Description: Rivers are an important transport route of anthropogenic litter from inland sources toward the sea. A citizen science approach was used to evaluate the litter pollution of rivers in Germany: schoolchildren within the project “Plastic Pirates” observed floating macrolitter at 282 sites and took meso-/microplastic samples (i.e. particles 1 mm - 25 mm) at over 164 sites across the entire country during the years 2016 and 2017. Floating macrolitter quantities ranged from 0 to 8.25 items m -1 h -1 (average of 0.34 ± 0.89 litter items m -1 h -1 ) and floating macrolitter was sighted at 54% of sampling sites. The quantities of floating meso-/microplastics ranged from 0 to 220 particles h -1 (average of 6.86 ± 24.11 meso-/microplastics h -1 ). They were present at 57% of the sampling sites. Given that only particles 〉 1 mm were sampled and analyzed, the pollution of rivers in Germany by microplastics is likely a ubiquitous problem, regardless of the size of the river. We identified six plastic pollution hotspots where 60% of all meso-/microplastics collected in the present study were found. The composition of the particles at these hotspots indicates plastic producers and possibly the construction industry and wastewater treatment plants as point sources. An identification of litter hotspots would enable specific mitigation measures, adapted to the respective source, and thereby prevent the release of large quantities of small plastic particles in rivers. The adopted large-scale citizen science approach was especially suitable to detect pollution hotspots by sampling a variety of rivers, large and small, and enabled a national overview of litter pollution in German rivers.

Description: One possible interaction between organisms is direct predation, where a predator consumes prey and thereby decreases its density which may influence more organisms in that trophic food chain (e.g. the prey's food source). Another interaction is based on most prey's capability to detect predators and adapt to that threat in behaviourial, morphological or life history traits. These adaptions can be quite costly and it is expected that there is a trade off between predator avoidance and the costs to do so. In aquatic environments this way of interaction is often communicated via chemical “risk cues“, which can either originate from the predator alone (kairomones) or from startled (disturbance cues), injured (alarm cues) or consumed and digested prey (dietary cues). These cues are used by potential prey to assess the risk of predation and adapt accordingly. This study focuses on the effects of alarm and dietary cues on the egg-production and the mating and feeding behaviour of the common periwinkle (Littorina littorea) by using either crushed (injured) snails – the stomach juice from the shore crab (Carcinus maenas) with and without the addition of a snails body – or the faeces of shore crabs feeding on periwinkles. The research took place on Helgoland, from March to May (2011) as a manipulative lab experiment with factorial design. It was found that injured conspecifics reduced the mating behaviour of L. littorea probably because of the higher mortality risk associated with forming mating pairs. The faeces of crabs had no effect on periwinkles but that may be due to the point of time the investigation took place: egg production and mating frequency were decreasing. Stomach juice with in vitro digested snails showed differing results, reducing the egg numbers in one experiment but not in the other. This may be because of methodical reasons: in the experiment showing an effect the devices applying the stomach juice were changed more often and the room temperature was higher which could mean that the enzymes in the stomach juice were working more efficiently on the added snail tissue. Therefore a possible effect of stomach juice with digested snail is favored. There was no evidence found that pure stomach juice influences the snails while crabs feedings on conspecifics clearly had an effect on the numbers of eggs laid and the mating behaviour, as former studies hypothesised. There was no evidence in any experiment where the amount of food consumption differed from a control treatment, probably because L. littorea does not prefer Fucus. The results suggest that the trait-mediated indirect interaction between the predator C. maenas and its prey L. littorea is not communicated via predator's kairomones but more likely via risk cues originating from the periwinkle (alarm or dietary cues).

Description: Floating anthropogenic litter provides habitat for a diverse community of marine organisms. A total of 387 taxa, including pro- and eukaryotic micro-organisms, seaweeds and invertebrates, have been found rafting on floating litter in all major oceanic regions. Among the invertebrates, species of bryozoans, crustaceans, molluscs and cnidarians are most frequently reported as rafters on marine litter. Microorganisms are also ubiquitous on marine litter although the composition of the microbial community seems to depend on specific substratum characteristics such as the polymer type of floating plastic items. Sessile suspension feeders are particularly well-adapted to the limited autochthonous food resources on artificial floating substrata and an extended planktonic larval development seems to facilitate colonization of floating litter at sea. Properties of floating litter, such as size and surface rugosity, are crucial for colonization by marine organisms and the subsequent succession of the rafting community. The rafters themselves affect substratum characteristics such as floating stability, buoyancy, and degradation. Under the influence of currents and winds marine litter can transport associated organisms over extensive distances. Because of the great persistence (especially of plastics) and the vast quantities of litter in the world’s oceans, rafting dispersal has become more prevalent in the marine environment, potentially facilitating the spread of invasive species.

