Coral Reefs最新文献

DNA metabarcoding is increasingly used in dietary studies, but this molecular technique has limitations including DNA extraction, primer choice suitability and completeness of DNA reference databases. Together, these limitations can create successive biases; some of which can be identified by careful data interrogation. Here, we examine some of the influential factors impacting DNA metabarcoding by focusing on the diet of the grazing coral reef parrotfish Scarus rivulatus (Labridae). The 16S V3-4 and 18S V4 gene regions were targeted to detect a wide range of taxa in the pharyngeal content, but genus-level amplicon sequence variant (ASV) assignments were ≤ 40%. Multiple universal 18S V4 primer sets, which amplified the same portion of the gene region, highlighted disparities that impacted resulting datasets and dietary data interpretation. Approximately 50% of ASVs overlapped among these 18S V4 datasets. Overall, our results show that protein-rich epilithic and endolithic microscopic photoautotrophs were consistently present and that S. rivulatus appears to rely on protein-rich taxa, especially dinoflagellates and cyanobacteria. Even if all qualitative limitations could be addressed, our data emphasise the difficulty of making straightforward quantitative conclusions about the diet composition of grazing fishes using DNA metabarcoding alone. Thus, until DNA metabarcoding reaches a state of maturity where quantitative data can be gained, additional support is required from other dietary analysis methods to provide robust interpretations and conclusions.

Elasmobranch (i.e. sharks, skates, and rays) behaviours have been found to align with moon phases; yet, it is not fully understood how the moon influences elasmobranchs’ foraging habits. In coastal ecosystems, tidal changes are typically seen as the primary influence on the behavioural rhythms of fishes, which are linked to the lunar cycle. Sharks have been documented to synchronise behaviours, such as foraging patterns, with the phases of the moon, but studies have yet to clearly separate and identify the mechanisms by which the lunar phase affects these patterns. The island of Moorea, French Polynesia, serves as a nursery habitat for neonatal blacktip reef and sicklefin lemon sharks within the South Pacific amphidromic system, which experiences minimal tidal ranges (~ 0.2 m). This setting provides a unique opportunity to isolate the lunar cycle’s effects from tidal influences. We compared catch rates of neonates of both shark species and foraging success, through stomach content analysis, of blacktip reef sharks across the lunar cycle. Our findings did not support the hypothesis of lunar-induced entrainment of foraging patterns for these neonatal reef sharks. However, understanding the environmental factors that shape the behavioural patterns and foraging strategies of neonatal reef sharks is becoming increasingly important against the backdrop of human disturbances.

Coral reefs in the Florida Reef Tract have seen protracted loss of coral over the past several decades due to a variety of disturbances from marine heat waves, cold snaps, and disease events. Corals have not recovered despite abundant herbivorous fishes and relatively low macroalgal cover, two factors thought to facilitate resilience of corals. Thus, factors affecting the replenishment of coral populations may be hindering the recovery of corals. To study the potential factors affecting coral recovery in reefs of the Florida Reef Tract, we assessed benthic abiotic variables (substrate slope, depth, structural complexity, and abundance of sediment), fish assemblages, and benthic composition in three different reef habitats (groove, spur wall, spur top) located on three low-relief reefs and three high-relief spur-and-groove reefs. Herbivorous fish biomass ranged (44.7–107 g m⁻²), which is above average for the Caribbean. Yet there was low coral cover (~ 1%) and low density (~ 1 coral m²) of small adult corals, which likely reflects the cumulative effects of years of disturbances. The presence and density of juvenile corals were negatively correlated with the depth of the sediment layer trapped within long, sediment-laden algal turfs (LSAT), which are particularly abundant (> 50% cover) in low complexity reef habitats (low-relief groove, low-relief spur top, and high-relief groove). Our results indicate that current unsuitable habitat conditions (high sediment load) for early life stage corals may be an important factor preventing coral recovery. Consequently, the abundance of herbivorous fishes and coral cover trajectories appear decoupled in the region, and additional management initiatives considering LSAT composition are required to aid reef resilience.

