Journal of Marine Systems最新文献

High-latitude marine environments, such as the Beagle Channel, are highly vulnerable to modifications related to climate change and anthropogenic impacts, which can rapidly affect the ecological attributes of plankton communities and thus alter ecosystem trophodynamics. This study compares the mesozooplankton community structure in the inner and outer (eastern) Beagle Channel during spring and assesses the interactions of the main mesozooplankton trophic groups with lower and higher trophic level organisms under an isotopic approach. Oceanographic data and biological samples, ranging from sediment and phytoplankton to pelagic squat lobsters (Grimothea gregaria), were collected along the channel during two research cruises conducted in November 2019. Mesozooplankton abundance and taxonomic composition differed between sectors, in agreement with their distinct environmental conditions. The inner sector was dominated by copepods, mainly Clausocalanidae spp., followed by cirripede and echinoderm larvae and appendicularians. In the outer sector, with shallower, saltier, and warmer waters than the inner one, mesozooplankton abundances were notably higher and both copepods and decapod larvae, mainly Peltarion spinosulum and G. gregaria zoeae, were dominant. This pattern in meroplankton abundance was consistent with the bathymetric distribution reported for benthic adults. Between-sector differences in taxonomic composition, e.g., Macruronus novaezelandiae (hake) larvae occurring only in the outer sector, may be attributed to the higher connectivity between this sector and the open ocean and the semi-enclosed character of the inner channel. Mesozooplankton spatial variability was partially reflected in the isotopic niche width of their different trophic groups such as copepods, euphausiids and decapod larvae. However, at the community level, trophic attributes (i.e., baseline resources, trophic positions, isotopic diversity metrics) were quite similar in the two sectors, suggesting similar basal and vertical trophic structures. According to Bayesian stable isotope mixing models, most trophic groups, including pelagic G. gregaria, rely on phytoplankton as their main carbon source. This reveals a weak predation pressure on mesozooplankton by the squat lobster and reinforces a bottom-up regulation during the spring season. This study contributes to our knowledge of trophic interactions in plankton communities and how they are regulated by bottom-up and top-down forces, which is imperative for monitoring and management purposes.

In the Strait of Gibraltar, the Blackspot Seabream (Pagellus bogaraveo, Brünnich 1768) is an economic resource of great commercial importance for the Spanish and Moroccan artisanal and Moroccan longline fleets. Given the great interest of the species for the fleets, it is of vital importance to know the dynamics of landings and how this can be influenced by environmental variability. From this arises the hypothesis of the present study: environmental mechanisms cause forcings in the dynamics of landings. To this end, we analysed the average annual dynamics of the time series of commercial landings of the Blackspot Seabream from 1983 to 2015 from a multivariate perspective. We applied trend, principal component (PCA) and time series clustering analyses to determine patterns and relationships between the fishery series and different oceanographic variables and climatic indices. In addition, we determined the influence of this set of variables on landings from a linear approach based on multiple linear regressions (MLRs) and generalized linear models (GLMs) and non-linear determined by generalized additive models (GAMs). The results obtained indicated the presence of common temporal patterns and the existence of significant influence between landings and ocean temperature with the current velocity modulus in specific layers and heat flux, causing lower fishing yields as we get colder waters with less intense currents. Such studies are of vital importance for the application of an ecosystem approach to the management of this resource by understanding the effect and influence of the environment on the dynamics of landings from the fishery.

The strength of the atmospheric Aleutian Low pressure system varies interannually and has a distinct impact on sea surface temperature (SST), sea level, and other oceanic parameters along the North Pacific subarctic front. These impacts are caused by variable zonal winds through their effects on meridional Ekman transport and air-sea fluxes. While the SST response is well known on an interannual (ENSO) to decadal (PDO) scale, the response of sea surface salinity (SSS) is less known due to relatively sparse observations. The SSS response originates in the western Pacific and is concentrated along the North Pacific subarctic front, reaching a few tenths of psu in the upper 100 m, as demonstrated by satellite SSS, Argo salinity data, and model simulations. SSS anomalies, in contrast to SST anomalies, behave like passive tracers that are advected eastward in the North Pacific Current across the whole basin and, unexpectedly, sometimes intensify to the east. After reaching the eastern boundary, they continue predominantly southward along the California coast, remaining detectable by satellite SSS all the way to the southern tip of the California peninsula.

