ABSTRACT Non‐indigenous copepods are increasingly reported in the Mediterranean Sea, where anthropogenically disturbed coastal environments may facilitate their establishment and their co‐occurrence with native congeners. This study provides the first record of the non‐indigenous calanoid Acartia tonsa along the Algerian coast and examines its spatio‐temporal distribution relative to the native A. clausi . Zooplankton was sampled during four seasonal campaigns covering a complete annual cycle at four coastal stations of Bordj El Kiffan (eastern Algiers Bay, 36°45′ N, 3°22′ E), arranged along an anthropogenic pressure gradient from a brine‐discharge outlet to an offshore reference station. We hypothesised that (1) disturbed conditions generated by brine discharge and coastal enrichment favour the establishment of A. tonsa , and (2) as an early‐stage invader, A. tonsa currently co‐occurs with A. clausi with a high degree of niche overlap rather than excluding it. A. tonsa was recorded at all stations and seasons (4.80–5280 adults m −3 ), with a marked summer maximum, and consistently reached higher abundances than A. clausi (5.60–371.20 adults m −3 ). Both species peaked in summer and were positively associated with temperature, and niche‐overlap indices remained high throughout the annual cycle, indicating spatial and temporal co‐occurrence rather than exclusion. The relative abundance of the two congeners decreased from the enriched nearshore stations towards the offshore reference station, linking the dominance of A. tonsa to the local anthropogenic gradient.
ABSTRACT Empirical studies demonstrating ecological speciation in marine invertebrates are limited. Two large abalone species— Haliotis discus discus and H. madaka —in the Japanese archipelago are considered to be involved in this process. Previous population genomic studies have indicated that hybridization between these two species continues because of incomplete reproductive isolation. However, owing to the limited number of samples in the previous study, the nature of hybridization remains unclear. In this study, we performed population genomic analyses of these two species using samples from multiple geographical regions. Analysis of 122 species‐diagnostic single‐nucleotide polymorphism loci revealed that observed heterozygosity was significantly higher in the H. madaka population than that in the H. discus discus population. ADMIXTURE analyses revealed biased introgression from H. discus discus into H. madaka populations, with the extent of introgression varying among regions. Most individuals with genomic introgression were classified as backcrosses, with no individuals demonstrating patterns consistent with F1 hybrids, indicating a bimodal hybrid zone. These findings suggest that selection may act against early‐generation hybrids and that ecological speciation proceeds under geographically variable selective pressures in marine environments.
ABSTRACT Migrant juvenile Atlantic herring ( Clupea harengus ) from across the greater Gulf of Maine (GoM) provide pelagic forage in the Grand Manan Island region, a major trophic hub. A centuries‐old weir fishery for herring juveniles, never monitored, has collapsed from chronic GoM overfishing. Razorbills ( Alca torda ) and Atlantic puffins ( Fratercula arctica ) nest on nearby Machias Seal Island, feeding their chicks with these herring. Using published data, this study demonstrates probabilistic relationships between weir‐fishery landings of juvenile herring (~availability) and relative portions of young herring fed to both razorbill and puffin chicks. Herring‐diet differences for razorbills suggest nuanced forecasting of prospective imminent fishery collapses. Facing collapse, razorbills are more likely to capture herring in addition to less‐pelagic alternate species (hake, sand lance), while puffins make more use of the alternates. Previous research, based on exploratory correlation and regression, did not demonstrate these connections for the Grand Manan region. As indicator “units,” the probabilistic herring‐seabird relationships raise the potential of interspecific corroboration in herring recruitment forecasts. For example, when landings are low, razorbill use is greater than puffin use, and razorbill herring biomass use remains moderate‐to‐high, fisheries for juveniles could place increased multiyear limits on prospective catches system‐wide. Such relationships could be of considerable precautionary use, since systemic fishing‐induced forage deficiencies have become the norm. With the erosion of resilience, ecosystem components are now at high risk of extirpation in the northeastern GoM. The concepts should increase understanding of Anthropocene challenges and the actions required of humans to prevent depletion of natural resilience in ecosystems.
