Coral Reef Ecosystems Research Articles

Assessment of Bleaching Stress Vulnerability of Lakshadweep Islands using Google Earth Engine (GEE)

Coral reefs, among the Earth’s most diverse and valuable ecosystems, face unprecedented challenges due to climate change. Coral bleaching is a phenomenon wherein corals lose their symbiotic zooxanthellae owing to various stressors, leading to a whitening effect of the coral tissues. In recent decades, climate change has intensified coral bleaching events. Multiple stressors, including elevated Sea Surface Temperature (SST), extreme irradiance levels, and various biotic and abiotic factors trigger bleaching events. Coral bleaching is primarily driven by thermal stress caused by elevated SSTs. Climate change has worsened bleaching’s frequency and intensity. Global bleaching events are often linked to planetary ocean-atmospheric circulation processes such as El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). This study focused on assessing the vulnerability of coral reefs in the Lakshadweep region of India from 2016 to 2023 using National Oceanic and Atmospheric Administration’s Climate Data Record Optimum Interpolation Sea Surface Temperature (NOAA CDR OISST) daily data. GOOGLE EARTH ENGINE (GEE) is a cloud computing platform which is used to collect and generate the base data for this study. The vulnerability assessment utilized two bleaching indices: SST anomaly and Degree Heating Week (DHW). Analysis of DHW data reveals that 2020 experienced the highest SST anomaly residence time due to IOD event of 2019, as compared to 2016 and 2023 which are known El Niño years. All Lakshadweep islands exhibited vulnerability, although in varying degrees across different areas. Based on the magnitude, intensity, and frequency of bleaching stress, the islands are categorized into different categories of vulnerability. This study identifies Baliyapaniyam, Cheriyam-Kalpeni and Suhelipar reefs as very highly vulnerable reefs in Lakshadweep. This study highlights the urgent need for monitoring and management measures to mitigate the impacts of climate change on coral reef ecosystems using spatial vulnerability patterns.

Research progress on coral reef growth factors and their ecosystem restoration

Healthy coral reef ecosystems have various functions such as reef-building, reef protection, reef stabilization, wave protection, shore protection, and the prevention of land erosion. Additionally, coral reef ecosystems are characterized by high biodiversity, often dubbed the “rainforest” of the ocean, as one of the most crucial ecosystems on Earth. In recent decades, global coral reefs have been significantly affected or damaged to varying degrees by climate change and human activities, posing threats to marine ecology and reef safety. This paper outlines the factors influencing coral reef growth, including global warming, ocean acidification, eutrophication, suspended solids, and tourism activities. It also discusses the status of coral reefs and viable restoration methods. Finally, this paper proposes an updated strategy for coral reef conservation, offering fresh insights into coral reef restoration efforts.

Coral Sr/Ca-SST calibration: SST records from Kenyan corals

To better understand the seasonal variability in SST in Kenyan coral reef ecosystems, Sr/Ca ratios have been measured in Kenyan coral skeletons as proxies of SST, and a new Sr/Ca = f(SST) calibration was established: Sr/Ca = − 0.053 (± 0.006) *SST + 10.43 (± 0.16). The slope was within the margins of − 0.04 and − 0.08 mmolmol−1 °C of previously published Sr/Ca-SST calibration equations. A reliability test revealed that the present calibration equation reproduces a previously published calibration equation developed for Kenyan corals. This calibration was applied to corals collected in reef ecosystems under different natural and anthropogenic influences: Tana Delta Ziwayu Island, Watamu National Marine Park, and Shimon Mupunguti Marine Reserve. Using the developed Sr/Ca-thermometry, the reconstructed Sr/Ca-SST revealed that reefs from the southern basin of the Kenyan Indian Ocean are exposed to warmer SSTs than reefs in the northern Basin are. Additionally, the results revealed that the seasonal variability on SST increased moving toward the southern basin of the Kenyan Indian Ocean. We use the local instrument SST as an SST reference, which is aligned against the Sr/Ca seasonal signals recorded in SMR3-18 (the nearest coral site), and the intensity of the third global coral bleaching (April and May 2016) is affirmed.

