lasseeli

• Eliassen, Lasse Krøger; Garvang, Even Sletteng; Andersen, Tom; Riemann, Lasse & Titelman, Josefin (2026). Metabarcoding and biomass quantification reveal seasonal parasite associations in copepods. Limnology and Oceanography. ISSN 0024-3590. 71(2). doi: 10.1002/lno.70327. Full text in Research Archive Show summary

  Abstract Parasites are important members of ecosystems, and recent metabarcoding efforts have revealed an abundance of microbial eukaryotic parasites in copepods. However, a putative linkage to host community biomass and composition has not been addressed. We performed zooplankton tows monthly for 2 yr at five stations in the Oslofjord, Norway. The samples were cleared of larger, non‐copepod zooplankton and contained mainly copepods and are henceforth referred to as copepod community samples. Metabarcoding was used to detect microbial eukaryotic parasites in the copepod community samples. We also metabarcoded water samples from one of the stations. Copepods were identified and their biomasses were estimated at three of the stations for 1 yr. Calanus spp. dominated biomass in winter, whereas Temora longicornis and other smaller, short‐lived coastal copepods prevailed during summer. Seasonality in the copepod community was less apparent in the deep waters (200 m) where larger, long‐lived copepods abound. The alveolate parasites Hematodinium and Chromidina were detected at most stations throughout the year and occupied a large proportion of the total reads. Although the microbial eukaryotic community in the copepod community samples reflected the seasonal copepod dynamics, common alveolate parasites (e.g., Syndinium , Blastodinium , and apostome ciliates) appeared year‐round. Co‐occurrence analysis suggested several pair‐wise associations between taxa of microbial eukaryotes and copepods. Parasites are a universal component of copepods in this fjord system and seem well‐adapted to seasonal fluctuations in host community composition. We hypothesize that the parasites may have host ranges that incorporate perennial copepods to maintain their presence in seasonally fluctuating environments.

• Eliassen, Lasse Krøger; Altin, Dag; Andersen, Tom; Riemann, Lasse; Dunthorn, Micah & Titelman, Josefin (2025). Long Term Copepod Culture Houses a Rich Microbial Eukaryotic Community Including New and Known Symbionts. Journal of Eukaryotic Microbiology. ISSN 1066-5234. 72(6). doi: 10.1111/jeu.70053. Full text in Research Archive Show summary

  Copepods, dominant marine zooplankton, are hosts to microbial eukaryotic symbionts, but the copepod eukaryome remains largely unexplored. We used 18S rRNA gene primers with reduced metazoan amplification to identify microbial eukaryotes in a culture of Calanus finmarchicus (Copepoda). Samples were taken from the inlet water (99.5% of reads from non‐copepod sources) and the contents of the culture, which included ambient water (99.7%), bulk (many crushed copepods, 60.2%), individual copepods (1%–41%, mean = 7.4), and bulk fecal pellets (74%). The microbial eukaryotic community in the culture differed from the inlet water. The culture contained saprotrophs and bacterivores typical of eutrophic aquacultures and known parasites of copepods. Individual copepod eukaryomes varied in richness (8–33 operational taxonomic units, mean = 16.1) and revealed variation in non‐copepod read yields related to specific taxa. Perkinsea, not previously reported in copepods, as well as Ascomycota and Basidiomycota (Fungi), formed the core eukaryome (found in > 90% of individuals), indicating potentially important symbiosis. The small eukaryome, relative to reported microbiomes in C. finmarchicus , suggests that ecological inferences from microbiomes, which largely address bacteria, are not readily applicable to the eukaryotic microbes. The study underpins the need for investigations of eukaryomes.

• Garvang, Even Sletteng; Eliassen, Lasse Krøger; Titelman, Josefin & Andersen, Tom (2024). Outbreak conditions and impacts of parasites in copepod populations. Ecosphere. 15(12), p. 1–18. doi: 10.1002/ecs2.70093. Full text in Research Archive
• Eliassen, Lasse Krøger; Garvang, Even Sletteng; Andersen, Tom; Engseth, Erik; Kristiansen, Kåre Andre & Wiik-Nielsen, Jannicke [Show all 7 contributors for this article] (2024). Conspicuous parasite modifies appearance and energetics of a marine copepod. ICES Journal of Marine Science. ISSN 1054-3139. 81(10), p. 2052–2064. doi: 10.1093/icesjms/fsae150. Full text in Research Archive Show summary

