Marine environmental research最新文献

Plankton communities are subjected to multiple global change drivers; however, it is unknown how the interplay between them deviates from predictions based on single-driver studies, in particular when trophic interactions are explicitly considered. We investigated how simultaneous manipulation of temperature, pH, nutrient availability and solar radiation quality affects the carbon transfer from phytoplankton to herbivorous protists and their potential consequences for ecosystem functioning. Our results showed that multiple interacting global-change drivers reduced the photosynthetic (gross primary production-to-electron transport rates ratios, from 0.2 to 0.6-0.8) and resource use efficiencies (from 9 to 1 μg chlorophyll a (Chl a) μmol nitrogen^-1) and prompted uncoupling between microzooplankton grazing (m) and phytoplankton growth (μ) rates (μ > m). The altered trophic interaction could be due to enhanced intra-guild predation or to microzooplankton growing at suboptimal temperatures compared to their prey. Because phytoplankton-specific loss rates to consumers grazing are the most significant uncertainty in marine biogeochemical models, we stress the need for experimental approaches quantifying it accurately to avoid bias in predicting the impacts of global change on marine ecosystems.

Intertidal microhabitats provide special conditions to the organisms that inhabit them and to some of their morpho-protective characteristics. Tidal pools, under the influence of acidified freshwater, may affect the characteristics of the protective shells of prey and have repercussions on predation. The shells of Perumytilus purpuratus from such tidepools are more fragile than those of their counterparts from the vertical intertidal walls of the same area. Those from the tidepools also have tissue content values intermediate between those from the lower and higher limits of the intertidal wall, possibly due to different feeding regimens of the bivalves. Also, the shells of tidepool individuals have a shell thickness that is intermediate between those from the lower and higher limits of their distribution. In a common garden, the predatory muricid Acanthina monodon prefers to attack individuals from the tide pool. This selection is not based on a higher energetic input from the prey, nor on the thickness of the prey's shell, but on the lower hardness of the shell that implies an easier and less-energetically expensive attack and possibly of shorter duration.

Zn is a common heavy metal pollutant in water bodies and accounts for the largest proportion of heavy metal pollutants in many rivers entering the sea. This study investigated the growth and physiological response characteristics of Sargassum fusiforme under different divalent Zn ion concentration gradients. We observed that low concentration Zn²⁺ treatment (<2 mg L^-1) exerted no significant effect on the growth rate, photosynthesis, and nitrogen metabolism-related indicators of S. fusiforme. Treatment with medium to high Zn²⁺ concentrations (2-25 mg L^-1) significantly affected the growth rate, photosynthetic activity, nitrogen absorption rate, antioxidant enzyme activity, membrane lipids, and DNA peroxidation damage-related indicators of S. fusiforme. Under medium-to-high concentration treatments, the SOD activity of S. fusiforme decreased with increasing concentration, and the CAT activity increased with increasing treatment concentration. The MDA and H₂O₂ contents increased with increasing Zn²⁺ concentrations. At a Zn²⁺ concentration of 5 mg L^-1, the relative conductivity of S. fusiforme significantly increased. Treatment with higher Zn²⁺ concentrations significantly increased the 8-hydroxydeoxyguanosine (8-OHdG) content, poly ADP-ribose polymerase (PARP) activity, and Histone H2AX content of S. fusiforme, thus indicating that Zn²⁺ stress causes DNA damage. All Zn²⁺ concentrations induced mannitol accumulation, and soluble protein content decreased with increasing Zn²⁺ concentration. In summary, we observed that a Zn²⁺ concentration of 2-5 mg L^-1 may be the critical value for the response of S. fusiforme to Zn²⁺ stress. Higher concentrations of Zn in the environment can exert toxic effects on the growth, development, and biomass accumulation of S. fusiforme. This study provides a reference for the risk assessment and aquaculture management of seaweeds.