BiP Proteins from Symbiodiniaceae: A “Shocking” Story

More than four decades ago, the discovery of a companion protein of immunoglobulins in myeloma cells and soon after, of their ability to associate with heavy chains, made the term immunoglobulin binding protein (BiP) emerge, prompting a tremendous amount of effort to understand their versatile cellular functions. BiPs belong to the heat shock protein (Hsp) 70 family and are crucial for protein folding and cellular stress responses. While extensively studied in model organisms such as Chlamydomonas, their roles in dinoflagellates, especially in photosynthetic Symbiodiniaceae, remain largely underexplored. Given the importance of Symbiodiniaceae-cnidarian symbiosis, critical for the sustaining of coral reef ecosystems, understanding the contribution of Hsps to stress resilience is essential; however, most studies have focused on Hsps in general but none on BiPs. Moreover, despite the critical role of light in the physiology of these organisms, research on light effects on BiPs from Symbiodiniaceae has also been limited. This review synthesizes the current knowledge from the literature and sequence data, which reveals a high degree of BiP conservation at the gene, protein, and structural levels in Symbiodiniaceae and other dinoflagellates. Additionally, we show the existence of a potential link between circadian clocks and BiP regulation, which would add another level of regulatory complexity. The evolutionary relationship among dinoflagellates overall suggests conserved functions and regulatory mechanisms, albeit expecting confirmation by experimental validation. Finally, our analysis also highlights the significant knowledge gap and underscores the need for further studies focusing on gene and protein regulation, promoter architecture, and structural conservation of Symbiodiniaceae and dinoglagellate BiPs in general. These will deepen our understanding of the role of BiPs in the Symbiodiniaceae-cnidarian interactions and dinoflagellate physiology.

Modelling Marine Heatwaves Impact on Shallow and Upper Mesophotic Tropical Coral Reefs

Abstract Coral reefs ecosystems, often compared to rain forests for their high biodiversity, are threatened by ocean warming causing coral bleaching when the symbiotic relationship between dinoflagellates and corals breaks under high ocean temperatures. Thermal stress from marine heatwaves occur both at the surface and subsurface with subsurface marine heatwaves lasting longer with potentially higher cumulative intensities. However, global coral bleaching models generally ignore the differences in thermal stress between surface and sea-bed levels. Here, we define marine heatwaves at sea-bed level to model coral bleaching with daily resolution from May 6th 1993 to December 31st 2023, for 9944 tropical coral reefs between 0 and 50m depths. We show that deeper reefs experience on average higher thermal stress and bleaching compared to surface reefs. Using surface temperature data to model bleaching for deeper corals underestimates bleaching intensities by an average of 6 ± 9% compared to the subsurface calibrated model. Our study is a starting point for more accurate coral bleaching modelling, providing additional evidence to reshape our perception of deeper coral reefs as potential refugees from climate change. 

Degradation of coral reef ecosystems: Mathematical-dynamical modeling approach

Abstract The review delves into the frontier of degradation of coral reef ecosystems, a pressing urgent issue to be addressed in marine ecological environments, and provides a critical assessment of current advances and future perspective on the topic. This study highlights the recent developments in coral bleaching, coral-algal phase shifts, coral disease, and natural enemy bloom, all of which are thoroughly documented and expounded. Special attention focus on the studies employing mathematical-dynamical modeling approaches. This review study also offers some valuable insights, illuminating ideas, and clear perspective into some current, emerging, and promising research directions for future studies, particularly those based on mathematical-biological modeling approaches. These approaches are anticipated to offer a theoretical foundation and provide crucial decision-making reference for the protection, restoration, and management of coral reef ecosystems.

