Microplastics Alter the Properties and Sinking Rates of Zooplankton Faecal Pellets

Abstract

Plastic debris is a widespread contaminant, prevalent in aquatic ecosystems across the globe. Zooplankton readily ingest microscopic plastic (microplastic, < 1 mm), which are later egested within their faecal pellets. These pellets are a source of food for marine organisms, and contribute to the oceanic vertical flux of particulate organic matter as part of the biological pump. The effects of microplastics on faecal pellet properties are currently unknown. Here we test the hypotheses that (1) faecal pellets are a vector for transport of microplastics, (2) polystyrene microplastics can alter the properties and sinking rates of zooplankton egests and, (3) faecal pellets can facilitate the transfer of plastics to coprophagous biota. Following exposure to 20.6 μm polystyrene microplastics (1000 microplastics mL(-1)) and natural prey (∼1650 algae mL(-1)) the copepod Calanus helgolandicus egested faecal pellets with significantly (P < 0.001) reduced densities, a 2.25-fold reduction in sinking rates, and a higher propensity for fragmentation. We further show that microplastics, encapsulated within egests of the copepod Centropages typicus, could be transferred to C. helgolandicus via coprophagy. Our results support the proposal that sinking faecal matter represents a mechanism by which floating plastics can be vertically transported away from surface waters.

Frequency of Microplastics in Mesopelagic Fishes from the Northwest Atlantic

“…Such studies have prompted researchers to investigate the impact on ecosystem processes. Indeed, Cole et al (2016) found that microplastics alter the sinking rates of copepod faecal pellets if ingested and in consequence may affect the downward flux of carbon to the ocean floor. With the increasing evidence that microplastics represent an ecosystem and environmental health concern, UNEP and the EU Commission have established bodies and efforts to guide in decision making and legislation (Galgani et al, 2013;UNEP, 2016).…”

Plastics in the Marine Environment

“…Timescales by which large objects are fragmented to microplastics by weathering-induced and biologically mediated processes, such as grinding in bird gizzards or biting by fishes (Kühn et al 2015), are not well constrained. Plastics that are initially buoyant may be transported to greater depth upon increased density caused by biofouling (Ye & Andrady 1991, Fazey & Ryan 2016, ingestion by vertically migrating species (Choy & Drazen 2013), or sinking within fecal pellets (Cole et al 2016) or marine aggregates (Long et al 2015). Some of these processes have been demonstrated in laboratory or field experiments, but their rates in the environment are unknown.…”

Microplastic-Associated Biofilms: A Comparison of Freshwater and Marine Environments

“…For example, microplastics may become transported away from surface waters via encapsulation within fecal pellets [81]. Although this topic has not been investigated in freshwater or marine environments, the gut bacteria of mealworms (larvae of Tenebrio molitor Linnaeus) can degrade polystyrene [82], and certain aquatic organisms could harbor microorganisms capable of modifying the surface properties of plastics and/or biodegrading them.…”