The Behavior of Planktonic Copepods Minimizes the Entry of Microplastics in Marine Food Webs

Microplastic pollution: Critical analysis of global hotspots and their impact on health and ecosystems

This paper examines microplastic hotspots and their drastic effects on human health and the environment pointing out microplastic pollution as one of the biggest global issues. Besides, it analyses the key sources including industrial effluent discharge, littered plastic wastes, and deterioration of synthetic products together with pathways and routes of exposure. The review also focuses on microplastic contamination in food systems such as meat, plant-based products, dairy, and seafood, detailing their entry into the food chain via soil, water, and air. On the other hand, this work also focuses on human health issues including cellular absorption, and bioaccumulation, which results in tissue oxidative stress, inflammation, hormonal imbalance and adverse long-term effects, including carcinogenicity and organ toxicity. The ultimate effects of microplastic pollution on the condition of the soil, water, and fauna and flora of the ecosystem, highlighting on the need for the prevention measures, were also addressed. This paper seeks to critically ascertain the problems posed by microplastics, including their slow biodegradation limit, the absence of proper regulations, and lack of a universally accepted standard. It also highlights that microplastic pollution requires interdisciplinary analyses, future studies, and high standards-compliant policies and regulations. This work raises the alarm for a collective international effort to protect the public health, food, and the earth.

Modeling the Vertical Transport of Copepod Fecal Particles under Nano/Microplastic Exposure

Nano- and microplastics (NMPs) may significantly impact the marine carbon cycle, and fecal pellets produced by the copepods are crucial for vertical carbon transport. In this study, we investigated the effects of NMP size, concentration, and diatom supply on the production and settling of fecal pellets by the marine copepod Parvocalanus crassirostris. By employing an aggregation-induced emission fluorescence imaging technique, we visualized the distribution of NMPs in fecal pellets, measured their size and production rate, and developed a fluid dynamic model to simulate the settling process of fecal pellets in the water column. Our results indicated that NPs and MPs exhibited uniform and nonuniform distributions in the produced fecal materials, respectively. NMPs reduced both the size and integrity of copepod fecal pellets. Copepods ingested MPs in the absence of diatoms, but exposure to 5000 μg/L of NMPs decreased the fecal pellet production by 52% in the presence of diatoms due to feeding selectivity. The sinking rates of fecal pellets of varying sizes, as obtained from modeling simulations, ranged from 10.9 to 103.1 m/day. When the proportion of participating polystyrene (PS) reached 50%, the sinking velocity decreased by 34%. Our study provides new insights into the vertical transport of copepod fecal pellets under NMP pollution.

Can Fish Escape the Evolutionary Trap Induced by Microplastics?

Microplastic (MP) ingestion acts as an evolutionary trap with various ecological consequences. Cues that lead animals to respond differently to MPs are key factors driving MP ingestion, yet they remain poorly understood. Here, we quantified the susceptibility of three fish species to different types of MPs across different social contexts. Our results showed that bass were more attracted to MPs that resembled food visually, whereas carp tended to select MPs that shared olfactory cues with food. Goldfish relied more on oral processing to make foraging decisions on MPs. Structural differences in the oropharynx supported these discriminated oral processes. Enlarged group size and fasting time altered the foraging behaviors of MPs of goldfish and bass, both of which were suction-feeding species. Such behavioral changes, regardless of whether fish ultimately ingested or rejected MPs, could pose indirect costs to fish. However, changed group sizes and fasting times did not affect the intake of MPs by the filter-feeding carp. We also proposed four pathways causing the MP-induced evolutionary trap and discussed the potential of fish to escape this trap. Our results contribute to experimental and theoretical understanding of the ecological risks posed by MPs to aquatic species.

