Tropical Marine Research Articles

Effects of cold stress on the blood-brain barrier in Plectropomus leopardus

BackgroundThe leopard coral grouper (Plectropomus leopardus) is a commercially valuable tropical marine fish species known to be sensitive to low temperatures. A comprehensive understanding of the molecular mechanisms governing its response to acute cold stress is of great importance. However, there is a relative scarcity of fundamental research on low-temperature tolerance in the leopard coral grouper.MethodsIn this study, a cooling and rewarming experiment was conducted on 6-month-old leopard coral groupers. Within 24 h, we decreased the ambient temperature from 25 °C to 13 °C and subsequently allowed it to naturally return to 25 °C. During this process, a comprehensive investigation of serum hormone levels, enzyme activity, and brain transcriptome analysis was performed.ResultsP. leopardus displayed a noticeable adaptive response to the initial temperature decrease by temporarily reducing its life activities. Our transcriptome analysis revealed that the differentially expressed genes (DEGs) were primarily concentrated in crucial pathways including the blood-brain barrier (BBB), inflammatory response, and coagulation cascade. In situ hybridization of claudin 15a (cldn15a), a key gene for BBB maintaining, further confirmed that exposure to low temperatures led to the disruption of the blood-brain barrier and stimulated a pronounced inflammatory reaction within the brain. Upon rewarming, there was a recovery of BBB integrity accompanied by the persistence of inflammation within the brain tissue.ConclusionsOur study reveals the complex interactions between blood-brain barrier function, inflammation, and recovery in P. leopardus during short-term temperature drops and rewarming. These findings provide valuable insights into the physiological responses of this species under cold stress conditions.

Insights into the degradation mechanism of Fe-40Ni-15Co superalloy exposed to marine atmospheric and high-temperature conditions

This study investigated the corrosion and oxidation mechanism of the Cr-free Fe-40Ni-15Co superalloy with exposure to a tropical marine atmosphere for one year and a subsequent high temperature of 650 °C for 300 h. The degradation behavior of the samples was evaluated based on surface characterization and analysis. In the tropical marine atmospheres, the corrosion process of the Fe-40Ni-15Co superalloy presented an initial localized type after one month of exposure and gradually developed into uniform. The corrosion products were mainly comprised of Fe2O3 and NiO, suppressing the pitting process. During the high-temperature oxidation process, all samples presented super-parabolic oxidation kinetics. Except for the initial active oxidation due to salt deposits, the corrosion products after atmospheric exposure could significantly enhance the oxidation resistance at 650 °C. An explanation for the degradation mechanism of the Fe-40Ni-15Co superalloy was developed based on the synergistic effects of atmospheric corrosion and high-temperature oxidation.

Heavy metal dynamics in riverine mangrove systems: A case study on content, migration, and enrichment in surface sediments, pore water, and plants in Zhanjiang, China

Mangroves serve a crucial role as metal accumulators in tropical and subtropical marine ecosystems, particularly in riverine mangroves, which frequently interact with terrestrial sources. In this study, we focused on the Gaoqiao and Jiuzhou Rivers within the Zhanjiang mangrove forest in Guangdong, China, and collected leaves and surface sediments from the dominant mangrove plant, Aegiceras corniculatum, near the riverbanks. We focused on seven heavy metals (Cr, Cu, Zn, As, Cd, Pb, and Hg) in mangrove leaves, surface sediments, and pore water due to their environmental significance and frequent occurrence in mangrove ecosystems. We employed multivariate statistical methods and pollution indicators to assess the potential sources and risk levels of heavy metals in these sediments. Our results reveal that the concentrations of the seven heavy metals in the sediments of the Gaoqiao and Jiuzhou Rivers varied significantly, ranging from 0.03 mg/kg to 100.00 mg/kg. Cd posed the highest ecological risk, followed by Hg and As. The comprehensive potential ecological risk in the Gaoqiao River was lower than that in the Jiuzhou River, likely due to the distribution of industrial enterprises (such as printing and cement plants) in the upper reaches of the Jiuzhou River. Additionally, the heavy metal content in the leaves and pore water of A. corniculatum ranged from 0.01 to 51.58 mg/kg and 0.001 to 133.70 μg/L, respectively. There was a significant correlation between the heavy metal concentrations in the leaves and the pore water of A. corniculatum. Notably, the leaves of A. corniculatum exhibited a remarkable Hg-enrichment capability, highlighting its potential as a mercury accumulator. Most heavy metals in A. corniculatum leaves, pore water, and sediment were concentrated in the middle and upper reaches of the river, primarily due to anthropogenic terrestrial inputs from residential production activities upstream. Consequently, heavy metal pollution in riverine mangroves is primarily associated with human activities such as aquaculture, agricultural planting, and industrial production.