ABSTRACT Variability in mesozooplankton (MZ) ecology and community structure in the Bay of Bengal (BoB) based on a meso‐scale process is presented during the summer monsoon (SM) of 2018. Cyclonic storm (CS) Daye impacted the northwestern BoB during this season. A coastal survey was conducted just after the cyclonic activity to investigate the impact of CS on the hydrography of coastal waters and the MZ species assemblage. The survey was conducted along eight transects representing a gradient of cyclonic impact from least to most affected by CS Daye . The northern transects (WBE and WBC) were least impacted, the central transects (ODP, ODR, and ODG) experienced moderate influence, and the southern transects (APB, APV, and APK) were highly impacted by the storm. There was a clear distinction in water quality and MZ community structure between the Northern and Southern transects. The Northern transects were characterized by high temperature, low salinity, low dissolved oxygen (DO), high nutrient concentration (except nitrate), high chlorophyll (Chl) a , high MZ biomass, and abundance. The opposite trend was noticed in the Southern transects. Gelatinous groups like Appendicularia, Ctenophora, Hydromedusae, and Thaliacea were present in high abundance in the Southern transects, while the Northern transects had a predominance of Copepoda. The Southern transects had a high predominance of Bestiolina similis , Euterpina acutifrons , Oithona brevicornis , and Salpa fusiformis , while the Northern transects had a dominance of Acartia ( Odontacartia ) spinicauda , Corycaeus crassiusculus , Undinula vulgaris , and Zonosagitta pulchra . A shift in the MZ community was recorded from Southern transects dominated by highly abundant cyclopoids and thaliaceans to Northern and Central transects characterized by predominantly calanoid species.
ABSTRACT Seagrass ecosystems are vital coastal habitats that deliver essential ecological services such as nutrient cycling, sediment stabilization, and long‐term carbon sequestration. As key blue carbon sinks, they play a pivotal role in regulating major biogeochemical cycles, particularly nitrogen, carbon, phosphorus, and sulfur through complex interactions between seagrass roots and associated microbial communities. Microbial functions like nitrogen fixation, phosphorus solubilization, and sulfide detoxification are integral to maintaining seagrass productivity, especially in nutrient‐poor, anoxic sediments. However, these ecosystems face increasing threats from anthropogenic activities such as eutrophication, habitat destruction, chemical pollution, and climate change, all of which disrupt microbial processes and nutrient fluxes. Such disruptions may transform seagrass meadows from carbon sinks to carbon sources, intensifying climate feedback mechanisms. This review emphasizes current knowledge on the ecological and microbial roles within seagrass systems, drawing attention to case studies from Indian coastal regions that highlight the impact of natural and human‐induced stressors on seagrass decline. Additionally, it explores the promise of advanced technologies such as artificial intelligence, remote sensing, and genomics for improving the monitoring, restoration, and spatial planning of seagrass habitats. Tools like deep learning algorithms, satellite imagery, and SNP genotyping provide precise data on ecosystem health and resilience. Integrating these innovations with national policies such as the National Environment Policy, Wildlife Action Plan, and Coastal Regulation Zone (CRZ) guidelines is essential for effective conservation. A multidisciplinary, ecosystem‐based strategy that emphasizes microbial diversity, genetic adaptation, and technological innovation is imperative to safeguard these critical marine habitats amid rapid environmental change.
ABSTRACT Ontogenetic niche shifts are a common characteristic of aquatic organisms with complex life cycles and are driven by changes in body form and size, environment, and behavior. The trophic niche of fishes can be highly variable over ontogeny, and previous studies suggest that trophic niche should vary predictably with body size in organisms with indeterminate growth. However, empirical tests of hypotheses linking trophic niche to changes in body size are lacking. To test hypotheses of ontogenetic changes in trophic niche position and breadth over a wide range of body sizes, we used stable isotopes to characterize isotopic trophic niche in Pacific halibut, Hippoglossus stenolepis (Schmidt 1904). We sampled individuals in seven size classes ranging from 500 to 2100 mm total length (TL). Both carbon (δ 13 C) and nitrogen (δ 15 N) isotopes were enriched with increasing body size, but the pattern was not consistent with a simple increase in body size and gape size. Isotopic trophic niche breadth increased with increased body size across the first three size classes, but then decreased sharply in the largest size class. Trophic niche position and breadth change across the wide range of body sizes observed in Pacific halibut. However, these changes in trophic niche may be driven by a combination of changes in body size and gape size, spatial and temporal variation in prey availability and vulnerability, ontogenetic and spawning migration patterns, and a behavioral response by the largest individuals. Thus, the simple assumption that trophic niche position and breadth of a predator will change, as a consequence of accumulation of more and larger prey species in the diet corresponding to increased predator body size or gape size only, is not supported in Pacific halibut.