Behavioral adaptations of cruise-feeding copepods to harmful algal blooms: Insights from the East China Sea

Harmful algal blooms (HABs) have become a global environmental concern, significantly impacting marine life and the fishing industry. However, the tolerance and adaptive mechanisms of zooplankton to HABs remain poorly understood. This study examines the behavioral and feeding responses of the cruise-feeding copepod Centropages dorsispinatus to summer HABs in the East China Sea (ECS), focusing on interactions with the blooming diatom (Skeletonema costatum) and dinoflagellates (Prorocentrum donghaiense, Karenia mikimotoi, and Alexandrium tamarense). Using short-term incubations and high-speed filming, we compared the ingestion rates and behaviors of C. dorsispinatus fed mono-algal diets and mixed diets containing neutral distraction particles (polystyrene beads). The results revealed that C. dorsispinatus obtained limited carbon from each algal diet (1.02-7.02 μg C cop.-1 day-1). The presence of distraction particles reduced carbon intake from S. costatum, P. donghaiense, and A. tamarense, but significantly increased intake from the healthy control, Platymonas helgolandica. Behavioral responses varied among algal diets: compared to P. helgolandica, C. dorsispinatus exhibited more frequent but shorter swims in S. costatum diets and less frequent swims in K. mikimotoi, and A. tamarense diets. These algal-specific responses were generally mitigated when copepods simultaneously exposed to the neutral distraction particles. Copepods achieved higher carbon intake with lower mechanical energy expenditure when grazing on large dinoflagellates compared to diatoms. We suggest that cruise-feeding copepods can actively adjust their behavior to adapt to varying food conditions, including the density, morphologic characteristics, and toxicity of algae. It allows copepods to better survive and forage in dinoflagellate HABs than in diatom HABs. However, the low ingestion rates observed limit the potential for cruise-feeding copepods to exert top-down control on HABs.

Behavioral responses of copepod Calanus sinicus to bloom-forming algae Prorocentrum donghaiense and Skeletonema costatum

Harmful algal blooms (HABs) severely threaten estuarine and coastal ecosystems in recent decades. The adverse impacts of HABs on zooplankton have been extensively studied, while the strategies employed by zooplankton to cope with HABs remain unclear. The copepod Calanus sinicus is the most dominant zooplankton species in the North Pacific Ocean during spring and early summer, coinciding with frequent blooms of the diatom Skeletonema costatum and the dinoflagellate Prorocentrum donghaiense. To investigate the behavioral responses and energy expenditures of C. sinicus under HAB conditions, we conducted both bottle incubations and high-speed video observations over 24 h. Incubation experiments revealed that the carbon intake rate of C. sinicus when feeding on these harmful algae was significantly lower (1.7 and 0.9 μg C Cop.-1 day-1 from P. donghaiense and S. costatum, respectively) compared to feeding on the healthy prey Platymonas helgolandica, with rates 5-10 times higher. This reduced intake barely met the daily basic metabolic requirements of the copepods. When exposed to P. donghaiense alone, copepods exhibited a pronounced escape-like jumping behavior characterized by high frequency, velocity and straight-line trajectory. In contrast, their swimming behavior differed when exposed to S. costatum alone, with a higher incidence of short, straight swim bouts likely related to the reorientation of diatom chains before ingestion. These specific behaviors were mitigated when alternative food sources were available alongside the harmful algae. We suggest that C. sinicus has evolved adaptive strategies to cope with blooms of P. donghaiense and S. costatum, including selective feeding on other phytoplankton and microzooplankton and either conserving energy by minimizing movement or rapidly escaping from bloom patches when food resources are severely depleted. These adaptive strategies of C. sinicus in HABs, highlighting the potential resilience mechanisms of zooplankton in fluctuating marine ecosystems, which could inform future conservation and management efforts in coastal waters.

Research trends in nano- and microplastic ingestion in marine planktonic food webs

Over the past decade, microplastic research on ingestion and impacts in marine biota has received significant attention. Zooplankton has become a subject of interest due to their crucial role in marine food webs. This review focuses on trends in nano- and microplastics (NMPs) ingestion studies in marine zooplankton. Four groups of organisms were considered: protozoans, holoplankton, meroplankton and ichthyoplankton. Of 120 reviewed articles, holoplankton was the most studied group, with laboratory experiments dominating over field studies. Although NMPs sizes and polymer types are diversifying in laboratory experiments, their characteristics are still far from representing the complexity of NMPs found in nature. Polystyrene (as polymer type) and beads (as shape) are overrepresented in laboratory experiments (54% and 79%, respectively). Furthermore, most NMPs concentrations used in the laboratory exceed those found in the field. The units used to report ingestion of NMPs in zooplankton vary greatly, with "microplastics per individual" being the most frequently used. In addition, certain planktonic groups (e.g., protozoans and ichthyoplankton) and behavioral traits, such as ambush feeding, have been poorly investigated. This variability hampers comparisons between studies and thus mechanistic insights into NMPs ingestion in marine zooplankton. This review identifies research gaps and it highlights the ongoing disparity between environmental and laboratory conditions in zooplankton ingestion studies. We encourage the scientific community to harmonize the reporting units for NMPs ingestion and focus on more environmentally realistic studies with a trait-based approach. Transitioning towards more hypothesis-driven experiments is crucial to clarify the mechanistic importance of environmentally relevant microplastic features.