Temporal dynamics of the bacterial community structure and functions associated with marine sponges collected off Karah Island, Terengganu, Malaysia

The marine sponge microbiome has been investigated for decades, yet its temporal fluctuation/stability is poorly understood. This study aimed to describe the seasonal dynamics of the bacterial composition and predicted functions associated with two tropical marine sponge species (Aaptos suberitoides and Xestospongia testudinaria) collected off Karah Island, Malaysia, in the three seasons (dry season, pre- and post-monsoon season) using 16S rRNA gene amplicon sequencing and Functional Annotation of Prokaryotic Taxa (FAPROTAX). The bacterial taxonomic structures demonstrated divergences among A. suberitoides, X. testudinaria, and seawater, regardless of seasons. Chloroflexi, Proteobacteria, Cyanobacteria, Actinobacteriota, and Acidobacteriota comprised the core bacterial communities in two marine sponge species throughout the seasons, however, there were differences in bacterial composition between the two marine sponges. In addition, A. suberitoides was enriched with Dadabacteria, Spirochaetota, and Bdellovibrionota, whereas X. testudinaria abundantly harbored Poribacteria, PAUC34f, and Anck6. At the genus level, SAR202 clade and Candidatus Synechococcus spongiarum group dominated marine sponge samples throughout the year. Several genera, such as SAR202 clade, Candidatus Synechococcus spongiarum group, and Entotheonellaceae, were discovered only in marine sponge samples. Spirochaeta and Dadabacteriales displayed higher relative abundances in A. suberitoides, while Poribacteria and PAUC34f were more abundant in X. testudinaria. SAR202 clade was positively correlated with dissolved oxygen (DO), pH, phosphate, and ammonia in A. suberitoides. Likewise, Candidatus Synechococcus spongiarum group was negatively correlated with salinity and nitrate in X. testudinaria. Predicted functions by FAPROTAX annotated the phototrophic-related functions in both marine sponges, which might be attributed to a sponge-specific taxon Candidatus Synechococcus spongiarum group. The functions “predatory or exoparasitic” and “fermentation” were highly detected in A. suberitoides, which might be related to the bacterial genera Bdellovibrio and Spirochaeta, respectively. This study guides a deep understanding of the bacterial community structures associated with tropical marine sponges and their temporal behavior.

Evidence of polybrominated diphenyl ethers (PBDEs) and alternative halogenated flame retardants (AHFRs) in wild fish species from the remote tropical marine environment, South China Sea