ABSTRACT Calamyzine worms are often found in mantle cavities of large chemosymbiotic bivalves in deep‐sea chemosynthesis‐based ecosystems, but the nature of trophic interactions between the worms and their clam hosts remains largely obscure. Here, we combine bulk tissue carbon and nitrogen stable isotope analyses with radiocarbon and nitrogen compound‐specific isotope analysis of amino acids (CSIA‐AA) to investigate the trophic relationship between the calamyzine worm Shinkai semilonga and its host vesicomyid clam, Archivesica kawamurai , from a methane seep in Nankai Trough, Japan. The trophic position (TP Glu/Phe ) of S. semilonga (2.6) was approximately one unit higher than that of the host clam gill (1.5), the organ where the clam hosts its symbiotic bacteria. Our results indicate that S. semilonga is a parasite feeding directly on the gill tissue and assimilating both host cells and the sulphur‐oxidising bacteria. Furthermore, the host clam mantle exhibited a higher than‐predicted TP Glu/Phe (2.5 rather than 2.0), suggesting that A. kawamurai may supplement its symbiont‐derived nutrition by filter‐feeding on particulate organic matter. These findings shed light on the interactions between calamyzine worms and their host bivalves, demonstrating the usefulness of CSIA‐AA in resolving complex trophic interactions in deep‐sea chemosynthetic communities.
ABSTRACT Tide pools are dynamic intertidal habitats that have attracted sustained scientific attention due to their ecological complexity and accessibility as natural study systems. This study provides a quantitative bibliometric analysis of tide pool research conducted between 1934 and 2023. We compiled a global database of 249 publications to examine temporal trends, thematic focus, geographic distribution, and research structure within the field. Our analysis reveals a marked increase in publication output over time, with a pronounced acceleration after 2010, indicating growing scientific interest. Research topics are unevenly distributed, with fish‐related studies representing the largest proportion of the literature, followed by experimental approaches. Other topics, including ecology, environmental drivers, and biodiversity, are present but comparatively less represented. Geographically, research effort is strongly concentrated in the Americas and Europe, while Africa and Asia remain underrepresented, highlighting significant spatial disparities in knowledge production. The diversity of research themes and their temporal evolution illustrate how tide pools have been used as model systems across multiple areas of marine science. At the same time, the observed imbalances in topic prevalence and geographic coverage point to important gaps in the current literature. Based on these patterns, we identify several forward‐looking directions for research development, including expanded geographic representation, improved comparability across studies, and broader integration of complementary methodological approaches. By systematically characterizing the structure of existing research, this study provides a quantitative foundation for understanding how tide pool science has developed over time and where future efforts may be most effectively directed.
ABSTRACT Symbioses between invertebrates and prokaryotes are widespread across various environments. This study focused on a stable microbial community localized in the buccal apparatus (teeth of the radula and jaws) of the nudibranch Cadlina laevis found near the MSU White Sea Biological Station. Distinct methodologies have been applied to characterize this microbial community. Electron microscopy revealed a morphologically uniform layer of bacteria consistently associated with the radular teeth of C. laevis . Sequencing of the V4 region of the 16S rRNA gene identified that representatives of the genus Polaribacter accounted for up to 95.2% of the dense biofilm on the buccal apparatus. This finding supports a specific association of Polaribacter representatives with the buccal apparatus, in contrast to the more heterogeneous microbiomes of other mollusk organ samples. Comparative genomic analysis revealed significant differences between the genomes of C. laevis ‐associated Polaribacter and other available genomes of Polaribacter representatives, indicating that a host‐associated lifestyle may require additional adaptations in bacteria. Metagenomic analysis revealed chitinase genes, rare in previously known Polaribacter ‐affiliated genomes, within the genome of these bacterial associates, suggesting their role in degrading chitin that covers the buccal apparatus. This observation of a stable microbial community in the C. laevis buccal apparatus could suggest that Polaribacter benefits from its ability to degrade chitin within the buccal apparatus, whereas the benefits to the mollusk remain unclear and will be the subject of further studies.
