Open research questions in Marine and coastal ecosystems

What the literature leaves open

• The study identifies technical challenges, such as the non-normal distribution of cell counts and the need for rarefaction to a relatively low number of reads. The research highlights domain challenges, including the complexity of microbial communities and the need for further research on their response to environmental disturbances.

  Community shift to picophytoplankton during the 2019 North Pacific marine heatwave · 2026 · DOI

• Lack of consideration for the nonmonotonic scale effect in previous studies.

  One-third of global lake nitrous oxide emissions are concentrated in the northern temperate zone (40°N–50°N) · 2026 · DOI

• Traditional methods for monitoring dissolved oxygen are limited in space and time. Remote sensing techniques can provide efficient and accurate inversions of water quality parameters, but the accurate prediction of dissolved oxygen levels is still a challenging task.

  Estimation of dissolved oxygen in reservoirs from UAV-drone, Sentinel-2 and Landsat-9 multisensor data using stacked-ensemble machine learning: review and case study experimental results · 2026 · DOI

• There is a need to understand the seasonal variations in nearshore phytoplankton communities. The relationships between environmental factors and phytoplankton community structure are not well understood.

  Seasonal Dynamics of Diatom–Dinoflagellate Relative Dominance and Its Environmental Determinants in a Shallow Coastal Nature Reserve: Insights from the Qingdao Amphioxus Municipal Nature Reserve, Yellow Sea · 2026 · DOI

• The strong land-sea interactions in the coastal South Yellow Sea have resulted in pronounced spatiotemporal heterogeneity of marine carbon sources and sinks. The study aims to address this gap by systematically analyzing the spatial variations, interannual trends, and key influencing factors of carbon sources and sinks in the coastal SYS.

  Spatiotemporal Characteristics of Carbon Source–Sink Dynamics in the Coastal Waters of the South Yellow Sea, China · 2026 · DOI

• The lack of an effective marine biomass utilization system for countermeasures of nutrient imbalance problems in enclosed seas. The need for a system that can enhance phytoplankton and seaweed growth in areas with nutrient deficiencies.

  Study on efficiency of marine biomass utilization system for countermeasures of nutrient imbalance in enclosed seas, part 2: fertilization effects for phytoplankton and seaweed · 2026 · DOI

• Further studies are needed to understand the effects of sea ice melting on the carbon cycle and primary production in the Southern Ocean. Research on the variability of POC: Chl a ratios in different sea ice environments is necessary. Investigations on the impact of climate change on sea ice production and carbon export to the depth are required.

  Biogeochemical controls on the concentrations and stable isotope compositions of sea-ice particulate organic matters in the Southern Ocean · 2026 · DOI

• The distinction between agricultural and non-agricultural sources of nitrate in coastal waters is particularly relevant along eastern boundary upwelling margins. Prior work has not fully addressed the seasonal nitrate, carbon and oxygen covariability in coastal receiving waters.

  Modelled Seasonal Nitrate, Carbon and Oxygen Covariability in Coastal Receiving Waters of Lambayeque, Peru (2022–2025) · 2026 · DOI

• It also notes the challenge of detecting reversals, or the release of sequestered carbon, and the need for continuous and adaptive monitoring. The paper mentions the challenge of varying regional MRV priorities and the need for tailored monitoring based on method and location.

  Monitoring, reporting, and verification of marine carbon dioxide removal: Exploring scientific consensus and divergences across continents · 2026 · DOI

• The lack of international agreement on MRV frameworks for mCDR. The scattered development of MRV frameworks by individual stakeholders. The need for a consolidated MRV framework that is widely accepted by the international scientific community.

  Monitoring, reporting, and verification of marine carbon dioxide removal: Exploring scientific consensus and divergences across continents · 2026 · DOI

• Prior work has not fully addressed the environmental drivers of phytoplankton distribution in this region.