Polybrominated diphenyl ethers (PBDEs) and their alternatives (e.g., dechlorane plus (DPs) and decabromodiphenyl ethane (DBDPE)) are ubiquitous in various environmental media. However, limited data is available on these chemicals in edible fish species from the wide-open South China Sea (SCS). In the present study, ten legacy PBDEs and three substitutions (DBDPE and two DPs) were analyzed in 16 wild fish species sampled from the open SCS to investigate their spatial and species-specific variations. The results showed that the total concentrations of PBDEs, DBDPE, and DPs in fish samples were in the range of 1.69 to 47.6, not detected (nd) to 21.0, and nd to 3.80 ng/g lipid weight (lw), respectively. BDEs 47, 209 and 100 were the dominant target PBDE congeners, representing 49.2%, 17.2% and 9.93% of the total PBDE concentrations, respectively. Higher concentrations of PBDEs, DBDPE, and DPs were found in fish species from the Wanshan Archipelago compared to those from the Mischief Reef and the Yongxing Island, suggesting the significant influence of anthropogenic activities. Species-specific differences in levels of PBDEs were observed, with the order of bathydemersal > demersal > pelagic ≈ reef-associated > benthopelagic species. The average fanti value of all fish samples was 0.68, suggesting commercial DP products as a contamination source. The levels of PBDEs, DPs, and DBDPE in fish samples were relatively low compared with those from other locations around the globe. Finally, the health risks concerning the ingestion of BDEs 47, 99, 153 and 209 via fish consumption collected from the SCS are negligible.

Hyperoxia does not improve the acute upper thermal tolerance of a tropical marine fish (Lutjanus apodus).

Fish can experience hyperoxia in shallow environments due to photosynthetic activity and this has been suggested to provide them with a metabolic refuge during acute warming. However, this hypothesis has never been tested on a tropical marine species. Thus, we fitted 29°C-acclimated wild schoolmaster snapper (Lutjanus apodus; a species known to experience diel hyperoxia in mangrove creeks and coastal waters) with Transonic® flow probes and exposed them to an acute increase in temperature (at 1°Ch-1) in respirometers under normoxia and hyperoxia (150% air saturation), until their critical thermal maximum (CTmax). The CTmax of both groups was ∼39°C, and no differences in maximum cardiac function were recorded as the fish were warmed. However, temperature-induced factorial aerobic scope was significantly greater in fish tested under hyperoxia. These data suggest that hyperoxia will not protect coastal tropical fish species during marine heat waves, despite its effects on metabolic scope/capacity.

Emergence of highly virulent and multidrug-resistant Escherichia coli in breeding sheep with pneumonia, Hainan Province, China.

Sheep are a rarely raised livestock in Hainan Island, China, because of the unfavorable tropical marine climate. Here, this article reports a severe pneumonia in the sheep breeding and domestication facility caused acute mortality during the winter 2021-2022. Six sheep were clinically dissected and histopathologically observed. The bacteria were isolated and cultured by traditional methods and identified by 16S rRNA sequencing. The genotypes, serotypes, virulence genes and antimicrobial resistance genes were analyzed by PCR and whole genome sequencing. The pubMLST website was used for phylogenetic analysis of related strains. Kirby-Bauer disk diffusion method was used for antimicrobial susceptibility test. The antimicrobial susceptibility test standard was referred to the Clinical and Laboratory Standards Institute (CLSI). The virulence of bacteria was detected by mouse infection model. Etiology and histopathology examination of the pneumonia reveled pulmonary abscess and alveolar neutrophilia and pulmonary fibrinous exudates. Escherichia coli was the only bacterial species isolated, primarily from the lungs and blood of the six dead or moribund sheep, a total of 29 E. coli strains were isolated. Antimicrobial resistance profiling shows that all the isolates were resistant to six agents (penicillin, ampicillin, cephalothin, neomycin, erythromycin, and vancomycin) belonging to five classes of antibiotics, classifying them as multi drug resistant (MDR). Furthermore, genotyping analysis revealed all strains were common with 11-17 virulence factors indicating high pathogenicity. The lab mice infection model shows that all strains severely affect the health status particularly weight loss, lethargy, pneumonia and shortly lead to death. The molecular epidemiological analysis indicated most strains share the same genotype as previously reported strains in humans and other farmed animals this suggests a high possibility of cross-species transmission (CST) of virulent and MDR isolates. This CST could be from sheep to humans and other farmed animals or from humans and other farmed animals to sheep. Therefore, this study indicates that E. coli is an emerging threat that causes sheep pneumonia in Hainan, and the quarantine of contacts is important to control the spread of virulent E. coli and the transmission of acquired resistance genes between humans and farmed animals such as sheep.

