MYSTIC –Mysid-Stickleback Interactions with Coastal Predatory Fish in the Baltic Sea

Many coastal fish communities in the Baltic Sea have experienced a regime shift where predatory fish (pike and perch) have been replaced by three-spined sticklebacks.

Hypotheses for the decline in top predators involve top-down control of adult fish by cormorants and seals, predation on the larvae by three-spined stickleback, and stickleback competition for zooplankton.

However, these hypotheses are largely based on correlative field observations at rather large spatiotemporal scales, making causal inference difficult.

To avoid poor management decisions and instead strive for accomplishing the best possible effect of management interventions, there is a need to understand the causal mechanisms behind observed shifts.

We propose that there may be other mechanisms driving the loss of predatory fish that previously have been overlooked. Invertebrate predators such as mysids have the capacity to outcompete top predators at the larval stage.

However, the role of invertebrates in this dynamic interaction is continuously disregarded due to the lack of monitoring data and realistic modeling attempts.

In this project, we will focus on the local scale, using high-frequency sampling and dynamic modeling to (1) evaluate the role of mysids in controlling the recruitment of pike/perch during the critical early phase of the spring season, (2) understand how stickleback dominance can evolve and be maintained and (3) identify which measures need to be taken to reverse the current situation.