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International Journal of Marine Science (online), 2025, Vol. 15, No. 6 ISSN 1927-6648 http://aquapublisher.com/index.php/ijms © 2025 AquaPublisher, registered at the publishing platform that is operated by Sophia Publishing Group, founded in British Columbia of Canada. All Rights Reserved. Latest Content Predictive Displacement Theory (PDT): An AI-Assisted Framework for Forecasting Jellyfish Movement Based on Citizen Observations and Environmental Drivers C. Taklis International Journal of Marine Science, 2025, Vol. 15, No. 6, 287-291 Bioavailability of Phosphorus in Marine Ecosystems: Sources, Transport, and Ecological Impacts Yeping Han, Wenfang Wang International Journal of Marine Science, 2025, Vol. 15, No. 6, 292-302 Health Management Techniques for Sustainable Marine Aquaculture Wenzhong Huang, Kaiwen Liang International Journal of Marine Science, 2025, Vol. 15, No. 6, 303-312 Roles of Marine Microorganisms in the Carbon, Nitrogen, and Sulfur Cycles Bing Wang, Qikun Huang International Journal of Marine Science, 2025, Vol. 15, No. 6, 313-319 Environmental Impact of Tropical Sea Cucumber Mariculture Practices Manman Li, Liping Liu International Journal of Marine Science, 2025, Vol. 15, No. 6, 320-328
International Journal of Marine Science, 2025, Vol.15, No.6, 287-291 http://www.aquapublisher.com/index.php/ijms 287 Research Article Open Access Predictive Displacement Theory (PDT): An AI-Assisted Framework for Forecasting Jellyfish Movement Based on Citizen Observations and Environmental Drivers C. Taklis Merman Conservation Expeditions Ltd., Edinburgh, United Kingdom Corresponding author: mermanconservation@gmail.com International Journal of Marine Science, 2025, Vol.15, No.6 doi: 10.5376/ijms.2025.15.0026 Received: 21 Aug., 2025 Accepted: 23 Oct., 2025 Published: 06 Nov., 2025 Copyright © 2025 Taklis, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Taklis C., 2025, Predictive Displacement Theory (PDT): an AI-assisted framework for forecasting jellyfish movement based on citizen observations and environmental drivers, International Journal of Marine Science, 15(6): 287-291 (doi: 10.5376/ijms.2025.15.0026) Abstract Jellyfish blooms are increasing in frequency and intensity across the Mediterranean Sea, posing growing challenges to tourism, fisheries, public safety, and coastal ecosystem monitoring. Despite the rise of citizen science platforms and the availability of real-time environmental data, no operational system currently exists to forecast jellyfish movement. This paper introduces the Predictive Displacement Theory (PDT), the first proposed framework for forecasting jellyfish drift by combining user-submitted sightings with environmental drivers such as wind, wave direction, sea surface currents, and atmospheric pressure. The concept is designed to operate through an AI-assisted application that ingests real-time observations and oceanographic data to generate short- and medium-term forecasts of jellyfish aggregations. As a proof of concept, the framework was retrospectively tested on the 2020~2023 Pelagia noctiluca blooms in Greece, with a focus on the Corinthian Gulf during 2021 and 2022, using Windy.com datasets and georeferenced observations from the iNaturalist platform and a Facebook group. Even without AI support, the model predicted southward jellyfish movement with up to 90% accuracy over five-day periods. These findings demonstrate the viability of PDT and its potential to evolve into the first real-time jellyfish forecasting system, supporting both ecological forecasting and timely public warning mechanisms. Keywords Jellyfish blooms; Predictive Displacement Theory; AI-assisted forecasting; Citizen science; Coastal ecosystem management 1 Introduction Jellyfish blooms have emerged as one of the most visible and disruptive phenomena in coastal marine ecosystems, particularly in semi-enclosed basins such as the Mediterranean Sea. In recent decades, reports of large jellyfish aggregations have increased in both frequency and spatial extent, attributed to a combination of climate change, overfishing of natural predators, eutrophication (Fernández-Alías et al., 2024), and changing oceanographic conditions (Gravili, 2020). These blooms not only disrupt local food webs but also interfere with human activities, including fisheries (Palmieri et al., 2015), aquaculture operations, power plants, and especially tourism, where jellyfish stings can deter swimmers and reduce coastal revenue. In the Mediterranean, species such as Pelagia noctiluca have become increasingly dominant (Bordehore, 2023) during summer months, forming large swarms that drift with currents and winds. However, despite their growing impact (Praved et al., 2021), there is currently no operational system capable of forecasting jellyfish movement in real time (Marambio et al., 2021). While citizen science platforms such as iNaturalist have improved spatial data availability, and while environmental datasets on wind, waves, and currents are widely accessible through services like Windy and Copernicus Marine, these data streams remain unconnected in any unified forecasting framework (Avazbek Furqat o’g’li et al., 2022) for jellyfish behavior. This paper introduces the Predictive Displacement Theory (PDT) as a novel theoretical and technical framework aimed at filling this gap. PDT proposes that jellyfish movement in coastal systems follows semi-deterministic paths (Edelist et al., 2022) influenced by physical oceanographic forces and initial population inputs. By leveraging citizen-submitted sightings as anchor points and combining them with dynamic environmental vectors, PDT offers