Implications of a Pervasive Climate Model Bias for Low‐Cloud Feedback

AbstractHow low clouds respond to warming constitutes a key uncertainty for climate projections. Here we observationally constrain low‐cloud feedback through a controlling factor analysis based on ridge regression. We find a moderately positive global low‐cloud feedback (0.45 W , 90% range 0.18–0.72 W ), about twice the mean value (0.22 W ) of 16 models from the Coupled Model Intercomparison Project. We link this discrepancy to a pervasive model mean‐state bias: models underestimate the low‐cloud response to warming because (a) they systematically underestimate present‐day tropical marine low‐cloud amount, and (b) the low‐cloud sensitivity to warming is proportional to this present‐day low‐cloud amount. Our results hence highlight the importance of reducing model biases in both the mean state of clouds and their sensitivity to environmental factors for accurate climate change projections.

Electrochemical molecularly imprinted polymer sensor for simple and fast analysis of tetrodotoxin in seafood

Tetrodotoxin (TTX) is a marine biotoxin whose biosynthesis is associated with the pufferfish. Its distribution is primarily focused in Asian and tropical marine areas. Currently, this group of toxins is classified as emerging in Europe, and its presence could be related to climate change. This incidence has prompted the European Union, with the European Food Safety Authority, to establish control and monitoring mechanisms for TTX in marine products in Europe. In this context, the development of analytical tools capable of ensuring the safety of food products, especially seafood and fish, is a crucial task. This study describes the development of a molecularly imprinted polymer (MIP) based electrochemical sensor for the analysis of TTX. The MIP was synthesized through the electropolymerization of a functional monomer, ortho-phenylenediamine in the presence of a dummy template, voglibose. The MIP sensor was constructed on a screen-printed gold electrode and characterized by cyclic voltammetry. Differential pulse voltammetry, using a redox probe ([Fe(CN)6]3-/4-), was used in the analysis protocol. The developed sensor exhibited a linear response between 5.0 μg mL−1 and 25.0 μg mL−1, with a limit of detection of 1.14 μg mL−1. Its high imprinting efficiency conferred outstanding selectivity towards TTX. The sensor's applicability was confirmed through recovery assays on spiked mussel samples, achieving recoveries of 81.0 %, 110.2 %, and 102.5 % for external standard addition at 30.0, 44.0, and 60.0 μg kg−1, respectively, with relative standard deviations below 15 %. These results are comparable to those obtained using Hydrophilic Interaction Liquid Chromatography coupled with Tandem Mass Spectrometry, a validated method carried out by the European Reference Laboratory for Marine Biotoxins. Thus, the MIP sensor represents a portable, simple, and fast tool with essential analytical functionalities for the sampling phase and pre-selection of laboratory samples for analysis.

Potential of Marine Sponge Metabolites against Prions: Bromotyrosine Derivatives, a Family of Interest.

The screening of 166 extracts from tropical marine organisms (invertebrates, macroalgae) and 3 cyclolipopeptides from microorganisms against yeast prions highlighted the potential of Verongiida sponges to prevent the propagation of prions. We isolated the known compounds purealidin Q (1), aplysamine-2 (2), pseudoceratinine A (3), aerophobin-2 (4), aplysamine-1 (5), and pseudoceratinine B (6) for the first time from the Wallisian sponge Suberea laboutei. We then tested compounds 1-6 and sixteen other bromotyrosine and bromophenol derivatives previously isolated from Verongiida sponges against yeast prions, demonstrating the potential of 1-3, 5, 6, aplyzanzine C (7), purealidin A (10), psammaplysenes D (11) and F (12), anomoian F (14), and N,N-dimethyldibromotyramine (15). Following biological tests on mammalian cells, we report here the identification of the hitherto unknown ability of the six bromotyrosine derivatives 1, 2, 5, 7, 11, and 14 of marine origin to reduce the spread of the PrPSc prion and the ability of compounds 1 and 2 to reduce endoplasmic reticulum stress. These two biological activities of these bromotyrosine derivatives are, to our knowledge, described here for the first time, offering a new therapeutic perspective for patients suffering from prion diseases that are presently untreatable and consequently fatal.

