Coral Reef Sediments Research Articles

Spatial variability of sedimentary assemblages reflects variations in bioerosion pressure of adjacent coral reefs.

The composition of coral-reef sediments is highly variable across space and time, and differences in the life histories of the dominant calcifying organisms on reefs contribute to the heterogeneity of reef sediments. Previous studies have suggested that variations in coral-reef bioerosion can influence spatial and temporal variations of sedimentary assemblages: elevated erosion rates of dead coral skeletons can trigger a pulse of coral-derived sediments and cause a shift in the dominance of sedimentary grains from coralline algae, such as Halimeda, to coral. We assessed the variability of the sedimentary composition and bioerosion rates of reefs at different spatial scales to determine the association between these two variables. We surveyed the benthic assemblages on reefs exhibiting different ecological states and collected samples of the associated sediments. We calculated the carbonate budget for each site and compared their variability at different hierarchical levels to the variability of their respective sedimentary assemblages. At the scale of sites (1-10 km), Halimeda cover was a significant predictor of the relative abundance of Halimeda grains. Both the relative abundance of coral grains and reef bioerosion rates varied significantly at the scale of locality (tens to hundreds of km), with high abundances of coral grains in the sediments coinciding with high rates of bioerosion. The main drivers of bioerosion at our localities were parrotfish assemblages dominated by large size classes of excavating species such as Sparisoma viride. Reef sediments may reflect the gross degree of bioerosion pressure that reefs experience, and historical changes in bioerosion rates could potentially be assessed by examining the sediments across temporal scales.

Assessment of heavy metal contamination and trophic status of coral reef sediments of the Lakshadweep Archipelago, Arabian Sea

This study investigated the distribution, contamination status, and ecological implications of heavy metals in the Lakshadweep Archipelago corals and coral reef sediments and the role of labile organic matter on metal accumulation in sediments. Heavy metal concentrations were relatively higher in the inter-tidal sediments than in the lagoon and the corals. The geochemical indices generally indicated the low anthropogenic contribution of heavy metals in sediments, and according to the sediment quality guidelines, there are no adverse effects on the biota. Sedimentary biochemical constituents are dominated by carbohydrates (CHO) followed by Lipids (LPD) and Proteins (PRT), and the low values of PRT: CHO and LPD: CHO ratios indicated aged, refractory organic matter with low nutritional quality. A portion of CHO may be derived from terrestrial sources, and statistical analyses revealed that CHO and LPD are the potential carriers of toxic metals such as Cd, Co and As into the coral reef environment. The biota-sediment accumulation factor (BSAF) showed Cd as a macro concentrator and Zn, Ni, V and As as micro-macro concentrators in Lakshadweep corals.

Development and validation of an experimental life support system to study coral reef microbial communities

In the present study, we developed and validated an experimental life support system (ELSS) designed to investigate coral reef associated bacterial communities. The microcosms in the ELSS consisted of coral reef sediment, synthetic seawater, and specimens of five benthic reef species. These included two hard corals Montipora digitata and Montipora capricornis, a soft coral Sarcophyton glaucum, a zoanthid Zoanthus sp., and a sponge Chondrilla sp.. Physicochemical parameters and bacterial communities in the ELSS were similar to those observed at shallow coral reef sites. Sediment bacterial evenness and higher taxonomic composition were more similar to natural-type communities at days 29 and 34 than at day 8 after transfer to the microcosms, suggesting microbial stabilization after an initial recovery period. Biotopes were compositionally distinct but shared a number of ASVs. At day 34, sediment specific ASVs were found in hosts and visa versa. Transplantation significantly altered the bacterial community composition of M. digitata and Chondrilla sp., suggesting microbial adaptation to altered environmental conditions. Altogether, our results support the suitability of the ELSS developed in this study as a model system to investigate coral reef associated bacterial communities using multi-factorial experiments.

