Stability Of Marine Ecosystems Research Articles

Design of clean energy based microplastic collection device

Abstract Microplastics are plastic particles with a particle size of less than 5 mm formed after the degradation of plastic by crushing. Microplastics are chemically stable and difficult to degrade, and they are also enriched with chemical poisons, microorganisms, and pathogenic bacteria[1]. Some microplastics migrate with ocean currents in the ocean, affecting the global distribution of pollution and causing great harm to the stability of marine ecosystems and the marine environment. There are a large number of microplastics in the ocean, and the number is increasing[2][3]. In order to realize the microplastic collection function, a microplastic collection device was designed to reduce operational requirements and costs while realizing microplastic salvage. The overall scheme of the system includes the design of subsystems consisting of a solar power generator, a collection mechanism, a filtration device, a buoyancy device, a lighthouse, an anchor device, and so on. According to the actual needs of the microplastic collection, the mechanical structure and dimensions of each subsystem were designed, the 3D modeling of the overall system was completed using SolidWorks, and a physical model of the microplastic collection device was produced for experimental testing.

A Comparison of new and age-old approaches treating microplastics in the marine environment

In recent years, microplastic pollution in the ocean has become a new environmental threat, posing a serious potential threat to marine ecology. Due to its high degradation resistance and bioaccumulation, it is an urgent and critical issue for the environment. Unfortunately, current technologies for removing, recycling, or degrading microplastics are not sufficient to eliminate them. The main sources of microplastics (MPs) in the ocean are ocean drift inputs, river inputs, fishing and shipping activities, microplastic emissions from human settlements, and atmospheric migration. Microplastics may pose a threat to marine life and affect the stability of marine ecosystems. Therefore, it is urgent to further study governance methods and analysis processes, and strengthen the source control of marine microplastic pollution. This study aims to analyze and discuss different methods for treating marine microplastics, analyze their respective advantages and limitations, and evaluate their feasibility and effectiveness in practical applications. The study ultimately emphasized the importance of effective management of marine microplastics, which is crucial for protecting marine ecosystems and human health. Through a comprehensive analysis of physical, chemical, and biological methods, this study provides valuable insights for marine environmental management and research institutions, thereby promoting the development and application of effective management technologies to achieve sustainable environmental outcomes.

A Chlorophyll-a Concentration Inversion Model Based on Backpropagation Neural Network Optimized by an Improved Metaheuristic Algorithm

Chlorophyll-a (Chl-a) concentration monitoring is very important for managing water resources and ensuring the stability of marine ecosystems. Due to their high operating efficiency and high prediction accuracy, backpropagation (BP) neural networks are widely used in Chl-a concentration inversion. However, BP neural networks tend to become stuck in local optima, and their prediction accuracy fluctuates significantly, thus posing restrictions to their accuracy and stability in the inversion process. Studies have found that metaheuristic optimization algorithms can significantly improve these shortcomings by optimizing the initial parameters (weights and biases) of BP neural networks. In this paper, the adaptive nonlinear weight coefficient, the path search strategy “Levy flight” and the dynamic crossover mechanism are introduced to optimize the three main steps of the Artificial Ecosystem Optimization (AEO) algorithm to overcome the algorithm’s limitation in solving complex problems, improve its global search capability, and thereby improve its performance in optimizing BP neural networks. Relying on Google Earth Engine and Google Colaboratory (Colab), a model for the inversion of Chl-a concentration in the coastal waters of Hong Kong was built to verify the performance of the improved AEO algorithm in optimizing BP neural networks, and the improved AEO algorithm proposed herein was compared with 17 different metaheuristic optimization algorithms. The results show that the Chl-a concentration inversion model based on a BP neural network optimized using the improved AEO algorithm is significantly superior to other models in terms of prediction accuracy and stability, and the results obtained via the model through inversion with respect to Chl-a concentration in the coastal waters of Hong Kong during heavy precipitation events and red tides are highly consistent with the measured values of Chl-a concentration in both time and space domains. These conclusions can provide a new method for Chl-a concentration monitoring and water quality management for coastal waters.