ABSTRACT The introduction of exotic species is one of the main drivers of biodiversity loss in aquatic ecosystems. The Harris mud crab Rhithropanopeus harrisii , native to the Atlantic coast of North America, was recorded in the Patos Lagoon estuary (southern Brazil) in the 1980s, likely introduced via ballast water. However, the effects of this invader on the native fauna were never evaluated. This study assessed the natural diet and trophic niche overlap between the invader and four native crab species ( Cyrtograpsus angulatus , Callinectes sapidus , Neohelice granulata , and Panopeus austrobesus ) along a salinity gradient in the estuary. Multivariate analyses were performed to identify dietary differences among species and sites, and the Morisita–Horn index was applied to estimate trophic overlap. Callinectes sapidus , Panopeus austrobesus , and Rhithropanopeus harrisii exhibited generalist feeding habits, consuming mollusks, crustaceans, polychaetas, plant material, and detritus, whereas Neohelice granulata showed a predominantly herbivorous diet, and Cyrtograpsus angulatus displayed trophic plasticity by alternating between animal and plant items. Significant differences in diet composition were observed among species, with low overall trophic overlap. The highest overlap was observed between Callinectes sapidus and Panopeus austrobesus , whereas the lowest overlap occurred between Neohelice granulata and Rhithropanopeus harrisii . Despite its generalist feeding behavior, Rhithropanopeus harrisii appears not to compete strongly with native species, likely exploiting unoccupied niches or using shared resources differently. The invader's high trophic plasticity may enhance its establishment in the estuary, while low overlap suggests niche differentiation or resource partitioning with native crabs.
Describing patterns of spatially-explicit population genetic structure and connectivity is vital for well-designed conservation or management policies for marine species. However, for species having high dispersal capabilities and large population sizes, describing significant genetic structure may be difficult. Perna canaliculus, the endemic New Zealand green-lipped mussel, is the cornerstone species of this country's aquaculture industry. Several studies performed with various genetic marker types have revealed two distinct genetic groups (northern and southern), but no further genetic differentiation. Here, we describe the first use of ddRAD-seq-derived SNPs to examine the genetic structuring of P. canaliculus. Using 185 neutral and 28 outlier SNPs from 32 sampling sites, two major genetic groups (northern and south-west-with a genetic break at similar to 42 degrees S, below the Cook Strait/Raukawa Moana region) were confirmed. The use of the outlier panel revealed stronger genetic differences in allelic frequencies than markers under neutral expectations. Moreover, the SNP data provided, for the first time, evidence of substructure over the extensive range of the population that was sampled: six further genetic subgroups were identified within the two main groups. Seascape analysis revealed that genetic variation correlates strongly with variables related to food availability, habitat composition and current speed, reflecting selective pressure and genetic signals of local adaptation, suggesting these processes play a key role modulating the genetic structure of the green-lipped mussel. Gene flow networks suggest migration from the south-west group into the northern group. This pattern of migration is also revealed in contemporary oceanographic models of larval dispersal, which indicate high historical gene flow between the two groups, and a minor influence of genetic drift. These results offer valuable insights into the genetic structure and factors influencing genetic divergence in P. canaliculus and how genetic stocks may be managed.
