Suppressed coral settlement following mass bleaching in the southern Persian/Arabian Gulf

Coral reefs in the southern Persian/Arabian Gulf have become increasingly degraded in the past two decades, mainly due to recurrent mass coral bleaching events. The recovery of these reefs will be largely contingent upon the arrival and settlement of coral larvae and their post settlement growth and survival. Spatial and temporal patterns of coral settlement were quantified on 10 sites spanning \u3e350 km of the southern Gulf using settlement tiles for two years when consecutive bleaching events occurred. Coral settlement was highly seasonal, with peak settlement occurring in summer each year (\u3e95% of spat), with the remainder of settlement in autumn. Coral settlement was \u3e2-fold greater in the first year (928 spat) compared to the second year (397 spat) representing overall settlement densities of 95 m−2 yr−1 versus 40 m−2 yr−1. The dramatic declines in larval settlement between years suggests bleaching-related impacts on fecundity occurred during the gametogenic cycle late in the first year, as well as impaired survivorship of larvae and/or spat during the second year when severe bleaching coincided with the peak settlement period. Poritids and merulinids (‘others’) comprised 4% and 94% of the spat, respectively, while acroporids were virtually absent (1 recorded spat), suggesting the continued extirpation of this formerly dominant group and a continuing shift towards more stress-tolerant assemblages. Settlement rates in the southern Gulf are low in comparison to other marginal reef environments, and the bleaching-related suppression of settlement observed here suggests that larval supply is unlikely to be sufficient to support recovery of these increasingly degraded habitats. Given the increasing frequency of bleaching events in the southern Gulf the prognosis for the future of regional reefs is grim

Temporal variation in macroalgal removal: insights from an impacted equatorial coral reef system

Macroalgal removal is a critical ecosystem function yet few studies have considered its temporal variability, especially on impacted reefs with limited herbivorous fish biodiversity. To address this, we quantified macroalgal removal and mass-standardised bite rates of herbivorous fishes monthly from July 2016 to June 2017 using a series of transplanted Sargassum ilicifolium assays and underwater video cameras on three degraded coral reefs in Singapore: Pulau Satumu, Kusu Island, and Terumbu Pempang Tengah. Our results revealed a distinct temporal pattern in macroalgal herbivory (proportion of biomass removed and mass-standardised bite rates) rates across all sites, increasing from July and decreasing from January, with the highest rates recorded in December (28.10 ± 3.05 g 3.5 h−1; 208.24 ± 29.99 mass-standardised bites 3.5 h−1) and the lowest in May (0.86 ± 0.17 g 3.5 h−1; 9.55 ± 3.19 mass-standardised bites 3.5 h−1). These coincided with the S. ilicifolium growth cycle, confirming previous evidence that herbivory rates are closely linked to macroalgal condition. Video analyses revealed nine species feeding over a year (31,839 bites; 8702.89 mass-standardised bites), with Siganus virgatus responsible for ∼ 80% of the total mass-standardised bites. Siganus virgatus took the largest proportion of bites monthly, except between April and June, when Scarus rivulatus was dominant, suggesting temporal constraints in functional roles

Macroalgal browsing on a heavily degraded, urbanized equatorial reef system

The removal of macroalgal biomass is critical to the health of coral reef ecosystems. Previous studies on relatively intact reefs with diverse and abundant fish communities have quantified rapid removal of macroalgae by herbivorous fishes, yet how these findings rel ate to degraded reef systems where fish diversity and abundance are markedly lower and algal biomass substantially higher, is unclear. We surveyed roving herbivorous fish communities and quantified their capacity to remove the dominant macroalga Sargassum ilicifolium on seven reefs in Singapore; a heavily degraded urbanized reef system. The diversity and abundance of herbivorous fishes was extremely low, with eight species and a mean abundance ~1.1 individuals 60 m -2 recorded across reefs. Consumption of S. ilicifolium varied with distance from Singapore's main port with consumption being 3- to 17-fold higher on reefs furthest from the port (Pulau Satumu: 4.18 g h -1 ; Kusu Island: 2.38 g h -1 ) than reefs closer to the port (0.35-0.78 g h -1 ). Video observations revealed a single species, Siganus virgatus, was almost solely responsible for removing S. ilicifolium biomass, accounting for 83% of the mass-standardized bites. Despite low herbivore diversity and intense urbanization, macroalgal removal by fishes on some Singaporean reefs was directly comparable to rates reported for other inshore Indo-Pacific reefs

