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Caddisfly larvae occur in streams and rivers, and many caddisfly species build protective cases using material from their habitat such as sand grains. At the same time, microplastics (MPs) are regularly deposited in aquatic sediments and are incorporated into caddisfly (Lepidostoma basale) cases in the field. However, it is unknown what the effects of MP incorporation into cases might be on the health of the caddisfly larvae. Hence, we offered two commonly used MPs (polyvinyl chloride (PVC) and polyethylene terephthalate (PET)) to L. basale larvae during a laboratory experiment. Both plastic types have a high density and co-occur with L. basale larvae in benthic habitats. In our experiment, L. basale actively used sand, PET and PVC MPs for building tube-like portable or emergency cases. The latter is a temporary shelter under which the larva can hide for immediate protection. Furthermore, case stability decreased with increasing PVC and PET particle content in the cases, suggesting that MPs may threaten caddisflies by destabilising cases. When case stability is reduced, the protective function of the cases is limited and the larvae may be more prone to predation. Additionally, larvae may be washed away by the current as plastic is lighter than sand. Both effects could limit the caddisfly’s survival, which could have far-reaching consequences as caddisfly larvae are important primary consumers in aquatic ecosystems.

Understanding shifts in benthic communities along gradients over time is of crucial importance in estuarine ecology and for conservation. Yet studies considering historical data and both taxonomic and functional aspects are rare. We analysed data of macrobenthic invertebrates of the highly modified Elbe Estuary (Germany) from 1889, 1985, 1986 and 2006 to assess community shifts and considered both taxonomic and functional aspects. The number of species, functional richness (FRic) and functional redundancy (FR) reached minimum values in 1985 and 1986 and were highest and similar in 1889 and 2006. However, beta-diversity analysis showed that species assemblages in 1889 and 2006 greatly differed, almost exclusively owing to species replacement. Most striking was the decline in gastropods after 1889 to levels approaching extinction in the estuary in the other sampling years, most likely due to elevated concentrations of chemical substances, such as tributyl tin. Functional beta diversity was mainly a result of functional nestedness and was exceptionally low in a comparison of data from 1889 to 2006, which indicated nearly complete functional recovery. Null models revealed that function loss in 1985 and 1986 was non-random, consistent with habitat filtering. All functional groups were present on all sampling dates, which suggested that FR might have provided protection from significant ecosystem function loss. Our results indicate that FRic and FR in 1889 could have promoted ecosystem resilience and stability.

The estuarine maximum turbidity zone (MTZ) can be assumed to be a stressful environment featuring special conditions of great biological importance with an excess of organic matter, high-deposition rates, large variations in salinity, and dredging activities. Under such harsh conditions, populations may remain below the carrying capacity and competition is assumed to be of little importance, as predicted by the stress-gradient hypothesis. Therefore, we hypothesized that invertebrates of similar feeding types may utilize the same resources. To test our hypothesis, we chose the three most abundant taxa classified in literature as deposit feeders (Bathyporeia pilosa, Boccardiella ligerica, Marenzelleria sp.) and two taxa classified as predominately predacious (Palaemon longirostris, Crangon crangon) and determined their isotopic niches based on a stable isotope analysis for the MTZ of the Elbe Estuary (Germany). We expected the isotopic niches of similar feeding types to show a clear overlap if our hypothesis was true. Our results showed that the isotopic niches of no two taxa overlapped within each feeding group, indicating different resource use and the absence of competition. The sediment analysis revealed that two of the deposit feeders inhabited significantly different mean grain sizes. The lack of overlap of isotopic niches within each feeding group may be due to differences in habitat and feeding behavior in the case of the deposit feeders and due to different migration behavior in the case of the predominately predacious species. However, competition may have occurred in the past, resulting in a divergence of feeding niches during evolution.