Anthropogenic litter is a novel habitat for aquatic macroinvertebrates in urban rivers

Abstract

Anthropogenic litter (solid manufactured waste) is an understudied but pervasive element of river systems worldwide. Its physical structure generally differs from natural substrates, such as gravel and cobbles (hereafter rocks). Consequently, anthropogenic litter could influence ecological communities in urban rivers by providing novel habitats. This study compares the macroinvertebrates recorded on anthropogenic litter with those on rocks to test whether the different substrates support distinct communities. Macroinvertebrates were collected from individual rocks and anthropogenic litter, predominantly plastic, metal, and glass, in three U.K. rivers. Macroinvertebrate communities on anthropogenic litter were consistently more diverse than those found on rocks, reflecting its greater surface complexity, but the density of macroinvertebrates was similar among substrates. The community composition also varied between substrates, with five taxa only recorded on anthropogenic litter. Community differences largely reflected greater abundances of common taxa on anthropogenic litter, which were relatively insensitive to environmental quality. Plastic and fabric anthropogenic litter communities were the most dissimilar to those on rocks, probably due to their flexibility, which could replicate the physical structure of aquatic macrophytes. Our findings indicate that anthropogenic litter supports a distinct and diverse community of macroinvertebrates in urban rivers, which are otherwise relatively homogenous in habitat structure. Removal of anthropogenic litter from urban rivers may not be beneficial for local biodiversity. Understanding the functional habitats provided by anthropogenic litter could help better manage urban rivers to replace habitat lost through urbanisation.

Interactions Between Plastic, Microbial Biofilms and Gammarus pulex: An Initial Investigation

“…The absence of any plastic shredding indicates that these types of macro-plastic films which pollute freshwater systems (Wilson et al 2021) are unlikely to be fragmented by G. pulex in the same manner that they are in marine systems by the amphipod O. gammarellus (Hodgson et al 2018) and the first hypothesis of this study can therefore be rejected. However, it should be considered that these conclusions may only be valid for plastic with a toughness and thickness the same or greater than that of the tested materials.…”

“…A further study which presented these choices with materials enclosed in fine mesh to prevent amphipods having contact with them [in a similar manner as Lange et al (2005)] would help to distinguish which of these factors is driving the results seen in this study. These findings may suggest that the significant associations seen between G. pulex and anthropogenic materials observed in rivers (Wilson et al 2021) may be due to the ability of these materials to provide physical shelter, rather than a fooddriven attraction of G. pulex to the attached biofilms.…”

“…In natural environments a significantly higher abundance of Gammarus sp. have been found associated with anthropogenic litter compared to natural rock (Wilson et al 2021) and in behaviour experiments G. pulex has demonstrated clear attraction to the chemosensory signature of microbial biofilms (Lange et al 2005). Previous studies have demonstrated the ingestion of biofilm-free microplastics 10-150 μm in size by G. pulex and other gammarids (Weber et al 2018;Mateos-Cárdenas et al 2020), but their interaction with larger, microbially colonised plastic remains unexplored.…”

Goals and approaches in the use of citizen science for exploring plastic pollution in freshwater ecosystems: A review

“…metals; Naqash et al, 2020) and biological sorption (Ma et al, 2020) as key toxicants posing severe impacts on freshwater ecosystems. This extends to comprehensive data on freshwater plastic abundance and fate, alongside the ecological effects of plastics on freshwater species (Winton et al, 2014), with some plastic litter potentially beneficial in supporting diverse assemblages of freshwater macroinvertebrates (Wilson et al, 2021).…”

“…In recent years, an increased focus on plastics in freshwater environments have started to emerge within the scientific literate (Schwarz et al, 2019;Bellasi et al, 2020;Wilson et al, 2021). However, the majority of these studies are dedicated to microplastics (Winton et al, 2020;van Emmerick et al, 2021), despite macroplastics being a key source of environmental plastic.…”