Multiple negative impacts of marine plastic pollution on tropical coastal ecosystem services, and human health and well-being

There is limited empirical evidence showing the impacts of marine plastic pollution on ecosystem services or on human health and well-being in Global South countries. We aimed to estimate these impacts in the tropical archipelago of Indonesia, one of the top emitters of marine plastics globally, through an iterative Delphi survey, with an expert panel (n = 42) consisting of equal numbers of Indonesian scientists, policymakers, and practitioners. After two rounds of the survey, the analysis of interquartile ranges indicated that the experts reached a consensus in their predictions. The experts agreed that, over the next 10 years, plastics would be mainly accumulated in the coastal area of Java, the most densely populated island, and mostly in mangrove ecosystems. While all ecosystem services were harmed by plastic pollution, the most vulnerable services were food provisioning, genetic materials, nursery habitat, and recreation supplied by the highly vulnerable coastal ecosystems of, in descending order, mangrove, coral reef, seagrass, and sandy beach. These impacts on ecosystem services influenced different dimensions of human health and well-being and were dependent on the ecosystem types, as indicated in several statistically significant positive correlations (Spearman's rank), including those between the decline of mangrove ecosystem services and reduced household income, and between the decrease of coral reef ecosystem services and both deteriorating mental health and reduced household income. Overall, this study provides the first indication of Indonesian coastal ecosystems and ecosystem services to be prioritized for mitigation and monitoring efforts. The focus on impacts on human health and well-being also incentivizes ongoing efforts by policymakers, industry and commerce, the third sector, and the public in the country to address the contribution to global marine plastic pollution.

Distinct bacterial and eukaryotic communities reflect the specificity of different coral reefs in the South China Sea

The microbial composition of surrounding waters is crucial for the health of coral reefs and holds significant value for understanding the complexity and environmental adaptability of coral reef ecosystems. This study reveals the spatial heterogeneity and diversity characteristics of bacterial and eukaryotic communities in different coral reef regions of the South China Sea. Chao and Shannon indices showed significant differences (p < 0.05) in diversity of bacterial and eukaryotic communities across different coral reefs. PCoA (principal coordinate analysis) indicates significant differences in community composition among regions, highlighting the crucial role of coral reef environmental heterogeneity on microbial community. NST (normalized stochasticity ratio) analysis indicates that community assembly in coral reef areas is more influenced by ecological stochastic processes. Major bacterial groups include Proteobacteria, Cyanobacteria, and Bacteroidota, while dominant eukaryotic groups include Dinophyceae, Apicomplexa, Bacillariophyta, Florideophyceae, Mamiellophyceae, Syndiniales, Prasino-Clade-VII, and Ascomycota, each showing significant abundance differences across coral reef regions (p < 0.05). High abundance of Rhodobacterales and Flavobacteriales are detected in all coral reef waters. Correlation analysis indicates that temperature, pH, and salinity are important factors affecting the bacterial and eukaryotic communities. This study reveals the spatial heterogeneity of microbial communities in coral reef regions of South China Sea and underscores the significant impact of marine environmental heterogeneity on community structure.

Mathematical insights into the influence of delay and external recruitment on coral-macroalgae system

As anthropogenic pressures on coral reef ecosystems continue to increase due to global warming and mass coral bleaching events, there is growing interest in developing conservation strategies to restore degraded coral reefs. One such approach is the transplantation of coral larvae onto degraded reefs. In this paper, we use a delayed coral-macroalgae model to explore the effects of external recruitment of coral. By analyzing the local and global stability of macroalgae-free equilibrium and coexistence equilibrium in the system, we find that sustained external recruitment of coral will favor coral competition with macroalgae. In addition, we choose delay as a bifurcation parameter and demonstrate that Hopf bifurcation may occur at a critical delay near the coexistence equilibrium. Interestingly, the delay may cause the globally asymptotically stable equilibrium in the ODE system to become unstable, resulting in the appearance of periodic solutions. Furthermore, we analyze population dynamics using optimal control theory and determine the effect of minimum external recruitment on the population dynamics. In the numerical simulation section, parameters of coral-macroalgae dynamics are estimated by using a 12-year (2005–2017) benthic cover dataset of coral reefs in the Gulf of Mannar, southeastern India. The theoretical results are validated and supported by numerical simulations.