Study of corrosion and failure mechanism of the galvanized steel pipes of meteorological tower serviced in the South China Sea

Corrosion issues of steel in the natural tropical marine atmospheric environment widely exist, and they can easily cause the failure of engineering equipment. However, the related studies are poor. Therefore, a deep analysis of the corrosion behavior and failure mechanism of steel materials in natural environments is urgent and important. In this work, the corrosion and failure mechanisms of galvanized steel pipes of a meteorological tower in the South China Sea were deeply studied. Results demonstrated that galvanized steel pipes at a low height happen a serious uniform and localized corrosion, while the bottom surface of each pipe facing the ground is severely corroded. The damage to the galvanized layer and the subsequent steel corrosion in high temperature and humidity conditions are mainly caused by bacteria and Cl−. Some bacteria with high corrosivity, such as Desulfovibrionales, Seminibacterium, Acinetobacter, Ralstonia, Proteobacteria Streptococcus, and Lactobacillus, are found beneath the rust layer, and they can significantly accelerate steel corrosion. The maximum localized corrosion rate is 0.20 mm/y.

Exploring intraspecific and interspecific variation of coral reef algae using a novel trait‐based framework

Abstract The development of trait‐based approaches has accelerated our understanding of how communities assemble, respond to environmental change and may best be managed in the Anthropocene. Understanding the magnitude and pattern of interspecific variability forms a critical underpinning of trait‐based approaches while exploring intraspecific variability can identify the potential of species to adapt to changing environmental drivers. Our work is motivated by the critical need for a novel conceptual framework for understanding the functional ecology of macroalgae, as the current paradigm is still mired in functional group models developed in the 1980s. Our objective was to quantify interspecific and intraspecific functional trait variability in three common and morphologically diverse species of tropical marine macroalgae by exploring traits relating to the ecological functions of resource acquisition, resistance to herbivory, and resistance to physical disturbance and the trade‐offs between them. We quantified intraspecific and interspecific variability of 11 functional traits for three common and morphologically diverse species of tropical macroalgae from five fringing reefs of Mo'orea, French Polynesia that were likely to capture a wide range of environmental variability. Differences in traits among species and sites were determined with PERMANOVA, visualised with non‐metric multidimensional scaling, and trade‐offs between pairs of traits explored with correlation. Finally, spatial patterns among select traits across all species were quantified. Species clustered together in distinctly different trait spaces driven by trade‐offs among suites of functional traits. Two of three species had considerable intraspecific variability, though this variability occurred at different scales, while one clustered tightly. Exploration of individual traits across species and sites revealed trade‐offs between two strategies for resource acquisition, growing tall and strong versus investing in large surface area. Synthesis. We captured novel patterns of interspecific and intraspecific variability for tropical marine macroalgae. We found fundamental differences in traits between species that may represent ecological strategies while considerable intraspecific variability demonstrates a wide range in abilities to respond to environmental drivers. Overall, our work provides novel insights into intra and interspecific trait variation that form an essential underpinning for using a trait‐based framework in a taxon that is increasingly dominant on tropical reefs.

Taxonomic Diversity and Interannual Variation of Fish in the Lagoon of Meiji Reef (Mischief Reef), South China Sea.