Biodiversity of Nematodes from Coral Reef Sediments in the South China Sea Based on eDNA Metabarcoding

Coral reef ecosystems in the South China Sea are one of the globally important marine biodiversity hotspots. However, there are few studies on nematode biodiversity in coral reef sediments. Here, we assessed nematode biodiversity in coral reef sediments in the South China Sea using eDNA metabarcoding. Eight sampling stations were set up in the region north of the South China Sea Basin (Xisha and Zhongsha Islands) and south of it (Nansha Islands), respectively. We also compared and analysed the nematode biodiversity and community structure in different regions, as well as the effects of environmental factors on the community structure. The results showed that a total of 503 operational taxonomic units (OTUs) were detected in 16 sediment samples. The nematodes identified belong to two classes, 10 orders, 37 families, 51 genera and 61 species, and all of them were Enoplea and Chromadorea, except for the unidentified taxa, which accounted for 97.26% of the total abundance. The analyses showed that the northern region had higher nematode abundance and diversity relative to the southern region. However, there was no significant difference in the nematode community structure between the two regions, which was less affected by geographic location. Similarly, environmental factors (total nitrogen, total phosphorus, copper, zinc, cadmium, lead and arsenic) have an effect on the abundance of specific nematode groups but not on the overall community structure. In summary, this study initially reveals the composition and diversity of nematode communities in coral reef sediments in the South China Sea and provides an important reference for further in-depth study of the South China Sea ecosystem.

Impact of Hurricane Irma on coral reef sediment redistribution at Looe Key Reef, Florida, USA

Abstract. Understanding event-driven sediment transport in coral reef environments is essential to assessing impacts on reef species, habitats, restoration, and mitigation, yet a global knowledge gap remains due to limited quantitative studies. Hurricane Irma made landfall in the Lower Florida Keys with sustained 209 km h−1 winds and waves greater than 8 m on 10 September 2017, directly impacting the Florida Reef Tract (FRT) and providing an opportunity to perform a unique comprehensive, quantitative assessment of its impact on coral reef structure and sediment redistribution. We used lidar and multibeam derived digital elevation models (DEMs) collected before and after the passing of Hurricane Irma over a 15.98 km2 area along the lower FRT including Looe Key Reef to quantify changes in seafloor elevation, volume, and structure due to storm impacts. Elevation change was calculated at over 4 million point locations across 10 habitat types within this study area for two time periods using data collected (1) approximately 1 year before the passing of Irma and 3 to 6 months following the storm's impact as well as (2) 3 to 6 months after and up to 16.5 months after the storm. Elevation change data were then used to generate triangulated irregular network (TIN) models in ArcMap to calculate changes in seafloor volume during each time period. Our results indicate that Hurricane Irma was primarily a depositional event that increased mean seafloor elevation and volume at this study site by 0.34 m and up to 5.4 Mm3, respectively. Sediment was transported primarily west-southwest (WSW) and downslope, modifying geomorphic seafloor features including the migration of sand waves and rubble fields, formation of scour marks in shallow seagrass habitats, and burial of seagrass and coral-dominated habitats. Approximately 16.5 months after Hurricane Irma (during a 13-month period between 2017 and 2019), net erosion was observed across all habitats with mean elevation change of −0.15 m and net volume change up to −2.46 Mm3. Rates of elevation change during this post-storm period were 1 to 2 orders of magnitude greater than decadal and multi-decadal rates of change in the same location, and changes showed erosion of approximately 50 % of sediment deposited during the storm event as seafloor sediment distribution began to re-equilibrate to non-storm sea-state conditions. Our results suggest that higher-resolution elevation change data collected over seasonal and annual time periods could enhance characterization and understanding of short-term and long-term rates and processes of seafloor change.

Influence of global warming and industrialization on coral reefs: A 600-year record of elemental changes in the Eastern Red Sea

The Red Sea has been recognized as a coral reef refugia, but it is vulnerable to warming and pollution. Here we investigated the spatial and temporal trends of 15 element concentrations in 9 coral reef sediment cores (aged from the 1460s to the 1980s AD) to study the influence of global warming and industrialization on the Eastern Red Sea coral reefs. We found Na, Ca, Cr, Fe, Co, Ni, and Sr concentrations were higher in the northern Red Sea (i.e., Yanbu), whereas Mg, P, S, Mn, and Cd concentrations were higher in the southern Red Sea (i.e., Thuwal & Al Lith) reef sediments. In the central (i.e., Thuwal) to southern (i.e., Al Lith) Red Sea, the study revealed diverse temporal trends in element concentrations. However, both reef sedimentation rates (−36.4 % and −80.5 %, respectively) and elemental accumulation rates (−49.4 % for Cd to −12.2 % for Zn in Thuwal, and −86.2 % for Co to −61.4 % for Cu in Al Lith) exhibited a declining pattern over time, possibly attributed to warming-induced thermal bleaching. In the central to northern Red Sea (i.e., Yanbu), the severity of thermal bleaching is low, while the reef sedimentation rates (187 %), element concentrations (6.7 % for S to 764 % for Co; except Na, Mg, Ca, Sr, and Cd), and all elemental accumulation rates (190 % for Mg to 2697 % for Co) exponentially increased from the 1970s, probably due the rapid industrialization in Yanbu. Our study also observed increased trace metal concentrations (e.g., Cu, Zn, and Ni) in the Thuwal and Al Lith coral reefs with severe bleaching histories, consistent with previous reports that trace metals might result in decreased resistance of corals to thermal stress under warming scenarios. Our study points to the urgent need to reduce the local discharge of trace metal pollutants to protect this biodiversity hotspot.