Sublethal effects of microplastic and oil co-exposure on biological rates and lipid profiles of keystone Arctic copepods

Microplastics (MPs) and petroleum hydrocarbons are contaminants of emerging concern in the Arctic, but little is known about their co-exposure effects. In this study, we present the first assessment of the sublethal impacts resulting from combined exposure to microplastics and oil in three key Arctic copepod species. Specifically, we investigated the effects of a 5-day exposure to oil alone (1 μL L-1) and in combination with MPs (polyethylene microspheres, 20 μm, 20 MP mL-1) and dispersant (Corexit 9500, 0.05 μL L-1) on the biological functions and lipid profiles of the planktonic copepods Metridia longa, Calanus finmarchicus, and Calanus glacialis. Exposure to oil alone caused a significant reduction (34-58%) in fecal pellet production, but neither microplastics nor dispersant increased the negative effect of oil on fecal pellet production. C. glacialis and C. finmarchicus exposed to the studied pollutants for 5 days produced eggs with delayed hatching and lower hatching success. The highest hatching inhibition (50%) was observed in eggs of C. glacialis exposed to oil plus MPs and dispersant for five days. This indicates that maternal transfer of oil components to eggs negatively affects embryonic development and hatching. Lipid content and fatty acids profiles varied among the studied copepod species but were not affected by the tested pollutants after five days of exposure. By microscopical observation of fecal pellets, ingestion of small oil droplets and MPs was confirmed in all species, but the estimated ingestion of MPs was low (<25 MPs cop-1 d-1, <0.2% of total offered MPs) suggesting avoidance of MP consumption in copepods. Our results indicate that virgin MPs did not increase the toxicity of oil to the studied Arctic copepods under co-exposure conditions, and dispersants can slightly increase certain adverse effects of oil (hatching). However, environmentally relevant concentrations of oil alone can negatively impact Arctic keystone copepods and potentially the biological carbon pump. These findings emphasize the need to reduce petrogenic pollution and the risk of oil spills in the sensitive Arctic ecosystem.

Effect of alternative natural diet on microplastic ingestion, functional responses and trophic transfer in a tri-trophic coastal pelagic food web

The patchy distribution of microplastics (MP) and their size range similar to planktonic organisms, are likely to have major ecological consequences, through MP ingestion, food dilution, and transfer across trophic levels. Our study applied a community module using tritrophic food chain with zooplankton as prey, and a planktivorous seabass fry as predator. We conducted a series of feeding experiments and recorded the direct uptake of MP under six different concentrations ranging from 25 to 800 particles L-1. We also estimated the indirect transfer of MP via trophic link. The ingestion rates for Brachionus plicatilis, Mesocyclops isabellae, and Lates calcarifer, were 3.7 ± 0.3 MP ind-1 min-1, 1.69 ± 0.1 MP ind-1 min-1, and 3.51 ± 0.52 MP ind-1 h-1, respectively. In the presence of a natural diet, rotifers and copepods ingested significantly lower number, whereas, fish fry ingested a higher number of MP, suggesting further vulnerability to the consumers of MP-contaminated fish and potential biomagnification at higher trophic levels. Overall, the MP uptake rate increased with increasing concentration, and finally leveled off, indicating a type II functional response to MP concentration. The presence of natural diet led to a lower Km value. In the indirect transfer experiment, 74 % of B. plicatilis and 78 % of M. isabellae individuals were contaminated with MP, when offered as prey. Brachionid mastax and MP particles were observed in the gut of copepods. The fish fry gut content also recorded brachionid mastax, MP-contaminated copepods, and MP particles, showing direct evidence of trophic transfer pointing to a cascading effect on higher trophic levels including humans via piscivory.

