"Decision makers in Governments, private sector and civil society want more robust information regarding plausible futures of biodiversity and ecosystem services. They want to understand how the drivers impacting biodiversity and ecosystem services might evolve in the future, and what the consequences might be for biodiversity, ecosystem services and nature's benefits to people. They also want to understand the implications of different policy choices on biodiversity and ecosystem services, and how to achieve policy targets." IPBES on Scenarios and Models of Biodiversity and Ecosystem Services (2017).
In the context of global change, mathematical models play a critical role in marine ecosystem management. Modelling scenarios are tools that bring science to the interface of policy and decision-making. Yunne Shin, Director of Research at IRD (Institut de Recherche pour le Développement), France, has developed the regional ecosystem model OSMOSE and end-to-end models, that allow the simulation of biodiversity scenarios that combine bottom-up and top-down effects of fishing and climate change to quantify global change impacts on marine biodiversity. Shin explained to the audience at her Annual Science Conference keynote lecture that while scenarios can prompt and guide policy and long-term strategy, and increase public awareness of future threats to biodiversity, scenarios are not predictions but a “description of how the future may develop based on a coherent and internally consistent set of assumptions about key driving forces and relationships".
Shin used her keynote to present some thoughts on uncertainties in models and scenarios on marine biodiversity. Moving on from traditional fisheries management models based on
single-stock assessments, multispecies considerations, and species
distribution models, the ecosystem approach to fisheries needs to be able to integrate fish stocks in an ecosystem perspective and a global change context, including the integration of the long term perspective into short term fisheries management. To address critical questions such as whether the combined effects of climate change and fishing are synergistic, there is a need for models which are able to handle multiple drivers, impacts, and feedbacks that are expected under global change, leading to the development of end-to-end models that combine oceanographic dynamics with organisms ranging from microbes to higher trophic level organisms including fish and humans. These models involve higher complexity, higher cost, and more uncertainty.
Shin presented the most complex end-to-end model her team has worked on, representing the spatial dynamics of the whole Mediterranean ecosystem at the basic scale, relying on the coupling of the physical, biochemical, and multispecies fish models (OSMOSE-MED). Using huge datasets of knowledge, they synthisized decades of research and the model represents the detailed life cycle of 100 species of fish and micro invertebrates – the growth, reproduction, predation mortality, starvation mortality – all life stages from age to terminal size, as well as the trophic level. Running climate change scenarios, the team are able to project species that are possible winners and losers.
However, the link to decision making is still loose and according to Shin one of the main reasons that management models (or single species stock assessment models) have more credibility is that they have a long history of evaluation and data.
There can be many different sources of uncertainty in ecosystem models which is often seen as a problem. Instead, Shin comments that this uncertainty could be interpreted as a whole space to manage socio-ecological systems in more desirable directions or according to multiple criteria. Ecosystem models need to confront the data and quantify the uncertainty if they are to become more useful for management decisions.
Uncertainty does not mean maintaining the status quo, inaction, or even acting blindly.
Within the highly variable Humboldt Current ecosystem, the Peruvian anchovy fishery has major societal and economic impacts. It employs more than 300,000 people and can land more than 5 million tonnes of catch per year. However, because of the high variability of the ecosystem, management is adaptive and based on short term projections.
"Whereas uncertainty is often seen as a problem", states Shin, "here it is used as a space for decision-makers to manage a socio-ecological system in more desirable directions".
How could the OSMOSE impact model better support decision making? Shin shows how parameters of uncertainty were categorized, enabling definition of a more rational range of variations for the parameters from high to low quality. Refining some parameters, the model can be used for longer-term perspective projecting climate change impacts on anchovy dynamics in the future or could be used to test the management procedure in critical environmental or employment situations.
In the future, we will encounter conditions that we have never encountered before. "If we just project correlations in the future that’s not
scientifically exciting and that’s not as robust in terms of projections. We must be prepared to address uncertainties from many angles. The task looks and is daunting", states Shin "but the challenges are urgent".
Watch Yunne Shin's keynote lecture Uncertainty in scenarios and models of biodiversity.
ICES Annual Science Conference 2021 took place virtually due to COVID-19 restrictions worldwide.