Coral reef fish are important groups of coral reefs, which have great economic and ecological value. Meiji Reef is a representative tropical semi-enclosed atoll in the South China Sea, with rich fish resources. Based on the data from hand-fishing, line-fishing, and gillnet surveys of fish in Meiji Reef from 1998 to 2018, this study summarized the fish species list of Meiji Reef and analyzed the species composition, inclusion index at the taxonomic level (TINCL), genus-family diversity index (G-F index), average taxonomic distinctness index (Δ+), and variation in taxonomic distinctness (Λ+) and their changes. The results revealed that from 1998 to 2018, there were 166 reef-dwelling fish species on Meiji Reef, belonging to 69 genera, 33 families, and 11 orders, of which 128 species were from 20 families of Perciformes, accounting for 77.10% of the total cataloged species. Regarding the dependence of fish on coral reefs, there were 155 reef-dependent species or resident species (accounting for 93.37%) and 11 reef-independent species or wandering species (accounting for 6.63%). The TINCL of the order, families, and genus of fish in Meiji Reef were very high. The genus diversity index (G index), family diversity index (F index), and G-F index of fish in Meiji Reef were very high, and the G index of fish in Meiji Reef in 1998-1999 was higher than that in 2016-2018. The Δ+ and Λ+ values of fish in Meiji Reef from 1998 to 2018 were 56.1 and 148.5, respectively. Compared with 1998-1999, Δ+ and Λ+ of fish increased during 2016-2018, reflecting that the relatives of fish in Meiji Reef became further distant, and the uniformity of taxonomic relationships among species decreased. The research findings indicated that fish exhibited a high taxonomic diversity in Meiji Reef; however, it also revealed significant fluctuations in the fish diversity of Meiji Reef over an extended period, emphasizing the urgent need for timely protection measures. This investigation significantly contributes to our comprehension of the intricate dynamics governing fish species within Meiji Reef and holds broader implications for biodiversity conservation in tropical marine ecosystems.

Fine-scale phylogeography of Tripneustes gratilla revealed a core-periphery pattern in the South China sea

The Core-Periphery Hypothesis (CPH) is a theoretical framework in phylogeography used to examine the spatial distribution of genetic diversity. The tropical Indian-Western Pacific (IWP), serving as a prominent marine biodiversity hotspot, constantly exports species and evolutionary novelties to peripheral habitats. Many species display genetic patterns consistent with CPH predictions from the IWP to periphery regions. However, the presence of CPH’s genetic signals in intermediate distribution zones remains underexplored. Here, we collected four sea urchin populations of Tripneustes gratilla in the South China Sea and analysed their population structure and evolutionary patterns using 13 morphological parameters, one mitochondrial 16S rRNA gene and nine polymorphic microsatellites. The results revealed substantial genetic homogeneity among the populations, implying a single origin from a glacial refugium. Nonetheless, morphological and microsatellite data distinctly differentiate the northernmost Fengjiawan population from the others, which could be attributed to increased environmental selection pressures such as temperature. Analysis of genetic diversity variation along latitudinal gradients and the relationship between geographic and genetic distances align with CPH expectations for both 16S and microsatellites, albeit to varying degrees of significance. This study enhances our understanding of tropical marine invertebrate evolution and supports the applicability of the CPH model at a fine-scale level.

Untargeted metabolomics profiling of tropical marine microalgae in batch culture system with different mobile phase using Liquid Chromatography-Orbitrap High-resolution Mass Spectrometry combined with chemometrics