Seasonal microplastic ingestion by carnivorous chaetognaths in Jiaozhou Bay, China: Field evidence revealing microplastic trophic transfer

Microplastics (MPs) are widely distributed in marine environments and ingested by marine organisms, especially zooplankton. Chaetognaths, typical carnivorous zooplankton, are pivotal in the food chain from secondary producers, such as copepods, to higher trophic level species. However, little is known about their MP ingestion. In this study, based on field observation data, for the first time, we studied seasonal characteristics and risks of MPs ingested by chaetognaths in Jiaozhou Bay and assessed effects of key prey copepods on MP ingestion by chaetognaths. MP/chaetognath values in February, May, August, and November were 0.19, 0.17, 0.15, and 0.39, respectively, showing no significant seasonal variation. Chaetognaths predominantly ingested MPs that were fiberous in shape, 101-400 µm in size and polyester in polymer type, with no significant seasonal variations. The risk of MP load in chaetognaths was low, but there are higher polymeric hazards and potential ecological risks. MP/chaetognath values were positively correlated with the copepod abundance and MP/copepod values. The characteristics of MPs ingested by chaetognaths were also highly similar to those of MPs ingested by copepods. However, the overall risk of biomagnification in the copepod-chaetognath food chain was low. This study provided field evidence for MP transfer in the planktonic food chain.

Microplastic ingestion in marine mesozooplankton species associated with functional feeding traits

Microplastic (MP, <5 mm) contamination in the ocean raises concern for zooplankton, as their prey and MPs fall within the same size range. This study aimed to evaluate the ingestion capacity of MPs among a diverse array of mesozooplankton taxonomic groups and species from the central Mexican Pacific, focusing on two functional traits: trophic group and feeding strategy. A total of 20 taxa belonging to eight taxonomic groups, 13 which were identified to species level, were exposed to microspheres (Ms) ranging in size from 38 to 53 μm, at a concentration of 100 Ms/mL. All experimental treatments were placed in 620 mL bottles and rotated on a plankton wheel for 2 h. The results demonstrate that the capacity to ingest MPs is closely related to the trophic group and the feeding strategy of each species, independent of taxonomic group. Omnivores and omnivore-herbivores which generate feeding currents were the most susceptible to MPs ingestion, while highly carnivorous species with active feeding strategies were the least prone. These findings highlight the importance of evaluating MP ingestion by zooplankton at the species level, due to the variability of feeding strategies within taxonomic groups, and the need for continued trait-based research at the species level. A more detailed understanding of zooplankton feeding behavior, especially in ecologically significant species, could enhance trait-based modeling at a biogeographic scale, predicting areas with the highest risk of MP ingestion by zooplankton communities and evaluating global impacts.

Do weathered microplastics impact the planktonic community? A mesocosm approach in the Baltic Sea

Microplastics (MPs) are ubiquitous pollutants of increasing concern in aquatic systems. However, little is still known about the impacts of weathered MPs on plankton at the community level after long-term exposure. In this study, we investigated the effects of weathered MPs on the structure and dynamics of a Baltic Sea planktonic community during ca. 5 weeks of exposure using a mesocosm approach (2 m3) mimicking natural conditions. MPs were obtained from micronized commercial materials of polyvinyl chloride, polypropylene, polystyrene, and polyamide (nylon) previously weathered by thermal ageing and sunlight exposure. The planktonic community was exposed to 2 μg L-1 and 2 mg L-1 of MPs corresponding to measured particle concentrations (10-120 μm) of 680 MPs L-1 and 680 MPs mL-1, respectively. The abundance and composition of all size classes and groups of plankton and chlorophyll concentrations were periodically analyzed throughout the experiment. The population dynamics of the studied groups showed some variations between treatments, with negative and positive effects of MPs exhibited depending on the group and exposure time. The abundance of heterotrophic bacteria, pico- and nanophytoplankton, cryptophytes, and ciliates was lower in the treatment with the higher MP concentration than in the control at the last weeks of the exposure. The chlorophyll concentration and the abundances of heterotrophic nanoflagellates, Astromoeba, dinoflagellate, diatom, and metazooplankton were not negatively affected by the exposure to MPs and, in some cases, some groups showed even higher abundances in the MP treatments. Despite these tendencies, statistical analyses indicate that in most cases there were no statistically significant differences between treatments over the exposure period, even at very high exposure concentrations. Our results show that weathered MPs of the studied conventional plastic materials have minimal or negligible impact on planktonic communities after long-term exposure to environmentally relevant concentrations.