ABSTRACT Shipwrecks can function as artificial reefs that enhance marine biodiversity and productivity by providing structurally complex habitats. However, ecological assessments of shipwrecks in the Western Indian Ocean, including Mauritius Island, remain scarce. This study presents the first systematic ecological evaluation of five shipwrecks around Mauritius, focusing on their ecological performance in terms of fish assemblages and benthic composition, and identifying environmental thresholds that favour biodiversity enhancement. Belt transects (2 m × 1.5 m) laid across the full width of each wreck were used to quantify fish assemblages, while benthic cover was assessed using line intercept transects. Environmental parameters including light, depth, temperature, dissolved oxygen, pH, salinity, and nutrient concentrations were recorded at each site. Fish biomass and community composition varied significantly among wrecks, with the highest mean biomass (138.6 ± 13.2 g m −2 ) and density recorded at shallower, well‐illuminated, structurally degraded wrecks. In contrast, coral cover peaked (21.9% ± 3.9%) on structurally intact wrecks under similar light regimes. Linear mixed‐model analysis identified light availability and pH as key drivers of fish biomass, while structural integrity supported coral cover. Principal Coordinates Analysis (PCoA) further indicated that depth, nitrate, and pH were key factors structuring both coral and fish assemblages. Building on these patterns, an exploratory framework termed the Optimal Ecological Performance Thresholds (OEPT) was derived to identify indicative environmental and spatial ranges representing conditions that can maximize coral cover and fish biomass. These thresholds provide a preliminary, science‐based reference for guiding future shipwreck deployments and ecosystem‐based coastal management.
ABSTRACT The H5N1 avian influenza (HPAI) outbreak that began in 2021 has led to widespread mortality in birds and mammals globally, significantly impacting seabird populations. This study examines the changes in the number of migratory great skuas ( Stercorarius skua ), a species particularly vulnerable due to its kleptoparasitic behavior and reliance on communal baths. Using a 59‐year migration time series from Cape Estaca de Bares (Galicia, NW Spain), we first characterized long‐term migration phenology. To evaluate the potential impact of HPAI, we then focused on the most standardized 20‐year period (2004–2023; 35,828 observations). We first built a climate‐based model using pre‐HPAI data (2004–2020) to quantify the influence of weather conditions on the number of migrating great skuas. This model was subsequently used to generate predictions for the post‐HPAI period (2021–2023) under observed weather conditions, allowing us to assess whether recent declines exceeded expectations based on weather variability alone. Migration counts revealed substantial interannual variation, with the sharpest decline in 2022 and 2023, coinciding with the HPAI outbreak. Importantly, observed migration numbers during the post‐HPAI period were consistently lower than predicted based on weather conditions alone, indicating that weather cannot explain the recent decline. These results might suggest that the reduction in the number of migrating great skuas reflects the impact of an additional large‐scale process consistent with the HPAI outbreak, mirroring similar trends observed in breeding colonies. Our findings highlight the critical role of long‐term monitoring of migration studies in understanding the broader ecological implications of HPAI. Further investigations are necessary to determine how predation pressures by great skua and the virus's effects are influencing seabird species that it kleptoparasites.
The biological productivity in the Southern Ocean is mainly driven by the abundance of phytoplankton, which changes with seasons, fluctuations in sea ice and iron as well as light availability. The distribution of biological productivity is further modulated by ocean currents. Diatoms are a key element in the Southern Ocean's food web; thus, the effects of environmental changes on diatom population sizes have important implications for the overall ecosystem's productivity. In this study, we employed genomic data to assess the effects of glacial cycles on the population sizes and connectivity of the diatom Fragilariopsis kerguelensis in the Atlantic sector of the Southern Ocean. We detected three distinct variants among the 47 strains sampled along a latitudinal transect, all found in sympatry along the Polar Front. Demographic inferences identified major events during the last 100,000 years for two variants, characterized by a large decrease in effective population sizes followed by a rapid increase. These events overlapped with the change in environmental conditions during Pleistocene glacial cycles. Further research on mutation rates, generation time estimates and how changing environmental conditions influence these parameters in diatoms will improve the accuracy of the inferences drawn from these kinds of data. Although the use of genomic approaches in diatom species is in its infancy, this study highlights their potential to provide new insights into diatom past population sizes, responses and resilience to climate change and its effects on other trophic levels in the Southern Ocean.