Characteristic of Microplastic on Coral Reef Sediment and Sea Urchin (Diadema sp.) in Tidung Island, Jakarta Bay, Indonesia

Microplastics are recognized as common contaminants of coral ecosystem in Tidung Island, affecting both sediment and sea urchins residing in this environment. Therefore, this study aimed to determine the characteristics of microplastics found in sediment, the mouth, and the digestive system of sea urchins (Diadema sp.), assessing the relationship between coral cover percentage and microplastic type and size, and the transfer of microplastics from sediment to sea urchins. Sampling was conducted twice, namely in October 2021 and October 2022. Microplastics in sediments were extracted using ZnCl2. The destruction process of sea urchins used 30% H2O2 and FeSO4.7H2O, while the microplastics were identified with Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR). The results showed that the microplastics found in the sediments and sea urchins were similar in terms of shape, color, size, and plastic polymers. The forms of microplastics found in this study were fibre, fragment, and foam with fibre predominance, based on the results obtained. The size of microplastics found in sediments and sea urchins was dominated by sizes >1000 µm. Fibres were found in hard coral (HC) and dead coral (DC) conditions while fragments and foams were present in turf algae (TA), sponge (SP), and soft coral (SC) conditions. The microplastics found in sea urchins originate in part from sediments because they have similar characteristics. Sea urchins ingested microplastics from sediment, particularly those grown by algae as a food source. The increase in the number of microplastics found in sediment could potentially result in higher abundance in the biota.

Meteoric diagenesis influenced by East Asian Summer Monsoon: A case study from the Pleistocene carbonate succession, Xisha Islands, South China Sea

The East Asian Monsoon (EAM) has significantly influenced various depositional and diagenetic processes in carbonate sediments in much of East and South Asia during the Cenozoic. The relationship between the EAM and marine carbonate platforms, which are widely developed in this region, however, remains largely unknown. Based on petrographic, mineralogical, and geochemical analyses of the carbonate succession (∼237 m thick) on the Xisha Islands, South China Sea, meteoric diagenesis and its relationship with the East Asian Summer Monsoon (EASM) during the Pleistocene were studied. Various petrographic features, stable isotopes (δ13C, δ18O), and trace elements (Sr, Fe, Mn, Rare Earth Elements and Y) indicate that this succession was extensively altered by meteoric diagenesis, producing four exposed surfaces embedded in the shallow coral reef sediments. Given this data, we suggest that the meteoric diagenesis that affected this succession occurred during periods of low sea-level, and was potentially related to the relative intensity of the EASM. During strong EASM periods, particularly during the Mid-Pleistocene Transition ∼0.9 Ma, meteoric diagenesis was intense, as suggested by the complete alteration of unstable minerals, extreme dissolution, the presence of reddish-brown iron oxides, and a large negative excursion of δ13C (−6.2‰). The influence of the EASM on meteoric diagenesis of Pleistocene carbonate platforms can be identified throughout the South China Sea. This study sheds light on the relationship between meteoric diagenesis and paleo-climate conditions in carbonate platform regions that are influenced by monsoons.

