Marine environmental research最新文献

Saltmarshes provide key ecosystem services, including atmospheric CO₂ sequestration and nitrogen burial in sediments. In recent decades, these blue carbon ecosystems have faced significant degradation from natural and anthropogenic stressors. In this study, rewilding of a desiccated saltmarsh in Cadiz Bay (SW Spain) was assessed as a nature-based solution to restore carbon (C_org) and nitrogen (N_T) storage. The rewilding process began in 2004 after breaching an external tidal wall. We evaluated changes in vegetated and unvegetated areas using Landsat satellite imagery (1994-2024) and quantified C_org and N_T stocks and burial rates in wild and rewilded sediments, including vegetated saltmarsh (Sarcocornia sp.) and bare sediments colonized by microphytobenthos (MPB). Vegetated saltmarsh cover increased by 85% over 20 years, at an average recovery rate of 5 ha y^-1, concurrent with a decrease in unvegetated tidal flats. Average C_org stocks in the top 1 m ranged from 32 to 57 t C_org ha^-1, with higher values in vegetated sediments. However, only 5-12% of C_org was stored during the rewilding period. C_org burial rates averaged 69 g C_org m^-2 y^-1, and N_T stocks were 55% higher in rewilded sediments than in wild ones (3.6 vs. 1.6 t N_T ha^-1). Despite vegetation recovery, burial rates of C_org and N_T did not increase clearly, suggesting that long-term storage may be influenced by factors beyond rewilding. Less than 8% of sedimentary C_org originated from saltmarsh vegetation, indicating the dominance of allochthonous sources. These findings highlight the complexity of biogeochemical recovery in rewilded saltmarshes and underscore the need for long-term monitoring to determine how much time is truly required for C_org and N_T recovery.

The Dashentang waters of Tianjin contain China's largest remaining natural oyster reef, an ecosystem facing multiple stressors, including overfishing, industrial pollution, and climate change. These pressures have led to measurable contraction in reef area and declining oyster population densities. However, limited knowledge exists regarding population dynamics of Crassostrea gigas in artificial oyster reef (Ax: A1-A5 five stations) and natural oyster reef (Nx: N1-N5 five stations) habitats and their tolerance to intra-annual water quality fluctuations. This study investigated the biological parameters of the C. gigas population dynamics and associated physicochemical water quality factors in both Ax and Nx habitats in the middle of the four target months (March, June, September, and December) of 2024. Condition index of C. gigas populations declined significantly in summer, reaching minima in autumn. Empty shells (EOS) markedly in autumn, while living oysters (LO) showed divergent trends during winter, increasing in Ax but decreasing in Nx. Precipitation of 227.00 mm reduced salinity to a range of 23.30-24.38 during September. Significant negative correlations emerged between EOS and salinity (P < 0.05), while a highly significant positive correlation was observed between LO and salinity in the Nx habitat (P < 0.01). During summer, the bottom layer total particulate matter (TPM) concentrations at station A1 was 168.53 mg L^-1, with EOS at 125.00 ind·m^-2 and complete absence of LO. In autumn, the bottom-layer TPM at station N5 measured 139.90 mg L^-1, while EOS was 375.00 ind·m^-2 and LO was 212.50 ind·m^-2. During the same season, the dissolved oxygen declined to 2.32 mg L^-1 at station A2, with EOS at 518.75 ind·m^-2 and LO was only 12.5 ind·m^-2. Supra-threshold hypoxia, salinity fluctuations, and elevated TPM loading collectively triggered mass mortality events in both reef habitats during autumn. In winter, recovery in Nx was constrained by TPM-mediated sedimentation and fishing pressure, while unique structure facilitated population reestablishment in Ax. Thus, implementing ecosystem-based fisheries management coupled with three-dimensional oyster reef optimization represents an effective restoration strategy. This study provides a practical reference and theoretical basis for the formulation of oyster reef restoration strategies.

Coastal marine environments are becoming increasingly degraded, particularly in urbanized areas where anthropogenic nutrient loading and climate change are contributing to the rise of extreme events such as heatwaves and hypoxia. These extreme events can result in adverse effects and mass mortalities of marine life, especially sessile animals such as bivalves. Bivalves are important economically but are also important contributors to ecosystem functioning via habitat creation, water filtration, and nutrient and carbon cycling. This study aims to characterize how eastern oysters (Crassostrea virginica) and soft-shell clams (Mya arenaria) physiologically and behaviourally respond to repeated hypoxia during a heatwave. This eight-day study aimed to mimic field conditions using water pumped directly from the estuary into a dock-side mobile lab. Water temperature and dissolved oxygen were manipulated to match observations of heatwave and hypoxic conditions in the study area (Prince Edward Island, Canada). The physiological and behavioural responses of oysters suggest that they perform better under high temperatures (27 °C) as they maintain metabolic rate while increasing feeding. Oysters were also able to tolerate repeated periods of hypoxia (<2 mg O₂ L^-1) during a heatwave by maintaining metabolic rate and reducing feeding costs. Conversely, soft-shell clams experienced stress under the induced heatwave and showed signs of metabolic depression. Repeated hypoxia during the heatwave resulted in elevated physiological responses in clams, suggesting elevated energy requirements under these stressors. This study provides insight into the vulnerability of these species under climate change scenarios at northern latitudes, with applicability to aquaculture and fisheries management.

