Deep-Sea Research Part I-Oceanographic Research Papers最新文献

We investigated phytoplankton dynamics in the southern California Current System (SCCS) in August 2014 during the early phase of the 2014-15 marine heat wave (MHW). Multi-day experiments were conducted at three inshore and two offshore sites, with daily depth profiles of dilution incubations on a drifting array to determine growth and grazing rates and shipboard assessments of nutrient effects. Picophytoplankton populations were analyzed by flow cytometry and eukaryotic phytoplankton by 18 S sequencing. Mixed-layer nutrients were low across the region, but inshore sites had substantial nitrate concentrations and prominent Chla maxima in the lower euphotic zone. Shoreward transport of warm-stratified waters from the offshore suppressed coastal upwelling and shifted picophytoplankton distributions toward increased onshore abundance of Prochlorococcus and decreased Synechococcus and picoeukaryotes. These trends were reinforced by higher-than-average growth of Prochlorococcus at inshore sites and higher grazing of Synechococcus and picoeukaryotes. Prasinophytes (Chlorophyceae) were notably important among eukaryotic taxa, and pennates replaced centric taxa as the dominant diatoms in inshore waters compared to normal upwelling. Despite substantial spatial variability in community composition, offshore and inshore experimental locations both showed growth-grazing balances, with microzooplankton consuming similar percentages (80%) of primary production. We thus confirm expectations that the 2014-15 MHW resulted in greater trophic flow through the microbial food web at the expense of reduced direct phytoplankton (Chla) consumption by mesozooplankton. However, impacts on mesozooplankton energy budgets were partially offset by increased trophic flow through protistan microzooplankton and higher phytoplankton C:Chla.

We investigated spatiotemporal variations of nutrients, dissolved organic pools (C, N, P), phosphomonoesterase (PME) and phosphodiesterase (PDE) activities, heterotrophic prokaryotic production and planktonic microorganisms within the mixed layer (ML) in the Eastern Mediterranean Sea. We characterized two contrasted situations: autumn 2018 (highly stratified period, deep chlorophyll maximum within 100 m depth) and winter 2019 (including a bloom period). We compared the distribution of biogeochemical variables within the mixed layer and hydrological vertical structure between the different stations using a principal component analysis. Six groups of stations were identified (one group in autumn, 5 in winter), based on variable physical descriptors but also environmental biogeochemical conditions related to i) the seasonal aspect (for instance, all stations sampled within the Ierapetra anticyclone in autumn clustered in one, single group); ii) transitions between cyclonic and anticyclonic structures with a large range of ML depths (18–269 m) and indications of intense, preceding winter convection events: iii) progression of a high phytoplankton bloom during the winter cruise inferred from a series of observations: a strong nitrate drawdown, important growth of Synechococcus, pico and nano eukaryotes, accumulation of chlorophyll a (>60 mg m⁻²), primary production rates up to 509 mg C m⁻² d⁻¹, changes in the pigments’ diversity, increase in biomass-specific ectoenzymatic activities and of heterotrophic prokaryotic production, all in conjunction with the vicinity of the Rhodes gyre. Here, we studied the distribution of biological and biogeochemical properties within the mixed layer, in particular by employing sensitive methods for the detection of low phosphate concentrations and of the labile dissolved organic phosphorus pool. From this data set, we demonstrate that the surface mixed layer classically considered as a P-depleted and uniform layer in the Eastern Mediterranean Sea was highly biologically dynamic, and prone to rapid spatio-temporal changes in phosphatase activities and phytoplankton dynamics. Altogether, these data reveal a strong short-term population dynamics. The results highlight the role of mixing episodes in winter, which provide pulsed supplies of phosphate and/or nitrate from the deeper layer to the euphotic zone, triggering transient blooms that often go undetected by satellites.

The deep-pelagic ecosystem is characterized by significant environmental gradients, particularly in food resources. The absence of primary production below the epipelagic zone leads to a decrease in food resources with depth. Two opposite feeding strategies have been described for this community in response to this decline in food resources: stochasticity, with species adopting opportunistic feeding strategies with a generalist diet, and determinism, with species segregating and specializing to mitigate strong interspecific competition through niche partitioning. To test these aspects, we analyzed the isotopic niches of 16 fish species using stable isotope analysis of carbon and nitrogen carried out on muscle samples. The data were collected in canyons of the Bay of Biscay between 25 and 1335 m. Our primary objective was to identify isotopic niche segregation or overlap and determine whether species sharing similar isotopic niches show depth-based segregation by grouping them into trophic guilds and comparing their depth distribution with trawl data. We then used null model comparisons to test whether competition resulted in smaller values of isotopic niche size and overlap within each depth assemblage compared to those obtained by chance. We found that several species with similar isotopic niches were segregated based on depth. The comparison with null models showed that competition drove species to reduce niche size and specialize to avoid strong interspecific competition in the epi- to bathypelagic layers. Utilizing isotopic diversity indices weighted by biomass, our calculation showed significant divergence within the community, indicating that species with the highest biomass had extreme isotopic values. The high degree of specialization of species raises concerns about their vulnerability to various pressures, including climate change and exploitation. At the community level, this vulnerability is also a concern in maintaining the integrity of ecological processes.