Microalgae have recently been identified as a valuable source of natural bioactive compounds, with potential applications suggested in areas such as food, animal feed, energy production (biofuels), fine chemicals, and pharmaceuticals. However, their chemical diversity remains largely unexplored and it is necessary to determine their potency for further application. This study will explore the diversity of chemical compound from six tropical marine microalgae with untargeted comparative metabolomics approach using a Liquid Chromatography-Orbitrap High Resolution Mass Spectrometry with different mobile phases. Six microalgae species were isolated from Jakarta Bay, Indonesia. Species identification was carried out using morphological and molecular identification. The isolates Chlorella vulgaris InaCC M205 (C5), Chlorella sp. 12 (C12), Tetraselmis subcordiformis InaCC M206 (T2), Tetraselmis sp. 5 (T5), Nannochloropsis oceanica InaCC 207 (N4), and Porphyridium purpureum (P) were then cultivated using f/2 media in 1 L glass photobioreactors, irradiated with daylight lamps (4000 lux) under a 12 h/12 h photoperiod at 25 0C for until cultures reached the stationary phase. Biomass harvesting and measurements were carried out at the end of the culture period. The freeze-dry biomass then was analyzed using liquid chromatography-high resolution mass spectrometry. The results showed that biomass production on day 12 was not significantly different. Biomass production ranged from 0.8 to 1 g/L, with the highest production obtained from the C5 strain and the lowest from the C12 strain. Chromatography analysis revealed that untargeted metabolomics profiling of microalgae, using water-acetonitrile as mobile phase, identified potential compound markers such as N-Methyl-2-pyrrolidone, l-(+)-Cysteine, TBHQ and L-Phenylalanine, which can differentiate between species. Compound such as Cyromazine, Arachidic acid and 13(S)-HOTrE were the potential compound markers when using Water-Methanol as mobile phase. Our research indicates that the metabolomic profile of microalgae can be used to differentiate species depending on the choice of mobile phase.

Insights into the biodegradation of polyhydroxyalkanoates by the tropical marine isolate, Nocardiopsis dassonvillei NCIM 5124.

The online version contains supplementary material available at 10.1007/s13205-024-04079-3.

Environmental factors that regulate Vibrio spp. abundance and community structure in tropical waters

Vibrio spp. is a group of heterotrophic bacteria that are ubiquitous in marine habitats, with various ecological and clinical importance. This study investigated the environmental factors that regulate Vibrio spp. dynamics in various tropical marine habitats, including nearshore (an estuary and a coastal beach) and offshore transects located northwest and southeast of Peninsular Malaysia, while focusing on the distribution of attached and free-living Vibrio spp., population growth, and community composition. The results showed that > 85% of the Vibrio spp. in nearshore waters occurred in attached form and correlated positively to total suspended solids (TSS) and Chlorophyll a (Chl a) concentrations. On the other hand, Vibrio spp. growth rates were positively correlated to dissolved organic carbon (DOC) concentrations, but negatively correlated to total bacterial counts, likely due to resource competition. In addition, high-throughput sequencing of 16S rRNA V3-V4 region showed that Vibrio spp. in these tropical waters contributed < 1 − 18% of the whole bacterioplankton community, and the six major Vibrio spp. taxa were V. alginolyticus group, V. brasiliensis, V. caribbeanicus, V. hepatarius group, V. splendidus group and V. thalassae. db-RDA (cumulative variance explicated = 93.53%) further revealed the influence of TSS, DOC, and dissolved organic nitrogen (DON) to the Vibrio spp. community profiles. The study highlighted the importance of suspended solids (TSS and Chl a) and dissolved organic nutrients (DOC and DON) towards Vibrio spp. dynamics in tropical marine waters.

Regional distribution differences of antibiotics in tropical marine aquaculture area: Insights into antibiotic management and risk assessment