  Seasonal Dynamics of Phytoplankton Community Structure and Environmental Drivers in the Coastal Waters of the Leizhou Peninsula, China · 2025 · DOI

• There is a need to investigate the ecological restoration and rational development of saline-alkaline lakes in northwest China. The research aims to fill this gap by analyzing the functional community structure of phytoplankton and its environmental drivers.

  Annual Dynamics of Phytoplankton Communities in Relation to Environmental Factors in Saline–Alkaline Lakes of Northwest China · 2025 · DOI

• The lack of a novel marker of stress in egg-carrying ectothermic planktonic organisms. The need for an efficient tool for demarcating reproductive efforts along with reference lines of packing constraints in bioindicator organisms. The limited understanding of reproductive strategies in keystone species like E. affinis.

  The Egg Packing Pressure Index of Calanoid Copepod as a Novel Eco-Indicator in Diverse Geographical Ecosystems · 2025 · DOI

• The paper identifies challenges related to the limited temporal resolution of the monitoring data, which can limit reliable assessments on shorter timescales. The paper also notes challenges related to the spatial representativeness of the dataset, which can be affected by wind, currents, mixing, and surface convergence.

  Phytoplankton Dynamics in a Large Lagoon: Nutrient Load Reductions, Climate Change, and Cold- and Heatwaves · 2025 · DOI

• The study also faced challenges in identifying species and genera, as some cells were unknown. The lagoon's poor condition and hyper-eutrophic state posed challenges for the study, as it affected the phytoplankton community structure and biomass.

  Seasonal Dynamics and Environmental Drivers of Phytoplankton in the Albufera Coastal Lagoon (Valencia, Spain) · 2025 · DOI

• The transient nature, rapid aggregation/disaggregation processes, and strong spatial and temporal variability of SPM complicate both field investigations and laboratory analyses, - Optical proxies require careful site-specific calibration, - The preparation of SPM samples for AFM may result in artefacts, - The study of SPM is limited due to their high mobility, reactivity, and difficulty…

  Mineralogical Investigation of Riverine Suspended Particulate Matter: A Comprehensive Review of Sampling, Characterization and Analytical Techniques · 2026 · DOI

• Emerging opportunities are offered by in-situ and autonomous sampling technologies, - Cryogenic and in-situ electron microscopy are promising techniques, - Machine-learning-based multimodal data fusion is a potential approach, - Harmonized sampling and analytical protocols are necessary for future…

  Mineralogical Investigation of Riverine Suspended Particulate Matter: A Comprehensive Review of Sampling, Characterization and Analytical Techniques · 2026 · DOI

• Investigate the use of other machine learning models for DO prediction, - Explore the application of SE-ML in other water quality parameters, - Examine the effect of different sensor data on DO…

  Estimation of dissolved oxygen in reservoirs from UAV-drone, Sentinel-2 and Landsat-9 multisensor data using stacked-ensemble machine learning: review and case study experimental results · 2026 · DOI

• The study uses a simulation model, - The regional empirical calibration is based on a limited number of satellite-in situ match-ups, - The study focuses on a specific tropical…

  Chlorophyll-a Dynamics in a Tropical Estuary from Satellite Observations and Coupled Hydrodynamic–Biogeochemical Modeling · 2026 · DOI

• The study identifies a gap in understanding the dynamics of chlorophyll-a in tropical estuaries, particularly in relation to river discharge and hydrodynamic processes.

  Chlorophyll-a Dynamics in a Tropical Estuary from Satellite Observations and Coupled Hydrodynamic–Biogeochemical Modeling · 2026 · DOI

• Suspended sediments, coloured dissolved organic matter (CDOM), and bottom reflectance in shallow waters may produce spectral signatures similar to harmful algal bloom signals, - Heterogeneity arising from atmospheric correction was not separated via alternative reprocessing workflows, - The Sentinel-2 MSI L2A product used in this study lacks per-pixel uncertainty…

  Multi-source satellite remote sensing of harmful algal blooms in the East China Sea: cross-sensor comparison of GOCI, Sentinel-2 and Sentinel-3 · 2026 · DOI