The input of macroalgal biomass into the deep sea is a crucial process for macroalgal carbon sequestration, but this process may be affected by anoxia. We compared the breakdown of kelp biomass in both normoxic (>4 mg/L O₂) and anoxic (<2 mg/L O₂) environments. Following 240 days of decomposition experiment, complete degradation of the kelp biomass occurred in normoxic conditions, whereas under anoxic conditions, relatively 13.58% residual biomass remained. Our results suggest that microorganisms facilitated the conversion of dissolved organic carbon (DOC) derived from kelp degradation into refractory dissolved organic carbon (RDOC), a process observed under both normoxic and anoxic conditions. However, different dissolved oxygen levels lead to different bacterial community successions, which affected the conversion process from labile dissolved organic carbon (LDOC) to RDOC differently. Bacteroidia, which possess sulfur metabolic capabilities, play a significant role in RDOC generation under both normoxic and anoxic conditions. In normoxic conditions, the relative abundance of CHO molecules was 2.57% less than that under anoxic conditions, whereas the proportions of CHON was 3.83% higher. Additionally, DBE_wa and Almod_wa values were 11.04% and 15.63% higher than those observed under anoxic conditions. At the end of the experiment, the relative content of RDOC under normoxic and anoxic conditions was 9.18% and 5.45%, respectively. Despite the reduced production of RDOC, anoxic conditions promote the preservation of a larger amount of macroalgae biomass. However, uncertainty exists regarding the extent to which stored POC reaches deep-sea sequestration. Consequently, it is challenging to assert that anoxia positively influences carbon sequestration in macroalgae.

Understanding the role of species interactions (e.g. competition and facilitation) in structuring communities is a fundamental goal of ecology. It is well established that large canopy-forming seaweeds (e.g. kelps and fucoids) exert a strong influence on community structure, by offering biogenic habitat, altering environmental conditions and interacting with other species. While many studies have manipulated the density of seaweeds to causatively examine their effects on the local environment and associated communities, they are biased towards certain regions and canopy-forming species. We conducted a manipulative experiment at two subtidal sites characterised by mixed Laminaria canopies, in southwest England, UK. Three treatments were established in multiple replicate circular plots (area of 7.1 m²): 0% kelp removal (i.e. unmanipulated control), 50% kelp removal (i.e. thinning), and 100% removal. Within each plot, temperature, light levels and sedimentation rates were monitored over 3 months, and after 5 months the density of juvenile kelp recruits, the biomass of understorey macroalgae and the abundance of recruiting fauna were quantified. We found kelp canopies had no impact on temperature or sedimentation rates but their removal led to marked increases in light availability, juvenile kelp recruitment and understorey macroalgal biomass. Overall, our study shows that physical disturbance to Laminaria canopies alters resource availability (i.e. light and space), leading to increased abundances of kelp recruits and understory algae. Significant reductions in kelp canopy density, driven by storm disturbance, harvesting or decreased water quality for example, would lead to shifts in community structure and ecological functioning.

Mangrove wetlands are strategic locations for mitigating climate changes. In order to address the harm of rapid climate change to mangrove ecosystems, it is necessary to scientifically predict the fate of mangrove ecosystems, which can be achieved by reconstructing the development history of mangrove forests. This study analyzes the contribution of mangrove-derived organic matter (CMOM) from sediment core F in Phang Nga Province, Thailand by using the endmember mixing model based on stable organic carbon isotopes (δ¹³C_org) and C/N (molar) ratio. The variations of CMOM over the past ∼3195 cal yr BP indicate that mangrove forests underwent three periods of flourishing: ∼3195-2620 cal yr BP, ∼2030-1130 cal yr BP, and ∼410-0 cal yr BP, and two periods of deterioration: ∼2620-2030 cal yr BP and ∼1130-410 cal yr BP. Among the potential factors that might affect the development of mangrove forests, relative sea level (RSL), regional hydrodynamics, and human activities do not have notable effects on mangrove flourishment/deteriorating. However, climate factors, particularly air temperature, rainfall, and sea surface salinity are the main factors influencing the flourishing/deterioration of mangrove forests. In the Andaman Sea, these climatic factors are mainly driven by the Indian summer monsoon (ISM).