The present study delves into the reproductive characteristics of Metapenaeopsis andamanensis, a commercially significant deep-water shrimp collected from Sakthikulangara, off Kollam, India (8°56′60.78″ N/76°32′34.27″ E) during September 2019 to May 2022. Despite its economic importance, the reproductive traits of this species remain elusive. This research comprehensively examines macroscopic and microscopic features associated with gonadal maturity stages, including determination of size at first maturity (CL₅₀), gonadosomatic index, and fecundity of M. andamanensis. Male-to-female sex ratio was noted as 1:1.03 using chi-square analysis. The smallest mature individuals were observed at 12 mm and 16 mm carapace length for males and females, respectively. Macroscopic observation categorized females into five groups based on gonadal coloration, while microscopic examination identified seven stages using histological characteristics. Notably, the absence of cortical crypts in the periphery of oocyte cytoplasm, a characteristic feature of the genus Metapenaeopsis, was observed in this species. Males were classified into two categories based on macroscopic and microscopic observation. The gonadosomatic index ranged from 4.25 to 10.13 for mature female individuals, exhibiting a significant increase until stage IV. Continuous spawning was observed, with a peak in May and November. The size at first maturity for females and males was determined as carapace length (CL) 23.05 mm and 17.53 mm, respectively. The average absolute fecundity was calculated as 53,889 with an average relative fecundity of 9934 oocytes. This investigation contributes valuable insights into the reproductive traits of the deep-water penaeid shrimp M. andamanensis, facilitating the development of effective management strategies for sustainable fisheries.

Fjords provide unique habitats for large cold-water coral (CWC) reefs, typically growing on sills and vertical walls. Fjord reefs are among the most thriving CWC reefs in Norway. Yet, these reefs, especially the wall reefs, are notoriously understudied. Here, we mapped the biomass, total carbon (C) stocks and C turnover (as respiration) of the reef-building coral Lophelia pertusa (syn. Desmophyllum pertusum), and dominant, large CWC reef-associated suspension feeders (the sponges Geodia barretti and Mycale lingua, the CWC Madrepora oculata and the bivalve Acesta excavata) within the Hardangerfjord, Norway. Remotely Operated Vehicle (ROV) recorded videos from wall and sill reefs were used to estimate species-specific biomass. Coupled with high resolution terrain data (2 × 2 m), predictive maps of species biomass were produced using a random forest (RF) model. The resulting biomass data were integrated with species-specific C content and C respiration rates from literature to estimate C stocks and C turnover of wall versus sill reefs. Area-specific results from the RF models reveal that wall reefs had a higher habitat suitability for all species except L. pertusa, which was more dominant on the sills. Accordingly, the wall reefs supported an up to 11 times higher biomass, C stock, and turnover for all species, except for L. pertusa, which had two-fold higher values on the sill reef. As a result, the wall reefs showed a 1.5 to 4.8 times higher total mean C turnover by dominant suspension feeders (all studied species) compared to the sill reefs. With their high C turnover and their presumably wide distribution in Norwegian fjords and globally, benthic wall reef megafauna may have a substantial, but overlooked biomass and functional role within CWC reef systems.

The Kuroshio ecosystem is an important nursery ground for various fish species. Because the prey biomass and composition influence the recruitment of larval and juvenile fish, we investigated the variation in the abundance, carbon biomass, and community structure of copepods, which are the main prey for larval and juvenile fish, along the Kuroshio from the eastern coast of Taiwan to the Boso Peninsula, Japan from 8–November 24, 2015, using 100 μm-meshed plankton net samples. We identified two groups of stations (A and B) by the cluster analysis based on the composition and abundance for adult copepods (Q-mode). The total copepod abundance and carbon biomass were higher in Group A than in Group B. Of the dominant species assemblages classified by cluster analysis (R-mode), the abundance of species assemblages S2b and S3, which were composed of small-sized species (e.g., Oithona and Oncaea species), did not differ between Groups A and B, indicating that they were distributed abundantly throughout the Kuroshio region. On the other hand, the species assemblages (S1 and S2a) including the medium-sized calanoid copepods of coastal species and subtropical species (e.g., Paracalanus aculeatus and Clausocalanus furcatus) contributed to the high abundance and biomass of Group A. Group A occurred in the north-frontal area of the Kuroshio axis near the Japanese archipelago where chlorophyll a was high. This indicates that the community was changed by the bottom-up processes driven by nutrient supply from the subsurface layer in the north-frontal area. These results show that although the small-sized copepods were usually dominant in numerical abundance in the Kuroshio region as well as other oligotrophic oceans, the medium-sized copepods were an important component in the copepod community in water with high primary production. We concluded that the ecosystem in the north-frontal area downstream of the Kuroshio might provide optimal prey environments for diverse fish larvae and juveniles.

