. Hindcast flushing times during the 2016 coral bleaching event (following 8 Degree Heating Weeks) were approximately 22 h, suggesting that flushing time likely had minimal influence on bleaching. Our analyses provide initial insights into the circulation of the Lizard Island system and aid understanding of the potential relationships between reef organisms and their physical environment, bridging the gap between ecology and hydrodynamics.

The ecological success of shallow water corals hinges on their association with photosynthetic Symbiodiniaceae algae. This is affected by environmental drivers among which sea temperature is pivotal. In 2016, a prolonged heat wave challenged New Caledonia reefs triggering a severe bleaching event. Here, we tracked 72 coral colonies comprising two species of Pocillopora and Porites from a cross-shelf gradient during the event and subsequent recovery period. Symbiodiniaceae association over time was assessed using the ITS2 marker. Bleaching prevalence and photosynthetic efficiency showed that 83% of Pocillopora and 29% of Porites colonies were affected, with corals from a mid-shelf site having been most impacted. The majority of tracked colonies recovered by December 2016, with a recorded 33% mortality of Pocillopora, while Porites showed higher resilience. Consistent with previous studies, genotyping data suggest stable, species- and site-specific associations between corals and Symbiodiniaceae.

Morphology, internal structure, and in situ facies distribution of mesophotic Halimeda bioherms from the Queensland Plateau (NE Australia) are presented based on hydroacoustic and oceanographic data, seafloor observations, and discrete sediment sampling carried out during RV SONNE cruise SO292 in 2022. Halimeda buildups consist of cone-like mounds up to 500 m in diameter and 3–10 m high, with gentle slopes (2°–5° on the top of Tregrosse Bank). Bioherms occur in water depths of 10–70 m, with most bioherm between 50 and 65 m. Their internal structure consists of aggrading low-amplitude reflections at the core of the bioherm interfingering with high-amplitude reflections to the flanks. Surface facies distribution displays one to four facies belts, from distal to proximal: Halimeda rudstone, Halimeda rudstone with living plants, Halimeda rudstone with coralgal debris, and coralgal boundstone (when present, occupied the top of the bioherms). It is proposed that the alternation of two key processes contributes to the formation of these bioherms: (1) in situ accumulation of Halimeda debris and (2) episodic dismantling of the mesophotic coralgal boundstone at the centre of the bioherm by severe storms. These storms may dismantle the mesophotic reef and export coralgal rubble to the flanks. Flanks may be recolonized by Halimeda during fair-weather periods. Due to their different geomorphic expressions, complex internal structure, and surficial facies distribution, we suggest that the buildups of the Queensland Plateau represent a new Halimeda bioherm morphotype, distinct from previously described bioherms on the adjacent Great Barrier Reef and elsewhere globally.