International Journal of Marine Science, 2025, Vol.15, No.6, 287-291 http://www.aquapublisher.com/index.php/ijms 288 the basis for an AI-powered forecasting system (Castro‐Gutiérrez et al., 2024) capable of predicting jellyfish aggregations (Marambio et al., 2021) over short (1~3 days) and medium (up to 10 days) timescales. To test the viability of this framework, we retrospectively applied PDT principles to a well-documented case: the widespread blooms of Pelagia noctiluca in the Greece but focused on the Corinthian Gulf between 2021 (Taklis, 2022) and 2022 (Taklis, 2023). Using geo-referenced observations from a facebook group, iNaturalist platform and environmental data from Windy.com, we simulated the southward movement of jellyfish swarms under realistic meteorological conditions (Berline et al., 2013). While the test did not include machine learning, it successfully replicated bloom drift with high accuracy, supporting the foundation of PDT as a predictive tool (Gauci et al., 2020). This paper presents the theoretical foundations of PDT, outlines its operational structure, and discusses the potential for its evolution into the first real-time jellyfish forecasting system, designed for use by scientists, coastal managers, tourism operators, and the general public. Unlike traditional hydrodynamic or ecological models, which depend heavily on numerical simulations and extensive in-situ oceanographic datasets, PDT provides a lightweight and adaptive framework by directly coupling citizen science observations with real-time environmental drivers. This integration of participatory data and openaccess oceanographic streams represents a novel approach to forecasting jellyfish movement, bridging the gap between community monitoring and applied ecological modeling. 2 Methodology 2.1 Overview of the PDT framework The Predictive Displacement Theory (PDT) (Castro‐Gutiérrez et al., 2024) is based on the hypothesis that jellyfish blooms do not disperse randomly (Edelist et al., 2022) but follow movement corridors shaped by environmental forces, such as wind, sea surface currents, and wave dynamics (Castro-Gutiérrez et al., 2022). PDT treats each jellyfish sighting as an origin point for displacement modeling, where jellyfish swarms are passively transported through marine physical vectors (Fossette et al., 2015). The proposed system is designed to operate as a modular forecasting tool that combines three data layers: Citizen science input: georeferenced observations submitted by users (Gutiérrez-Estrada et al., 2021) via a mobile or web-based app. Environmental data streams: real-time meteorological and oceanographic parameters from open-access platforms. AI or rule-based simulation engine: a model that processes the above inputs to generate spatial forecasts of jellyfish movement. The initial implementation of PDT relies on vector-based simulations, but future versions are intended to incorporate AI models trained on historical bloom data. 2.2 Data Sources 2.2.1 Citizen observations Jellyfish sighting data were sourced from the Facebook group “Jellyfish in Greece,” a public citizen science community where users submit reports including date, location, photographs, and species-level identifications. For the purposes of this study, records of Pelagia noctiluca from the Corinthian Gulf between 2021 and 2022 were extracted, filtered for accuracy, and aggregated to identify spatiotemporal patterns and likely bloom initiation zones. Data quality was ensured through a multi-step filtering process. Duplicate reports and those lacking geolocation or time stamps were removed. Only records supported by photographic evidence were retained, and species-level identifications were cross-validated using community consensus on iNaturalist and additional expert review. This reduced the dataset to 150 verified observations between 2020 and 2023, with higher concentrations during June to September. Reports were aggregated into weekly intervals and mapped to subregions of the Corinthian Gulf to establish bloom initiation zones and subsequent displacement patterns. 2.2.2 Environmental data Environmental inputs were retrieved from Windy.com and related APIs, including: Wind speed and direction at 10 m altitude; Surface current velocity and direction; Wave height, period, and direction; Sea surface temperature (SST); and Atmospheric pressure maps.