Water samples were analyzed with an optical laser device (LISST 200×) to determine the properties of suspended sediments in the saline front of the Magdalena River mouth (Colombia, South America), a micro-tidal delta with high fluvial discharge of regional influence. The study aimed to determine variability of textural properties, suspended sediment concentration, effective density, and settling velocity under non-stationary, stratified, and turbid conditions. The suspended sediment consisted of 84.3% silt-size material (3.9–62.5 μm), with the remaining 15.7% a sand-size fraction (62.5–177 μm). Nevertheless, most of these fractions consisted of flocs, up to 995 μm in size, composed of primary particles that ranged in size from 9 to 35 μm. Most sediments were very poorly sorted, near symmetrical and platykurtic, with mean volumetric suspended sediment concentration, settling velocity, and effective density values of 253.1 μl l⁻¹, 5.8 × 10⁻³ mm s⁻¹, and 0.96 kg m⁻³, respectively. These properties exhibited significant depth-related differences regardless of tidal phase. Data dispersion also increased with depth. Our findings illustrate the influence of stratification on suspended sediment properties, with marked vertical variability over short time scales. Textural properties highlighted different multi-modal features of grain-size distribution. The study also revealed spatial and temporal transitions associated with contrasting sediment transport conditions. Textural analysis enabled comprehensive interpretation of large datasets obtained through laser diffraction measurements.

Using hydrographic and zooplankton sampling along with stable isotope analyses, we determined the influence of freshwater input and of oceanic water ingress at the Golfo de Penas to the Baker Channel (47°S), central Patagonia, on the zooplankton community during mid-spring. Our results show that different taxonomic and functional groups occurred within the mesozooplankton community along an offshore-inshore-oriented transect. Some groups occurred mostly offshore (i.e. euphausiids, fish larvae, stomatopods, amphipods), while others occurred in higher abundance inshore (i.e. medusae, chaetognaths, siphonophores, ostracods). Early life stages of ecologically key species, such as Euphausia vallentini and pelagic stages of Munida gregaria, occurred mostly at the Golfo de Penas. Higher trophic positions estimated from δ¹⁵N occurred in mesozooplankton groups inshore (Baker Channel) and lower at the Golfo de Penas, coinciding with the decrease in C:N ratio in zooplankton and with an increase in chlorophyll-a values in the seawater seawards. The δ¹³C distribution in the zooplankton groups along the offshore-inshore transect showed a positive gradient from the inshore most stations towards the Baker Channel mouth, suggesting a negative relationship with freshwater carrying terrestrial organic carbon and a positive relationship with seawater. However, from the channel mouth seawards, a decrease in δ¹³C in most zooplankton groups occurred. Within the Baker Channel, low δ¹³C values occurred in particulate organic matter (POM) at the surface layer, higher values at intermediate depths, and low values at the deepest zones. This uneven distribution of δ¹³C values in POM and zooplankton, along with the presence of different water masses at different depths suggest an along-basin transport of organic carbon of different sources at different layers: of terrestrial origin at surface, marine origin at mid depth, and from degraded organic matter from offshore entering at higher depths. Thus, a complex scenario of lateral transport of water of different characteristics modulates the presence of zooplankton in different locations and their food sources along the area. These findings resemble others observed in further south in the Beagle Channel (57°S) also in spring but the relative contribution of different carbon sources may differ between Patagonian systems.

The increasing input of terrestrial pollutants is one of the major threats to coastal marine ecosystems. However, the impacts of pollutants discharged off the Changjiang Estuary (CJE) on the coastal waters of Zhejiang Province have not been quantitatively investigated. In this study, we focus on the transport processes of conservative pollutants discharged off the CJE using Eulerian tracers and Lagrangian particles coupled with a reliable 3D hydrodynamic model. The results show significant seasonal variations in pollutant transport and dispersion, which are highly associated with river discharge variation, the East Asian monsoon, and shelf circulations. Approximately 79% and 94% of the released pollutants are transported into the Zhejiang coastal waters in autumn and winter, respectively, which are mainly controlled by the Zhe-Min Coastal Current. We further reveal that, winter pollution covers ∼68% larger area in the Zhejiang coastal region, with ∼40% higher peak concentration value and ∼9 day longer duration compared to autumn pollution. Our study suggests that the water quality in the Zhejiang coastal region is potentially more vulnerable to pollutants discharged off the CJE in autumn and winter than in the other seasons, due to the influence of the coastal currents.

Dissolved organic matter (DOM) plays a crucial role in the biogeochemistry of coastal ecosystems, particularly nutrient cycling and distribution. Little is known about these processes in the highly productive Southern Patagonian shelf. This study was conducted to better understand the sources, composition, and behavior of DOM and inorganic nutrients in the sector between 51 and 56°S and 64–69°W with particular emphasis on inorganic nitrogen and DOM fractions. Surface water samples taken during late austral summer from the Beagle Channel (BCW), Subantarctic (SAW), Subantarctic Shelf (SASW), Grande Bay (GBW) and Tierra del Fuego Waters (TFW) and were analyzed for properties of fluorescent DOM (FDOM), dissolved organic carbon (DOC) and inorganic nutrients. Data were related to hydrographic and plankton conditions. Highest values of ammonium, DOC, humic-like FDOM (FDOM_C and FDOM_M peaks) and humification index (HIX) were found in BCW, and the lowest in SAW, suggesting that terrigenous input is a main source of ammonium and refractory carbon in this region, which is supported by a highly significant inverse correlation of these parameters with salinity. In contrast, nitrate, phosphate, silicate and the fluorescence index (FI) were positively correlated with salinity, pointing to the contribution of autochthonous FDOM from the saltier and nutrient-rich Antarctic Circumpolar Current to the Southern Patagonian shelf. In TFW and GBW, high nitrite concentrations, accompanied by elevated values of BIX (biological activity index of DOM), circulation patterns and high particle residence times computed from model results suggest the occurrence of regeneration processes that deserve further investigation of the poorly known dynamics of the nitrogen-rich water in this region.