MICROPLASTIC CONTAMINATION AROUND CORAL REEFS DIVING SPOT IN TIDUNG ISLAND, KEPULAUAN SERIBU, JAKARTA

Research on microplastic in coral ecosystems in Indonesia is infrequent. This research will observe Microplastic on the coral reef dive tourism in Tidung Island, Kepulauan Seribu, Jakarta Bay. The number of microplastics varied between 60 to 340 particles/kg dry weight. Fiber was the most microplastic type found in all stations; it ranged from 67% to 100%. Size of microplastic found in this study ranged <100 to >1100 𝞵𝞵m. We found four types of polymers (polybutylene, polyethylene, polypropylene, and polyester) with the highest percentage of polyethylene at 61.76%. We assume that microplastics observed in coral reef sediment on Tidung island originated mainly from anthropogenic sources. Waste management must be tightened and enhanced in the Kepulauan Seribu and neighboring areas, such as the western area of Java Island and its adjacent areas.

Microplastics in coral reef sediments underestimated? They may hide in biominerals

Microplastics (MPs) may be underestimated in coral reef sediments. Current pretreatments for determining MPs in the sediments are mainly density separation and organic matter removal, ignoring MPs that may be embedded or encrusted in biominerals. This could lead to discrepancies in assessing the potential risk of MPs contamination. To confirm whether MPs in coral reef sediments are underestimated, a two-step sequential digestion, including organic matter removal (H2O2 digestion) and biomineral removal (HCl digestion), was performed on sediments from the coral reef area of the South Penghu Marine National Park (SPMNP, Taiwan). The MPs abundance and characteristics of the two steps were analyzed separately. The results showed that the average MPs abundance after HCl digestion (78 ± 42 MPs/kg) was significantly higher than that of H2O2 digestion (38 ± 25 MPs/kg). The MPs diversity integrated index (MPDII) in coral reef sediments was low (MPDII = 0.35), and MPs were mainly small (<2.0 mm, 91.3 %), fibrous (93.5 %), colored (60.9 %), and rayon polymers (73.9 %). Correlation analysis showed that MPs in biominerals mainly dominated MPs in the sediments. These results confirm that current assessments of MPs contamination levels in biomineral-rich sediments may be underestimated and uncertain. In addition, the mineralization of organisms in SPMNP reef regions was affected by MPs from moderate to high levels, depending on the proportion of MPs in biominerals.

Microbial fuel cells in coral reef sediments as indicator tools for organic carbon eutrophication

Eutrophication with organic carbon (OC) can be harmful for corals and their reefs due to its stimulating effects on associated and sedimentary microbes, leading to oxygen deficits. Mitigation measures require real-time monitoring of wastewater pulses close to coral reefs, where biogenic carbonate sands act as biocatalytic filters for OC. Microbial fuel cells (MFCs) where the anode is deployed in sediments and the cathode is in contact with the overlying water can directly generate electricity from the microbial degradation of OC in sediments, but their application in coral reefs has not yet been tested. During a laboratory experiment, we thus investigated if MFCs, vertically deployed in coral reef sands, can be used as indicator tools for eutrophication with artificial wastewater (AW, prepared from organic compounds and chemicals) at OC concentrations of 20, 40, or 52 mg C L-1 higher than controls. AW pulses were repeated three times at every concentration, with five weeks between the first and second pulse, and six months between the second and third pulse. Results revealed significant increases in current densities in all AW treatments (means up to 11, 36, and 39 mA m−2, respectively), while controls remained stable and low (-1 to 3 mA m−2). Current densities and OC concentrations correlated significantly (rrm = 0.64), and the slope of the correlation increased with each consecutive AW pulse. This highlights the functionality of the MFC as a qualitative indicator tool for OC pulses even months after deployment. The response time of the MFCs was fast (<1 day) compared to other indicators for water quality (e.g., coral colony- or community measures that take weeks to years to respond), and they successfully detected OC concentrations expected for wastewater effluents. Measurements can be automated for continuous monitoring, and no laboratory facilities are required (as for OC analysis), making MFC sensors a suitable tool for remote locations. Overall, these findings emphasize the high potential of these low-cost (<20 € per MFC) MFCs as indicator tools for OC pulses in coral reef environments.

