Translational effects of trait changes in aquatic ecosystems

Thursday, June 17 at 02:15am (PDT)
Thursday, June 17 at 10:15am (BST)
Thursday, June 17 06:15pm (KST)

SMB2021 SMB2021 Follow Wednesday (Thursday) during the "MS17" time block.
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Hanna Schenk (German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig; Leipzig University, Germany), Michael Raatz (Max Planck Institute for Evolutionary Biology, Germany)


Aquatic ecosystems contribute to human wellbeing by providing food, clean water, economic and recreational benefits. Anthropogenic and environmental changes impact the functioning and output of these ecosystems, often via inducing changes in traits of key species. Overfishing, temperature or acidity changes and landscape transformations are only some of the possible drivers at play. Changes in species’ traits, whether plastic or evolutionary, influence their interactions and population dynamics and thus propagate across trophic levels and scales. Such ecosystem-wide effects, but also the immediate effects on exploitability and usability indicate the far-reaching consequences of trait changes in aquatic ecosystems. Owing to this complexity of ecological, societal and economic feedback, transdisciplinary approaches are necessary to fully understand these dynamics. Tackling problems such as overfishing and biodiversity decline while incorporating stakeholders’ interests requires a translational approach of applying results from basic research to concrete problems and specific case studies. This symposium discusses how modelling can account for these diverse aspects and sheds light on the translational significance of trait changes in aquatic ecosystems.

Ken H. Andersen

(Center for Ocean Life, Natl. Inst. of Aquatic Resources, Technical University of Denmark, Denmark)
"Using size-spectrum models to address global food security"
Our assessments of the biomass, production, and future trajectory of fish communities on a global scale relies on process-based models calibrated to observations. The scarcity of observations in the vast oceanic regions places a large burden on the quality of the process descriptions that underpins model predictions. Here I review a novel class of trait-based “size spectrum” models that simulate fish communities and their response to fishing. Size spectrum models are based around predator-prey interactions between smaller prey and larger predators. The models resolve the growth of individuals from eggs, with a size of around 1 mg, to the size of adults. All physiological processes are parameterized with respect to the size of individuals. Differences between species are represented by the maximum size, which varies from 1 g for small meso-pelagic fish to 100’s of kg for large pelagic predators like tuna. The models are in the form of coupled partial differential-integro equations that can be solved efficiently with standard techniques. I will show examples of how size spectrum models simulates regional fish communities or the global biogeography of fish biomass, and how they are used for strategic fisheries management and climate change projections.

Andrea Campos Candela

(The Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Germany)
"Towards a mechanistic understanding of phenotypic trait changes, adaptive behaviour and life history based on dynamic energy budgets"
Understanding phenotypic trait changes in spatial and temporal environmental gradients needs understanding the fitness consequences of phenotypic trait variation. This challenge requires connecting behavioural and physiological traits that mediate survivorship and reproductive success with the environmental context. Mechanistic frameworks such as the Dynamic Energy Budget (DEB) theory linking individual internal state dynamics with immediate changes in environmental conditions offer a new perspective to improve such understanding. Drawing on first bioenergetics principles informed by DEB theory, I present a dynamic state-dependent behavioural and life history model to explore the optimal strategies that maximize fitness in ecological contexts varying in food availability and predation risk. Novel contributions of this framework are manifold: 1) I encourage the use of DEB theory in the adaptive context to meet mortality payoff functions integrating ecological extrinsic risks as predation; and, specifically 2) explore the behavioural processes of energy acquisition and the bioenergetics processes of energy mobilization and energy allocation, that 3) together link emerging optimal phenotypic traits with individual internal and external states. Finally, 4) by assuming state-dependent dynamic trade-offs, DEB primary parameters can be dynamic during ontogeny, which breaks down the fixed rules within DEB while opening an interesting research line for future model developments. Results within the exploratory simulated scenarios support that processes related with energy mobilization and allocation can absorb more of the selective pressure driven by the extrinsic risk of mortality, while the process related with energy acquisition strongly correlates with food. I would like to motivate debate about feasible ways of extending this framework, with a physiological and mechanistic-based perspective, to more complex and meaningful scenarios.

Maite Erauskin-Extramiana

(AZTI BRTA, Spain)
"The influence of climate change and fishing pressure in global top predator abundance and body size in the future"
Tunas and billfishes are the main large pelagic commercial fished species. Tunas comprised around 5.5 million tonnes and USD 40 billion in 2018, being an economically important contribution to many nations. Tuna stocks are well covered by management assessments which estimate that 13% of the stocks are still overfished and 22% are at intermediate levels. Climate change studies and projections forecast that current global fish catches might decrease by the end of the century. However, there are sparse studies and projection for the higher trophic levels where tunas and billfishes belong. A combined Size-Spectrum and Dynamic Bioclimatic Envelope Model (SS-DBEM) was used to project the effects of climate change and fishing for 19 globally distributed large pelagic fishes under climate change (RCP 2.6 and 8.5) and fishing scenarios (0.8 to 1.2 times Maximum Sustainable Yield, MSY). The results suggest that high trophic level species will be more impacted by climate change than by fishing pressure if kept close to the Maximum Sustainable Yield. Projected impacts trends were more driven by species sizes than by the group they belong to. There are mixed responses of main commercial tuna stocks biomass by RFMOs with projections of decreases up to 43% and increases up to 68% by 2050, whereas some stocks can have higher increases up to 168% by 2100. Furthermore, their size is expected to decrease 15% on average by 2050 and 10% by 2100 except for the yellowfin East Pacific stock. Price and demand are often driven by body size, therefore this can reduce the revenue by the fishing industry due to climate change even in stocks that benefit from an increase of biomass. Industry can adopt adaptation strategies such as increase value of their products through added value processing to increase revenue with the same catches, or reduce fuel consumption and time at sea with higher digitalization and the use of decision support systems to reduce searching time and optimize routes considering environmental conditions, or through certified sustainability actions. Reducing fuel reduction would be also a mitigation measure to climate change since it reduces vessels emissions, i.e. a win-win for industry and the environment.

Hanna Schenk

(German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig; Leipzig University, Germany)
"Optimal harvest of evolving fish"
A side effect of targeting large fish is a strong selection pressure on a smaller size at maturation. This has resulted in fisheries-induced evolution of earlier maturation in several fish species. Due to life-history trade-offs fish that mature at a younger age also grow more slowly. The fisheries-induced evolution thus reduces the economic benefits for fisheries, especially as large fish are proportionally more valuable than small fish. We include these processes in an economic-ecological-evolutionary demographic fishery model to study economic implications of fisheries-induced evolution and to derive optimised fishing management strategies. Economic benefits of fishing depend on the size structure of catches, as prices depend on the size of the fish caught. Economic costs of fishing depend on the size of the fish population and the gear. We apply the model to the North Sea cod fishery and find that the optimal fishing strategy is sensitive to discounting. Whereas for a low discount rate the optimal strategy is to rebuild a population structure with late maturation and strong growth the optimal strategy for a high discount rate would not attempt to reverse the fisheries-induced evolution and rather continue to fish on the evolved population.

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