Accurately predicting the flow speed is crucial for applications of coastal ocean circulation simulations such as sediment, larval or contaminant dispersal. This study aims to assess the accuracy of simulated flow speed in a coastal circulation model in comparison with field observations. Deviation between simulated and observed flow speed was assessed in four shallow, coastal locations and four deep, offshore locations in the Gulf of Lion (NW Mediterranean Sea) using six indicators (bias, relative bias, root mean square error, Hanna & Heinold index, correlation and scatter index). Statistical distributions of indicators were calculated during reference periods with low wind, no waves and no stratification. During these periods, relative bias indicated the model displayed a higher performance in predicting transport at shallow stations than at deep stations probably due to grid refinement at these stations. However, there was a low correlation between simulated and observed flow speed, indicating short term time/space mismatches, at all stations during reference periods. Indicators were then calculated during three types of events (wind, waves and stratification) when model assumptions were expected to be violated and their corresponding probability during reference periods indicated that neither wind, wave nor stratification events worsens model’s performance.

This study aimed to evaluate the relative importance of autochthonous (microplankton (i.e., phytoplankton and small heterotrophs), and Macrocystis pyrifera detritus) and allochthonous (terrestrial detritus) sources to the first levels of the planktonic trophic web supporting fish larvae in the Beagle Channel. Monthly samplings were conducted along the mid area of the Beagle Channel from March 2015 to February 2016, covering all seasons. Larval fish were present throughout the year, of which Patagonotothen spp. were dominant, particularly in spring. Bayesian stable isotope mixing models revealed that autochthonous carbon sources were more important for the particulate organic matter in surface (POM) and the particulate organic matter in sediment (SPOM) than allochthonous sources, which only slightly contributed to the POM. Also, seasonality in the contribution was observed. Microplankton was more important to the POM from the autochthonous carbon sources analysed, particularly in winter and spring. In addition, parts of the giant kelp M. pyrifera (blade, stipe and holdfast) equally contributed to the SPOM in all seasons. Microzooplankton organisms in the Beagle Channel depended on the POM and microplankton almost all the year, except in spring when SPOM gained relevance as a carbon source. Although fish larvae fed mainly on microzooplankton, a significant contribution of SPOM was also observed. Therefore, the giant kelp forests, in addition to providing refuge for fish larvae in the Beagle Channel, constitute an important carbon source for their planktonic prey during spring through the detrital pathway.

The viral shunt and microbial loop are trophic pathways in the microbial food web, recognized as major drivers of carbon and nutrient cycles in the sea. The Beagle Channel, located at the southernmost extreme of South America, is a subantarctic marine environment influenced by terrestrial runoff and glacial meltwater with high temporal and spatial variability. There is a knowledge gap on the trophic pathways and the microbial food web in the eastern part of the Channel. We herein present for the first time a comprehensive and spatially wide study of the effects of physicochemical and bio-optical parameters on the microbial food web along the Eastern Beagle Channel. The study took place under winter hydrographic conditions, featuring weak vertical stratification of the water column and low chlorophyll a concentrations (0.13 ± 0.07 mg m⁻³). Biogeochemical gradients were notable between the inner and outer (easternmost) sectors of the Channel, separated by a shallow sill at Mackinlay Strait. As a chemical water mass tracer, the presence of the highest concentrations in bottom waters of NO₃ + NO₂ in the inner channel and the difference in the T-S diagram indicate the Subantarctic Pacific origin of this water mass. Structural equation models showed that the specific UV absorbance of water (SUVA₂₅₄, a proxy for the aromatic carbon content) and NO₃ + NO₂ were the main parameters affecting the microbial food web in surface/subsurface waters suggesting that prokaryotes biomass was partially supported by allochthonous dissolved organic matter (DOM) derived from river discharges. Our results show a major role of the viral shunt in surface/subsurface waters retaining nutrients in the basal levels of the food web. We suggest that the viral shunt in surface/subsurface waters and the water residence time west of Mackinlay Strait allows infected cells and viral lysis products to reach bottom waters propelling the production of recalcitrant and labile DOM there.