Fear effects and group size interact to shape herbivory on coral reefs

Fear of predators (‘fear effects’) is an important determinant of foraging decisions by consumers across a range of ecosystems. Group size is one of the main behavioural mechanisms for mitigating fear effects while also providing foraging benefits to group members. Within coral reef ecosystems, fear effects have been shown to influence the feeding rates of herbivorous fishes, a key functional group that prevents macroalgal overgrowth. Yet, how fear effects and group size interact to shape macroalgal removal on coral reefs remains unclear. Here, we conducted field-based experiments using models of a common piscivorous fish, the leopard coral grouper Plectropomus leopardus and a series of macroalgal Sargassum ilicifolium assays positioned at increasing distances from the models (1, 2, 3 and 4 m) on two coral reefs in Singapore to investigate how acute fear effects shape the intensity of herbivory, and whether these effects were influenced by variation in the group size of herbivorous fishes feeding on the assays. We found acute fear effects strongly influenced the foraging behaviour of herbivorous fishes over small spatial scales. Rates of Sargassum biomass removal, feeding rates and the total number of individual feeding events were all lower near the predator model. These effects dissipated rapidly with increasing distance from the predator model and were undetectable at a distance of 4 m. We also found generally larger group sizes of herbivorous fishes further from the predator model, presumably reflecting decreased risk. Furthermore, the number of individual bites/event increased significantly with increasing group size for two common browsing fishes, Siganus virgatus and Siganus javus. Our findings highlight that acute fear effects influence the distribution and intensity of herbivory over small spatial scales. Fear effects also interacted with herbivore group size resulting in changes in the number of individual feeding events and bite rates that collectively shape the realized ecosystem function of macroalgal removal on coral reefs. Group size is an important context-dependent factor that should be considered when examining fear effects on coral reefs. A free Plain Language Summary can be found within the Supporting Information of this article

Fear effects and group size interact to shape herbivory on coral reefs

Fear of predators (‘fear effects’) is an important determinant of foraging decisions by consumers across a range of ecosystems. Group size is one of the main behavioural mechanisms for mitigating fear effects while also providing foraging benefits to group members. Within coral reef ecosystems, fear effects have been shown to influence the feeding rates of herbivorous fishes, a key functional group that prevents macroalgal overgrowth. Yet, how fear effects and group size interact to shape macroalgal removal on coral reefs remains unclear. Here, we conducted field-based experiments using models of a common piscivorous fish, the leopard coral grouper Plectropomus leopardus and a series of macroalgal Sargassum ilicifolium assays positioned at increasing distances from the models (1, 2, 3 and 4 m) on two coral reefs in Singapore to investigate how acute fear effects shape the intensity of herbivory, and whether these effects were influenced by variation in the group size of herbivorous fishes feeding on the assays. We found acute fear effects strongly influenced the foraging behaviour of herbivorous fishes over small spatial scales. Rates of Sargassum biomass removal, feeding rates and the total number of individual feeding events were all lower near the predator model. These effects dissipated rapidly with increasing distance from the predator model and were undetectable at a distance of 4 m. We also found generally larger group sizes of herbivorous fishes further from the predator model, presumably reflecting decreased risk. Furthermore, the number of individual bites/event increased significantly with increasing group size for two common browsing fishes, Siganus virgatus and Siganus javus. Our findings highlight that acute fear effects influence the distribution and intensity of herbivory over small spatial scales. Fear effects also interacted with herbivore group size resulting in changes in the number of individual feeding events and bite rates that collectively shape the realized ecosystem function of macroalgal removal on coral reefs. Group size is an important context-dependent factor that should be considered when examining fear effects on coral reefs

Latitudinal variation in monthly-scale reproductive synchrony among Acropora coral assemblages in the Indo-Pacific