International Journal of Marine Science, 2025, Vol.15, No.6, 287-291 http://www.aquapublisher.com/index.php/ijms 289 These variables were extracted at a 3-hour resolution, interpolated where necessary, and matched to the timing and location of citizen observations. 2.3 Displacement modeling process The PDT simulation applies a simplified particle advection model in which each sighting is treated as a release point for a virtual jellyfish swarm. The swarm is then projected forward using a composite vector equation: D = αW + βC + γV + δT Where: D is the displacement vector; W = wind vector; C = current vector; V = wave vector; T = temperature gradient; α–δ are weighted coefficients reflecting the relative influence of each factor. In the absence of AI, coefficients were manually calibrated based on observational alignment with bloom progression over time. Each sighting generated a prediction envelope, producing a forward simulation of likely jellyfish distribution for the following 1~5 days. 2.4 Limitations and assumptions This pilot version of PDT assumes passive drift behavior for jellyfish swarms and does not account for: Vertical migration patterns (Malul et al., 2024) (e.g. diel movement (Hays et al., 2012)); Active swimming behavior in some species; Biological factors like reproduction or bloom collapse; Coastal geomorphology (e.g. barriers, eddies, bathymetric influence). In addition, the current approach is deterministic and not probabilistic, which may limit its precision during periods of highly variable weather. 3 Results To evaluate the feasibility of the Predictive Displacement Theory (PDT) as a forecasting framework, we retrospectively applied its core principles to the extensive blooms of Pelagia noctiluca that spread through the Aegean Sea in the Corinthian Gulf between 2020 and 2023. These blooms were among the most persistent and widely reported in recent Mediterranean history, significantly impacting tourism, fisheries, and public safety across coastal regions of Greece. 3.1 Observation dataset Over 150 georeferenced Pelagia noctiluca observations were retrieved from the Facebook Group “Jellyfish in Greece” and iNaturalist platform, concentrated in the summer months (June to September) from 2021 to 2022. These included user-submitted photos and estimated abundances along northern and southern shores of the Corinthian Gulf. Sightings showed clear temporal clustering, often appearing in bursts following periods of sustained northerly winds and calm sea states. 3.2 Environmental drivers Environmental data collected from Windy.com revealed recurring meteorological patterns during peak bloom events: Northerly winds exceeding 20 km/h sustained for 24~48 hours. Weak east-to-west surface currents within the semienclosed Gulf. Warm sea surface temperatures exceeding 25 °C. Low wave energy in the southern coastline areas. These conditions were considered favorable for jellyfish drift from the south-eastern coasts toward south-western regions, particularly from Kiato to Derveni. 3.3 Forecasting simulation Using the PDT model in a manual, rule-based mode (without AI), jellyfish sightings were treated as initial displacement nodes. Based on contemporaneous wind, current, and wave data, forward trajectories were simulated for 5-day intervals during peak bloom periods. Key outcomes include: Southward movement predictions aligned with observed bloom locations in 2021 and 2022 with up to 90% spatial accuracy over 5-day windows. The strongest predictive alignment occurred during episodes of northerly winds combined with low wave heights (<0.8 m), which facilitated passive surface drift. Areas such as
International Journal of Marine Science, 2025, Vol.15, No.6, 287-291 http://www.aquapublisher.com/index.php/ijms 290 the southern Corinthian Gulf coastlines consistently received aggregations 2 to 4 days after initial observations were reported along southern shores. While the forecasting in this phase did not use AI or machine learning, the results demonstrated strong correspondence between predicted and actual bloom displacement. 4 Discussion The retrospective application of the Predictive Displacement Theory (PDT) to the Pelagia noctiluca blooms in the Greece from 2020 to 2023 and specifically in the Corinthian Gulf from 2021 to 2022, provides a promising indication that jellyfish movement can be forecast with reasonable accuracy using a combination of citizen science data and environmental information. Despite the absence of artificial intelligence in this initial phase, the model’s ability to predict southward drift with up to 90% accuracy over a five-day period demonstrates the potential of PDT as a foundation for real-time forecasting tools. The integration of citizen observations with open-access environmental data streams such as those provided by Windy.com offers a cost-effective and scalable method for ecological monitoring. Public contributions through platforms like iNaturalist not only enhance spatial coverage but also improve temporal resolution, which is critical for capturing dynamic bloom behavior. The Corinthian Gulf’s physical characteristics, including its semi-enclosed geography and prevailing current and wind patterns, make it particularly suitable for applying the PDT framework. The consistent pattern of northerly winds driving jellyfish swarms toward the southern coastline is well captured by the model, reflecting the semideterministic displacement corridors hypothesized in the theory. Looking ahead, incorporating artificial intelligence and machine learning techniques will be essential for refining the model, enabling automated data processing, and producing probabilistic