Appendicularians are planktonic marine tunicates with elaborate filter‐feeding houses that can efficiently trap particles as small as 0.2 μm. While marine viruses are seldom considered outside their role in disease transmission, we conducted a controlled laboratory experiment to determine if the appendicularian Oikopleura dioica can trap and ingest the Emiliania huxleyi virus (EhV; 160–180 nm diameter). Removal and retention of EhV during 2.5 h and overnight incubations at 15°C were measured using flow cytometry and quantitative polymerase chain reaction specific for the mcp gene of EhV. The fate of retained EhV was tested by quantifying EhV DNA in three biological compartments: house‐trapping, ingestion/digestion, and defecation. Clearance rates for EhV varied from approximately 2 mL ind−1 d−1 to 50 mL ind−1 d−1, with highest rates for 4–5 d‐old animals. EhV particles were cleared by O. dioica at rates similar to those reported for larger food particles, with mean clearance rates in the 2.5 h incubations ranging from approximately 2 mL ind−1 d−1 to 50 mL ind−1 d−1. This demonstrates efficient virus removal by O. dioica and a previously overlooked link between the microbial loop and the classical marine food web. EhV DNA was readily detectable above background levels in O. dioica houses, gut contents, and faecal pellets, suggesting that appendicularian houses and faecal pellets may contribute to the dispersal of viruses. Furthermore, clearance of EhV and presumably other viruses by O. dioica may be a significant sink for viruses and thus an important factor in regulating the population dynamics of viruses and their hosts.

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Kelps and fucoids are important members of temperate seaweed communities, but may be negatively impacted by climate change and non-native species. We used a field experiment to investigate the effect of higher temperatures and a non-native seaweed, Sargassum muticum, on the kelp Saccharina latissima and fucoid Fucus serratus. All three are canopyforming species which may grow together in the infralittoral and upper sublittoral zones in southwestern Norway. Artificial assemblages with different combinations of the species were placed in the shallow sublittoral, and length changes, weight changes and survival of the thalli were measured. This was done over a hot summer and again over a cool summer. The results showed that the species and their competitive interactions were affected by the different thermal conditions. Saccharina latissima was the most successful species in the cool summer and had an impact on the other two species, but it was strongly negatively affected by the hot summer. Under these conditions, Fucus serratus became the most successful species, gaining the most weight. The effect of Sargassum muticum on the native species was no larger than the effect of intraspecific competition within those species. At the end of both summers S. muticum was in poor condition, potentially caused by low seawater nutrients resulting in low internal nitrogen.