Nutrient characteristics driven by multiple factors in large estuaries during summer: A case study of the Yangtze River Estuary

Nutrients directly control the level of primary productivity and are crucial for the stability of marine ecosystems. Focusing on the survey results in August 2020 of the Yangtze River Estuary, this study elucidated the distribution characteristics and controlling factors of three nutrients: NO3-N, PO4-P, SiO3-Si. The results showed that the concentrations of NO3-N, PO4-P, SiO3-Si in the study area were generally higher near the shore than far shore, with average concentrations of 11.40, 0.70, and 23.73 μmol/L, respectively. The ocean currents drove the distribution of nutrients, and the transport of CDW and YSCC increased the nutrient levels. The resuspension of sediment caused by factors such as terrain and weather may lead to an abnormal increase in nutrients in the bottom waters. The main controlling factors of the three nutrients were different. NO3-N was significantly affected by human activities, PO4-P and SiO3-Si were mainly affected by natural factors.

Deciphering Preferences for Shelter Volume and Distribution by Coral Reef Fish, Using Systematic and Functional Grouping

Global degradation of coral reefs is reflected in the destruction of shelters in various environments and threatens the stability of marine ecosystems. Artificial shelters offer an alternative, but their design could be more challenging due to limited knowledge regarding desired inhabitants’ shelter characteristics and preferences. Investigating these preferences is resource-intensive, particularly regarding small shelters that mimic natural reef conditions. Furthermore, for statistical analysis in small shelters, fish abundance may need to be higher. We propose a method to characterize the species-specific shelter preferences using low-volume data. During a study conducted from January 2021 to April 2022, round clay artificial shelters (RAS) were deployed on an abandoned oil pier to examine a coral reef fish community. We recorded 92 species from 30 families and grouped them into systematic (families) and functional (dietary group) classes. Grouping enabled us to examine each group’s preference, while crossing these group preferences revealed species-specific preferences, which matched field observations. This approach proved effective in profiling the shelter preferences of 17 species while having limited resources. These profiles may later allow the establishment of ecological-oriented artificial reefs. Moreover, this method can be applied to other applications using other shelter designs, sizes, and research sites.

Distribution patterns of six metals and their influencing factors in M4 seamount seawater of the Western Pacific

Metals are crucial to the stability of marine ecosystems, and it is important to analyze their spatial heterogeneity. This study examined the distribution and influencing factors of six metals such as manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu) and cadmium (Cd) in M4 seamount of the Western Pacific. The results showed that the factors affecting the distribution of metals are complex. The concentration ranges of Mn, Fe, Co, Ni, Cu, and Cd in the M4 seamount were 0–0.05, 0–0.44, 0–0.0014, 0–0.082, 0.12–0.16, and 0–0.013 μg/L, respectively, roughly equivalent to those of other open seas, however, there were also some differences. Specifically, the distribution of ferromanganese nodules and Co-rich crusts, resulted in a significant increase in the concentration of metals such as Mn, Fe, and Co in the bottom. This study will significantly contribute to our understanding of the spatial heterogeneity of metals in seamount areas.

Cadmium isotopic evidence for reduced deep-water marine primary productivity during the end-Permian mass extinction