forecasts. Such advancements could facilitate real-time alerts for stakeholders, including coastal managers, fisheries, and the general public. To achieve this, future development should focus on expanding training datasets, improving data validation protocols, and integrating additional environmental variables such as vertical water column profiles and biological behavior patterns. Limitations of the current study include the assumption that jellyfish move primarily as passive drifters, without accounting for vertical migration, active swimming, or biological life cycle events. Furthermore, finer-scale coastal geomorphological features were not included in the model, which may affect local swarm behavior nearshore. Overall, this study lays the groundwork for the first operational jellyfish forecasting system. By combining community science with environmental modeling, PDT offers a novel approach to managing the increasing ecological and socio-economic impacts of jellyfish blooms in the Mediterranean and beyond. While the retrospective validation of PDT demonstrates strong predictive potential, several limitations should be acknowledged. First, the reliance on citizen science introduces seasonal and geographic biases, as reports are concentrated during summer months and near populated coastal areas, leaving offshore and winter dynamics underrepresented. Second, data sparsity and uneven spatial coverage may limit the accuracy of predictions in undersampled regions. Third, the integration of real-time AI poses computational and logistical challenges, including automated data validation, continuous assimilation of environmental streams, and the infrastructure required to support large-scale forecasting applications. Addressing these limitations will be critical for scaling PDT into a fully operational forecasting tool across the Mediterranean. Acknowledgements I gratefully acknowledge the valuable contributions of citizen scientists who submitted jellyfish observations to the iNaturalist platform, and the Facebook group “Jellyfish in Greece”, without whom this study would not have been possible. References Avazbek Furqat o’g’li, A., Kalandarovna O.X., and Rubio Fátima S., 2022, Jellyfish diversity, trends and patterns in Southwestern Mediterranean Sea: a citizen science and field monitoring alliance, Journal of Plankton Research, 44(6): 819-837. https://doi.org/10.1093/plankt/fbac057
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International Journal of Marine Science, 2025, Vol.15, No.6, 292-302 http://www.aquapublisher.com/index.php/ijms 292 Review Article Open Access Bioavailability of Phosphorus in Marine Ecosystems: Sources, Transport, and Ecological Impacts Yeping Han , Wenfang Wang Institute of Life Science, Jiyang College of Zhejiang A&F University, Zhuji, 311800, Zhejiang, China Corresponding author: yeping.han@jicat.org International Journal of Marine Science, 2025, Vol.15, No.6 doi: 10.5376/ijms.2025.15.0027 Received: 20 Sep., 2025 Accepted: 30 Oct., 2025 Published: 20 Nov., 2025 Copyright © 2025 Han and Wang, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Han Y.P., and Wang W.F., 2025, Bioavailability of phosphorus in Marine ecosystems: sources, transport, and ecological impacts, International Journal of Marine Science, 15(6): 292-302 (doi: 10.5376/ijms.2025.15.0027) Abstract Phosphorus is an indispensable nutrient element in Marine ecosystems and plays a key role in the Marine food web and biogeochemical cycles. Phosphorus in the ocean exists in various chemical forms and is constantly cycled and transformed through biological and abiotic processes. This study Outlines the main sources of Marine phosphorus and its migration and transformation mechanisms in the Marine environment. The key environmental and biological factors influencing the bioavailability of phosphorus were analyzed. By comparing the relationship between primary productivity and phosphorus limitation in different sea areas, and combining regional cases such as the Mediterranean Sea, the South China Sea, and the North Atlantic, the impact of phosphorus supply changes on plankton communities and ecosystems is revealed. Finally, the evolution trend of the Marine phosphorus cycle under the background of global change and human activities is discussed, as well as the problems of eutrophication and red tides caused by phosphorus excess. The future research and management of the Marine phosphorus cycle are also prospected. Keywords Marine phosphorus cycle; Bioavailability; Phosphorus limitation; Primary productivity; Eutrophication 1 Introduction The importance of phosphorus (P) to Marine life is almost self-evident. It, like nitrogen (N) and carbon (C), is the most fundamental nutrient for life activities, but its role is more inclined to be a "connector between energy and genetics". The key molecules such as DNA, RNA and ATP all rely on the participation of phosphorus. Even the cell membrane needs phospholipids to maintain structural stability (Murphy et al., 2021). However, phosphorus is not always an abundant resource in the ocean. Often, it is the "bottleneck" for the growth of phytoplankton. Once there is a shortage of available phosphorus, the efficiency of photosynthesis will decline, and the chain effect will eventually be passed on to higher trophic levels. In contrast, there is a gaseous exchange pathway in the nitrogen cycle, while there is no such link in the phosphorus cycle. It mainly flows back and forth between the hydrosphere and the lithosphere in the form of dissolved and particulate states (Jin et al., 2024). As for the supply of phosphorus in the ocean, it mainly depends on two aspects: terrestrial