ALBERT

Description: Microplastic pollution is an emerging threat to marine biota. Uptake of microplastics can impair nutrition and affect the performance of organisms. However, the vulnerability to microplastics seems to vary between species for yet widely unexplored reasons. We investigated the stomach content of the brown shrimp, Crangon crangon, from the southern North Sea and performed feeding experiments and anatomical studies of the digestive organs to comprehend the distribution of fluorescent microparticles within the shrimp. Shrimp collected in their natural environment contained between 51 and more than 3,000 sand grains and fragments of bivalve shells in their stomachs. Sand grains may have been ingested to exploit the associated biofilm or to support maceration of food. Bivalve shell fragments were particularly abundant in summer when shrimp fed on freshly settled mussels. Shrimps’ stomach can be cleaned from ingested particles by regurgitation. In an experimental approach, we administered fluorescent microbeads of 0.1, 2.1, and 9.9 μm diameter. Only the smallest particles (0.1 μm) entered the midgut gland, which is the principal site of nutrient resorption in crustaceans. A fine-meshed chitinous filter system in the stomach of the shrimp prevents the passage of particles larger than about 1 μm. C. crangon appears well adapted to handle natural microscopic particles. This trait might also be advantageous in coping with microplastic pollution.

Description: Industrialization and unconscious consumerism introduced plastic into our every day’s life. Due to poor recycling strategies, synthetic material is now one of the greatest challengers in the marine environment. Under suitable environmental conditions, plastic is prone to degrade further into microplastics. The wide size range make the microplastics available to different marine fauna. Apart from the synthetic microparticles, marine organisms are in their habitat persistently surrounded by various suspended organic microparticles (remains of bivalves, cellulose fibers, chitinous remains) and inorganic microparticles (silica frustules, sediment grains). The goal of this doctoral project is to determine the differences in antioxidant defense of specimen, subjected to the microparticles of different origin. To investigate this issue, the brown shrimp were exposed to 20 mg L-1 of natural (clay, diatoms) and synthetic (TiO2, PVC, PLA) microparticles. Incubation lasted for 6, 12, 24 and 48 h, until the shrimp were dissected, and the midgut gland was withdrawn. Analyses of antioxidant enzymes such as superoxide dismutase, glutathione peroxidase and reductase followed. Additionally, antioxidant potential was measured. The preliminary results show that the microparticle origin was not detrimental for the cellular stress in the brown shrimp, but the exposure time. Early findings suggest, C. crangon better copes with microplastic pollution then others marine organisms. Similar exposure experiments with crustaceans of other habitual or feeding traits would be advised, to better understand the high stress resistance towards microplastic pollution in the brown shrimp.

Description: Brown shrimp, Crangon crangon, inhabit highly productive sandy and muddy grounds of the southern North Sea. The stomachs of the shrimp contain variable and often high numbers of sediment grains. The function of sediment grains inside the stomach and the purpose of their ingestion are only poorly understood. We tested in laboratory experiments whether sediment and associated organic material complement the natural food of C. crangon or if sand grains may be used by the shrimp to support trituration and maceration of ingested food. The shrimp showed no notable preference for sediment with natural organic content over sediment with reduced organic content, limited ingestion of sediment upon starvation, and no additional uptake of sand grains after feeding. Instead, C. crangon took up sediment only while feeding on regular food, suggesting that sand grains are not ingested intentionally but rather incidentally as a side effect of hasty gobbling. This conclusion is supported by the highly variable uptake of sand grains among individuals. Under experimental conditions, sand grains from sediments do not seem to have a crucial function in food processing and digestion in brown shrimp.

Description: Plastic has become indispensable for human life. When plastic debris is discarded into waterways, these items can interact with organisms. Of particular concern are microscopic plastic particles (microplastics) which are subject to ingestion by several taxa. This review summarizes the results of cutting-edge research about the interactions between a range of aquatic species and microplastics, including effects on biota physiology and secondary ingestion. Uptake pathways via digestive or ventilatory systems are discussed, including (1) the physical penetration of microplastic particles into cellular structures, (2) leaching of chemical additives or adsorbed persistent organic pollutants (POPs), and (3) consequences of bacterial or viral microbiota contamination associated with microplastic ingestion. Following uptake, a number of individual-level effects have been observed, including reduction of feeding activities, reduced growth and reproduction through cellular modifications, and oxidative stress. Microplastic-associated effects on marine biota have become increasingly investigated with growing concerns regarding human health through trophic transfer. We argue that research on the cellular interactions with microplastics provide an understanding of their impact to the organisms’ fitness and, therefore, its ability to sustain their functional role in the ecosystem. The review summarizes information from 236 scientific publications. Of those, only 4.6% extrapolate their research of microplastic intake on individual species to the impact on ecosystem functioning. We emphasize the need for risk evaluation from organismal effects to an ecosystem level to effectively evaluate the effect of microplastic pollution on marine environments. Further studies are encouraged to investigate sublethal effects in the context of environmentally relevant microplastic pollution conditions.

