Juvenile and Adult Three-Spined Sticklebacks Exhibit Different Habitat Use in Shallow Baltic Sea Bays

Three-spined sticklebacks (Gasterosteus aculeatus) have become dominant in many Baltic Sea coastal fish assemblages, yet life-stage-specific habitat use remains poorly understood. We surveyed shallow water habitats along the coast of Gotland, Sweden, to examine how juvenile and adult stickleback abundances relate to variables such as submersed aquatic vegetation (SAV) biomass and vertical structure, macrophyte species richness, biomass of drift filamentous algae and potential invertebrate prey abundance. Juvenile stickleback abundance increased with SAV variables, macrophyte species richness, and drift filamentous algae, whereas, in contrast, adult abundance was only significantly associated with potential prey (invertebrate abundance). Our findings reveal life-stage-specific habitat associations of three-spined sticklebacks and highlights the importance of both long-living vegetation and ephemeral drift algae in supporting juvenile sticklebacks. This study contributes to a better understanding of sticklebacks' coastal ecology in the central Baltic Sea.