Marine primary productivity is a key control on the stability of marine ecosystems. Decreasing marine primary productivity might have led to the end-Permian mass extinction, although this is debated. However, the changes in primary productivity at different seawater depths during the end-Permian mass extinction remain poorly constrained. We investigated the Cd isotopic systematics of shallow-water (Dajiang) and deep-water (Shangsi) sedimentary sections in South China. Combined with previously published data from an intermediate–deep-water section (Meishan), we were able to reconstruct the depth changes in marine primary productivity. In the Dajiang section, prior to the mass extinction, the Cd isotopic compositions of seawater (δ114/110CdSW) varied from +0.73‰ to +0.92‰, with an average of +0.83‰±0.13‰ (2SD; n=11). During and after the mass extinction, δ114/110CdSW varied from +0.73‰ to +0.91‰, with an average of +0.81‰±0.12‰ (2SD; n=12). In the Shangsi and Meishan sections, prior to the mass extinction, δ114/110CdSW varied from +0.47‰ to +0.85‰, with an average of +0.66‰±0.16‰ (2SD; n=35). During and after the mass extinction, δ114/110CdSW varied from −0.19‰ to +0.36‰, with an average of −0.02‰±0.27‰ (2SD; n=27). During the end-Permian mass extinction, the marine primary productivity recorded by Cd isotopes in the relatively deep-water sections was considerably reduced, which may have caused the destruction of relatively deep-water marine ecosystems. We suggest that upward expansion of sulfidic and anoxic deep water, possibly due to the volcanic eruption of the Siberian Traps large igneous province, was one of the causes of the decrease in marine primary productivity. However, the marine primary productivity did not change in the shallow-water section during the end-Permian mass extinction, although changes in the types of marine primary producers are evident from the fossil record. This change in the types of primary producers may have contributed to the mass extinction in shallow-water platform environments. Vertical variations in the changes in primary productivity indicate that the environmental factors leading to the extinction event mainly began in deep waters during the end-Permian mass extinction.

The evolution of China’s policies on marine and coastal ecosystems in climate change adaptation

Marine and coastal ecosystems play a crucial role in adjusting the process of climate change. Mitigation and adaptation activities involve interdependent carbon and water cycles. Excessive carbon emissions burden the carbon storage capacity of the ocean and then affect the balance and stability of marine ecosystems, leading to global ocean issues such as ocean acidification and the calcification of marine life. While many studies have been conducted on this issue, there is a lack of policy analysis on how countries deal with climate change, particularly in the area of marine and coastal ecosystems’ policies. In 1992, China ratified the United Nations Framework Convention on Climate Change, and China actively participated in the governance of marine and coastal ecosystems adapting to climate change. This article reviews and textually analyses China’s policies related to the adaptation of marine and coastal ecosystems to climate change in 1992–2023. It adopts policy-oriented jurisprudence to illustrate natural and social factors which drive the evolution of China’s policies on marine and coastal ecosystems in climate change adaptation. To achieve the optimal policy results, this article recommends further enhancing the mechanism of policy implementation and management, innovating the system of policy incentives and supervision, and optimizing the framework of policy effectiveness evaluation on the basis of further policy goals.

Effects of masks on marine animals

Due to the global pandemic, we are producing a large number of discarded masks every day. At the same time, some of them will find their way into the ocean and affect the Marine ecology. This paper will analyze the damage of waste masks to the ocean, and give solutions for reference. Through case analysis, this paper concludes that waste masks have brought certain impacts on various Marine organisms and destroyed the stability of Marine ecosystems, but there are still some solutions to improve the problem. This article will provide solutions that can be adopted by governments today, as well as some directions and goals that can be developed in the future. In the future, we can better protect the Marine ecology and pay attention to environmental protection although there will be some cost burden for the government. To protect animals while improving the overall environment of the earth on which human live.

Relationship between cell volume and particulate organic matter for different size phytoplankton

