Ecosystem models: The key for sustainable marine management

Sustainable management of natural resources has been a major aim for governments during the past two decades. However, to reach sustainability seems to be a challenge which demands a view of the “complete picture”. In other words, it demands that we manage ecosystems instead of single resources. Ecosystems are complex natural systems formed by living and non-living entities which exchange energy. Therefore, if we want to manage them, we first need to understand how they work and how we, as humans, influence them.

If we visualize coastal areas 50 years ago, most of them looked very different [1]. The continuous increase of human population and the expansion of coastal cities around the world have resulted in huge pressures on coastal ecosystems and their resources, with the subsequent alteration of ecosystems and displacement of local fauna [2]. This, in turn, has had an impact on human activities.

One example is the effect on fisheries. Lots of fishermen around the world have started to decrease their fishing activity [3], taking the decision to move to new, more profitable and less risky professions, primarily due to the absence of viable fish populations [4]. 

What went wrong?

Basically, one thing: we did not plan for the future. Now, governments, scientists, industry, and the general public are all attempting to rectify the problem but, in order to do so, a tool is needed to guide decision-making.

One such tool is the use of mathematical equations to represent our ecosystem and its constituent parts, i.e. a model. A model is simply a predictive tool, which is developed by scientists based on what is known about an ecosystem, and which will allow them to predict future states of the ecosystem under different conditions, e.g. levels of human influence, or extraction of a particular marine resource.

The continuous increase of human population and the expansion of coastal cities around the world have resulted in huge pressures on coastal ecosystems and their resources, with the subsequent alteration of ecosystems and displacement of local fauna [2]. This, in turn, has had an impact on human activities.

How does the ecosystem model work?

An ecosystem model is based on layers. Firstly, the representation of the physical characteristics of the ecosystems are defined, including currents, temperature and climatic conditions. This is known as the Hydrographic sub-model. Secondly, the ecological sub-model is constructed. Here, we focus on the species we want to predict, including their sources of food and their predators, i.e. other animals by which this species is eaten. 

Although it may sound simple, this is the most critical part of this approach, because it not only predicts effects on the target fish, but also highlights what would happen to other animals in the ecosystem when this fish is removed or reduced in quantity.

The third layer is the human uses sub-model. This is the part we possess more control over. Once we know the amount of fish in the ocean, or an area which requires protection, etc., we could link that to the socio-economic interactions and economic indicators, such as the number of jobs supported by the ecosystem, revenues from certain resource extraction, number of communities supported by the ecosystem, etc.

How is the model used?

Once an ecosystem model has been tested and adequately evaluated for a particular ecosystem, the goal is to make it useful as a guide for policy-makers and stakeholders.

The power of a model is simple but effective. It allows experimentation according to the administrator’s goals, giving an estimated result in a matter of minutes. For example, imagine that you need to determine how much anchovy can be caught during a year. A typical approach would be to look at the amount of fish estimated to be in the ocean, and would designate a percentage according to human demands and biological indicators of the species, such as minimum catch length, percentage of juveniles in a population, etc. However, the problem with this approach is that it totally ignores the relationship of the target species with the ecosystem, neglecting possible effects on other resources, the state of the resource in the long-term, and the collateral damage to ecosystem health.

By applying an ecosystem model, a percentage of the total biomass - let’s say 50% - can be set as the maximum to be extracted, thereby allowing us to evaluate the effect on fishing revenue. At the same time, you could see how much this removal would affect the population of birds, marine mammals, and other animals which depend on anchovies as a food source. The obvious advantage is the ability to evaluate the consequences of your decision before it is actually implemented. Thus, the fishing target – or other parameter of interest - can be adapted to the current needs, context, and priorities of the manager and community. It would also allow evaluation of the future impact of global phenomena, such as climate change, over both economic indicators and the ecosystem response. Simply put, it can be used to predict which species will remain present and which are most likely to diminish.

The power of a model is simple but effective. It allows experimentation according to the administrator’s goals, giving an estimated result in a matter of minutes.

Ecosystem modelling as a tool to support decision making is not new. In fact, scientists have recently been advocating for more implementation and use of models in the development of policies, and the evaluation of their impacts over economic indicators [5]. There have been successful reports of policies driven by ecosystem modelling experiments and predictions such as, for example, the RITMARE project [6], which implemented a multi-model approach in the Italian waters of the Mediterranean Sea.

The RITMARE model has helped Italian politicians to implement a management strategy to minimize the impact of fisheries over the marine ecosystem. Its implementation also helped to identify questions which the model could not answer, leading to subsequent refinement and improvement of the tool [5].

But fisheries are not the only positive application of ecosystem modelling. One of the most complete models worldwide, ATLANTIS, was used in Norway to evaluate the impact of an invasive species - the snow crab - in the Barents Sea waters. The results showed, against all expectations, that there were some positive impacts such as increased stock of the capelin - a small fish which is eaten by cod and haddock [5]. Since the invasion, snow crab has become a more common prey of the cod, thereby allowing recovery of a small capelin fishery.

What are the limitations?

Not all is perfect with ecosystem modelling of course. One major limitation is that a model needs a good amount of high-quality data in order to refine its prediction power. Another typical issue is that models are usually developed by academics and scientists working at research institutes or universities, who have little or no connection with actual policy makers and decision makers. However, both of these problems have been identified and solutions proposed.

In places where not enough data are available, monitoring programs have been implemented which will be the future source of material to improve models. Additionally, models which can work with little data-input are starting to be the focus of next generation ecosystem modelers.

To address the second issue, scientists and governments are starting to combine efforts to identify the management questions which models could help to answer, and the gaps where models need further improvement [5]. The Italian RITMARE project is a good example of such a partnership.

As we have seen, the approach we choose to manage our natural resources will definitely have an impact on their status for future generations. In the past, many societies did not really think of themselves as part of nature, or notice the impact of their actions. However, scientific knowledge has helped to change this perception, and we now recognize that what we do to the environment will, inevitably, have a consequence for us.

Scientists and governments are starting to combine efforts to identify the management questions which models could help to answer, and the gaps where models need further improvement [5]. The Italian RITMARE project is a good example of such a partnership.

References

[1] Small, C., & Nicholls, R. J. (2003). A global analysis of human settlement in coastal zones. Journal of coastal research, 584-599.

[2] Martínez, M. L., Intralawan, A., Vázquez, G., Pérez-Maqueo, O., Sutton, P., & Landgrave, R. (2007). The coasts of our world: Ecological, economic and social importance. Ecological economics, 63(2-3), 254-272.

[3] Food and Agriculture Organization of the United Nations. (1995). Review of the State of World Fishery Resources: Marine Fisheries. FAO Fisheries Circular No. 884. Rome, Italy: FAO.

[4] Burke, L., Kura, Y., Kassem, K., Revenga, C., Spalding, M., McAllister, D., & Caddy, J. (2001). Coastal ecosystems. Washington, DC: World Resources Institute.

[5] Heymans, J.J., Skogen, M., Schrum, C., Solidoro, C. (2018) Enhancing Europe’s capability in marine ecosystem modelling for societal benefit. Larkin, K.E., Coopman, J., Muñiz Piniella, A., Kellett, P., Simon, C., Rundt, C., Viegas, C., Heymans, J.J. [Eds.] Future Science Brief 4 of the European Marine Board, Ostend, Belgium. 32 pp. ISBN: 9789492043580 ISSN: 2593-5232.

[6] http://www.ritmare.it/