Threshold of motion of coral reef sediment under currents in flume experiments

AbstractThis study experimentally documented the thresholds of critical motion for tropical shallow marine carbonate sediments by conducting a total of 225 laboratory experiments that included the analysis of nine median sediment diameters and five water depths. A shape factor, Sf, which quantifies the shape of a single particle, was evaluated during the investigation. Both the critical Shields parameter and the incipient mean velocity were used to represent the critical thresholds of motion. The thresholds of motion for coral reef sediment were then compared with the results from quartz sand. The experimental results show that the critical threshold of motion is smaller for coral reef sediment than for quartz sand of the same median sieve diameter due to differences in particle shape in spite of the coral reef sediment being of higher density. For diameters higher than 1.425 mm, the critical Shields parameters and incipient mean velocities tend to have similar values to quartz sand. The differences between the two increased significantly for median sieve diameters &lt;1.075 mm. Based on the experimental data, Shields curve bands and equations for the incipient mean velocity for sediments of differing shape factors were obtained for tropical shallow marine carbonate sediments as well as marine carbonate grains.

Reconstructing Millennial-Scale Variability in Reef Shark Communities Across The Isthmus of Panama

Shark populations have declined over the last half century, but the patterns of change vary across space. Long-term records of shark abundance are limited, making it challenging to determine how local environmental conditions influence pre-exploitation shark baselines and their susceptibility to human impacts. We use shark scales (dermal denticles) preserved in coral reef sediments to reconstruct shark communities during the mid-Holocene and today across the Isthmus of Panama. We interpret these data alongside records of primary productivity, habitat, and fish abundance to explore energy flow to higher trophic levels on each coast. The Tropical Eastern Pacific is a productive system driven by seasonal upwelling with a long history of shark exploitation. The Caribbean coast, on the other hand, is oligotrophic and environmentally stable, with lower rates of harvesting. We find that denticle accumulation rates, a proxy for shark abundance, are an order of magnitude greater in Pacific Panama (Gulf of Panama) than in Caribbean Panama (Bocas del Toro). Primary productivity and fish abundance are also higher in Pacific Panama, helping to support these large predator populations. Denticle accumulation rates declined by 71% since the mid-Holocene in Caribbean Panama, including a selective loss of pelagic sharks. In contrast, modern denticle accumulation rates in Pacific Panama are comparable to their range of variability during the mid-Holocene, and the composition of denticle assemblages remained similar through time—suggesting that sharks in the Gulf of Panama have persisted despite intensive fishing. We postulate that the region’s high productivity might underlie its high shark abundance and apparent resilience by increasing available resources for predators. Our findings shed light on the role of energy in shaping natural variability in shark baselines and recovery potential. They also highlight the importance of incorporating oceanographic context into shark management.

Change and stasis of distinct sediment microbiomes across Port Everglades Inlet (PEI) and the adjacent coral reefs.

Deep water ports are human built coastal structures that by definition welcome ship traffic and disturbance. Evidence is accumulating that enhanced port activities such as dredging or deepening have negatively affected nearby natural habitats. Port Everglades Inlet (PEI) is a large active South Florida cargo port for over two million people and lies adjacent to coral reefs, dwindling mangroves, and recreational beaches. In this study, the microbial communities of PEI and adjacent reef sediments were characterized to serve as indicators for change due to dredging and assess anthropogenic influence on these sensitive ecosystems by sequencing the V4 region of 16S rRNA ahead of a large-scale port deepening event. For the first time, this study established baseline bacterial community characterizations and their patterns of diversity prior to and after a maintenance dredging event. PEI samples were collected for two consecutive years 2020 (Phase I, before maintenance dredging) and 2021 (Phase II, after maintenance dredging) from PEI sediments and adjacent coral reef sediments. In spite of their proximity and tidal connections through the PEI, reef and PEI sediment microbial communities were distinct. Changes in microbial diversity within the intracoastal waterway (ICW), a route for community exchange or transfers, were the greatest after maintenance dredging occurred. Microbial diversity in reef sediments also changed after dredging, indicating potential influence from resuspended sediments due to an associated increase in trace metals and decrease in cyanobacterial diversity. Sediments were identified as a possible source of human and coral pathogens, although dredging did not affect the relative abundances of these indicator microorganisms. This study highlighted the utility and relative ease of applying current molecular ecology methods to address macroscale questions with environmental management ramifications.