Research on mesophotic reefs has increased thanks to technological advances such as remotely operated vehicles (ROV). The aim of this study was to evaluate differences in ichthyofaunal assemblages between shallow (<30 m) and mesophotic (>30 m) reef zones in three sites of the Parque Nacional zona marina del Archipiélago de Espíritu Santo (PNZMAES), a Marine protected area from the Gulf of California. To accomplish this objective, we used 14 video transects recorded with an ROV in October 2019 between 13 and 72 m depth. From these recordings, we determined species richness and abundance to analyze community structure and estimate biomass. A permutational multivariate analysis of variance was used to analyze differences between zones, sites, and their interaction. The abundance and estimated biomass of trophic groups were plotted to describe the trophic structure of the depth zones at PNZMAES. We also analyzed functional structure, functional richness (FRic), functional evenness (FEve), functional divergence (FDiv), functional specialization (FSpe), and functional originality (FOri) by depth zone and video transect based on six biological traits and estimated biomass. The taxonomic and functional indices were the response variables of linear models, while the explanatory variables were in situ temperature, light, and dissolved oxygen. At PNZMAES, 61 species were registered: 42 species in the shallow zone (high abundance and estimated biomass of planktivorous) and 40 species in the mesophotic zone (high abundance of planktivorous and high estimated biomass of piscivores). When comparing the ichthyofaunal community structure, differences were observed in richness, abundance, and estimated biomass associated with the depth zone, site, and the interaction of these variables. An overlap of more than 60% in the functional volume between zones was observed. Higher values of FRic, FDiv, and FSpe in the deep zone indicated that ecological functions were equivalent to those in the shallow zone. Finally, the linear models indicated an effect of environmental variables on the ecological indicators. The mesophotic reefs of PNZMAES are potential refuges for certain species (some of them endangered) and should be considered in the proposal of management strategies to protect them from future anthropogenic threats.

Oxygen minimum zones (OMZs) are characteristic of highly productive upwelling ecosystems and create unique conditions for benthic organisms that can adapt to hypoxic conditions and high quantities of organic material. Community structure, macrobenthic organism diversity, and biomass of giant filamentous bacteria (Candidatus Marithioploca) were studied along a bathymetric gradient from 79 to 935 m, including depths within and below the OMZ. Sediment samples were taken in both Huacho (11°S) and Callao (12°S) on the central coast of Peru using a van Veen grab sampler and multi-corers in October and November 2008. In addition to the biomass of Candidatus Marithioploca, the abundance, biomass, species richness, and structure of the macrobenthos were estimated on the surface as well as in the sediment column (i.e., 0–1, 1–2, 2–5, and 5–10 cm). The results indicate that, within the OMZ, there was a lower abundance and biomass of the macrobenthos but higher biomass of Candidatus Marithioploca. Within the OMZ, polychaetes were the dominant group, whereas below the OMZ, a diversity of taxonomic groups was recorded. The community structure reflects the gradient at depth as dissimilarity increases with depth. Diversity and evenness were lower within the OMZ and higher below the OMZ. The consistency of this pattern stands when compared to macrobenthos in the OMZ of other regions. The results of the present study highlight the importance of the OMZ as a modifying factor of benthic composition along depth gradients, particularly in diversity patterns.

Accurate sea surface temperature (SST) prediction is of great significance for fishery farming, marine ecological protection, and planning of maritime activities. In this paper, the stacked generalization ensemble is demonstrated for SST prediction to improve every single deep-learning model. Long-term high-resolution satellite-derived SST is used with the sub-regions of the Taiwan Strait and East China Sea taken as the study area. We select the Multilayer Perceptron, Long short-term memory (LSTM), Convolutional Neural Networks (CNN), CNN-LSTM as individual learners, and Convolutional LSTM as the meta-learner. The individual learners are trained and validated on the retained data subset I, while the meta-learner is trained and validated by constructing the samples with the predictions of validated individual learners on the retained data subset II. The two types of models are evaluated on the same test dataset with root-mean-square error and coefficient of efficiency as the scoring criteria. We find that the meta-model outperforms any individual model and other baselines for the one-day-/three-day-ahead forecasts in the Taiwan Strait and one-day-/three-day-/five-day-ahead predictions in the East China Sea. Furthermore, when the lead time is 1 day and 3 days, the meta-model has a better spatial distribution of prediction metrics across all grid points in the Taiwan Strait sub-area. For the East China Sea sub-region, the meta-model advantage is extended to the lead time of 5 days. Probably due to the higher quality of offshore satellite data, the prediction ability enhancement of the stacked ensemble applied in the East China Sea is better than that in the Taiwan Strait. The better-performing meta-model prediction suggests that the stacked generalization ensemble is encouraging and promising for improving the short-term prediction of the daily SST field.