  Parasitism is an important driver of ecosystem processes. Copepods are fundamental trophic links in marine food webs and harbour many microeukaryotic parasites, but unreliable access to infected individuals limits quantitative studies of parasite infection costs. Calanus spp., (helgolandicus or finmarchicus), infected with the Yellow-Hyphal Parasite become pigmented and are found near the surface, suggesting predator-mediated dispersal. Conventional markers prevented phylogenetic inference but confirmed that the parasite is not Ichthyophonus hoferi, as previously thought. We identified the pigments, quantified the pigment content and respiration rate, and derived stable isotope signatures of infected and uninfected Calanus spp. to examine costs of infection. We found that the pigments were astaxanthin and β-carotene, associated with the host and parasite, respectively. Parasitized hosts had increased astaxanthin content, reduced respiration rate, and lower lipid content. Ultrastructure imaging revealed parasitic cells associated with lipids in the haemocoel. The changes to host phenotype have detrimental impacts on energetics and the ecology of Calanus. We discuss the role of pigments in parasite-host interactions and suggest that the parasite produces β-carotene pigment for its physiological benefits. The trade-off between physiological benefits of pigments and conspicuousness for parasites is relevant in zooplankton-host systems, as zooplankton rely heavily on transparency for survival.

• Humborstad, Odd Børre; Eliassen, Lasse Krøger; Siikavuopio, Sten Ivar; Løkkeborg, Svein; Ingólfsson, Ólafur Arnar & Hjelset, Ann Merete (2021). Catches in abandoned snow crab (Chionoecetes opilio) pots in the Barents Sea. Marine Pollution Bulletin. ISSN 0025-326X. 173(Part A), p. 1–7. doi: 10.1016/j.marpolbul.2021.113001. Full text in Research Archive Show summary

  During a 2018 retrieval cruise for abandoned snow crab (Chionoecetes opilio) pots in the Barents Sea, approximately 8600 pots abandoned 1.5 years earlier were recovered. Forty-three percent of a subsample of 1000 pots contained snow crabs, with an average of three crabs per pot. Most of the crabs were alive (~98%) and dominated by large males. Pinch injuries and limb loss were common and tended to decline with increasing crab size. Reflex testing showed that the crabs were vital (i.e. the crabs moved their legs, chelipeds and maxillipeds when stimulated), which was supported by a relatively high meat content. However, energy reserves in the digestive glands (hepatopancreas reserves) were low, indicating overall energy deficiencies. Our results indicate considerable unaccounted mortality due to self-baiting, continued catch and cannibalism. The findings demonstrate that snow crab pots which are lost or abandoned in the Barents Sea fishery maintain huge potential for ghost-fishing impacts.

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• Eliassen, Lasse Krøger; Garvang, Even Sletteng; Andersen, Tom; Engseth, Erik; Kristiansen, Kåre Andre & Wiik-Nielsen, Jannicke [Show all 7 contributors for this article] (2023). A parasite-copepod association and its effects on host pigmentation and lipids. Full text in Research Archive
• Garvang, Even Sletteng; Eliassen, Lasse Krøger; Titelman, Josefin & Andersen, Tom (2022). Modeling the parasites of copepods. Full text in Research Archive
• Eliassen, Lasse Krøger; Garvang, Even Sletteng; Andersen, Tom; Engseth, Erik; Kristiansen, Kåre Andre & Wiik-Nielsen, Jannicke [Show all 7 contributors for this article] (2022). The yellow-hyphal parasite in Calanus finmarchicus. Full text in Research Archive
• Eliassen, Lasse Krøger; Humborstad, Odd Børre; Hjelset, Ann Merete; Hustad, Anette; Løkkeborg, Svein & Martinsen, Gustav [Show all 8 contributors for this article] (2022). Catches in abandoned snow crab pots in the Barents Sea. Full text in Research Archive
• Titelman, Josefin; Eliassen, Lasse Krøger; Garvang, Even Sletteng & Andersen, Tom (2021). Parasite disease in coastal zooplankton. Full text in Research Archive
• Titelman, Josefin; Eliassen, Lasse Krøger; Garvang, Even Sletteng & Andersen, Tom (2021). Parasite disease in coastal zooplankton. Full text in Research Archive

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