Coloration in fishes plays central roles in communication, defense, and sexual selection, and is mediated by specialized pigment cells (chromatophores). In many species, red and orange hues derive from dietary carotenoids that are metabolically modified and intracellularly transported. The Garibaldi, Hypsypops rubicundus, a long-lived and iconic damselfish endemic to the eastern Pacific, displays a striking carotenoid-based orange-red coloration. To provide genomic resources for studying coloration genes in this species, we generated and assembled a high-quality genome using Oxford Nanopore long reads, yielding a 781.7 Mb assembly with 96% BUSCO completeness. As a proof of concept, we investigated the carotenoid-associated transport gene kif5b, which encodes a kinesin-1 motor protein involved in intracellular pigment mobilization. The kif5b gene in H. rubicundus comprises 25 exons and shows conserved organization relative to other damselfishes, but exhibits a unique amino acid substitution within a conserved nucleotide-binding motif (N3). Specifically, position 238 contains a leucine in H. rubicundus, whereas other damselfishes possess a glutamic acid or serine at this site. This substitution replaces a polar residue with a hydrophobic one, potentially affecting protein conformation or function. Phylogenetic analyses based on mitochondrial genomes and kif5b exons were largely congruent with published relationships. Our results establish the H. rubicundus genome as a valuable resource and identify a candidate molecular change that may contribute to its distinctive carotenoid-based coloration.
Outside the breeding season, small pelagic seabirds are particularly challenging to study due to their large geographic ranges and high mobility. Consequently, their non-breeding distribution and activity patterns are often poorly known. However, the non-breeding period is of critical importance, encompassing both migration and flight feather moult. We combined miniaturised geolocator-immersion loggers (GLS) with carbon and nitrogen bulk and compound-specific stable isotope analyses of rectrix feathers. Using this approach, we investigated the annual phenology, migratory routes, moult locations, non-breeding activity patterns and distribution of two Antarctic storm-petrel species: Wilson's Storm-petrel Oceanites oceanicus and Black-bellied Storm-petrel Fregetta tropica. Stable isotope data revealed a narrower isotopic niche and less intraspecific variation in trophic positions for Black-bellied Storm-petrels (n = 15) compared to Wilson's Storm-petrels (n = 15). GLS data suggested the non-breeding season of Wilson's Storm-petrels to last from around mid-April to end of November. All individuals (n = 7) migrated transequatorial in a clockwise pattern. Three individuals initially stayed at a non-breeding site in the South Atlantic Ocean. The main non-breeding sites of all individuals were in the North Atlantic Ocean, along the eastern coast of Canada and the United States, where flight feather moult took place from July to September, inferred from a period of reduced flight activity (measured by time on water). The foraging activity of Wilson's Storm-petrels was higher at night than during the day. This was not influenced by lunar phase but is likely linked to prey behaviour. The single successfully tracked Black-bellied Storm-petrel also crossed the equator but spent the non-breeding period in the Indian Ocean, mainly in the Arabian Sea. This indicates spatial segregation from Wilson's Storm-petrels. We present the first ever GLS tracking data of Wilson's and Black-bellied Storm-petrels, improving our understanding of their non-breeding behaviour. Future research including more individuals alongside environmental variables will be necessary to examine the drivers of the observed inter- and intraspecific non-breeding spatial and trophic segregation.
Emerging infectious diseases are novel threats to marine ecosystems. Although elucidating the temporal and spatial dynamics of such diseases is critical for managing ecosystems, it is generally challenging because many are invisible and cryptic, making it difficult to conduct long-term surveys at large spatial scales. Here, by analyzing web images on the social network platform X (formerly Twitter), I examined the infection dynamics of the parasitic copepod Lernaeenicus cf. ramosus, which causes pathological impacts on economically important marine fishes. Although previous studies indicated that infections increased after the 2000s in Japanese waters, there is no long-term data. Based on 3390 posts containing images of two host fish species (yellow grouper Epinephelus awoara and grub fish Parapercis sexfasciata) posted from 2012 to 2024, I found the copepods emerged and increased substantially around 2016-2019 in grub fish but declined in yellow grouper. Infection levels tended to be higher in autumn and winter, and methods of fish collection influenced the detectability of parasites. Moreover, I also identified new localities of the copepods, which fall outside of their previously known range, suggesting that their distribution is rapidly expanding north (east) ward. My study showed that analyzing web images sheds important insights into how aquatic diseases emerge and spread.