Coral reef fish visual adaptations to a changing world

Abstract Coral reef ecosystems show fluctuations in their prevailing light environment in response to both regular (e.g. between seasons) and more prevalent stochastic events (e.g. human‐induced sediment runoff). In these shifting environments, phenotypic plasticity provides an essential mechanism for coral reef fishes to adjust their visual capability to meet changing sensory requirements. Here, we evaluate the growing area of research that highlights the many genetic and ecological mechanisms that affect the plastic responses of coral reef fish vision to environmental cues. With an increasing number of disturbances in the marine environment, it is critical to understand the extent and limits of visual plasticity under natural and disturbed conditions. With our current knowledge and drawing upon a large body of work in freshwater fishes, we speculate whether coral reef fishes can adapt to the changes to their visual environment and where the limitations could lie. Whilst coral reef fishes have shown visual adaptations under different light environments, the degree of plasticity is inconsistent between species. Thus, plasticity may not only be functionally significant in maintaining the performance of visually guided behaviours for single species but, more broadly, is likely key to sustaining ecosystem function. Read the free Plain Language Summary for this article on the Journal blog.

Coral reefs of Pakistan: a comprehensive review of anthropogenic threats, climate change, and conservation status

The coral reefs along Pakistan’s coastline are of ecological and economic significance. However, they are increasingly threatened by anthropogenic threats and climate change. These vulnerable ecosystems are declining due to various factors such as sedimentation, climate change, overfishing, destructive fishing practices, marine pollution, and tourism development. We found that 29%, 24%, 26%, 16% and 18% of the studies exceeding, marine pollution, overfishing/destructive fishing, coastal tourism, climate change and sedimentation, respectively; thus, indicating inadequate water quality status in part of Pakistan coastal water. These influences lead to several negative impacts, such as jeopardized coral health, decline in biodiversity, and the simplification of reef structures. In response to these threats, conservation efforts are imperative. This literature review provides an in-depth analysis of anthropogenic threats, climate change and the conservation of coral reefs in Pakistan. This review provides suggestions on how the country could better conserve its coral reef ecosystem. These include (1) initiatives such as establishing marine protected areas (MPAs), (2) encouraging sustainable fishing practices and reducing pollution, (3) developing the country as an ecotourism destination and implementing climate change adaptation measures, and (4) community engagement through awareness campaigns and fostering collaboration among, governmental organizations, non-governmental organizations (NGOs) and scientists. These comprehensive conservation policies address human-caused and other challenges, safeguarding their ecological, economic, and cultural relevance for future generations.

ANALYSING THE POTENTIAL OF CORAL REEF ECOSYSTEMS FOLLOWING THE COVID-19 PANDEMIC IN BONDALEM, BULELENG, BALI

Coastal and marine areas have considerable biological resource potential, because they are supported by three main ecosystems, namely mangrove ecosystems, seagrass beds and coral reefs. Coral reefs are one of the coastal ecosystems that contribute greatly to coastal areas. But behind the great potential, it is also very vulnerable to damage, both caused by nature and human activities on land and in sea waters. As an effort to maintain the existence of these ecosystems, ecosystem monitoring is needed to find out how much potential is still available in the coastal area. The purpose of this study was to determine and provide information related to the potential and condition of coral reefs in Bondalem Village. This research used descriptive quantitative method with purposive sampling technique. The data taken is primary data that includes observations of coral reefs based on the form of growth (lifeform). Coral reef data collection was carried out using the UPT (Underwater Photo Transect, Underwater Photo Transect) method. The results obtained, coral reefs at the observation station have a total of 18 lifeforms. The percentage of coral cover obtained at a depth of 3 meters has a coral cover ranging from 35.34%, while at a depth of 10 meters the result of coral cover is 26.30% (medium category). The coral reef ecosystem uniformity index ranges from 0.96 - 0.97 (high). The diversity index of coral reef ecosystems in Bondalem Village ranged from 1.25 which is included in the relatively medium category (1&lt;H'&lt;3). The dominance index of coral reef ecosystem in Bondalem Village ranged from 0.064 - 0.066 (low).