Early research into coral reproductive biology suggested that spawning synchrony was driven by variations in the amplitude of environmental variables that are correlated with latitude, with synchrony predicted to break down at lower latitudes. More recent research has revealed that synchronous spawning, both within and among species, is a feature of all speciose coral assemblages, including equatorial reefs. Nonetheless, considerable variation in reproductive synchrony exists among locations and the hypothesis that the extent of spawning synchrony is correlated with latitude has not been formally tested on a large scale. Here, we use data from 90 sites throughout the Indo-Pacific and a quantitative index of reproductive synchrony applied at a monthly scale to demonstrate that, despite considerable spatial and temporal variation, there is no correlation between latitude and reproductive synchrony. Considering the critical role that successful reproduction plays in the persistence and recovery of coral reefs, research is urgently needed to understand the drivers underpinning variation in reproductive synchrony

Latitudinal variation in monthly-scale reproductive synchrony among Acropora coral assemblages in the Indo-Pacific

Early research into coral reproductive biology suggested that spawning synchrony was driven by variations in the amplitude of environmental variables that are correlated with latitude, with synchrony predicted to break down at lower latitudes. More recent research has revealed that synchronous spawning, both within and among species, is a feature of all speciose coral assemblages, including equatorial reefs. Nonetheless, considerable variation in reproductive synchrony exists among locations and the hypothesis that the extent of spawning synchrony is correlated with latitude has not been formally tested on a large scale. Here, we use data from 90 sites throughout the Indo-Pacific and a quantitative index of reproductive synchrony applied at a monthly scale to demonstrate that, despite considerable spatial and temporal variation, there is no correlation between latitude and reproductive synchrony. Considering the critical role that successful reproduction plays in the persistence and recovery of coral reefs, research is urgently needed to understand the drivers underpinning variation in reproductive synchrony

MinION-in-ARMS: Nanopore Sequencing to Expedite Barcoding of Specimen-Rich Macrofaunal Samples From Autonomous Reef Monitoring Structures

Autonomous Reef Monitoring Structure (ARMS) are standardized devices for sampling biodiversity in complex marine benthic habitats such as coral reefs. When coupled with DNA sequencing, these devices greatly expand our ability to document marine biodiversity. Unfortunately, the existing workflow for processing macrofaunal samples (\u3e2-mm) in the ARMS pipeline—which involves Sanger sequencing—is expensive, laborious, and thus prohibitive for ARMS researchers. Here, we propose a faster, more cost-effective alternative by demonstrating a successful application of the MinION-based barcoding approach on the \u3e2 mm-size fraction of ARMS samples. All data were available within 3.5–4 h, and sequencing costs relatively low at approximately US$3 per MinION barcode. We sequenced the 313-bp fragment of the cytochrome c oxidase subunit I (COI) for 725 samples on both MinION and Illumina platforms, and retrieved 507–584 overlapping barcodes. MinION barcodes were highly accurate (∼99.9%) when compared with Illumina reference barcodes. Molecular operational taxonomic units inferred between MinION and Illumina barcodes were consistently stable, and match ratios demonstrated highly congruent clustering patterns (≥0.96). Our method would make ARMS more accessible to researchers, and greatly expedite the processing of macrofaunal samples; it can also be easily applied to other small-to-moderate DNA barcoding projects (\u3c10,000 specimens) for rapid species identification and discovery

Characterization of fungal biodiversity and communities associated with reef macroalga Sargassum ilicifolium reveals fungal community differentiation according to geographic locality and algal structure

Marine environments abound with opportunities to discover new species of fungi even in relatively well-studied ecosystems such as coral reefs. Here, we investigated the fungal communities associated with the canopy forming macroalga Sargassum ilicifolium(Turner) C. Argardh (1820) in Singapore. We collected eight S. ilicifolium thalli from each of eight island locations and separated them into three structures—leaves, holdfast and vesicles. Amplicon sequencing of the fungal internal transcribed spacer 1 (ITS1) and subsequent analyses revealed weak but significant differences in fungal community composition from different structures. Fungal communities were also significantly different among sampling localities, even over relatively small spatial scales (≤ 12 km). Unsurprisingly, all structures from all localities were dominated by unclassified fungi. Our findings demonstrate the potential of marine environments to act as reservoirs of undocumented biodiversity that harbour many novel fungal taxa. These unclassified fungi highlight the need to look beyond terrestrial ecosystems in well-studied regions of the world, and to fully characterize fungal biodiversity in hotspots such as Southeast Asia for better understanding the roles they play in promoting and maintaining life on our planet