The western Indian continental shelf (eastern Arabian Sea) exhibits contrasting biogeochemical features. This area becomes highly productive due to summer monsoon-driven coastal upwelling in the south and winter monsoon-induced convective mixing in the north. Additionally, in the northern self, the eastern boundary of the Oxygen Minimum Zone (OMZ) persists but is absent in the south. Phytoplankton blooms are dominated by diatoms that contribute to sedimentary phytodetritus flux supplying major elements (C, N, Si) and food for benthic biota and hence important to address. Here we present the data on organic matter content, diatom frustule flux, abundance, and diversity using surface sediments (core tops collected using a multicorer) from 6 locations (11-21° N) along the shelf in a 2° interval at 200 m isobaths. The organic matter retrieved from the core top was relatively fresh (nearly ∼4.5 years old) as evident from ²¹⁰Pb profiles. Frustule abundance and diversity (the maximum at 15° N and minimum at 19° N) varied from 0.10-18.46 × 10⁴ valves g^-1 and 0.79-2.32, respectively. A total of 36 diatom genera were found with two centric (Thalassiosira and Coscinodiscus), and one pennate (Nitzschia) diatoms as major contributors. The higher contribution of Thalassiosira was observed throughout the shelf dominating the south (11, 13, 15° N), whereas, in the north (17, 19, 21° N) Coscinodiscus was dominant. The highest organic matter content (3.4%) and frustule abundance (18.46 × 10⁴ valves g^-1) were seen at 15° N despite low diatom valve flux (3.3 × 10³ valves cm^-2 yr^-1) and could be due to the influence of OMZ, where organic matter is well preserved. Contrarily, the upwelling-influenced station in the south (at 11° N) exhibited the highest diatom valve flux (10.14 × 10³ valves cm^-2 yr^-1), however low organic matter content (1.6 %) and frustule abundance (4.99 × 10⁴ valves g^-1) were attributed to faster mineralization. This study suggested that the preservation potential of organic matter varies across the shelf and is likely to control its recycling, impacting nutrient release and resources for the benthic community.

Nucleocytoplasmic large DNA viruses (NCLDVs) are known to infect phytoplankton and play a significant role in regulating their population dynamics. In this study, we aimed to investigate the co-occurrence patterns between phytoplankton and NCLDVs in the southern coastal ecosystem of South Korea. We collected seawater every month from March 2018 to December 2020 and analyzed the samples using Cytochrome c Oxidase subunit I metabarcoding and metagenomic analyses. Chlorophyta (36.08%) was the most abundant eukaryotic taxon, with Bathycoccaceae (58.25%) and Mamiellaceae (41.51%) being the most dominant families within Chlorophyta. Bathycoccaceae was dominant in winter, whereas Mamiellaceae was dominant in summer. In the NCLDV community, Phycodnaviridae (75.12%) was found to be the major family. The co-occurrence pattern of Phycodnaviridae showed a high correlation with Bathycoccaceae and Mamiellaceae, which is explained by the "boom-and-bust" concept. In particular, we predicted co-occurrence patterns between Bathycoccus prasinos and Prasnovirus, with known infectious relationships, and confirmed co-occurrence patterns between B. prasinos and Coccolithovirus and Micromonas pusilla and Prymnesiovirus, with unknown infectious relationships. These co-occurrence patterns between Chlorophyta and Phycodnaviridae provide valuable insights into the control of pico-sized primary production and the microbial loop of the coastal ecosystem.

The hermit crabs are 'ecosystem engineers' and are a critical link in the oceanic food web. Six species of genus Coenobita are reported in the group of Andaman and Nicobar Islands namely, Coenobita rugosus, C. brevimanus, C. violascens, C. perlatus, C. cavipes and Birgus latro. In the present study, Coenobita rugosus, C. brevimanus, and C. violascens were chosen and handpicked randomly during low tides at two locations along the Port Blair Coast. During the study, important morphometric parameters viz, shield length (SL), carapace length (CL), cheliped propodus length (ChPL), cheliped dactylus length (ChDL), left third pereopod propodus(L3PL) and left third pereopod dactylus length(L3DL) were measured using a vernier calliper. Among the six parameters, shield length (SL), Cheliped Propodus length (ChPL) and cheliped dactylus length (ChDL) are important for species differentiation. Identification of hermit crabs belonging to the same or different genera becomes easier with the use of morphometric data along with the taxonomic keys in the absence of colour patterns. One-way ANOVA showed that there are significant differences in SL values among the three species. It was found that the mean values of SL varied significantly between males and females for C. rugosus (one-way ANOVA) and C. violascens, but there was no significant variation of SL values between males and females of C. brevimanus. The results showed that C. rugosus occupied variety of gastropod shells belonging to families Turbinidae, Muricidae, Trochidae, Strombidae, Buccinidae, Neritidae, Cerithidae, Cymatidae, Olividae and, plastic debris like discarded bottle caps. Whereas C. violascens preferred shells of Turbinidae and Muricidae but the C. brevimanus chose only the shells of Turbinidae at least during the present study period. The sex ratio was highest (1.58) in C. rugosus followed by C. violascens (1.14) and the lowest (0.39) in C. brevimanus. The individuals of C. brevimanus were significantly larger while C. rugosus were smaller based on the cheliped and carapace length and the body weight.