Untargeted Metabolomics Approach for the Discovery of Salinity-Related Alkaloids in a Stony Coral-Derived Fungus Aspergillus terreus

As a part of the important species that form coral reef ecosystems, stony corals have become a potential source of pharmacologically active lead compounds for an increasing number of compounds with novel chemical structures and strong biological activity. In this study, the secondary metabolites and biological activities are reported for Aspergillus terreus C21-1, an epiphytic fungus acquired from Porites pukoensis collected from Xuwen Coral Reef Nature Reserve, China. This strain was cultured in potato dextrose broth (PDB) media and rice media with different salinities based on the OSMAC strategy. The mycelial morphology and high-performance thin layer chromatographic (HPTLC) fingerprints of the fermentation extracts together with bioautography were recorded. Furthermore, an untargeted metabolomics study was performed using principal component analysis (PCA), orthogonal projection to latent structure discriminant analysis (O-PLSDA), and feature-based molecular networking (FBMN) to analyze their secondary metabolite variations. The comprehensive results revealed that the metabolite expression in A. terreus C21-1 differed significantly between liquid and solid media. The metabolites produced in liquid medium were more diverse but less numerous compared to those in solid medium. Meanwhile, the mycelial morphology underwent significant changes with increasing salinity under PDB cultivation conditions, especially in PDB with 10% salinity. Untargeted metabolomics revealed significant differences between PDB with 10% salinity and other media, as well as between liquid and solid media. FBMN analysis indicated that alkaloids, which might be produced under high salt stress, contributed largely to the differences. The biological activities results showed that six groups of crude extracts exhibited acetylcholinesterase (AChE) inhibitory activities, along with 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging and antibacterial activities. The results of this study showed that the increase in salinity favored the production of unique alkaloid compounds by A. terreus C21-1.

Low incidence of microplastics in coral reefs of Kāneʻohe Bay, Hawaiʻi, USA

This study investigated microplastic and other micro-debris pollution in sediment, seawater, sea cucumbers, and corals from fringing and patch reefs in Kāneʻohe Bay, Oʻahu, Hawaiʻi, USA. Microplastic pollution in Kāneʻohe Bay Bay was low compared to other tropical coral reefs. Microplastics were detected in sediments (29 %), sea cucumbers (9 %), and coral (0–2 %) samples but were not quantifiable. Seawater had quantifiable microplastic (< 0.5 mm) and macroplastic (> 0.5 mm) pollution, with mean concentrations ranging from 0.0061 to 0.081 particles m−3. Most particles detected in seawater samples were larger, floating plastic debris consisting mostly of polyethylene, polypropylene fragments, and fibers. Across the other matrices, the most detected particles were polyester, polypropylene, and cotton fibers. These results provide baseline data for this important coral reef ecosystem, and further monitoring is recommended to understand the seasonal and long-term trends in microplastic pollution and its potential future impacts.

Quantifying attributes of boring bivalve populations in corals using micro-computed tomography

Bioerosion plays a crucial factor in shaping the structure and function of coral reef ecosystems, with bioeroders actively altering both the physical and ecological dynamics of coral substrates. Despite their importance, studying internal bioeroders in corals presents significant challenges owing to their cryptic nature within the skeletal structures. Additionally, invasive methods are often required to reveal the subtle and microscopic bioerosive alterations they induce in calcium carbonate substrates. Here, we demonstrate the effectiveness of high-resolution micro-computed tomography (μCT) in quantifying the abundance, size, distribution, and growth directions of coral bioeroders such as cryptic calcareous bivalves in the northern Red Sea. We scanned three coral species inhabited by bioeroders, followed by the utilization of three-dimensional image analysis software to identify, count, and measure each bivalve within the coral skeleton, along with quantifying boring cavity volumes. We revealed that μCT captures small boring cavities (&amp;lt; 1mm), providing more accurate abundance estimates of live and dead boring bivalves than the skeleton decalcification technique, with the added benefits of being rapid and non-destructive in contrast to traditional methods. Furthermore, measurements of empty cavity volumes enabled the estimations of the contribution of bioeroders to the overall coral skeletal porosity. Overall, our study highlights μCT as a practical and effective tool for studying cryptic coral bioeroders, providing novel ecological insights into bioeroder population ecology and coral-bioeroder interactions.