Phytoplankton biomass is an intuitive indicator to evaluate the stability of marine ecosystems. How to obtain phytoplankton biomass quickly and accurately is the focus of marine research. In this work, we selected 12 phytoplankton species to explore the relationship between cell volume and cellular compounds. Results indicated that the volume of 12 species spanned 6 orders of magnitude from 0.11 μm3 (Synechococcus sp. XM-5) to 1.26 × 105 μm3 (Ditulum brightwellii). Besides, a strong negative linear correlation between cell abundance and volume was observed. For per-cell of phytoplankton, the log-log relationship between cell volume and particulate organic carbon (POC), particulate organic nitrogen (PON), chlorophyll a (Chl-a) results reflected a positive correlation. On the contrary, the density of cellular compounds (POC, PON and Chl-a) presented a negative correlation in cell volume. In addition, for ratio of particulate organic carbon and particulate organic nitrogen (C/N), the average value was 5.46, diatoms had the lowest values, 4.72. Moreover, the ratio of carbon and chlorophyll a (C/Chl-a) varied from 15.09 to 79.75, indicating that the C/Chl-a values affected by the different categories. Meanwhile, diatoms usually have a lower C/Chl-a value for their special structure. Finally, we excluded the Synechococcus group of small individuals and found that the slope of their corresponding carbon-volume relationship was not very different, indicating that the smaller individuals had no effect on the assessment of carbon-volume relationship. The physiological variation, based on the cell volume, provides us with a new perspective to simplify the relationship between carbon and volume, and further simplify the methods and analysis of experiments and model simulations of ecosystem biological rate and flux.

Online Monitoring of Seawater Carbon Dioxide Based on an Infrared Rear Beam Splitter.

The ocean is one of the most extensive ecosystems on Earth and can absorb large amounts of carbon dioxide. Changes in seawater carbon dioxide concentrations are one of the most important factors affecting marine ecosystems. Excess carbon dioxide can lead to ocean acidification, threatening the stability of marine ecosystems and species diversity. Dissolved carbon dioxide detection in seawater has great scientific significance. Conducting online monitoring of seawater carbon dioxide can help to understand the health status of marine ecosystems and to protect marine ecosystems. Current seawater detection equipment is large and costly. This study designed a low-cost infrared carbon dioxide detection system based on molecular theory. Using the HITRAN database, the absorption spectra and coefficients of carbon dioxide molecules under different conditions were calculated and derived, and a wavelength of 2361 cm-1 was selected as the measurement channel for carbon dioxide. In addition, considering the interference effect of direct light, an infrared post-splitting method was proposed to eliminate the interference of light and improve the detection accuracy of the system. The system was designed for the online monitoring of carbon dioxide in seawater, including a peristaltic pump to accelerate gas-liquid separation, an optical path structure, and carbon dioxide concentration inversion. The experimental results showed that the standard deviation of the gas test is 3.05, the standard deviation of the seawater test is 6.04, and the error range is within 20 ppm. The system can be flexibly deployed and has good stability and portability, which can meet the needs of the online monitoring of seawater carbon dioxide concentration.

Warming and parasitism impair the performance of Baltic native and invasive macroalgae and their associated fauna

AbstractGlobal warming, bioinvasions, and parasitism affect single‐species performances and species interactions, substantially impacting the structure and stability of marine ecosystems. In light of accelerated global change, the information derived from studies focusing on single species and single drivers is insufficient, calling for a multi‐stressor approach under near‐natural conditions. We investigated the effects of warming (+3°C) on the performance of a benthic community composed of native and invasive macroalgae, consumers and a trematode parasite in a mesocosm setting. We also assessed the effects of warming and parasitism on the survival and growth of gastropods and mussels and the thermal dependency of trematode performance. Our findings show that warming and grazing by infected gastropods had a large detrimental effect on the invasive macroalga growth. Furthermore, the single and interactive effects of parasitism and warming were detrimental to intermediate host survival and growth, especially to large mussels. Finally, cercarial emergence positively correlated to the natural peaks of summer temperatures, while infection intensity in mussels was higher in larger individuals. Our findings suggest that grazing and warming will be detrimental to the invasive macroalga, favoring the native alga. Moreover, parasitism will enhance grazing, especially in summer, when higher temperatures trigger parasite development. However, parasite‐enhanced grazing may be buffered by higher mortality or a shift in the size of infected intermediate hosts under warming. Our findings demonstrate how complex effects of ocean warming can be on food webs and how they can be mediated by parasitism and, as a result, influence native and invasive macroalgae differently.