Description: Rivers are an important transport route of anthropogenic litter from inland sources toward the sea. A citizen science approach was used to evaluate the litter pollution of rivers in Germany: schoolchildren within the project “Plastic Pirates” observed Floating macrolitter at 282 sites and took meso-/microplastic samples (i.e. particles 1 mm - 25 mm) at over 164 sites across the entire 28 country during the years 2016 and 2017. Floating macrolitter quantities ranged from 0 to 8 items m-1 h-1 (average of 0.34 ± 0.89 litter items m-1 h-1) and floating macrolitter was sighted at 54% of sampling sites. The quantities of floating meso-/microplastics ranged from 0 to 220 particles h-1 (average of 6.86 ± 24.11 meso-/microplastics h-1). They were present at 57% of the sampling sites. Given that only particles 〉 1 mm were sampled and analyzed, the pollution of rivers in Germany by microplastics is likely a ubiquitous problem, regardless of the size of the river. We identified six plastic pollution hotspots where 60% of all meso-/microplastics collected in the present study were found. The composition of the particles at these hotspots indicates plastic producers and possibly the construction industry and wastewater treatment plants as point sources. An identification of litter hotspots would enable specific mitigation measures, adapted to the 38 respective source, and thereby prevent the release of large quantities of small plastic particles in rivers. The adopted large-scale citizen science approach was especially suitable to detect pollution hotspots by sampling a variety of rivers, large and small, and enabled a national overview of litter pollution in German rivers.

Description: Rivers are an important source of marine anthropogenic litter, but the particular origins of riverine litter itself have not been well established. Here we used a citizen science approach where schoolchildren examined litter at riversides and identified possible sources at over 250 sampling spots along large and small rivers in Germany, during autumn 2016 and spring 2017. Litter densities have an overall median of 0.14, interquartile range 0–0.57 items m−2 and an overall average (±standard deviation) of 0.54 ± 1.20 litter items m−2. Litter quantities differed only little by sampling year. The principal litter types found were plastics and cigarette butts (31% and 20%, respectively), followed by glass, paper, and metal items, indicating recreational visitors as the principal litter source. At many sites (85%), accumulations of litter, consisting principally of cigarettes and food packaging, have been found. At almost all sampling sites (89%), litter potentially hazardous to human health has been observed, including broken glass, sharp metal objects, used personal hygiene articles and items containing chemicals. In the search for litter sources, the schoolchildren identified mainly people who use the rivers as recreational areas (in contrast to residents living in the vicinity, illegal dumping, or the river itself depositing litter from upstream sources). These results indicate the urgent need for better education and policy measures in order to protect riparian environments and reduce input of riverine litter to the marine environment.

Description: Rivers are an important transport route of anthropogenic litter from inland sources toward the sea. A collaborative (i.e. citizen science) approach was used to evaluate the litter pollution of rivers in Germany: schoolchildren within the project “Plastic Pirates” investigated rivers across the entire country during the years 2016 and 2017 by surveying floating macrolitter at 282 sites and taking 164 meso−/microplastic samples (i.e. particles 24.99–5 mm, and 4.99–1 mm, respectively). Floating macrolitter was sighted at 54% of sampling sites and floating macrolitter quantities ranged from 0 to 8.25 items m−1 h−1 (average of 0.34 ± 0.89 litter items m−1 h−1). Floating meso−/microplastics were present at 57% of the sampling sites, and floating meso−/microplastic quantities ranged from 0 to 220 particles h−1 (average of 6.86 ± 24.11 items h−1). As only particles 〉1 mm were sampled and analyzed, the pollution of rivers in Germany by microplastics could be a much more prevalent problem, regardless of the size of the river. We identified six plastic pollution hotspots where 60% of all meso−/microplastics collected in the present study were found. These hotspots were located close to a plastic-producing industry site, a wastewater treatment plant, at and below weirs, or in residential areas. The composition of the particles at these hotspots indicates plastic producers and possibly the construction industry and wastewater treatment plants as point sources. An identification of litter hotspots would enable specific mitigation measures, adjusted to the respective source, and thereby could prevent the release of large quantities of small plastic particles in rivers. The adopted large-scale citizen science approach was especially suitable to detect pollution hotspots by sampling a variety of rivers, large and small, and enabled a national overview of litter pollution in German rivers.