Sedimentary diatom assemblages are sensitive bio-archives that can be used to reconstruct past environmental conditions in aquatic ecosystems. However, quantitative sedimentary records capable of precisely resolving anthropogenic impacts from natural variability in highly dynamic estuaries remain poorly understood. Here, we conducted a high-resolution diatom analysis of two ²¹⁰Pb-dated sediment cores (Z4-2 and Z5-2) from the Pearl River Estuary (PRE), covering the period 1938-2023 and 1893-2023, respectively. Our results identified a total of 66 diatom species and revealed a profound ecological shift. Prior to 2000, the diatom assemblage was dominated by planktonic taxa such as Cyclotella striata and C. stylorum, whose fluctuations reflected natural climate variability. In contrast, the period after 2000 was characterized by the dominance of the benthic species Paralia sulcata, which exceeded 50% abundance, accompanied by a sharp decline in freshwater species. This trajectory quantitatively demonstrates that anthropogenic forcing, including industrial pollution and coastal development, has surpassed natural climate variability as the primary driver of environmental change in the estuary in recent decades. These findings provide a critical baseline for distinguishing natural cycles from human-induced shifts, thereby offering a scientific basis for informed management decisions in the PRE and other anthropogenically influenced estuary ecosystems.

In recent decades, due to the anthropogenic CO₂ concentration increase in the atmosphere, the chemistry of seawater has been seriously altered, producing the phenomenon known as Ocean Acidification (OA). Of all the dissolved inorganic carbon (DIC) present in seawater, only 1% is in the form of CO₂. However, if anthropogenic CO₂ emissions to the atmosphere continue, it will no longer be a limiting resource. Part of the response of marine photosynthetic organisms to these changes depends on their carbon physiology. The presence and effectiveness of carbon concentration mechanisms (CCM) can define the production and growth of macroalgae under OA conditions. Although CCMs are not essential when the seawater concentration of inorganic carbon is high, species that do not use them can see their performance improved. Our goal was to determine the presence or absence of CCMs in a total of 19 species of common macroalgae in the Canary Islands through a pH drift experiment and to establish their primary production rates through incubations and measurements of the O₂ variation. Samples of each species were incubated during 8, 24 and 32 h in isolated containers and under controlled lighting and temperature conditions. Of the 19 species studied, 11 presented CCM and 8 did not present CCM. Five of the eight species that did not show the presence of CCMs in the present study are present in the CO₂ seeps of Fuencaliente and one of them, H. scoparia is a dominant species.

Climate change is altering ocean conditions such as sea surface temperature, salinity, stratification, and dissolved oxygen, reshaping habitat suitability for yellowfin tuna (Thunnus albacares, YFT) and bigeye tuna (Thunnus obesus, BET). This study integrated Taiwanese longline catch-per-unit-effort (CPUE) data from 1981 to 2014 with environmental covariates using a Vector Autoregressive Spatio-Temporal (VAST) framework to develop Habitat Suitability Index (HSI) models. Fishing effort increased from ∼200,000 hooks in 1991 to nearly 820,000 in 2002, before declining to ∼400,000 by 2021. YFT dominated catches until 2000, after which BET became predominant. Spatial analyses indicated BET hotspots in the tropical central and eastern Pacific, whereas YFT were more abundant in the western Pacific with smaller hotspots in the east. Suitability curves showed BET favored cooler, moderately saline, oxygen-rich waters, while YFT preferred warmer, saltier, and slightly less oxygenated conditions. Coupling HSI models with CMIP6 projections under SSP1-2.6 and SSP5-8.5 revealed contrasting redistribution patterns: BET habitats are projected to contract and shift eastward by the end of the century, while YFT habitats are expected to expand across wider Pacific regions. These findings demonstrate that climate-driven changes in tuna distribution will likely reshape fishery productivity and management requirements. Region-specific quota adjustments, flexible management zones, and strengthened multinational cooperation will be necessary. Incorporating the HSI outputs into quota setting and spatial planning can help sustain Taiwan's distant-water tuna fisheries in a changing climate.