The stability and collapse of marine ecosystems during the Permian-Triassic mass extinction

The history of Earth's biodiversity is punctuated episodically by mass extinctions. These are characterized by major declines of taxon richness, but the accompanying ecological collapse has rarely been evaluated quantitatively. The Permian-Triassic mass extinction (PTME; ∼252 mya), as the greatest known extinction, permanently altered marine ecosystems and paved the way for the transition from Paleozoic to Mesozoic evolutionary faunas. Thus, the PTME offers a window into the relationship between taxon richness and ecological dynamics of ecosystems during a severe extinction. However, the accompanying ecological collapse through the PTME has not been evaluated in detail. Here, using food-web models and a marine paleocommunity dataset spanning the PTME, we show that after the first extinction phase, community stability decreased only slightly despite the loss of more than half of taxonomic diversity, while community stability significantly decreased in the second phase. Thus, taxonomic and ecological changes were unequivocally decoupled, with species richness declining severely ∼61 ka earlier than the collapse of marine ecosystem stability, implying that in major catastrophes, a biodiversity crash may be the harbinger of a more devastating ecosystem collapse.

Comparison of short-term toxicity of 14 common phycotoxins (alone and in combination) to the survival of brine shrimp Artemia salina

Toxic harmful algal blooms (HABs) can cause deleterious effects in marine organisms, threatening the stability of marine ecosystems. It is well known that different strains, natural populations and growth conditions of the same toxic algal species may lead to different amount of phycotoxin production and the ensuing toxicity. To fully assess the ecological risk of toxic HABs, it is of great importance to investigate the toxic effects of phycotoxins in marine organisms. In this study, the short-term toxicity of 14 common phycotoxins (alone and in combination) in the marine zooplankton Artemia salina was investigated. The 48 h LC50 of the 14 phycotoxins varied from 0.019 3 µg/mL to 2.415 µg/mL. The most potent phycotoxin was azaspiracids-3 (AZA3; with a LC50 of 0.019 3 µg/mL), followed by azaspiracids-2 (AZA2; 0.022 6 µg/mL), pectenotoxin-2 (PTX2; 0.046 0 µg/mL) and dinophysistoxin-1 (DTX1; 0.081 8 µg/mL). For the binary exposure, okadaic acid (OA) induced potential additive effects with DTX1, probably due to their similar structure (polyether fatty acid) and mode of action (attacking the serine/threonine phosphoprotein phosphatases). On the other hand, OA showed potential antagonistic effects with PTX2, which might be accounted for by their activation on the detoxification activity of cytochrome P450 activity. In addition, DTX1 induced potential synergetic effects with saxitoxin (STX), yessotoxin (YTX) or PTX2, suggesting the hazard potency of the mixtures of DTX1 and other phycotoxins (like STX, YTX and PTX2) with regard to the ecological risk. These results provide valuable toxicological data for assessing the impact of phycotoxins on marine planktonic species and highlight the potential ecological risk of toxic HABs in marine ecosystems.

Bottom Trawling Threatens Future Climate Refugia of Rhodoliths Globally

Climate driven range shifts are driving the redistribution of marine species and threatening the functioning and stability of marine ecosystems. For species that are the structural basis of marine ecosystems, such effects can be magnified into drastic loss of ecosystem functioning and resilience. Rhodoliths are unattached calcareous red algae that provide key complex three-dimensional habitats for highly diverse biological communities. These globally distributed biodiversity hotspots are increasingly threatened by ongoing environmental changes, mainly ocean acidification and warming, with wide negative impacts anticipated in the years to come. These are superimposed upon major local stressors caused by direct destructive impacts, such as bottom trawling, which act synergistically in the deterioration of the rhodolith ecosystem health and function. Anticipating the potential impacts of future environmental changes on the rhodolith biome may inform timely mitigation strategies integrating local effects of bottom trawling over vulnerable areas at global scales. This study aimed to identify future climate refugia, as regions where persistence is predicted under contrasting climate scenarios, and to analyze their trawling threat levels. This was approached by developing species distribution models with ecologically relevant environmental predictors, combined with the development of a global bottom trawling intensity index to identify heavily fished regions overlaying rhodoliths. Our results revealed the importance of light, thermal stress and pH driving the global distribution of rhodoliths. Future projections showed poleward expansions and contractions of suitable habitats at lower latitudes, structuring cryptic depth refugia, particularly evident under the more severe warming scenario RCP 8.5. Our results suggest that if management and conservation measures are not taken, bottom trawling may directly threaten the persistence of key rhodolith refugia. Since rhodoliths have slow growth rates, high sensitivity and ecological importance, understanding how their current and future distribution might be susceptible to bottom trawling pressure, may contribute to determine the fate of both the species and their associated communities.