Elevated temperatures cause mass coral bleaching, leading to reef degradation. The frequency of bleaching events is increasing, and severe bleaching events have been predicted to occur annually in the next few decades. However, the ability of corals to acclimate and adapt to these unprecedented stresses remains unknown. In this study, we investigated how three years of consecutive thermal stress affect the adult fragments of the coral Acropora tenuis. The fragments were exposed to temperature treatments of ~ 28 °C (control) and ~ 31 °C (heat stress) until they began to bleach. We measured the survival rate, maximum quantum yield of photosystem II (Fv/Fm) of the symbiotic algae, and algal density of the fragments. The survival rate of the fragments under thermal stress decreased over the three-year period, reaching 20% by the end. Additionally, we observed a decrease in Fv/Fm and a reduction in algal density in the stressed fragments compared to those in the control fragments during all three years of the thermal stress period. These findings collectively suggested that consecutive bleaching-level thermal stress increases the susceptibility of corals to heat.

Coral reef ecosystems host diversified and highly productive communities, but corals are degrading in many places worldwide. Picking suitable locations to maximize coral conservation and restoration efforts is critical. From a mass balance point of view, the supply of new nutrients is crucial to support a productive and reef-building coral ecosystem. Quantifying and qualifying available nutrients provide information to set region-specific thresholds for anthropogenic pollution monitoring and to generate research hypotheses. Here, we report the inorganic and organic nutrient levels from twenty-three sampling sites in coral reefs and coastal waters covering regions from high to low coral coverage, including two remote islands, Dongsha Atoll and Taiping Island, in the South China Sea. Some of the surveyed reefs received external inorganic nutrient supply via upwelling or submarine groundwater discharge (SGD), suggesting sites potential for new production (i.e., reef-building). Production or removal of organic matter at various sites is evidenced by their elevated or depleted organic carbon and nitrogen concentrations, respectively. The degree of impact by the upwelling and SGD on various inorganic and organic nutrient distribution varies. Among all sites, organic nitrogen accounts for most of the total nitrogen and is potentially a significant nitrogen source for the environment. The highly correlated total organic nitrogen (TON) concentrations and their C-to-N ratios (C/N_-TON) suggest the production of TON with low C/N_-TON and preferential removal of N during remineralization processes, leaving “leftover” TON with high C/N ratios. Furthermore, we found that high coral diversity and coverage sites are featured in low organic matter with high C/N, while macroalgae-dominating sites had elevated organic matter. The new data are valuable to generate hypotheses for future research to test, for example, whether sites with low organic matter are more suitable for restoring reef-building corals than sites with high organic matter.

Thermal stress triggers the breakdown of the obligate symbiosis between the cnidarian coral host and its autotrophic dinoflagellates of the family Symbiodiniaceae. This diverse family exhibits pronounced functional variation that has large implications for the survival of their coral host. In this study, we explored patterns of symbiont community composition and diversity in the coral Turbinaria reniformis, a turbid reef specialist, along a latitudinal and environmental gradient in Western Australia. Using metabarcoding of the internal transcribed spacer region 2, we explored symbiont community patterns, their environmental drivers, and potential associations with host genetic structure. Our findings reveal a predominance of Cladocopium across our study area, with distinct regional composition influenced primarily by sea surface temperature. Geographical distance and host genetic data did not align with symbiont community divergence, suggesting a complex interplay of environmental and genetic factors t shaping the community structure. This study underscores Cladocopium stability in Western Australia across large distances and strong environmental gradients. It also highlights the highly diversified lineage community that may explain T. reniformis ability to thrive in a wide range of environmental conditions.

Sexual propagation of corals is a promising strategy for coral restoration, but one of the main challenges is the high mortality of coral spat due to competitive interactions with macroalgae during the early life history stages. Optimising the properties of settlement substrates such as material types and surface roughness has the potential to improve the survival of spat by limiting the recruitment and growth of macroalgae. In this study, we assessed the effects of modifying surface roughness across three different tile materials (alumina-based ceramic, calcium carbonate (CaCO₃), and concrete) on the settlement success and post-settlement survivorship of Acropora kenti coral larvae in six mesocosm tanks, each with different established macroalgal communities. The macroalgal community compositions on the tiles were significantly different among material types, but not surface roughness, although the type and abundance of macroalgal species were heavily influenced by the established tank communities. Increasing surface roughness did not affect larval settlement success or spat survivorship. Substantially higher larval settlement density was found on concrete tiles (1.92 ± 0.10 larvae cm⁻²), but spat survival was the highest on CaCO₃ tiles (73.4 ± 4.2% survived). Very strong competitive interactions were observed between spat and macroalgae, with overgrowth by the crustose coralline alga Crustaphytum sp. and the brown alga Lobophora sp. being the primary cause of spat mortality. Overall, when taking into account both settlement and survival rates, concrete was the best performing among the tile types tested here.