The endosymbiotic communities of corals are major contributors to the evolutionary success of scleractinian corals as the main reef-building organisms in modern coral reefs. The most studied endosymbiotic taxa associated with scleractinian corals are dinoflagellate family Symbiodiniaceae (previously the genus Symbiodinium), but corals are truly holobionts with a myriad of other microorganisms living together in what is known as the coral microbiome. The goal of this research was to characterize the genetic variability of the microbiome (based on 16S rRNA) and Symbiodiniaceae (based on ITS2) associated with the eurybathic Caribbean sheet coral Agaricia lamarcki along a depth gradient. This plating-crustose coral is found along a wide depth distribution from shallow coastal reefs at approximately 10 m down to mesophotic depths at > 75 m in southwest Puerto Rico. Environmental conditions vary across this gradient, leading us to expect significant differences in zooxanthellae clades and microbiome community composition. We collected fragments of 36 A. lamarcki colonies along a shallow-mesophotic depth gradient from 20 to 70 m at Black Wall in southwest Puerto Rico. PCR and Next-generation sequencing targeting 16S rRNA and ITS2 genes were performed on DNA extracted from coral biomass containing coral tissue and surface mucus layer. Despite no differences in alpha-diversity/richness metrics, our study found significant differences in coral-associated bacterial community composition between shallower reefs (20-30 m) and mesophotic reefs (50-70 m). Contrastingly, we found no significant differences in the Symbiodiniaceae composition of A. lamarcki across the depth gradient, indicating a uniform algal endosymbiont community in this location. Given the increasing loss of shallow water coral reefs, understanding coral adaptation mechanisms to mesophotic environmental conditions becomes ever more important to establish proper management and conservation efforts.
Global climate forcing and anthropogenic pressures are increasingly destabilizing marine ecosystems, pushing high-productivity upwelling zones toward unpredictable ecological tipping points. In the southeastern Caribbean, the eastern Venezuelan coastal region supports one of the world's most significant fisheries for the sardine Sardinella aurita, a species whose population stability is governed by a narrow thermal window (18 degrees C-25 degrees C). Utilizing two decades (2002-2023) of high-resolution MODIS-Aqua satellite data, we applied an early warning signal (EWS) framework based on critical slowing down (CSD) theory to diagnose the loss of resilience in this vital habitat. By contrasting the coastal sardine fishing area (SFA) with the offshore exclusive economic zone (EEZ), we analyzed temporal trends in sea surface temperature (SST) variance (standard deviation) and temporal autocorrelation (AR(1)). Our results reveal a significant divergence in thermal stability: while minimum and mean SSTs show increasing persistence (AR(1)), signaling a classic loss of resilience, the maximum SST in the coastal domain exhibits a sharp increase in volatility (SD) and erratic behavior. These "anti-CSD" signals in maximum SST indicate that extreme thermal events, such as marine heatwaves, are becoming more frequent and intense, frequently trespassing the physiological thresholds of S. aurita. By prioritizing physics-based indicators of habitat stability over confounded fishery-dependent data, this study demonstrates that the coastal sardine habitat is approaching a nonlinear regime shift. These findings provide a robust, proactive diagnostic tool for fisheries management, offering a critical lead time for adaptive strategies before biological collapses become statistically detectable.
Zostera marina, commonly referred to as eelgrass, is a marine flowering plant frequently growing in some water-saturated sediments along the coastal regions of Japan. We examined the bacterial communities in the sediment of three eelgrass areas to compare the bacterial composition of vegetated sediments (eelgrass sediments) with that of nearby unvegetated sediments. We also revealed the core bacterial groups commonly detected in all eelgrass beds examined. The bacterial communities varied between the eelgrass sediment and the surrounding unvegetated sediment. Deltaproteobacteria and Epsilonproteobacteria were showed significantly higher relative abundance in eelgrass sediment compared to the unvegetated sediment. As core taxa, 38 OTUs/phylotypes consistently appeared across the three eelgrass sediments and are considered unique to the eelgrass beds, indicating potential specific interactions with Z. marina. The most prevalent core taxa in eelgrass sediment were Gammaproteobacteria, Deltaproteobacteria, and Flavobacteriia, which include members involved in key biogeochemical processes. Additionally, environmental variables such as temperature, salinity, pH, DO, and total organic carbon (TOC), emerged as the key drivers of variation within the bacterial community. This study contributes to the understanding of bacterial diversity associated with Z. marina sediments and highlights differences in microbial community composition between eelgrass and adjacent unvegetated sediments. Deeper sequencing in future studies will further improve the resolution of rare bacterial diversity associated with eelgrass sediments.
