Viral diversity and Interactions in a Changing Environment on Kelp

Kelps are brown algae from the order Laminariales that predominate along rocky coastal areas with cold and relatively shallow waters around the world. Like other marine photosynthetic organisms, kelps fuel secondary production via macroalgal detritus; thereby supporting complex food webs in coastal zones. Since they grow in dense groupings, like underwater forests, they also provide physical habitat, nursery ground and food for organisms, such as marine mammals, fishes, crabs, sea urchins, mollusks, other algae and epibiota. Kelp forest can alter local oceanography and ecology by dampening wave surge, which influence water flow, coastal erosion, sedimentation, benthic productivity (primary and secondary) and recruitment. Kelp is not just a key species for the marine environment, but also for us. Their multiple industrial applications have led to an increase in the economic importance of seaweed aquaculture. However, 38% of the world's kelp forests have been in decline over the past five decades possibly due to coastal eutrophication and rising sea temperatures, among others. Norwegian Kelp populations have been fluctuating without an obvious reason and, the recent discovery of Phaeoviruses infecting Kelp species opens a new door for studying viral infection as a possible vector for this regime shift. Domesticated seaweeds are more susceptible to abiotic stressors, disease, and parasites. If they are a reservoir for disease, besides the economic burden, they can impact natural populations. ViralICE project therefore aimed to find out whether and how kelp viruses affect the natural kelp forest in Norway and kelp aquaculture under the current climate change situation. Laminaria hyperborea and Saccharina latissima are two relevant kelp species due to their commercial interest; the first one as raw material for alginate production, and the second one as animal feed. A total number of 799 samples from both species were either provided by our industry partners, IFF and Ocean Forest, or harvested with the research vessel “Hans Brattstrom” along the Norwegian coast (from Troms and Finnmark county, to Rogaland, including the Norwegian fiords: Sognefjorden and Hardangerfjorden). Phaoeviruses were discovered some years ago in England, however, they had not been previously studied in Norway. Therefore, the obtained samples were used to investigate the prevalence of Phaeoviruses in Norway. To investigate this, we extracted the kelp DNA and screened for Phaeoviruses using PCR-technology. Our results showed that more than 90% of our samples were positive for Phaeoviruses and, after sequencing some of these positives, up to three different viral master variants were found in the same algal individual. Two of these viral variants had been previously found, however, the third one had never been reported before. During ViralICE project we have focused on outreaching activities to show young students about the importance of the kelp forest ecosystem, like our annual participation in The national science week in Norway (Forskningsdagene UNG). We also wrote and illustrated a children’s book: “Olle Kråkebolle og tareskogens mysterier”, Vormedal Forlag, ISBN 978-82-93885-10-8. This book has been part of our dissemination plan, and main educative tool during the school visits at HVL. To learn more about the ViralICE-project, please visit: https://www.hvl.no/prosjekt/2512209/

Our research efforts focused on Phaeoviruses infecting relevant kelp species, both for the aquaculture industry and for the natural ecosystem. After our extensive screening along the Norwegian coast, our results revealed that these viruses are widespread and highly prevalent. Sequencing also revealed the high diversity among Phaeoviruses, even opening a window for future research, after finding a putative new member of an unclassified phycodnavirus genus. In this way, we have followed up with our premise of enhancing our knowledge about viral diversity, biology and ecology. The role of Phaeoviruses is still not well understood. Our results also supported previous research, in which more than one viral variant co-exists within the same kelp plant, but we still do not know how these viral variants interact among them, and with their hosts. Now we have a potential new player not belonging to the Phaeovirus genus, and it will be interesting to know more about these interactions, especially under climate change. ViralICE also intended to build a network connecting national and international researchers, and this has been accomplished satisfactorily. There has been an excellent communication during the whole project with national and international researchers, as well as with our industry partners. We have met in different online meetings, but we have also had the possibility to visit and participate in our industry’s partners facilities and activities. The PI has also had the possibility to go work with our partners in Bergen, but also with our international partners in the USA, increasing the possibilities for future collaborations. Our project has also been shared within the research community through two research/review articles (Viruses and Frontiers in Aquaculture), two posters (The Microbiology Society Annual Conference 2024 at Edinburgh, Scotland; and 18th Annual Institute for Molecular Virology Symposium (IMV) at the University of Minnesota, Minnesota, USA), and a workshop (Aquaconnect workshop “Communicating aquatic research”, NORCE, Bergen, Norway). ViralICE has also been present publicly in local news media, as well as in our research institutions’ channels. The importance of kelp ecosystems as well as the role of marine viruses was captured in the book “Olle Kråkebolle og tareskogens mysterier”, published by Vormedal Forlag (ISBN 978-82-93885-10-8). The book has been used as a main educational tool during our school visits, organizing related activities around it in our facilities, like our labs and aquariums.

Being the most abundant and diverse entities in planet Earth, marine viruses have been proved to control their host populations, acting as driving force for the inter- and intra-species competition and succession. Their outstanding roles in food webs, competitive interactions, biodiversity patterns, and the regulation of keystone species, manifest therefore, their contribution structuring ecological communities and impacting ecosystem functioning. However, we still do not completely understand how viruses interact with their hosts. Kelp forest (brown algae from the order Laminariales) impacts local oceanography and ecology, and constitute enormous energy sources for coastal benthic secondary production supporting fisheries worldwide; from temperate, to polar rocky ecosystems. Kelp deforestation has been reported globally and, after the recent discovery of Phaeoviruses on kelp, viral diseases should be taken into consideration. Evidence posses that host-pathogen interactions will become more frequent and intense in the future, leading to higher virus multiplication rates, increased transmission and host species jumps. Wild seaweed domestication is making crops more susceptible to abiotic stressors, disease and parasites, and these may act as a disease reservoir which could impact natural populations. Therefore, viral infection could not only affect natural kelp forest, but also impact the Norwegian blue bioeconomy. ViralICE has been designed to throw some light into viral diseases that could potentially affect kelp communities and relevant species to the Norwegian industry. This project intends to contribute with Phaeoviral infection knowledge in brown algae, and we will: 1) study Phaeoviral diversity, 2) study the Phaeoviral host-range, 3) study the potential ecological consequences of climate change on algal-pathogen interactions, and 4) build relevant networks between research communities, industry and government.