transport and internal regeneration. Any fluctuation in any link will affect the balance of the entire ecosystem. On a global scale, the picture of the phosphorus cycle is more like a long-term "deposition and regeneration" game. Rock weathering and river transportation are the starting points of most Marine phosphorus. After entering the ocean, phosphorus does not exist in isolation but is classified into various forms such as dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP), and particulate phosphorus, constantly flowing through absorption, sedimentation, and decomposition. In the vertical direction, phosphorus in surface seawater is often rapidly consumed by phytoplankton, while in the deep layer, more phosphate accumulates due to the decomposition of organic matter (Zhao et al., 2020). When the upwelling brings these phosphorus-rich water bodies back to the surface, the "biological pump" cycle is completed. However, this cycle is not balanced across different sea areas: for instance, the phosphorus concentration in the deep water of the Pacific Ocean is usually higher than that in the Atlantic Ocean, which is the result of long-term accumulation. Overall, phosphorus remains in the ocean for an extremely long time, often for tens of thousands of years, but this does not mean that it is evenly distributed. On the contrary, regional
International Journal of Marine Science, 2025, Vol.15, No.6, 292-302 http://www.aquapublisher.com/index.php/ijms 293 differences are obvious. In some areas, phosphorus is almost depleted, while in others, it is enriched due to geological or hydrological conditions (Zhang et al., 2025). The research on the bioavailability of Marine phosphorus has long trantioned academic discussions in significance. As a key limiting element, phosphorus almost determines the upper limit of primary productivity and also shapes the structure of ecosystems. Clarifying the utilization methods and control mechanisms of different forms of phosphorus can not only explain the community turnover of phytoplankton but also help understand the changes in Marine carbon sinks. In reality, human influence has long permeated this cycle. The use of chemical fertilizers and the discharge of sewage have led to a continuous increase in the phosphorus load of coastal water bodies, causing eutrophication and even ecological disorders (Hao et al., 2025); Meanwhile, atmospheric deposition and climate change are rewriting the phosphorus input pattern in the distant-water areas, causing some sea areas that were originally nitrogen-restricted to gradually shift towards phosphorus-restricted. For this reason, the research on the bioavailability of phosphorus is not only related to theoretical improvement, but also to Marine management and climate response. 2 Chemical Forms and Distribution Characteristics of Phosphorus in the Ocean 2.1 Main components and transformations of inorganic and organic phosphorus Phosphorus in the ocean can be divided into two major categories: inorganic phosphorus and organic phosphorus. Inorganic phosphorus mainly refers to dissolved inorganic phosphorus (DIP, that is, phosphate ions), which can be directly absorbed and utilized by phytoplankton and microorganisms. Organophosphorus includes dissolved organophosphorus (DOP) and granular organophosphorus (POP), which exist in organic molecules and decomposition products in organisms. Generally, it needs to be converted into inorganic phosphorus through enzymatic hydrolysis before it can be assimilated (Murphy et al., 2021). Marine organisms absorb DIP and construct phosphorus into their own organic matter. When organisms die or excrete, DOP and POP are produced. After microbial decomposition, phosphate is released again, achieving the re-conversion of organic phosphorus to inorganic phosphorus (Jin et al., 2024). In addition, under specific conditions, phosphates in the environment can combine with metal ions and precipitate into granular inorganic phosphorus (such as apatite), which then settles to the seabed. 2.2 Vertical distribution and spatiotemporal variation patterns of phosphorus in seawater The vertical distribution of phosphorus in Marine water bodies shows a typical feature of being low in the surface layer and high in the deep layer: the phosphorus concentration in the surface layer is often close to depletion due to the rapid absorption by phytoplankton. In the middle and deep layers, due to the decomposition of settled organic particles, inorganic phosphates are released, making the deep seawater rich in phosphorus (Duhamel, 2024). During seasonal changes, vertical mixing of seawater in winter can bring deep phosphorus to the surface layer, temporarily increasing the phosphorus content in the surface layer. In spring and summer, phytoplankton multiply vigorously and consume a large amount of phosphorus, causing the surface layer to become scarce again. In terms of spatial scale, there are significant differences in phosphorus levels among different sea areas: The surface phosphorus concentration is relatively high in coastal and estuarine areas due to river input and upwelling (Brady et al., 2022); On the contrary, in closed waters such as the subtropical circulation center of the open sea, the surface phosphorus level is extremely low throughout the year. Due to the limitations of light or iron in high-latitude seas, phytoplankton do not fully utilize phosphorus, and a certain amount of phosphate is often retained in the surface layer. 2.3 Differences in phosphorus dynamics among various ecological zones There are obvious differences in the dynamics of phosphorus cycling in different ecological regions of the ocean. Coastal and estuarine areas are strongly influenced by terrigenous substances, and the phosphorus concentration in water bodies fluctuates with the seasons and human activities: During the wet season, river runoff carries a large amount of inorganic phosphorus and particulate phosphorus, leading to a sharp increase in local phosphorus content. The input decreased during the dry season and the phosphorus concentration dropped (Zhang et al., 2025). In contrast, in oligotrophic sea areas such as oceanic circulation centers, phosphorus supply is chronically scarce and changes gently. Ecosystems can only rely on mechanisms such as microbial loops to repeatedly recycle trace