Natural history museums house the largest biodiversity collections in the world and represent an enormous repository of genetic information. Much of this information, however, has remained inaccessible until recently. Emerging technologies, such as techniques for isolation of historical DNA (hDNA) and target enrichment sequencing of ultraconserved elements (UCEs) that can utilize degraded DNA as input material, have the potential to unlock museum collections for genomics research. Here, we demonstrate that hDNA extracted from dried Pocillopora coral specimens, collected up to 90 yrs ago, can be used as input for UCE target enrichment sequencing. The resulting sequence data can be used in phylogenetic studies to resolve questions about taxonomic species identities, biogeographic distributions, and evolutionary histories. Our results provide a blueprint for research groups seeking to take advantage of untapped genetic information stored in natural history museum collections.

The tropical southwest Indian Ocean is a coral biodiversity hotspot, with remote reefs physically connected by larval dispersal through eddies and a complex set of equatorial and boundary currents. Based on multidecadal, 2 km resolution hydrodynamic and larval dispersal models that incorporate temporal variability in dispersal, we find that powerful zonal currents, current bifurcations, and geographic isolation act as leaky dispersal barriers, partitioning the southwest Indian Ocean into clusters of reefs that tend to consistently retain larvae, and therefore gene flow, over many generations. Whilst exceptionally remote, the Chagos Archipelago can broadcast (and receive) considerable numbers of larvae to (and from) reefs across the wider southwest Indian Ocean, most significantly exchanging larvae with the Inner Islands of Seychelles, but also the Mozambique Channel region. Considering multi-generational dispersal indicates that most coral populations in the southwest Indian Ocean are physically connected within a few hundred steps of dispersal. These results suggest that regional biogeography and population structure can be largely attributed to geologically recent patterns of larval dispersal, although some notable discrepancies indicate that palaeogeography and environmental suitability also play an important role. The model output and connectivity matrices are available in full and will provide useful physical context to regional biogeography and connectivity studies, as well as supporting marine spatial planning efforts.

Coral–algal interactions are pivotal in reef ecosystems globally as they can scale up ecosystem levels and lead to dominance shifts. In this study, we conducted a systematic review of global coral–algal interactions, identifying the most studied locations, species, and types of interactions. We then assessed how these interactions may be impacted by consumers and climate change. Over the past 20 years (2001–2020), coral and algae interactions were mostly explored in the Pacific, and the Caribbean and US East Coast, where branching and massive corals were the focus, while other coral growth forms received less attention, and effects on algae were often overlooked. Adult corals were generally reported to be damaged when directly interacting with algae through physical abrasion or allelopathy. Conversely, algae interactions were found to have a positive impact on juvenile corals by facilitating larval recruitment and settlement. As expected, coral–algal interactions and the type of coral–algal relationships vary globally, most likely due to differences in abiotic conditions, community composition and the number of studies performed in a region. Despite the large emphasis on the role of consumers in controlling coral–algal interactions, few studies directly explored the effects of herbivory on coral–algal interactions. Given the growing evidence that ocean warming and acidification can reduce the competitive ability of corals, understanding the dynamic relationships between coral, algae, and consumers under future climate change conditions is crucial in predicting future coral recruitment potential and reef composition patterns. Here, we highlight the main findings from coral–algal interaction studies performed in the last 20 year and point to future directions, such as: 1) diversifying location, coral species, growth forms and life phases; 2) considering effects on both sides of interaction, not neglecting effects on algae; and 3) taking a closer look into the role of consumers and microbiomes. Advancing our understanding of coral–algal interactions, as well as how these interactions shift under changing conditions, is critical in predicting how coral reef ecosystems may operate in the future.