First assessment of anthropogenic particle ingestion in Pontellid copepods: Pontella mediterranea as a potential microplastic reservoir in the Neuston

Hyponeustonic species, living at the interface between the atmosphere and the oceans, comprise one of the most understudied and vast critical marine biotope, constantly exposed to high concentrations of anthropogenic contaminants and microplastic (MPs). Copepods of the Pontellidae family represent the primary components of this biotic assemblage worldwide, and their interaction with MPs is still unknown. We studied this interaction for the first time in Pontella mediterranea, assessing the ingestion of anthropogenic particles (APs) in 2793 individuals collected by manta trawl in the Northern Alboran Sea. We observed P. mediterranea abundances ranging from 41.67 to 1174.83 ind/m3, with a mean ingestion of 0.11 APs/ind, predominantly composed of MPs. These results confirm the low ingestion values observed for other copepod taxa. However, given its abundance, this species could retain an average of 45.15 and a maximum of 220 APs per m3 of seawater (APs/m3), mostly composed of cellulose acetate and cotton fibers. The abundances of APs were evaluated in surface (0-12 cm) and sub-surface waters (5 m depth) by combining manta trawl and Continuous Underway Fish Egg Sampler sampling. The AP abundances found (surface waters: 0.67 ± 1.04 APs/m3; subsurface waters: 3.85 ± 2.67 APs/m3) were consistent with those previously observed in the Mediterranean basin, confirming that the ingestion values observed in P. mediterranea are not due to a local accumulation of environmental MPs. Results highlight how this neustonic copepod could represent one of the largest reservoirs of APs within the upper layers of the oceans, representing an entry point for these particles within food webs. Considering the worldwide distribution and abundance of this family of copepods, the results are of environmental concern.

Tracking Nano- and Microplastics Accumulation and Egestion in a Marine Copepod by Novel Fluorescent AIEgens: Kinetic Modeling of the Rhythm Behavior

Nano- and microplastics (NMPs) are now prevalent in the marine environment. This study quantified the uptake and depuration kinetics of spherical polystyrene NMPs of different particle sizes (200 nm/30 μm) and functional groups (-NH2/-COOH) in a temperate calanoid copepod Calanus sinicus (C. sinicus), which exhibited rhythmic feeding patterns in natural environments. Aggregated-induced emission (AIE) fluorescent probes were employed to track and quantify the kinetics of NMPs with excellent photostability and biocompatibility. The results showed that C. sinicus consumed all NMPs types, with preference of NMPs to small size and amino group. Increased diatom concentrations also inhibited the bioaccumulation of NMPs. Influenced by rhythmic behavior, the bioaccumulation of NMPs by C. sinicus was nonstationary during the 6 h uptake phase. After 1-3 h of rapid uptake, the body burden peaked and then slowly declined. During the 3 h depuration phase, C. sinicus rapidly and efficiently removed NMPs with a mean half-life of only 0.23 h. To further quantify the body burden of C. sinicus under the influence of rhythmic feeding behavior, a biokinetic model was established, and the Markov chain Monte Carlo method was used to estimate the parameter distribution. Our results highlighted that copepods exhibited unique rhythmic feeding behavior under environmentally relevant concentrations of NMPs exposure, which may influence the bioaccumulation, trophic transfer, and environmental fate of NMPs.

Feeding Behavior Responses of the Small Copepod, Paracalanus parvus, to Toxic Algae at Different Concentrations

