Josefin Titelman

• Kline, Simon Hasselø; Hyvärinen, Olli Petteri; Valestrand, Louise; Andersen, Tom; Eikrem, Wenche & Titelman, Josefin [Show all 8 contributors for this article] (2026). 15-year shift in protist communities and a decline of heterotrophic dinoflagellates in the Oslofjord and Skagerrak. Frontiers in Marine Science. 13. doi: 10.3389/fmars.2026.1876109. Full text in Research Archive
• 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.

• Garvang, Even Sletteng; Heuschele, Jan David; Konestabo, Heidi Sjursen; Andersen, Tom; Riemann, Lasse & Titelman, Josefin (2025). Parasite infection shapes the pathobiome and behavior of marine zooplankton. Limnology and Oceanography Letters. 11(1). doi: 10.1002/lol2.70078. Full text in Research Archive Show summary

  When assessing the total impact of disease in a host, it is important to consider not only the disease‐carrying agent but also all symbionts, as they affect and are affected by the course of disease. This concept of a pathobiome is increasingly recognized in disease ecology, but is not well‐investigated in natural systems. Copepods are key organisms in marine ecosystems and host a variety of symbionts, including bacteria and eukaryotic parasites. We investigated the impact of a taxonomically uncertain yellow‐hyphal parasite (YHP) on its copepod host Calanus helgolandicus with an incubation experiment, comparing survival, behavior, and microbiomes of uninfected and infected hosts. Infected hosts suffered higher mortality, and altered behavior which can increase predation risk. The microbiomes differed between infected and uninfected hosts, likely caused by a combination of direct effects of infection, and environmental effects driven by parasite‐induced behavioral change. We identified several potential contributing taxa to the Calanus ‐YHP pathobiome using model‐based ordination.

• 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.

• Vereide, Emilie Hernes; Utne-Palm, Anne Christine; Titelman, Josefin; Pedersen, Geir; Strand, Espen & Mihaljevic, Marina [Show all 13 contributors for this article] (2025). Zooplankton mortality and distribution around a seismic survey. Scientific Reports. 15. doi: 10.1038/s41598-025-09465-2. Full text in Research Archive Show summary

  Anthropogenic underwater noise from seismic airguns is increasing, posing a potential threat to marine life. Despite their ecological importance, knowledge of the impacts of seismic surveys on zooplankton remains limited. In the North Sea, we utilized various methods to assess potential effects on zooplankton around an ongoing seismic survey. A seismic airgun array (3060 inch3) performed a survey along parallel lines, while we sampled from a research vessel positioned at the end of three of these lines. The airgun-generated noise reached a maximum broadband sound exposure level of 182 dB re 1µPa2s at the closest proximity (~50 m). Zooplankton biomass exhibited a consistent distribution in line with hydrography and chlorophyll distribution, before and after airgun exposure. Immediate mortality in Calanus spp. was uniform across sound levels, never exceeding 35.9%. Cultured Calanus finmarchicus were exposed while submerged in bags. These displayed low immediate mortality (<10%), with an increasing trend (<30%) up to 7 days post-exposure. These findings highlight the interplay between sound exposure, environmental conditions, and the impact on zooplankton in areas of seismic activity, indicating that immediate impacts of seismic surveys on zooplankton may be limited. However, delayed impacts that could lead to population effects require further investigation.

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• Nyeggen, Margot Ulfsdatter; Christiansen, Svenja; Garvang, Even Sletteng; Andersen, Tom; Heuschele, Jan David & Titelman, Josefin (2025). Zooplankton community dynamics in Oslofjorden. Full text in Research Archive
• Garvang, Even Sletteng; Heuschele, Jan David; Konestabo, Heidi Sjursen; Andersen, Tom; Riemann, Lasse & Titelman, Josefin (2025). Replication Data for: Parasite infection shapes the pathobiome and behavior of marine zooplankton. doi: https:/scholar.google.com/citations?view_op=view_citation&hl=sv&user=ycTVkNkAAAAJ&sortby=pubdate&citation_for_view=ycTVkNkAAAAJ%3A3s1wT3WcHBgC. Full text in Research Archive Show summary

  We collected Calanus helgolandicus from the Oslofjord, both healthy individuals and infected with a conspicuous" yellow-hyphal" parasite that changes the host behavior. We incubated them for 7 days and measured behavior and survival. At the start and end of the incubation we sampled animals for 16S rRNA microbial community analysis. Infected Calanus had higher mortality, more risky behavior and altered microbiomes compared to the uninfected.

• Titelman, Josefin (2025). Parasite disease in copepods. Full text in Research Archive
• Heuschele, Jan David; Markova, Yana; Striebel, Maren; Andersen, Tom & Titelman, Josefin (2025). Uferflucht - Shore avoidance and other zooplankton dynamics in a coastal ecosystem. Full text in Research Archive
• Garvang, Even Sletteng; Heuschele, Jan David; Konestabo, Heidi Sjursen; Andersen, Tom; Riemann, Lasse & Titelman, Josefin (2025). Parasite infection shapes the pathobiome and behavior of copepods. Full text in Research Archive

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