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1. Trophic transfer of microplastics in an estuarine food chain and the effects of a sorbed legacy pollutant

   https://doi.org/10.1002/lol2.10130  

   Athey, Samantha N.; Albotra, Samantha D.; Gordon, Cessely A.; Monteleone, Bonnie; Seaton, Pamela; Andrady, Anthony L.; Taylor, Alison R.; Brander, Susanne M. (January 2020, Limnology and Oceanography Letters)

   Abstract Microplastics are of increasing concern as they are readily ingested by aquatic organisms. This study investigated microplastic trophic transfer using larval inland silversides (Menidia beryllina) (5 d posthatch) and unicellular tintinnid (Favellaspp.) as a model food chain relevant to North American estuaries. Low‐density polyethylene microspheres (10–20 μm) were used to compare direct ingestion of microplastics by larval fish and trophic transfer via tintinnid prey. Dichlorodiphenyltrichloroethane (DDT)‐treated microspheres were used to determine sorbed pollutant effects on microplastic ingestion. Larval fish exposed directly to microspheres ingested significantly fewer than those exposed via contaminated prey. Larvae ingested significantly more ciliates containing DDT‐treated microspheres than ciliates containing untreated plastics but did not discriminate when exposed directly. Larvae reared for 16 d following a direct 2 h exposure had significantly lower wet weight values than unexposed controls. Our results demonstrate that trophic transfer is a significant route of microplastic exposure that can cause detrimental effects in sensitive life stages. 

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2. Relative exposure to microplastics and prey for a pelagic forage fish

   https://doi.org/10.1088/1748-9326/ac7060  

   Chavarry, J M; Law, K L; Barton, A D; Bowlin, N M; Ohman, M D; Choy, C A (June 2022, Environmental Research Letters)

   Abstract In the global ocean, more than 380 species are known to ingest microplastics (plastic particles less than 5 mm in size), including mid-trophic forage fishes central to pelagic food webs. Trophic pathways that bioaccumulate microplastics in marine food webs remain unclear. We assess the potential for the trophic transfer of microplastics through forage fishes, which are prey for diverse predators including commercial and protected species. Here, we quantify Northern Anchovy ( Engraulis mordax ) exposure to microplastics relative to their natural zooplankton prey, across their vertical habitat. Microplastic and zooplankton samples were collected from the California Current Ecosystem in 2006 and 2007. We estimated the abundance of microplastics beyond the sampled size range but within anchovy feeding size ranges using global microplastic size distributions. Depth-integrated microplastics (0–30 m depth) were estimated using a depth decay model, accounting for the effects of wind-driven vertical mixing on buoyant microplastics. In this coastal upwelling biome, the median relative exposure for an anchovy that consumed prey 0.287–5 mm in size was 1 microplastic particle for every 3399 zooplankton individuals. Microplastic exposure varied, peaking within offshore habitats, during the winter, and during the day. Maximum exposure to microplastic particles relative to zooplankton prey was higher for juvenile (1:23) than adult (1:33) anchovy due to growth-associated differences in anchovy feeding. Overall, microplastic particles constituted fewer than 5% of prey-sized items available to anchovy. Microplastic exposure is likely to increase for forage fishes in the global ocean alongside declines in primary productivity, and with increased water column stratification and microplastic pollution. 

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3. Effects of mixotroph evolution on trophic transfer

   https://doi.org/10.1093/plankt/fbae053  

   Honig, Meredith_A; Barbaglia, Gina_S; Doyle, Margaret_D; Moeller, Holly_V; Beisner, ed., Beatrix_E (September 2024, Journal of Plankton Research)

   Abstract Plankton form the foundation of marine food webs, playing fundamental roles in mediating trophic transfer and the movement of organic matter. Increasing ocean temperatures have been documented to drive evolution of plankton, resulting in changes to metabolic traits that can affect trophic transfer. Despite this, there are few direct tests of the effects of such evolution on predator–prey interactions. Here, we used two thermally adapted strains of the marine mixotroph (organism that combines both heterotrophy and autotrophy to obtain energy) Ochromonas as prey and the generalist dinoflagellate predator Oxyrrhis marina to quantify how evolved traits of mixotrophs to hot and cold temperatures affects trophic transfer. Evolution to hot temperatures reduced the overall ingestion rates of both mixotroph strains, consequently weakening predator–prey interactions. We found variability in prey palatability and predator performance with prey thermal adaptation and between strains. Further, we quantified how ambient temperature affects predator grazing on mixotrophs thermally adapted to the same conditions. Increasing ambient temperatures led to increased ingestion rates but declines in clearance rates. Our results for individual, pairwise trophic interactions show how climate change can alter the dynamics of planktonic food webs with implications for carbon cycling in upper ocean ecosystems. 

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4. Field measurements reveal exposure risk to microplastic ingestion by filter-feeding megafauna

   https://doi.org/10.1038/s41467-022-33334-5  

   Kahane-Rapport, S. R.; Czapanskiy, M. F.; Fahlbusch, J. A.; Friedlaender, A. S.; Calambokidis, J.; Hazen, E. L.; Goldbogen, J. A.; Savoca, M. S. (November 2022, Nature Communications)

   Abstract Microparticles, such as microplastics and microfibers, are ubiquitous in marine food webs. Filter-feeding megafauna may be at extreme risk of exposure to microplastics, but neither the amount nor pathway of microplastic ingestion are well understood. Here, we combine depth-integrated microplastic data from the California Current Ecosystem with high-resolution foraging measurements from 191 tag deployments on blue, fin, and humpback whales to quantify plastic ingestion rates and routes of exposure. We find that baleen whales predominantly feed at depths of 50–250 m, coinciding with the highest measured microplastic concentrations in the pelagic ecosystem. Nearly all (99%) microplastic ingestion is predicted to occur via trophic transfer. We predict that fish-feeding whales are less exposed to microplastic ingestion than krill-feeding whales. Per day, a krill-obligate blue whale may ingest 10 million pieces of microplastic, while a fish-feeding humpback whale likely ingests 200,000 pieces of microplastic. For species struggling to recover from historical whaling alongside other anthropogenic pressures, our findings suggest that the cumulative impacts of multiple stressors require further attention. 

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5. Penguin guano suppresses the grazing rate and modifies swimming behavior in Antarctic Krill (Euphausia superba)

   https://doi.org/10.3389/fmars.2025.1508287  

   Hellessey, Nicole; Weissburg, Marc; Fields, David M (March 2025, Frontiers in Marine Science)

   Fernandez, J (Ed.)

   Antarctic krill (Euphausia superba) are a key component of the Antarctic ecosystem linking primary and some secondary production to higher trophic levels including fish, penguins, seals, and whales. Understanding their response to environmental stimuli therefore provides insights into the trophic ecology of Antarctic systems. This laboratory study quantified the influence of penguin guano, a presumptive predator cue, chlorophyll concentration and flow speed on krill swimming behavior. In addition, ingestion rates with and without guano were measured. Such inquiries are necessary to determine if predator risk cues modify krill activities in ways that have consequences for other members of the Antarctic trophic web. Krill often exhibited acute turns when guano was present and varied their swimming speeds more when guano was present. These are both indicators of avoidance behavior to the negative chemical cues represented by penguin guano. Similarly, krill’s ingestion rates dropped significantly for a prolonged period of time in the presence of guano. This decrease in feeding will have impacts on krill’s nutritional value to their predators, prey uptake rates (prey survival) and the sequestration of carbon to the deep ocean as krill decrease their defecation rates. This study supports the hypothesis that krill use chemical signals to detect and behaviorally respond to food and predation risk. 

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