Description: Petroleum-based plastics are integral components of daily life. Huge quantities of mostly disposable plastic products are in use. Low environmental consciousness and inappropriate waste management causes drastic plastic littering in terrestrial and aquatic environments. Plastics are very persistent, but UV radiation and mechanical stress induce degradation of larger plastic objects into numerous so-called microplastics. Increasing public awareness raises concern about microplastic pollution. However, research on the effects of microplastics on organisms often provides inconclusive results. Comparing how organisms cope with natural microparticles in their habitats allows drawing conclusions on the susceptibility to the potential effects of synthetic microparticles. Therefore, the objective of this thesis is to investigate the uptake, the internal allocation, and the cellular effects of natural and synthetic microparticles in marine invertebrates. This study contributes to a better understanding and distinction between the reactions to natural microparticles and the effects induced by anthropogenic microparticles. Coastal and estuarine regions are characterized by turbid waters and may contain up to one gram per litre of suspended particulate matter (SPM) in the µm-size range. Ingestion of natural indigestible microparticles is common in marine invertebrates. Stomach content analysis of brown shrimp, Crangon crangon, collected in their natural environment revealed quantities of up to several hundred natural microparticles, mainly sand grains and fragments of bivalve shells, per individual. Most indigestible items leave the body through the gut as faecal pellets within 24 hours. Larger particles are regurgitated through the flexible esophagus. Experimentally administered fluorescent microbeads of 2.1, and 9.9 μm diameter passed through the stomach and gut of the shrimp. Only the smallest particles of 0.1 μm entered the midgut gland, which is the principal site of nutrient resorption in crustaceans. A fine-meshed chitinous filter system in the stomach of the shrimp prevents the passage of particles larger than about 1 μm into the midgut gland, where particles can be absorbed and interact with the cells of the midgut gland epithelium. Indigestible material, including particulate matter, which enters the midgut gland, is presumably deposited in vacuoles of specific digestive cells, the B cells, and released by cell rapture into the lumen of the digestive tract to be evacuated with the rest of faeces. These results suggest that accumulation of microparticles in shrimp is unlikely. Incorporation of microparticles in the cells of the midgut gland may entail various cellular reactions. A frequently reported effect is the induction of oxidative stress due to the production of reactive oxygen species (ROS), but the underlying mechanisms are not sufficiently identified. A suggested source of ROS is the NADPH-oxidase enzyme complex, which is well investigated in vertebrate neutrophils. NADPH-oxidase is also present in shrimp midgut gland tissue as revealed by transcriptome analysis and immunological verification. Excess formation of ROS is counterbalanced by a complex cascade of antioxidants. The induction of superoxide dismutase (SOD) is an important indication of oxidative stress. Significant SOD induction appeared in the Atlantic ditch shrimp, Palaemon varians, within few hours upon microplastic ingestion, but was lacking in C. crangon. Moreover, overall SOD-activities were significantly lower in C. crangon than in P. varians. This result is surprising, but clearly indicate that even closely related species may react differently to microplastic exposure. Moreover, C. crangon showed no differential oxidative stress response after administration of synthetic or natural microparticles at environmentally relevant SPM-concentrations of 20 mg per litre. The differences between species may be related to differential formation of ROS or differential protection against ROS. Both aspects demand further research in marine invertebrates, particularly the NADPH-oxidase and the enzymatic and non-enzymatic anti-oxidative defence system. In summary, this study provides important insight into the interaction of marine invertebrates with natural or anthropogenic microparticles. Marine invertebrates are exposed to much higher concentrations of natural microparticles than anthropogenic microplastics. Microparticles are ingested, as shown for brown shrimp, but most of these particles cannot advance into sensitive organs due to anatomical barriers. Smaller particles in the sub-micrometer size range may enter the cells of the midgut gland. However, they seem to cause differential biochemical stress reaction between species. C. crangon did not show any stress response following the ingestion of natural or anthropogenic microparticles suggesting that species from habitats with high natural particle load have evolved specific anatomical and biochemical properties to cope with a high SMP-load in turbid waters. These species will likely be less affected by anthropogenic microplastics and, thus, may be favored in future scenarios of continuously increasing environmental microplastic pollution.