Integrated Estimation of the Sustainability of Baltic and White Seas Ecosystems for Ensuring Environmental Safety of Shelf Resource Development

Theoretical aspects of the stability of marine ecosystems under the influence of the dynamics of hydrometeorological conditions are considered. Groups of natural factors of the ecosystems of the Baltic and White seas defining a level of stability – biocenotical, dynamic hydrological, the dynamic oceanological and corresponding to them estimated indicator indices with assessment of their information significance are justified. Rating of values of indicator indices is executed. Three versions of the integral index of assessment of stability of AISE (integrated assessment of sustainable existence) based on accounting of 6, 9 and 15 indicators indices are developed. On the basis of the received integral estimates zoning of ecosystems of the Baltic and White seas in relation to their stability is executed. Need of accounting of a level of stability of specific water areas in the course of planning and implementation of sea economic activity – navigation, dredging operations, mounting of underwater infrastructure, industrial fishing is justified.

Characteristics of Eukaryotic Plankton Communities in the Cold Water Masses and Nearshore Waters of the South Yellow Sea

Eukaryotic plankton are important parts of the marine biome and play an important role in maintaining the stability of marine ecosystems. In order to characterize the eukaryotic plankton communities in the South Yellow Sea Cold Water Mass (CWM) and the South Yellow Sea nearshore waters (NW) in October 2019, Illumina high–throughput sequencing was performed using the 18S rDNA V9 region as the target gene. Environmental factors (depth, pH, salinity, temperature, Chl a, nitrate, nitrite, ammonium, silicate, phosphate) in two sea areas were measured, and their correlations with abundance and diversity of eukaryotic plankton were analyzed. A total of 807 species of plankton were identified, of which 663 species in 24 categories were from the CWM area, and 614 species in 26 categories were from NW. The total phytoplankton abundance in CWM waters was higher than that in NW. Dinophyta and Bacillariophyta were the most abundant phyla of phytoplankton in the two areas. Arthropoda and Cnidaria were the major zooplankton taxa. The dominant fungal population was mainly Basidiomycota. Both the CWM and NW have effects on dissolved inorganic nutrient concentrations and plankton abundance. Environmental factor correlation analysis showed that the concentration of dissolved inorganic nutrients within the CWM increased with water depth and the abundance of plankton gradually increased. Ammonium salts, nitrates, phosphates, silicates and water depth were important factors affecting phytoplankton growth. Phytoplankton abundance increased with increasing concentrations of inorganic nutrients. Bacillariophyta showed a strong positive correlation with silicates and depth. Depth and microscopic phytoplankton abundance were important factors influencing the structure of the zooplankton community.

Microplastics in different tissues of wild crabs at three important fishing grounds in China

