Download Models help to predict the future of the Baltic Sea

Models help to predict the future of the Baltic Sea
Ecosystem modelling tools are necessary to explore how various human effects might affect Baltic
Sea. But how complex the models should be? And how far into the future can we forecast?
What will the future Baltic Sea look like? Will cod recover to the historical levels? Will algal blooms
continue? How can we combine all the diverse needs and interests of people around the Baltic Sea to
ensure the best outcome for nature and society? While these questions have been of interest to people
and marine scientists for years, they are becoming increasingly urgent. More importantly, questions about
the future about the Baltic Sea are also becoming increasingly complex and inter-disciplinary. As we learn
more, we realize that physical (temperature, salinity, nutrient run-off), biological (seals-cod-herring-spratplankton) and socioeconomic (fisheries, agriculture, political process, oil spills, shipping) processes are
closely interconnected and cannot be studied in isolation. Understanding how changes in one process will
affect the Baltic Sea therefore requires taking into account those interactions. For this purpose scientists
and managers resort to using models that help us understand the nature of real world. Models always are
an abstraction of reality, and the main challenge is to find that best approach for the question at hand, a
model that is, to quote A. Einstein, “as simple as possible, but not simpler”. Have we managed to identify all
the essential species and links that will determine the future of the Baltic Sea and its response to
environmental change?
To discuss these questions, scientists developing and using marine models have met in a workshop on
“Baltic Sea ecosystem models and their applications for management”. A lot of interesting things and
results have come out of it, often demonstrating that, even though building and testing models is a huge
task, many questions simply cannot be answered without them. Take, for example, the Baltic Sea Action
Plan. This plan is a result of a realisation that serious reduction in nutrient run-off (pollution) is needed if
we want to stop and avoid massive algal blooms. It was clear that all countries around the Baltic Sea must
work together if there is any hope to succeed. But it was less clear how much should the nutrient load be
reduced and how quickly can we expect to get clear Baltic Sea waters back. This is where a large modelling
and communication effort was required, and luckily sufficient funds were provided to complete it. Without
such effort the agreement among countries might have been along the lines – “do whatever possible” and
that usually leads to nothing. Now the Baltic Sea Action Plan has numbers about the nutrient reduction
expected from each country. “Perhaps those numbers are not entirely correct, perhaps some countries will
fail to achieve this level of reduction, but having concrete model outcomes and concrete numbers at least
gives us a background for negotiation and accountability” – says Dr Bo Gustafsson, the Director of the Baltic
Nest Institute, and one of the lead scientists in this research and negotiations.
Including complex species interactions in models may give new and unexpected insights. For example, most
people want Baltic Sea to be full of large and healthy cod. Since cod eats sprat, one might assume that
having more sprat simply means more cod. But things are not that simple. This is because not all sprat is
equal to cod. If cod prefers small sprat, as evidence
suggests, then having too many middle sized sprat
will create competition for small ones and will
reduce food availability for cod. Prof. Andre de
Roos (University of Amsterdam) summarises the
model outcomes in one simple phrase - “Care for
cod? Catch some sprat!”. This means that
managing the fish community in the Baltic Sea will
not only require careful consideration of the
feeding relations between the species involved,
but will also sometimes ask for counterintuitive
management strategies like culling the currently
dense population of Baltic sprat. The consequences
of such management might not only benefit cod,
but also reduce the risk of algal blooms and even
improve living conditions for certain sea bird
species.
What happens if you include the fact that sprat prefers to eat only certain zooplankton? On top of that we
should add climate change, where sprat and cod and herring and salmon will most likely respond differently
to salinity and temperature changes in the Baltic Sea. And what happens when we also include fishing,
pollution and some regulations? Some of these questions have been addressed with a different model,
suggesting that despite increases in global pressures such as climate change, the regional management of
fishing and nutrient loads can play a key role in defining the future of the Baltic Sea ecosystem. As Dr Susa
Niiranen (Stockholm Resilience Center) puts it: “For cod climate conditions may set boundaries for the total
production due to, for example, deteriorating recruitment conditions. However, with appropriate
management of fishing and eutrophication relatively high cod abundances could still be sustained in the
future”. And what about evolution? Is it essential to include evolution in models? If we always keep
catching largest and fastest growing fish, it is natural to expect that with time fish will evolve to be smaller
and start reproducing as early as possible, to have a chance to reproduce at least once before they are
caught. But reproduction takes energy (a lot of energy!), so earlier reproduction also often means that fish
will have less energy to grow and will often be smaller. “Such reductions in size or earlier maturation age
have actually been observed in Baltic Sea cod and pikeperch. Yet, we will have little understanding of how
this might affect productivity of these species. Smaller body size often means higher probability of being
eaten, because who eats whom in the sea very much depends on size. Size matters to fish” – says Dr Asta
Audzijonyte (University of Helsinki).
Models of different spatial scales and
complexity are necessary to address the
diverse array of questions that scientists and
managers are faced with. Some include the
entire Baltic Sea, others are focused on
considerably smaller areas. For example, the
City of Helsinki Environment Centre is
developing a model for the coastal area
around Helsinki. “The model will be used in
monitoring water quality and might help in
planning the position and sampling frequency in monitoring stations” – presents the lead responsible
scientist Emil Vahtera. Modelling coastal ecosystems in fact remains one of the important challenges for
scientists studying the Baltic Sea. “Currently, the majority of modelling targets issues related to open water
and fishery, and we still lack sufficient resources to study near-coastal processes. Yet, coastal areas are
diverse and productive, they play essential role as food and nursery areas for fishes and birds, they support
important ecosystem functions and services communities, and also are places where human activities are
concentrated” – comments Dr Jonne Kotta, from the University of Tartu. Coastal areas also are places
where new invasive species usually appear. “Although invasion of new species in the Baltic Sea is one of the
key threats to the ecosystem, none of the currently available Baltic Sea ecosystem models address this big
challenge so far” – says Dr Letizia Tedesco from the Finnish Environment Institute. Another big challenge
facing ecosystem modellers is in clearly defining the limits of what we know. Most of the physical,
ecological and social processes in and around the Baltic Sea cannot be estimated and predicted with
certainty. As a result we need robust and fast methods to evaluate the uncertainty in our predictions. “If
the models are to be used to support decision making, the uncertainty related to their predictions must be
quantified. Here, statistics meets the ecology to produce such estimates." – says Dr Jarno Vanhatalo from
the University of Helsinki.
There is still a lot of work to do and that is exciting. Scientists from different disciplines of chemistry,
biology, evolution, economics, computer sciences, machine learning are learning how to talk in a common
language and to develop new tools that could improve our understanding about what is important in
aiming for the shared goal of clean and beautiful Baltic Sea for everybody.
* To look at the presentation of the
http://www.helsinki.fi/science/fem/workshop/talks
public
session
of
the
workshop,
go
here