Microplastic pollution in tropical coral reef ecosystems from the coastal South China Sea and their impacts on corals in situ

Coral reefs possess extremely high ecological value in tropical and subtropical waters worldwide. Microplastics as emerging and pervasive pollutants pose a great threat to the health of coral ecosystems. However, in situ studies on microplastics pollution and its impacts in coral ecosystems globally are limited. The occurrence characteristics of microplastics in the environment mediums and reef-dwelling organisms were investigated in coral reef areas from the southern Hainan Island, and the impacts of microplastics on corals in situ were evaluated in this study. Average microplastics abundance was 9.48 items L-1 in seawater, 190.00 items kg-1 in sediment, 0.36 items g-1 in coral, 1.50 items g-1 in shellfish, 0.48 items g-1 in fish gill, and 1.71 items g-1 in fish gastrointestinal tract. The prevalent microplastics in the above samples were characterized as being less than 1000 µm in size, fibrous, and transparent, with predominant polymer types as polyethylene terephthalate, polypropylene, polyethylene, and rayon. The microplastic enrichment capacity of different corals varied (Pocillopora >Acropora >Sinularia). Notably, microplastics were more abundant on the surface of corals compared to their interiors, with distinct characteristics observed, including larger-sized (>500 µm) and fiber-shaped polyethylene terephthalate microplastics on the surface and smaller-sized (20–200 µm) fragmented polyethylene microplastics within coral interiors. Furthermore, the investigation showed species-specific impacts of microplastics on corals in situ, including photosynthetic activity of photosymbionts and antioxidant and immune activities of corals. Furthermore, the ecological risks of microplastics were minor across most environmental media in the studied areas, with exceptions in the bottom seawater and surface sediment of YLW, which exhibited extreme and medium risk levels, respectively. Coral risk levels were generally medium, except for dangerous levels in DDH and high levels in LHT. The potential sources of microplastics in the marginal reefs of southern Hainan Island were primarily tourism, residential, and fishing activities.

Observations of waves and currents on the fore-reef and reef flat of a coral reef atoll in the South China Sea

Understanding the wave and current conditions of coral reef ecosystems is essential for maintaining their health, as many reef processes are controlled by these hydrodynamic conditions. In this study, high-frequency measurements of tides, waves, and currents were made using acoustic, electromagnetic, and pressure instruments over a 28-d period on the fore-reef and reef flat of a coral reef atoll in the South China Sea. The research revealed wave transformation, tidal and wave modulation of flow, and wave setup conditions for the first time at this typical atoll. Three large wave processes dominated by gravity waves (GWs) are observed in the fore-reef. The GWs are significantly attenuated on the reef flat, whereas infragravity (IG) waves strengthened. The tidal modulation of GWs and IG waves on the reef flat is significant when the incident wave height exceeded 1 m. In the fore-reef, the modulation of progressive tidal waves and large waves leads to relatively stronger upper-layer currents, and weak near-bottom currents are primarily attributed to the dissipation of tidal wave energy by the rough coral terrain. In calm conditions, flow variations on the reef flat are modulated by tides, thereby allowing seawater flow to pass through the reef flat during spring tides. Conversely, during periods with large waves, tidal modulation of flow on the reef flat is less significant, and the cross-reef flow velocity increases with increasing incident wave height. The occurrence of wave setup on the reef flat enhances cross-reef flow towards the lagoon. The wave setup is positively linearly correlated with the incident wave height. The magnitude of wave setup is associated with the distance between the measurement sites on the fore-reef and reef flat.