• Point-level accuracy metrics, area-level IoU against an independently interpreted boundary, temporal agreement and cross-sensor RMSD remain the appropriate targets for a future validation campaign, - A future study could quantify the discrepancy between OLCI…

  Multi-source satellite remote sensing of harmful algal blooms in the East China Sea: cross-sensor comparison of GOCI, Sentinel-2 and Sentinel-3 · 2026 · DOI

• Long-term monitoring of water quality using remote sensing tools, - Investigation of the effects of DANA events on other coastal…

  Flash-Flood-Induced Changes in the Hydrochemistry of the Albufera of Valencia Coastal Lagoon · 2025 · DOI

• Further studies should investigate the effects of other environmental factors on phytoplankton community structure, - Research should focus on the ecological environments of saline-alkaline lands and their impact on phytoplankton communities, - Studies should explore the potential applications of using fisheries to manage salinity in saline-alkaline water…

  Annual Dynamics of Phytoplankton Communities in Relation to Environmental Factors in Saline–Alkaline Lakes of Northwest China · 2025 · DOI

• Further study on the relationship between packing pressure index and clutch size, - Investigation of the effects of global warming and severe heat shock on the packing pressure index, - Research on the presence of an egg sac membrane among Copepoda…

  The Egg Packing Pressure Index of Calanoid Copepod as a Novel Eco-Indicator in Diverse Geographical Ecosystems · 2025 · DOI

Most-cited papers in Marine and coastal ecosystems

• Isotopic Variations in Meteoric Waters · Science · 1961 · 7,044 citations
• Spreading Dead Zones and Consequences for Marine Ecosystems · Science · 2008 · 5,630 citations
• Primary Production of the Biosphere: Integrating Terrestrial and Oceanic Components · Science · 1998 · 5,424 citations
• Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate · Nature · 1987 · 3,471 citations
• Biogeochemical Controls and Feedbacks on Ocean Primary Production · Science · 1998 · 2,373 citations
• Global carbon dioxide emissions from inland waters · Nature · 2013 · 2,272 citations
• Particulate organic matter flux and planktonic new production in the deep ocean · Nature · 1979 · 2,052 citations
• Twenty-first century ocean warming, acidification, deoxygenation, and upper-ocean nutrient and primary production decline from CMIP6 model projections · Biogeosciences · 2020 · 717 citations
• Coastal phytoplankton blooms expand and intensify in the 21st century · Nature · 2023 · 601 citations
• Global mapping reveals increase in lacustrine algal blooms over the past decade · Nature Geoscience · 2022 · 578 citations

Most recent work

• Linking hypolimnion to epilimnion in a stratified arctic lake: Machine learning-based estimation of hypolimnetic water quality from epilimnetic measurements · Water Research · 2026
• Molecular-weight-dependent mixing behavior of organic phosphorus and carbon in a subtropic river-estuary-bay continuum · Water Research · 2026
• Global inland waters trophic status from space observation: scientific advances and future challenges · Water Research · 2026
• Cascade Reservoirs Regulate Molecular Signatures and Biogeochemical Pathways of Dissolved Organic Matters in the Lancang River · Environmental Science & Technology · 2026
• Bridging causality and deep learning for harmful algal bloom prediction · Water Research · 2026
• Widespread presence of anthropogenic compounds in marine dissolved organic matter · Nature Geoscience · 2026
• Ocean biological carbon pump: The evolution and prospects · Journal of CO2 Utilization · 2026
• Advancing Earth System Science With the NASA Plankton, Aerosol, Cloud, Ocean Ecosystem ( PACE ) Satellite Mission · Global Change Biology · 2026
• Global Responses of Phytoplankton Size Structure to Marine Heatwaves · Global Biogeochemical Cycles · 2026
• A Revised Estimate of Calcium Carbonate Dissolution in Coastal and Shelf Sediments Suggests Large Shelf Exports in the Marine CaCO 3 Cycle · Global Biogeochemical Cycles · 2026

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