Crabs are an indispensable component of the benthic ecosystem and represent a type of seafood that is easily obtained and frequently eaten by humans. However, little is known about microplastic (MP) accumulation in different tissues of crabs in important fishing areas. In this study, the abundances and characteristics of MPs in different tissues of four species of wild crabs (Portunus trituberculatus, Charybdis japonica, Dorippe japonica, and Matuta planipes) were investigated across 9 sites at three important fishing grounds (Haizhou Bay, Lvsi and Yangtze River Estuary fishing grounds) in China. Crabs from all sites were found to contain MPs, with a total detection rate of 89.34%. The MP abundance in crabs from all sites ranged from 2.00 ± 2.00 to 9.81 ± 8.08 items/individual and 0.80 ± 1.09 to 22.71 ± 24.56 items/g wet weight. The abundance of MPs exponentially increased with decreasing MP size. The MPs were dominated by fibers in terms of shape, black-gray and blue-green in terms of color and cellophane in terms of composition. MPs were found in the gills and guts of the crabs, but not in the muscles. The abundance and size of the MPs in the guts were significantly higher than those in the gills, but there was no significant difference in color or shape. In addition, crab eating patterns have a significant impact on the abundance of MPs in different species. The abundance of MPs in the saprophytic crabs was significantly higher than that in the predatory crabs. MP contamination in crabs is worthy of attention for human health and the stability of marine ecosystems.

Taxonomic Richness and Diversity of Larval Fish Assemblages in the Oceanic Gulf of Mexico: Links to Oceanographic Conditions

Biodiversity enhances the productivity and stability of marine ecosystems and provides important ecosystem services. The aim of this study was to characterize larval fish assemblages in pelagic waters of the northern Gulf of Mexico (NGoM) and identify oceanographic conditions associated with areas of increased taxonomic richness (TF) and Shannon diversity (H’). Summer ichthyoplankton surveys were conducted in the NGoM in 2015 and 2016 using neuston net (surface layer; upper 1 m) and oblique bongo net (mixed layer; 0-100 m) tows. Over 17,000 fish larvae were collected over the two-year study, and 99 families of fish larvae were present. Catch composition in the surface layer was relatively similar to the mixed-layer catch, with carangids (jacks), scombrids (mackerels, tunas) and exocoetids (flyingfishes) being numerically dominant; however, deep-pelagic species, including myctophids (lanternfishes), gonostomatids (bristlemouths), and sternoptychids (marine hatchetfishes), were present almost exclusively in the mixed layer samples. Generalized additive models were used to evaluate the effect of oceanographic conditions on ichthyoplankton abundance and biodiversity. Salinity and sea surface height (SSH) were the most influential oceanographic conditions, with higher occurrence, higher TF, and higher H’ all present in areas of lower salinity and lower SSH. This study highlights the ecological importance of cyclonic mesoscale features and areas of upwelling as areas of increased biodiversity for larval fishes, and also indicates that the mixed layer in the NGoM is essential habitat for deep-pelagic fishes during the early life interval.

Trapping of swimming microalgae in foam.

Massive foam formation in aquatic environments is a seasonal event that has a significant impact on the stability of marine ecosystems. Liquid foams are known to filter passive solid particles, with large particles remaining trapped by confinement in the network of liquid channels and small particles being freely advected by the gravity-driven flow. By contrast, the potential role of a similar retention effect on biologically active particles such as phytoplankton cells is still relatively unknown. To assess if phytoplankton cells are passively advected through a foam, the model unicellular motile alga Chlamydomonas reinhardtii (CR) was incorporated in a bio-compatible foam, and the number of cells escaping the foam at the bottom was measured in time. Comparing the escape dynamics of living and dead CR cells, we found that dead cells are totally advected by the liquid flow towards the bottom of the foam, as expected since the diameter of CR remains smaller than the typical foam channel diameter. By contrast, living motile CR cells escape the foam at a significantly lower rate: after 2 hours, up to 60% of the injected cells may remain blocked in the foam, while 95% of the initial liquid volume in the foam has been drained out of the foam. Microscopic observation of the swimming CR cells in a chamber mimicking the cross-section of foam internal channels revealed that swimming CR cells accumulate near channels corners. A theoretical analysis based on the probability density measurements in the micro chambers has shown that this trapping at the microscopic scale contributes to explain the macroscopic retention of the microswimmers in the foam. At the crossroads of distinct fields including marine ecology of planktonic organisms, fluid dynamics of active particles in a confined environment and the physics of foam, this work represents a significant step in the fundamental understanding of the ecological consequences of aquatic foams in water bodies.