Exploring resilience and adaptation in a changing sea

How do species respond to human activities or changes in their environment? This and other research questions relating to the resilience of coastal organisms and ecosystems are the focus of a group of CCR researchers centred at the Institute of Marine Research (IMR), Flødevigen at Hisøy outside Arendal.

IMR Flødevigen has closely monitored the Norwegian Skagerrak coast for more than a century to detect changes in recruitment of coastal fish species. Since 1919, annual beach seine surveys have been conducted to assess fish assemblages, covering more than 130 stations along the coast, from Kristiansand to the Swedish border. Marked changes in species composition has occurred over this time, a period in which the Skagerrak has experienced significant warming. Warm-water species have increased in variety and abundance. In contrast, cold-water species are in decline (Barcelo et a. 2016). Besides warming of the oceans, there are numerous other factors influencing marine life in the Skagerrak. One of the species facing considerable pressure in this region is the Atlantic cod. Characterizing the effects of harvesting and habitat destruction, as well as climatic challenges, is crucial in order to ensure better protection of cod populations. Besides annual beach seine surveys, several projects characterize the distribution and state of cod and other coastal fishes.

Atlantic cod population dynamics

Molecular methods for characterizing within- and between-species biodiversity are rapidly developing
for both research and monitoring. Consequently, the
lab facilities at IMR Flødevigen have been substantially upgraded in recent years to facilitate implementation of these advances. These new molecular methods can be used to understand the geographic distribution of fish stocks as well as interactions between different stocks. In coastal Skagerrak, two Atlantic cod ‘ecotypes’ partially coexist: a coastal cod that mainly inhabits fjords and an offshore cod that is more abundant in outer skerries, as well as in the North Sea (Sodeland et al 2016; Knutsen
et al 2018). Together with national and international collaborators, CCR leader Professor Halvor Knutsen and colleagues have characterized these populations and found that they not only differ genetically along the coast, but also show important ecological and physiological differences. That is, they display differences in patterns of growth and annual abundance (Knutsen et al. 2018). A recent study has also shown that these ecotypes show different sensitivity to temperature (Chung et al. 2021), which may affect their future distributions under climate change.

Mapping spawning and nursing grounds

Since fish assemblages in coastal waters are under pressure from climatic warming and other human impacts, mapping and surveying habitat use at different life stages is essential for understanding how species distributions are affected by these challenges.

In an ongoing collaboration between IMR and UiA lead by Dr. Sigurd H. Espeland, molecular tools are being developed for more accurate and cost-effective species identification of both codfishes and flatfishes. These tools will be implemented in a national IMR program aimed at mapping spawning and nursery areas for commercially exploited fish species along the Norwegian coast. Implementation of novel molecular tools greatly advances both the accuracy and efficiency of these surveys.

The research also involves several student projects, providing students opportunities to experience and learn approaches that are likely to be central in the future of coastal surveillance. Student contribution is valuable to the researchers as well, as their efforts are enhancing the knowledge of coastal species and ecosystems.

Thermal adaptation of Atlantic cod

Populations within a species can adapt genetically to the different environments they might experience. These local adaptations can affect the responses of populations to changes in their environment, such that environmental changes like climate change can affect different populations differently. A collaboration between IMR, UiA, UiO, and Dalhousie University in Canada, led by Dr. Rebekah Oomen and Dr. Jeffrey Hutchings, has investigated whether local adaptations to temperature exist in Atlantic cod along coastal Norway, with a focus on fine-scale adaptation between inner fjord and outer oceanic environments along the Skagerrak coast. Using the aquarium and molecular labs at IMR Flødevigen and the Norwegian Sequencing Centre at UiO, they combine experiments raising cod larvae at different temperatures with advanced molecular techniques like RNA sequencing, which measures which genes are turned on and how much they are expressed. This has revealed that warmer waters expected to occur more frequently due to climate change cause a broad physiological stress response in cod larvae that is associated with lower survival. Importantly, these responses differ between and within populations along the coast, depending on the ecotype, location, and specific genetic variants caused by rearrangements within chromosomes. Overall, this suggests that ocean warming due to climate change will make it more difficult for coastal cod to survive to adulthood. On the other hand, variation in temperature responses reflects potential to adapt to future conditions if sufficient genetic diversity and population sizes are maintained through effective coastal monitoring and management actions (Oomen et al. 2021).