International Journal of Marine Science, 2025, Vol.15, No.6, 292-302 http://www.aquapublisher.com/index.php/ijms 294 amounts of phosphorus. In the upwelling area, due to the influx of deep phosphorus-rich seawater, the surface phosphorus is relatively abundant, maintaining high primary productivity. However, in some semi-enclosed sea areas with severe stratification (such as deep water anoxic basins), phosphorus accumulates in large quantities in the deep layers but cannot be replenished to the surface, resulting in a pattern of phosphorus-poor upper layers and phosphorus-rich deep layers (Zeng et al., 2022). Due to the differences in hydrological, topographic and biological factors, the phosphorus cycle in different ecological zones shows unique dynamics, which require separate studies for specific environments. 3 Major Sources of Marine Phosphorus 3.1 Terrestrial inputs: river runoff, agricultural, and industrial discharges Land-based input is an important exogenous source of Marine phosphorus, among which river runoff plays a key role. Phosphate released from the weathering of terrestrial rocks flows into the ocean via rivers. Meanwhile, a large amount of phosphorus-containing pollutants produced by human agricultural fertilization, animal husbandry and industrial life emissions are also carried into the coastal areas through rivers. The phosphorus output in modern river basins has significantly increased compared to the natural situation, resulting in a significant increase in the phosphorus load of estuarine and nearshore water bodies (Jin et al, 2024). A portion of the phosphorus transported by rivers exists in dissolved form and can be directly utilized by Marine organisms. Another part was adsorbed on the sediment and deposited in estuaries and continental shelves in the form of granular phosphorus (Wang et al., 2021). An appropriate amount of phosphorus input can support high primary productivity and fishery resources along the coast, but excessive phosphorus can cause environmental problems such as eutrophication, algal blooms and even hypoxia. Therefore, the input of land-based phosphorus plays a profound role in regulating the coastal ecosystem, and its control is crucial for maintaining the Marine ecological balance. 3.2 Atmospheric deposition and phosphorus transport via dust In the sea far from the shore, people often rely on things that fall from the sky to get some nourishment. The wind sweeps up dust from the arid continent, which contains phosphorus mineral particles. After transoceanic flight, it falls into the sea, adding a handful of phosphorus to the surface water (Dam et al., 2021). The example in the North Atlantic is quite intuitive: Sahara dust not only brings phosphorus but also iron, benefiting phytoplankton. However, not all the phosphorus that falls is effective. Most of the phosphorus in mineral dust is in insoluble inorganic form. However, during flight, acidic gases are encountered. Some of the phosphorus is "pre-treated" and becomes soluble, making it easier for organisms to utilize (Hu et al., 2025). In recent years, the climate has been changing, and so has the dust: drier continents and stronger winds may increase the output of dust. However, when the temporal and spatial distribution of rainfall changes, the rhythm of sedimentation also becomes disrupted. The result is that the way and intensity of phosphorus reception in the open sea areas have been rewritten, and primary productivity and carbon sink capacity may also fluctuate accordingly. 3.3 Contributions from seafloor geological processes and sediment release There are also mechanisms for the release of phosphorus through geological and sedimentary processes within the ocean. Submarine volcanic eruptions and hydrothermal activities release phosphorus-containing substances into seawater. Although this part of the flux is relatively small and localized, it may contribute to the surrounding phosphorus levels in areas with frequent volcanic activities (Liu et al., 2023). More commonly, there is the re-release of phosphorus from sediments: the ocean uses biological pumps to deposit large amounts of phosphorus on the seabed, and sediments become huge phosphorus reservoirs. When the bottom water body is hypoxic, phosphorus combined with oxides such as iron in the sediment is desorbed due to reduction and diffuses into the overfacing seawater (Guo et al., 2020); Phosphorus produced by the decomposition of organic matter can also be released into the water column from pore water. The disturbance of benthic organisms can also bring out some buried phosphorus and integrate it into the cycle. However, most of the phosphorus that enters the sediment is eventually fixed and buried in the geological layer in the form of minerals, so the seabed process is generally the "destination" of Marine phosphorus. Only a small amount of sedimentary phosphorus released under special conditions remains an indispensable part of the nutrient supply in some local sea areas.
