How do a dominant predator and climate shape fish biodiversity over space and time in large marine ecosystems?

Summary: Over-exploitation and collapse of top predators in marine ecosystems are well recognized, but its impact on biodiversity at the ecosystem level is only poorly understood. On the Scotian Shelf in the Northwest Atlantic the cod population has been dramatically reduced, with a collapse on the eastern shelf in the early 1990s. Our analyses shows that this has resulted in large changes in the fish biodiversity with increased variability in the bottom fish community. This means that the fish communities were more homogeneous when cod was more prevalent in the system. In the Barents Sea the cod population has increased dramatically both in numbers and distribution over large spatial scales, i.e. a rather unique situation for marine ecosystems. The Barents Sea cod population is currently the largest in the world. At the same time, the climate in the Barents Sea has changed during the last decades, with increased sea temperature and declining sea ice. Our predictions are a more homogeneous bottom fish community with an increasing cod population in the Barents Sea. Simultaneously, but working in the opposite direction, our expectation would be increased fish diversity as a consequence of increasing sea temperature. Here we will evaluate the role of the dominant predator cod and climate in shaping fish biodiversity over space and time in large ecosystems. Through these studies, we aim to provide a new methodological approach that is expected to give an earlier warning on changes in ecosystems than more traditional statistical methods. Obviously, such early warnings are important for the management authorities. 2014-2015: The project has been carried out according to the plan. We had a kick-off meeting with all national project participants and international participants from Canada and Russia in March 2014, and a project workshop with participants from NINA, UiT, IMR, Canada and Russia in April 2015. In addition, we have communicated via Skype with national and international participants. We started with processing of all data from the Barents Sea. We have worked on how to best divide the Barents Sea into rational sub-areas based on drivers in the system; temperature and cod. This will be essential for our analyses of the patterns of biodiversity in space and time. We gave a presentation at the 49th European Marine Biology Symposium in 2014 in Russia, focusing on the drivers. We have published one international popular article in International Innovation (2014), where the background for our project and the goals were presented. We have published a paper in Journal of Animal Ecology (Ellingsen et al. 2015), where we examined data from the Scotian Shelf, Canada. We found that the dramatic decline in cod populations caused by overfishing has resulted in large changes in the diversity of the fish community. We made a news story published at forskning.no, nina.no and framsenteret.no, and it has later been published by Nationen, Bladet Vesterålen, Kyst og Fjord, Alt om Fiske and Jakt & Fiske. We have published a paper in Nature Climate Change (Ingvaldsen et al. 2015). The paper is a reply to a paper published in the same journal, where climate researchers simulated that cod would find suitable environmental conditions in the Barents Sea by around 2060-2100. The problem is that cod are already present in these areas, and we suggest a careful evaluation and selection of climate models. NTB made a news story on this, and it has later been published by forskning.no, nrk.no/troms and E24.no. In addition, we did a number of analyses on data from the Barents Sea. 2016: The project is going according to the plan. We had a mini-workshop in Halifax, Canada in January 2016 with participants from NINA, UiT and Canada. We had a project workshop with participants from NINA, UiT, IMR and Canada in April 2016. In addition, we have communicated via Skype with national and international participants, in particular with the participant from New Zealand. We have published one popular article in Ottar (Ellingsen et al. 2016), where the whole project is presented, but with a special focus on the result from the paper by Ellingsen et al. (2015). We have worked on three new papers. The first is based on a presentation at a symposium in Russia in 2014, but we have done a number of additional analyses (Johannesen et al. ms). The paper is focusing on habitat use by cod in the Barents Sea. The second is focusing on patterns of biodiversity in space and time in the Barents Sea, and the role of cod and temperature for structuring fish biodiversity (Ellingsen et al. ms). This is a comparative study where we compare the results from the Barents Sea with our results from the Scotian Shelf, Canada (Ellingsen et al. 2015). In addition, we have written a third paper with a special focus on the Svalbard archipelago (Bergstad et al. submitted).

Over-exploitation and collapse of apex predators in marine ecosystems are well recognized, but its impact on biodiversity at the ecosystem level is only poorly understood. On the Scotian Shelf in the Northwest Atlantic the cod population has been dramatic ally reduced, with a collapse on the eastern shelf in the early 1990s. Preliminary analyses suggest that this has resulted in large changes in the fish biodiversity with increased heterogeneity in the demersal fish community. This means that the fish comm unities were more homogeneous when cod was more prevalent in the system. In a northern ecosystem, the Barents Sea, the cod population has increased dramatically both in numbers and distribution over large spatial scales - a rare situation for marine ecosy stems. The Barents Sea cod population is currently the largest in the world. At the same time, the climate in the Barents Sea has changed during the last decades, with increased sea temperature and declining sea ice. Our predictions are a more homogeneous demersal fish community with an increasing cod population in the Barents Sea. Simultaneously, but working in the opposite direction, our expectation would be increased fish diversity as a consequence of increasing sea temperature. Here we propose to eval uate the role of the dominant predator cod and climate in shaping fish biodiversity over space and time in large ecosystems. The ecosystem states and changes in the Barents Sea and on the Scotian Shelf are both sufficiently similar and different to make a comparison insightful. Through these studies, we aim to provide a new multivariate methodological approach that is expected to give an earlier warning on changes in ecosystems than more traditional statistical methods. Obviously, such early warnings will be relevant for the management authorities. Although, the choice of biodiversity measure may have large consequences for the interpretation of the results, this has often been overlooked in previous studies.