The feeding relationship between copepods and phytoplankton has immense ecological significance. This study investigated the feeding behavior of copepods by studying the feeding selectivity of Paracalanus parvus, a key small copepod species, using a high-speed camera. The feeding behavior of P. parvus separately fed on three algae, Prorocentrum minimum, Alexandrium minutum, and Thalassiosira weissflogii, was studied at five different concentrations. The factors characterizing feeding behavior, including the beating frequency (BF), beating time (BT), and rejection behavior, were analyzed. The average BT and BF of P. parvus fed on toxic algae were significantly lower than those of copepods fed on nontoxic algae, indicating that the toxic algae negatively affected their feeding behavior. There were no significant differences in feed rejection among the three algae during the short period of experimentation, indicating that the rejection behavior was insignificant in the early period (within 20 min) of feeding on toxic algae. The feeding behavior was inhibited when the concentration reached 250 cells/mL. The BT was initially affected at increasing concentrations followed by the BF, and P. minimum and A. minutum reduced the BF at concentrations of 250 and 1000 cells/mL, respectively. Analysis of the average BFs revealed that P. parvus was more significantly affected by P. minimum containing diarrheal shellfish poison than by A. minutum containing paralytic shellfish poison. The BF of copepods fed on P. minimum was significantly lower than that of copepods fed on A. minutum at 250-500 cells/mL but was not significantly different from that at 1000 cells/mL. This indicated that the inhibitory effect of P. minimum on the feeding behavior was more significant at concentrations observed at the onset of red tide blooms (0.25-0.5 × 102 cells/mL), but insignificant at concentrations reaching those in advanced red tides (>103 cells/mL). This study demonstrates that toxic dinoflagellates alter the feeding behavior of copepods and describes the variations in their feeding response to different algal species and concentrations. The findings provide crucial insights for further studies on the feeding relationship between copepods and phytoplankton and on functional assessment of plankton ecosystems.

First determination on two kinds of microplastic-air partition coefficients of seven per- and polyfluoroalkyl substances under environmentally relative conditions: Experiment measurement and model prediction

Microplastics (MPs) in the environment are the sink and vector of organic contaminants, including per- and polyfluoroalkyl substances (PFASs). Although PFASs are low- and non-volatile compounds, they have the potential to partition and diffuse from MP into the gas phase in the environmental functions. Herein, the MP-air partition coefficient (KPA) of seven PFASs was measured using a solid-fugacity meter. The PFAS KPA values in two MPs (high-density polyethylene (HDPE) and thermoplastic polyurethane (TPU)) were determined under different times, temperatures, and relative humidities (RH), and a model was developed to predict the PFAS KPA values based on the measured data. The results showed that the KPA of PFASs increased with the prolonged partition time until 90 mins, and higher temperature and RH facilitated the distribution of PFASs in MPs into the air phase, leading to smaller KPA values. Moreover, the derived equation for predicting PFAS log KPA values was robust with 0.79 of an adjusted square of correlation coefficient (R2adjusted = 0.79) and 0.35 of root mean squared error (RMSE = 0.35). These findings provided the first knowledge for understanding the partition behavior and fate of PFASs in the MP-air microenvironment.

Is Zooplankton an Entry Point of Microplastics into the Marine Food Web?

Microplastics (MPs) overlap in size with phytoplankton and can be ingested by zooplankton, transferring them to higher trophic levels. Copepods are the most abundant metazoans among zooplankton and the main link between primary producers and higher trophic levels. Ingestion of MPs has been investigated in the laboratory, but we still know little about the ingestion of MPs by zooplankton in the natural environment. In this study, we determined the concentration and characteristics of MPs down to 10 μm in zooplankton samples, sorted calanoid copepods, and fecal pellets collected in the Kattegat/Skagerrak Sea (Denmark). We found a median concentration of 1.7 × 10-3 MPs ind-1 in the zooplankton samples, 2.9 × 10-3 MPs ind-1 in the sorted-copepods, and 3 × 10-3 MPs per fecal pellet. Most MPs in the zooplankton samples and fecal pellets were fragments smaller than 100 μm, whereas fibers dominated in the sorted copepods. Based on the collected data, we estimated a MP budget for the surface layer (0-18 m), where copepods contained only 3% of the MPs in the water, while 5% of the MPs were packed in fecal pellets. However, the number of MPs exported daily to the pycnocline via fecal pellets was estimated to be 1.4% of the total MPs in the surface layer. Our results indicate that zooplankton are an entry point of small MPs in the food web, but the number of MPs in zooplankton and their fecal pellets was low compared with the number of MPs found in the water column and the occurrence and/or ingestion of MPs reported for nekton. This suggests a low risk of MP transferring to higher trophic levels through zooplankton and a quantitatively low, but ecologically relevant, contribution of fecal pellets to the vertical exportation of MPs in the ocean.