International Journal of Marine Science, 2025, Vol.15, No.6, 292-302 http://www.aquapublisher.com/index.php/ijms 295 4 Transport and Transformation Mechanisms of Phosphorus in the Marine Environment 4.1 Transport pathways of dissolved and particulate phosphorus The migration of phosphorus in the ocean occurs through two pathways: dissolved state and particulate state. Dissolved phosphorus (including DIP and soluble DOP) spreads with the flow of seawater: Ocean currents and upwelling transport phosphorus-rich water masses to other areas, and vertical mixing carries deep dissolved phosphorus to the surface (Murphy et al., 2021). These hydrodynamic processes shape the large-scale distribution pattern of phosphorus. In contrast, granular phosphorus mainly migrates along the vertical direction through gravitational sedimentation. Organic debris particles formed by plankton sink downward, transporting phosphorus from the surface to the deep sea. This "biological pump" process causes surface phosphorus to continuously move out and accumulate in the deep sea (Browning et al., 2017). Some of the sinking particles are decomposed during the process, and the phosphorus assimilated re-dissolves into the surrounding water body. The undecomposed ones eventually sink into the seabed sediments. In addition, phosphorus-containing sediment suspended in coastal waters can also be carried by coastal currents and transported horizontally near the bottom layer. The long-distance transport in dissolved form and the sedimentation in granular form jointly determine the spatiotemporal redistribution of Marine phosphorus. 4.2 Microbially driven degradation and remineralization of organic phosphorus The degradation and remineralization of organic phosphorus in the ocean are highly dependent on microbial activities. Heterotrophic bacteria and other microorganisms secrete phosphatases that hydrolyze DOP into inorganic phosphates, converting the originally unusable organic phosphorus into an absorbable form. When phosphorus is scarce, many phytoplankton and microorganisms can significantly increase the production and activity of alkaline phosphatase (AP), "extracting" phosphorus from the surrounding organic matter and alleviating environmental phosphorus limitation. In the sediment, a large amount of buried organic phosphorus is also decomposed under the action of anaerobic microorganisms, releasing phosphorus into the pore water and then diffusing into the overlying water body. The degradation rate of microorganisms is affected by environmental conditions: the higher the temperature, the faster the decomposition of organic matter and the remineralization of phosphorus. Oxygen conditions determine the decomposition pathways and efficiencies of certain organophosphorus compounds (Duan et al., 2025). 4.3 Phosphorus release and regeneration at the sediment–water interface The sediment-water interface is an active exchange site in the phosphorus cycle. After phosphorus-containing particles sink to the seabed, some of the phosphorus in them can be re-released into the water body at the interface. On the one hand, the sedimentary organic matter is decomposed by anaerobic microorganisms, and phosphate is released into the pore water of the sediment and diffuses along the concentration gradient to the bottom seawater (Jin et al., 2024). On the other hand, when the bottom water is oxygen-deficient, the iron and manganese oxides that originally adsorbed phosphate in the sediment are reduced and dissolved, and the phosphorus bound to them is desorbed and released into the water. Under oxidative conditions, the opposite process occurs: phosphorus is readily adsorbed and fixed by metal oxides in sediments to form precipitates (Randolph-Flagg et al., 2023). Periodic disturbances (such as storms and benthic activities) can enhance interfacial exchange, enabling phosphorus released from sediments to enter the overlying water layer cycle more quickly. Phosphorus regeneration at the sedimentwater interface regulates the nutrient supply of bottom water and surface water at a local scale: in eutrophic waters, it can act as an internal phosphorus source, intensifying phosphorus accumulation in the water body. When in overall equilibrium, sediments tend to act as terminal sinks for phosphorus. 5 Key Environmental and Biological Factors Affecting Phosphorus Bioavailability 5.1 Regulatory roles of physicochemical conditions The physicochemical conditions of the Marine environment regulate the bioavailability of phosphorus by influencing its form and flow. The higher the temperature, the faster the rate of organic matter decomposition and phosphorus remineralization usually is, but the high stratification of seawater can also inhibit the transport of deep phosphorus to the surface. The pH value of water bodies affects the dissolution equilibrium of phosphorus: under
International Journal of Marine Science, 2025, Vol.15, No.6, 292-302 http://www.aquapublisher.com/index.php/ijms 296 acidic conditions, phosphate adsorbed on particles is more likely to be released into water, and in alkaline environments, phosphate tends to combine and precipitate with cations such as calcium and magnesium (Wu et al., 2021). The REDOX state is even more crucial: under oxygenated conditions, phosphorus is easily adsorbed and fixed by iron and manganese oxides. Once the environment turns oxygen-deficient, these oxides are reduced and dissolved, and the phosphorus adsorbed on them is released in large quantities, resulting in an increase in the phosphorus concentration of the surrounding water. Furthermore, the mixing condition of water bodies determines the efficiency of nutrient re-supply. Strong vertical mixing (such as storms, winter convection) can bring deep phosphorus sources back to the surface and alleviate surface phosphorus limitation (Zhou et al., 2021); Long-term stable stratification leads to the depletion of surface phosphorus without replenishment. The combined effect of these physical and chemical factors shapes the effective supply level of phosphorus in different regions and seasons. 