Microbial Community Diversity of Coral Reef Sediments on Liuqiu Island, Southwestern Taiwan

Microbes in coral reef sediments are thought to play an important role in organic matter remineralization and nutrient recycling. Microbial communities also reflect the environmental conditions, such as nutrient status, of an ecosystem. This study investigates the relationship between microbial community diversity in the reef sediments and environmental conditions at Liuqiu Island. We sampled sediments seasonally from four sites around the island, Beauty Cave, Geban Bay, Houshi Fringing Reef, and Lobster Cave, from 2015–2020. The V5–V6 hypervariable region of 16S rRNA was amplified and sequenced using the Illumina MiSeq platform to identify the microbial communities. The results showed that the high abundance of Pseudomonadota, Planctomycetota, and Bacteroidota might reflect the eutrophic environments of the sediments on Liuqiu Island. Second, the identification of putative pathogens and human-related genera suggests that human activities have affected the marine environment of Liuqiu Island. Third, the insignificant spatial differences and the significant temporal differences in the microbial communities of Liuqiu Island indicate that annual or periodical events, such as the Kuroshio Branch Current and South China Sea Surface Current, could shape the microbial communities of Liuqiu Island. Furthermore, the abundance of human-related genera—Cutibacterium, Herbaspirillum, Corynebacterium 1, Escherichia-Shigella, and Kocuria—increased dramatically in the Lobster Cave site in September 2015 and may have been induced by a strong climate event, such as a typhoon or heavy rainfall. Our results revealed that the microbial communities of Liuqiu Island are dynamic and sensitive to adjacent environmental conditions. The sedimented microbial communities could monitor the bacteria and pathogens related to human activities and even reveal the putative events that could affect the ecological environments.

COI metabarcoding of large benthic Foraminifera: Method validation for application in ecological studies.

Monitoring community composition of Foraminifera (single-celled marine protists) provides valuable insights into environmental conditions in marine ecosystems. Despite the efficiency of environmental DNA (eDNA) and bulk-sample DNA (bulk-DNA) metabarcoding to assess the presence of multiple taxa, this has not been straightforward for Foraminifera partially due to the high genetic variability in widely used ribosomal markers. Here, we test the correctness in retrieving foraminiferal communities by metabarcoding of mock communities, bulk-DNA from coral reef sediment samples, and eDNA from their associated ethanol preservative using the recently sequenced cytochrome c oxidase subunit 1 (COI) marker. To assess the detection success, we compared our results with large benthic foraminiferal communities previously reported from the same sampling sites. Results from our mock communities demonstrate that all species were detected in two mock communities and all but one in the remaining four. Technical replicates were highly similar in number of reads for each assigned ASV in both the mock communities and bulk-DNA samples. Bulk-DNA showed a significantly higher species richness than their associated eDNA samples, and also detected additional species to what was already reported at the specific sites. Our study confirms that metabarcoding using the foraminiferal COI marker adequately retrieves the diversity and community composition of both the mock communities and the bulk-DNA samples. With its decreased variability compared with the commonly used nuclear 18 S rRNA, the COI marker renders bulk-DNA metabarcoding a powerful tool to assess foraminiferal community composition under the condition that the reference database is adequate to the target taxa.

Heavy metals in coral reef sediments of Kavaratti Island, India: An integrated quality assessment using GIS and pollution indicators

The present study aims to document the contamination levels and ecological risks of heavy metals in the sediments of Kavaratti lagoon, India. A total of 15 sediment samples were collected for the analysis of Al, Pb, Cd, Cu, Cr, Mn, Ni and Zn. The decreasing trend of heavy metals was observed in the lagoon sediment as Pb > Zn > Al > Mn > Ni > Cr > Cd > Cu. The Geo-accumulation index (Igeo) results indicate that Cu, Cr, Mn, Ni and Zn were uncontaminated, while Cd was strong to extremely contaminated and Al and Pb were moderately contaminated. The enrichment factors (EF) of Cd and Pb range from moderate to extremely high (EF > 1) indicating that they have anthropogenic origin on Kavaratti Island. The Contamination factor (Cf) indicated that Cd, Pb and Al belong to a high risk of contamination (Cf > 6). The pollution load index (PLI) value near one suggested that a moderate level of pollution occurs in the study area. The modified degree of contamination (mCd) shows that Al, Cd and Pb have an ultra- higher degree of contamination (mCd ≤ 32). The potential ecological risk (RI) index confirmed that Pb and Cd have considerable to the serious thread of ecological risk (RI > 600). Additionally, multivariate statistical analysis and pollution indexes showed that the Kavaratti lagoon is moderate to considerably polluted by heavy metals. Diesel-based power generation, activities related to shipping, untreated sewage, fishing and tourism activities are the main anthropogenic sources of heavy metal pollution on Kavaratti Island.

