An infochemical found on marine plastic debris elucidates a novel mechanism for plastic ingestion by marine wildlife.

In terrestrial systems, the green wave hypothesis posits that migrating animals can enhance foraging opportunities by tracking phenological variation in high-quality forage across space (i.e., “resource waves”). To track resource waves, animals may rely on proximate cues and/or memory of long-term average phenologies. Although there is growing evidence of resource tracking in terrestrial migrants, such drivers remain unevaluated in migratory marine megafauna. Here we present a test of the green wave hypothesis in a marine system. We compare 10 years of blue whale movement data with the timing of the spring phytoplankton bloom resulting in increased prey availability in the California Current Ecosystem, allowing us to investigate resource tracking both contemporaneously (response to proximate cues) and based on climatological conditions (memory) during migrations. Blue whales closely tracked the long-term average phenology of the spring bloom, but did not track contemporaneous green-up. In addition, blue whale foraging locations were characterized by low long-term habitat variability and high long-term productivity compared with contemporaneous measurements. Results indicate that memory of long-term average conditions may have a previously underappreciated role in driving migratory movements of long-lived species in marine systems, and suggest that these animals may struggle to respond to rapid deviations from historical mean environmental conditions. Results further highlight that an ecological theory of migration is conserved across marine and terrestrial systems. Understanding the drivers of animal migration is critical for assessing how environmental changes will affect highly mobile fauna at a global scale.

Plastic pollution has pervaded almost every facet of the biosphere, yet we lack an understanding of consumption risk by marine species at the global scale. To address this, we compile data from research documenting plastic debris ingestion by marine fish, totaling 171,774 individuals of 555 species. Overall, 386 marine fish species have ingested plastic debris including 210 species of commercial importance. However, 148 species studied had no records of plastic consumption, suggesting that while this evolutionary trap is widespread, it is not yet universal. Across all studies that accounted for microplastics, the incidence rate of plastic ingested by fish was 26%. Over the last decade this incidence has doubled, increasing by 2.4 ± 0.4% per year. This is driven both by increasing detection of smaller sized particles as a result of improved methodologies, as well as an increase in fish consuming plastic. Further, we investigated the role of geographic, ecological, and behavioral factors in the ingestion of plastic across species. These analyses revealed that the abundance of plastic in surface waters was positively correlated to plastic ingestion. Demersal species are more likely to ingest plastic in shallow waters; in contrast, pelagic species were most likely to consume plastic below the mixed layer. Mobile predatory species had the highest likelihood to ingest plastic; similarly, we found a positive relationship between trophic level and plastic ingestion. We also find evidence that surface ingestion‐deep sea egestion of microplastics by mesopelagic myctophids is likely a key mechanism for the export of microplastics from the surface ocean to the seafloor, a sink for marine debris. These results elucidate the role of ecology and biogeography underlying plastic ingestion by marine fish and point toward species and regions in urgent need of study.

Plastic pollution is an anthropogenic stressor in marine ecosystems globally. Many species of marine fish (more than 50) ingest plastic debris. Ingested plastic has a variety of lethal and sublethal impacts and can be a route for bioaccumulation of toxic compounds throughout the food web. Despite its pervasiveness and severity, our mechanistic understanding of this maladaptive foraging behaviour is incomplete. Recent evidence suggests that the chemical signature of plastic debris may explain why certain species are predisposed to mistaking plastic for food. Anchovy ( Engraulis sp.) are abundant forage fish in coastal upwelling systems and a critical prey resource for top predators. Anchovy ingest plastic in natural conditions, though the mechanism they use to misidentify plastic as prey is unknown. Here, we presented wild-caught schools of northern anchovy ( Engraulis mordax ) with odour solutions made of plastic debris and clean plastic to compare school-wide aggregation and rheotactic responses relative to food and food odour presentations. Anchovy schools responded to plastic debris odour with increased aggregation and reduced rheotaxis. These results were similar to the effects food and food odour presentations had on schools. Conversely, these behavioural responses were absent in clean plastic and control treatments. To our knowledge, this is the first experimental evidence that adult anchovy use odours to forage. We conclude that the chemical signature plastic debris acquires in the photic zone can induce foraging behaviours in anchovy schools. These findings provide further support for a chemosensory mechanism underlying plastic consumption by marine wildlife. Given the trophic position of forage fish, these findings have considerable implications for aquatic food webs and possibly human health.

It's the prey that matters: Although many people think of dinosaurs as being the largest creatures to have lived on Earth, the true largest known animal is still here today—the blue whale. How whales were able to become so large has long been of interest. Goldbogen et al. used field-collected data on feeding and diving events across different types of whales to calculate rates of energy gain (see the Perspective by Williams). They found that increased body size facilitates increased prey capture. Furthermore, body-size increase in the marine environment appears to be limited only by prey availability. Science , this issue p. 1367 ; see also p. 1316