5.2 Binding effects of metal ions, mineral particles, and organic matter The activity of phosphorus in seawater is affected by its combination with various metals and particles. Phosphate has a strong affinity for metal oxides such as iron and aluminum, and is easily adsorbed on their surfaces or precipitated with calcium ions to form insoluble phosphate minerals, thereby removing phosphorus from the aqueous phase and turning it into a solid phase. This means that even if the total phosphorus content in the environment is not low, some of it may be fixed on particles and temporarily unavailable (Yan et al., 2022). Finegrained sediment and clay minerals can also adsorb phosphate ions, causing phosphorus to settle with the particles (Brady et al., 2022). Dissolved organic matter can affect the availability of phosphorus through multiple effects: some organic colloids can combine with phosphorus to form complexes, hindering its direct uptake by organisms; Some organic ligands, when combined with metal ions, weaken the fixation effect of metals on phosphorus, indirectly increasing the bioavailable ratio of phosphorus. 5.3 Metabolic regulation by microbial communities and phytoplankton When there is not enough phosphorus, Marine life will not just sit and wait to die. Phytoplankton usually "transform" themselves: reducing components with high phosphorus demands, such as replacing some membrane phospholipids with sulfur-containing lipids; It will also increase the production of phosphatase and "extract" some usable phosphorus from the surrounding DOP. Sometimes, when there is too much phosphorus, they will absorb a little more and stockpile polyphosphates to prepare for the subsequent "famine" (Fru et al., 2023). The appetite for phosphorus varies greatly among different organisms. Small phytoplankton, due to their large surface area and small volume, have a higher absorption efficiency and are often the winners in phosphorus-poor sea areas. Large algae grow fast but consume a lot. Once they lack phosphorus, they will fall behind. As for the internal part of the microbial community, it is not monolithic either. Bacteria can decompose organic matter and release phosphorus, providing nutrients for algae. But sometimes they also compete with algae for inorganic phosphorus, and this competition is no less intense (Zhang et al., 2025). Overall, both microorganisms and phytoplankton are making subtle metabolic adjustments to enable the ecosystem to respond flexibly to the amount of phosphorus, and as a result, the phosphorus utilization pattern of the entire ocean is constantly changing. 6 Relationship Between Marine Primary Productivity and Phosphorus Limitation 6.1 Effects of phosphorus limitation on phytoplankton growth and community structure When the available phosphorus in seawater is lower than the demand of phytoplankton, both their growth rate and community composition will change. Insufficient phosphorus can slow down the cell division and photosynthesis of phytoplankton and cause physiological changes, such as depletion of intracellular phosphorus reserves and a decrease in photosynthetic pigment content. Some large populations that rely on high phosphorus (such as macrodiatoms) gradually decline under the condition of continuous phosphorus deficiency, while some small algae and blue-green algae that tolerate low phosphorus have the advantage with lower nutrient requirements and higher absorption efficiency, resulting in the succession of community structure towards miniaturization and low diversity (Figure 1) (Browning and Moore, 2023). Meanwhile, under phosphorus restriction, the intracellular carbonphosphorus ratio (C:P) of phytoplankton cells increases, the nutritional quality declines, and the growth and reproduction of zooplankton may be hindered after feeding (Lin et al., 2023). It can be seen from this that the level
International Journal of Marine Science, 2025, Vol.15, No.6, 292-302 http://www.aquapublisher.com/index.php/ijms 297 of phosphorus supply directly affects the productivity and composition of phytoplankton and has a chain effect on higher trophic levels through food web transmission. Figure 1 Experimentally derived nutrient limitation patterns on a background of estimated nitrate upwelling (Adopted from Browning and Moore, 2023) 6.2 Nutrient competition and adaptive mechanisms under phosphorus-limited conditions In a phosphorus-deficient environment, various organisms fiercely compete for the limited phosphorus resources and simultaneously evolve multiple adaptive strategies. Phytoplankton have developed a high-affinity phosphorus uptake system and a "luxury absorption" mechanism: once there is a brief phosphorus input into the environment, they quickly absorb it and store it in the form of polyphosphates for later use (Wang, 2025). Heterotrophic bacteria gain a competitive edge under low DIP conditions by virtue of their ability to utilize organic phosphorus. They obtain phosphorus from dissolved organic matter, reducing their reliance on inorganic phosphorus. The competition between algae and bacteria depends on conditions: in phosphorus-poor water bodies rich in organic matter, bacteria often have the upper hand; In environments with abundant sunlight and fleeting DIP, algae seize the initiative (Zhang et al., 2022). To adapt to phosphorus deficiency, many algae secrete more phosphatases to break down environmental DOP or replace certain cellular components with phosphorus-free substances to reduce the phosphorus requirement. Some nitrogen-fixing cyanobacteria also reduce their nitrogen-fixing activity when phosphorus is insufficient, prioritizing the limited phosphorus for basic growth (Lin et al., 2023). Through these competitive and adaptive mechanisms, ecosystems can still maintain certain functional operations under severe phosphorus constraints. 6.3 Regional differences in phosphorus utilization across oceanic areas Due to the different nutritional supply conditions, there are significant differences in the utilization strategies of phosphorus by plankton in various sea areas. In high-productivity seas such as coastal and upwelling areas, nitrogen is often the main limiting factor, while phosphorus is relatively abundant. Phytoplankton tend to grow rapidly and store excess phosphorus, and are not sensitive to phosphorus restrictions (Huang and Han, 2025). However, in the oligotrophic circulation centers of the ocean, the long-term low-phosphorus environment has created highly efficient "phosphorus-saving" communities: those plankton have an extremely high absorption affinity for trace phosphorus, can fully utilize DOP, and repeatedly recover phosphorus through the microbial loop, enabling the communities to operate at extremely low phosphorus concentrations (Jin et al., 2024). In addition, in some regions, due to high exogenous N input and a relatively large N-P ratio (such as the Mediterranean), phytoplankton, in order to adapt to the relatively phosphorus-deficient environment, will rely more on organic phosphorus and phosphatase pathways to obtain phosphorus.
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