Light as a Cue for Life in Arctic and Northern Seas

Light is the primary source of energy for most life on Earth. In this respect, only few other environments are as hostile to life as the Arctic waters during the polar night. Yet, latest studies have revealed light-synchronized biological activity in the marine Arctic even during the darkest period of year. Which species are responsible for this activity is still partially a mystery. In LightLife, we have been able to shed light on which species are present in the light-driven vertical migration in Svalbard waters in the high Arctic during the polar night by using multi-tool approach by combining traditional plankton nets, acoustics and the latest molecular techniques. Our results revealed previously unknown movement patterns as a response to both natural and artificial light in various zooplankton species. Zooplankton, which is fundamental to the marine Arctic ecosystem, has adapted to react to extremely small light differences present during the polar night. Even though light conditions during the polar night may be extreme, natural fluctuations have been quite predictable. Sea-ice reduced by climate change and increasing light pollution are about to alter the light dynamics, and it is unclear how well the Arctic zooplankton can cope with these disturbances. By studying closely related key zooplankton species we have found out that some species which look very similar can react differently to light throughout the year or see slightly different colors of light. Thus, changing light environment is likely to affect different species differently. Not all light in the oceans comes from above the surface. There are plenty of marine species producing their own light by bioluminescence during the polar night. Bioluminescent signals are variable and even though the phenomenon itself is well known, a deeper understanding about its species-specific details and ecological significance is still missing. In LightLife, we have determined characteristics related to the color and duration of bioluminescence in several zooplankton species found in the Arctic and sub-Arctic waters. These results are collected into publicly available bioluminescence reference databases and can be used to identify zooplankton species based on their bioluminescence or to study ecological relationships.

The main outcomes of the LightLife project can be divided into three categories: scientific content, methodological proceedings and educational achievements. The scientific findings of LightLife encompass holistic knowledge on biodiversity present during the polar night in the high-Arctic, species-specific details on the abilities of Arctic and Northern zooplankton to detect and produce light, and how they react to changes in the light climate by increased artificial light. Adopting and developing new methodology has been a central aspect of the project. LightLife has successfully utilized novel technologies such as adaptive sampling with multiple autonomous underwater vehicles reporting real-time data combined with targeted sampling to provide better match with sampling towards understanding of plankton patchiness, environmental DNA analysis to assess biodiversity and species-specific behavior as well as AI assisted tracking in laboratory behavior experiments. The project has resulted in publicly available databases which enable using the characteristics of bioluminescent emission in the identification of zooplankton. LightLife has also contributed to educating the next generation of marine biologists. Four students have completed their master’s degree within the project and most of them are already employed in positions corresponding to their education. One of the goals of the LightLife project has been to attract public awareness of anthropogenic stressors and future risks for marine Arctic and Nordic ecosystems and thus contribute to the EU Blue Growth strategy and address goal 14 and 17 of the United Nations Development Program. The project has increased awareness of the impact of light pollution and changes in the light scape in general in the Arctic ecosystem through extensive dissemination efforts and participation in public conversation. LightLife has contributed to a better understanding of the fine-scale differences in the photobiology of zooplankton in marine Arctic and Nordic ecosystems, which helps to understand the ecological interactions and improve the predictions related to climate change-induced alterations. The outcomes and effects of LightLife will reach beyond the project period. The data collected and collaborations created during the project will lead to several peer-reviewed publications and further increase interest and knowledge related to the effect of light on the marine organisms. Importantly, the methods developed can be used in a wide range of scientific fields, and the public dissemination hopefully has a long-term effect on the people's behavior.

Global warming is causing reduction in both sea-ice thickness and coverage in the Arctic with substantial effects on high latitude ecosystems. In combination with constantly increasing light pollution and climate change-induced alterations in ambient light conditions this puts Arctic and Nordic marine ecosystems under pressure. The visual systems of aquatic animals in high latitude environments, however, are adapted to living in very dim light conditions and almost complete darkness during the polar night. It has been discovered recently that light-guided behaviour occurs throughout the year in the Arctic, even though the light intensities eliciting this behaviour are barely measurable with modern acquisition systems. LightLife brings together experts from different fields of biology to quantify the effects of light to the biological relationships and key functions in Arctic and Nordic ecosystems, focusing on zooplankton species which form the basis of the ecosystems. The project consists of three work packages (WPs). In WP 1, plankton species dynamics and role of light in vertical migration during the Arctic spring bloom will be determined by combining automatically acquired light data from the Arc-Light observatorium in Svalbard with species data gained by echolocation, net sampling and latest technologies around metabarcoding. WP 2 concentrates on the natural functional light regime in key species with emphasis on latitudinal effects. In this WP we determine the intensity scope for visual functions and its acclimation capacity in certain zooplankton species by laboratory experiments and electrophysiology. In WP 3, the contribution of bioluminescence as a light source and its role in the ecological interactions will be studied by state-of-the-art techniques both in the laboratory and in the field. The WP will also lead to a tool for identifying bioluminescent species by their luminous fingerprint.