In recent years, global demand for marine aquaculture products has led to a significant rise in antibiotic use, particularly in tropical coastal aquaculture areas However, research on antibiotic residues in these environments remains limited, hindering a comprehensive understanding of their environmental presence and associated risks. This study investigates the regional distribution, ecological risks, and sources of 44 antibiotics in seawater across four coastal aquaculture areas in Hainan island (Wenchang, Sanya, Danzhou, and Wanning). Among the 44 antibiotics tested across 42 sampling sites, all were detected with a 100 % detection rate. Antibiotics such as Trimethoprim (TMP), Sulfanitran (APNPS), Sulfaquinoxaline (SQ), Sulfadimethoxine (SDT), Chloramphenicol (CHP), and Florfenicol (FLO) were consistently detected across all sampling sites. Total concentrations of detected antibiotics ranged from 0 to 818.79 ng.L−1, with sulfonamide antibiotics ranging from 0 to 629.49 ng.L−1, chloramphenicol antibiotics from 0 to 87.39 ng.L−1, tetracyclines from 0 to 221.39 ng.L−1, and fluoquinolones from 0 to 272.08 ng.L−1. The highest levels of antibiotic pollution were observed at the W5 sampling site in Wenchang, attributed to aquaculture wastewater discharge, while no antibiotics were found at D12 in Danzhou. In these regions, source analysis identified aquaculture and domestic sewage as the primary contributors to antibiotic pollution in these regions. Correlation analysis with environmental factors revealed significant influences of factors such as SAL, kPa, TN, SPC, and pH on sulfonamide and chloramphenicol antibiotics. Health risk assessment indicated moderate to high risks to aquatic organisms from antibiotics like NOR, CIP, ENR, OFL, TMP, and SMX in the study areas, underscoring the need for preventive measures, stricter regulation of antibiotic use, and enhanced ecological risk monitoring in aquaculture regions. This study provides critical insights into antibiotic contamination in Hainan's coastal aquaculture areas, highlighting the urgent need for further research into the occurrence and ecological impacts of these emerging pollutants in marine environments.

Functional reproductive morphology of the snapping shrimp genus Synalpheus Spence Bate, 1888 (Decapoda, Alpheidae)

Abstract Shrimp of the genus Synalpheus (Caridea) are commonly found in subtropical and tropical marine habitats around the world. The present work aims to provide the first description of the reproductive system of this genus using histological, histochemical, and morphological perspectives to elucidate the gonochoric or hermaphrodite sexual system in this genus. Males have a slender and very translucent reproductive system that is challenging to observe. The entire cephalothorax was histologically sectioned to ensure that all regions of the reproductive system could be identified. This non-gambarelloides group shows a gonochoric condition. The caridean pattern of the reproductive system was observed where the male has a pair of testes and a pair of very thin vasa deferentia, ending at the opening of the gonopore. Spermatophore structure is absent, without any layers surrounding the spermatozoa which are aggregated in a sperm mass. In females, the reproductive system consists of a pair of ovaries that extend to the end of the pleon. The extension of the ovary has a particular pattern compared to other caridean shrimps. Here, we hypothesize that males invest energy on somatic morphological structures to protect the host and female, using the larger pistol-like cheliped, while females invest energy in reproduction, since all the members of this group are typical “pair-bond” examples. The observed pattern of the reproductive male morphology could also be evidence of a possible synapomorphy for this genus within the infraorder.

Swimming performance, but not metabolism, is related to a boldness-activity syndrome in schoolmaster snapper (Lutjanus apodus).

Commercial overexploitation and climate change can alter the physiology and behavior of marine organisms, although intraspecific phenotypic responses to such changes can vary greatly depending on the environment, species, and severity of the stressor. Under the pace-of-life syndrome (POLS) hypothesis, behavior, physiology, and life-history traits are linked, and thus, affected by selection targeting any aspect of organismal biology. However, these links are understudied in tropical marine fishes, and further work is needed to better understand the impacts of fisheries and climate change on wild stocks. Moreover, tropical regions have a greater reliance on fisheries; thus investigations should focus on species with substantial socioeconomic value to ensure benefits at the local level. This study aimed to address this need by measuring the behavior (boldness and activity), metabolism, and swimming performance (using a critical swim speed [Ucrit] test) of schoolmaster snapper Lutjanus apodus in Eleuthera, the Bahamas. We report a strong positive correlation between boldness and activity, high repeatability of these behavioral metrics, and two groupings that were consistent with "proactive" and "reactive" behavioral types. These behavioral types differed significantly in their swimming performance, with reactive individuals having a 13.1% higher mean Ucrit. In contrast, no significant differences were found in the measured metabolic parameters between behavioral types. This study is the first to investigate the intraspecific links between behavior and physiology in a snapper species, using the novel and ecologically relevant comparison of Ucrit with behavioral syndrome types. These data suggest that additional research is needed to better predict the success of proactive/reactive tropical fish if overexploited and as influenced by climate change.