Natural stressors, including predation risk, can affect the response of organisms to anthropogenic contamination. Copper, used as an antifouling agent, can affect non-target organisms. We tested for effects of excess copper on survival with and without predator cues in five species of coastal copepods. We exposed adult copepods to four copper concentrations (0-1350 μg L^-1, 48h) on an automated imaging platform and analysed the data using the reduced General Unified Threshold model for Survival (GUTS) to detect potential species differences in underlying toxico-kinetics and -dynamics. Calanoid copepods had elevated mortality during early copper exposure compared to a harpacticoid and a cyclopoid species. Species-specific dominant rate constants, which represents the time it takes for damage to reach a steady state, best explained the time-dependent toxicity. Over time, most predicted mortalities converged to a similar level regardless of species. Predation risk reduced mortality at the intermediate copper concentration, potentially explained by reduced copper bioavailability by binding of copper to kairomone molecules, or other intrinsic and extrinsic factors. Models like GUTS can reveal the underlying toxicity mechanisms and improve toxicity predictions in a multi-stressor world.

This study investigates the individual and combined effects of cadmium (Cd²⁺) and poly (butylene adipate-co-terephthalate) (PBAT), a biodegradable macroplastic, on the marine diatom Phaeodactylum tricornutum (P. tricornutum). Interestingly, co-exposure with PBAT mitigates Cd²⁺ toxicity, except at high Cd²⁺ concentrations. Using a non-invasive Fourier-transform infrared (FTIR) spectroscopy protocol with robust acquisition parameters and principal component analysis, specific biochemical changes in membrane composition were monitored, with notable decreases in carbohydrate and lipid contents, while protein levels remained unaltered. Morphological observations revealed a shift toward the oval morphotype under exposure to Cd²⁺ and PBAT, alone and in combination, featuring a stress response. Additionally, the light-harvesting pigments, chlorophyll-a and fucoxanthin, increased in a dose-dependent manner upon Cd²⁺ exposure, while no significant β-carotene changes were observed, except at high Cd²⁺ concentrations in the presence of PBAT. This effect is further amplified under co-exposure conditions, the presence of PBAT leading to a marked increase in all three pigments, β-carotene included. The experimental protocol, which involved the aging of PBAT macroplastics in seawater for a short period, suggests that the degradation products of PBAT themselves are responsible for these observed biological effects. It is worth noting that morphotype shifts occur at lower Cd²⁺ concentrations than those affecting photosynthesis and photoprotective systems. These findings highlight the potential of P. tricornutum membrane fingerprints and morphotype shifts as sensitive ecotoxicological indicators of metal and plastic pollution, particularly in relation to degradation by-products in marine environments.

In tropical coastal ecosystems, monsoonal rainfall is a critical driver of seasonal variability, inducing shifts in hydrological parameters such as temperature, salinity, and nutrient concentrations, which subsequently regulate zooplankton community structure. This study investigated the influence of the southwest monsoon on coastal water quality and zooplankton composition along the Mumbai coast, India. Sampling was conducted in the pre-monsoon (May 2022) and post-monsoon (September 2022) periods, corresponding to early (EMP) and later (LMP) monsoonal phases, during which the region receives 1500-2000 mm of precipitation. Analyses revealed distinct hydrological changes and a significant reorganisation of the zooplankton assemblage between phases. Total zooplankton abundance was lower in the EMP compared to the LMP. Among the 25 taxonomic groups identified, Copepoda dominated the community, represented by 27 species (23 Calanoida, 2 Harpacticoida, and 2 Cyclopoida), with families Acartidae and Paracalanidae comprising 70 % of the copepod population. Statistical and biological trait-based analyses demonstrated significant temporal shifts in copepod community composition and functional structure. Temperature, salinity, and nutrient levels were identified as the primary environmental factors shaping the distribution of copepod functional groups. Eleven copepod taxa served as indicator species for specific monsoonal phases. Trophic structure analysis showed a prevalence of omnivorous copepods during the EMP, likely due to reduced phytoplankton availability under lower nutrient concentrations and fluctuating salinity, favouring opportunistic feeding. In contrast, the LMP, characterised by elevated nutrient inputs and stabilised salinity, supported a more complex food web with a balanced representation of herbivorous, omnivorous, carnivorous, and detritivorous functional groups. Herbivores were numerically dominant in both periods. The increased co-dominance of meroplankton (pelagic larvae of benthic invertebrates) during the LMP highlighted their ecological role in coupling benthic and pelagic subsystems. These findings elucidate the mechanistic links between monsoonal hydrography and zooplankton functional ecology, providing a scientific basis for informed conservation and management of monsoon-influenced coastal ecosystems.