Possible sink of missing ocean plastic: Accumulation patterns in reef-building corals in the Gulf of Thailand

Individual coral polyps contain three distinct components—the surface mucus layer, tissue, and skeleton; each component may exhibit varying extent of microplastic (MP) accumulation and serve as a short- or long-term repository for these pollutants. However, the literature on MP accumulation in wild corals, particularly with respect to the different components, is limited. In this study, we investigated the adhesion and accumulation of MPs in four coral species, including both large (Lobophyllia sp. and Platygyra sinensis) and small (Pocillopora cf. damicornis and Porites lutea) polyp corals collected from Si Chang Island in the upper Gulf of Thailand. The results revealed that MP accumulation varied significantly among the four coral species and their components. Specifically, P. cf. damicornis exhibited the highest degree of accumulation (2.28 ± 0.34 particles g−1 w.w.) [Tukey's honestly significant difference (HSD) test, p < 0.05], particularly in their skeleton (52.63 %) and with a notable presence of high-density MPs (Fisher's extract test, p < 0.05). The most common MP morphotype was fragment, accounting for 75.29 % of the total MPs found in the coral. Notably, the majority of MPs were black, white, or blue, accounting for 36.20 %, 15.52 %, and 11.49 % of the samples, respectively. The predominant size range of MP particles was 101–200 μm. Nylon, polyacetylene, and polyethylene terephthalate (PET) were the prevalent polymer types, accounting for 20.11 %, 14.37 %, and 9.77 % of the identified samples, respectively. In the large polyp corals, while MP shapes, colors, and sizes exhibited consistent patterns, remarkable differences were noted in the polymer types across the three components. The findings of this study improve the understanding of MP accumulation and its fate in coral reef ecosystems, underscoring the need for further investigation into MP-accumulation patterns in reef-building corals worldwide.

Influence of submarine groundwater discharge on the nutrient dynamics of a fringing-reef lagoon

Study regionThis study investigates nutrient distribution and flux dynamics in a coral reef lagoon in Quintana Roo, Mexico, located on a permeable limestone coast of the Mesoamerican Barrier Reef System. Study FocusEmphasis is placed on submarine groundwater discharge (SGD) as a crucial contributor to nutrient pathways, including ammonium (NH4+), nitrate and nitrite (NOx-), hydrogen silicate (HSiO3-), hydrogen phosphate (HPO42-), and urea. Inputs vary with SGD magnitudes and sources and by proximity to active spring discharges. Groundwater multi-tracer analysis and multiple linear regression identify 226Ra as explaining NH4+ variability due to long-term groundwater processes, while 223Ra predicts NOx-, HSiO3-, and urea due to short-term inputs. No significant relationship was found between HPO42- and any radium isotope, indicating complex behavior in coastal karst aquifers. New hydrological insights for the regionThe findings highlight complex nutrient dynamics in coastal karst settings, with SGD-derived fluxes primarily consisting of dissolved inorganic nitrogen (DIN) and HSiO3-. Although lower in concentration, HPO42- and urea fluxes are significant compared to other karst environments. Radium isotopes distinguish between short-term and long-term, as well as new and recycled nutrient inputs. Groundwater inputs transport fresh nutrients to healthier reefs, whereas processed, recycled inputs were detected near degraded reefs. These insights are essential for understanding global nutrient cycles and coral health, particularly in the context of global change and anthropogenic disturbances affecting coral reef ecosystems.

Synergistic impacts of reduced grazing and nutrient enrichment on biofouling assemblages in a degraded coral reef ecosystem

While the coral reefs in the Persian Gulf have adapted to withstand some of the most challenging environmental conditions, overfishing and eutrophication can disrupt the structure of their associated biofouling assemblages. In the present study, the effects of reduced grazing pressure and eutrophication on the assemblage structure of biofouling functional groups in the coral reefs of Hengam Island (Persian Gulf) was investigated using a 21-month manipulative experiment utilizing settlement tiles. A total of 40 biofouling taxa were identified, none of which belonged to reef-building corals or the key facilitators of coral settlement. The effect of grazers on cover percentage was overshadowed by nutrient enrichment; suggesting a bottom-up control mechanism rather than top-down regulation in the coral ecosystem of the island. Our results suggest that grazers can reduce the coral-competing functional groups only in the absence of other confounding factors such as nutrient pollution