Screening, Characterization, and Isolation of Pigments from Bacteria in Mesophotic Depths of the Benham Bank Seamount, Philippine Rise Region

The exploration for pigment-producing bacteria and structurally novel pigment continues to increase, and the marine environment has recently become an attractive research site for these investigations because of its rich yet untapped biodiversity. In this study, 16S rRNA gene sequencing and HPLC (high-performance liquid chromatography) profiling of the microbial pigments produced by marine heterotrophic bacteria were described. Seven phenotypically distinct isolates of marine pigmented heterotrophic bacteria (MPHB) were isolated from near-bottom waters and coral reef sediments at mesophotic depths of the Benham Bank Seamount – namely, isolates BR14, BR61, BR63, BR100, BR101, BR144, and BR146. Four promising isolates were subjected to 16S rRNA gene sequencing and revealed that strains BR61 and BR100 were related to members of the genus Cytobacillus, whereas isolates BR144 and BR146 clustered with Meridianimaribacter flavus and Pseudoalteromonas rubra, respectively. Growth of the seven isolates on three media – natural sea water (NSW) Reasoner’s 2A (R2A), marine agar (MA), and tryptic soy agar – revealed variable pigment production and growth yield. MA appeared to be a superior substrate, resulting in darker pigmentation and higher biomass yield. Through a liquid-liquid partitioning approach, isolates BR14 and BR100 produced pigments that were acetone-soluble, whereas isolates BR101, BR144, and BR146 are hexane soluble. Moreover, the BR146 red pigment was proposed to be a mixture of putative prodiginine analogs. The putative prodiginines produced by isolate BR146 can stain fabrics, supporting a proof-of-concept that marine bacteria can be utilized as fabric colorants. The data presented here provided new insights into the utilization of local Philippine marine microbial resources for natural marine pigments with industrial applications.

Records of sea-level highstand over the Meghalayan age/late Holocene from uranium-series ages of beachrock in Weizhou Island, northern South China Sea

Beachrock is considered a good archive for past sea-levels because of its unique formation position (intertidal zone). To evaluate sea-level history in the northern South China Sea, three well-preserved beachrock outcrops (Beigang, Gongshanbei, and Hengling) at Weizhou Island, northern South China Sea were selected to examine their relative elevation, sedimentological, mineralogical, and geochemical characteristics. Acropora branches with well-preserved surface micro-structures were selected from the beachrocks and used to determine the ages of these beachrocks via U-series dating. The results show that the beachrocks are composed of coral reef sediments, terrigenous clastics, volcanic clastics, and various calcite cements. These sediments accumulated in the intertidal zone of Weizhou Island were then cemented in a meteoric water environment. The U-series ages of beachrocks from Beigang, Gongshanbei, and Hengling are 1712–768 ca. BP, 1766–1070 ca. BP, and 1493–604 ca. BP (before 1950 AD) respectively. Their elevations are 0.91–1.16 m, 0.95–1.24 m, and 0.82–1.17 m higher than the modern homologous sedimentary zones, respectively. Therefore, we concluded that the sea-level in the Meghalayan age (1766–604 ca. BP) was 0.82–1.24 m higher than the present, and that the sea-level over this period showed a declining trend.

The study of sediments on coral reefs: A hydrodynamic perspective

There is a rich literature on coral reef sediments. However, this knowledge is spread among research fields, and the extent to which major sediment reservoirs and reservoir connecting processes have been quantified is unclear. We examined the literature to quantify where and how sediments have been measured on coral reefs and, thereby, identified critical knowledge gaps. In most studies, sediments in one reservoir or one sedimentary process were quantified. The measurement of water column sediments (55% of reservoir measurements) and sediment trapping rates (42% of process measurements) were over-represented. In contrast, sediments on reef substrata, and the transition of sediments from the water column to the benthos, were rarely quantified. Furthermore, only ~20% of sediment measurements were accompanied by the quantification of hydrodynamic drivers. Multidisciplinary collaborative approaches offer great promise for advancing our understanding of the connections between sediment reservoirs, and the sedimentary and hydrodynamic processes that mediate these connections.