Predator biomass and vegetation influence the coastal distribution of threespine stickleback morphotypes

Abstract

Intraspecific niche differentiation can contribute to population persistence in changing environments. Following declines in large predatory fish, eutrophication, and climate change, there has been a major increase in the abundance of threespine stickleback (Gasterosteus aculeatus) in the Baltic Sea. Two morphotype groups with different levels of body armor—completely plated and incompletely plated—are common in coastal Baltic Sea habitats. The morphotypes are similar in shape, size, and other morphological characteristics and live as one apparently intermixed population. Variation in resource use between the groups could indicate a degree of niche segregation that could aid population persistence in the face of further environmental change. To assess whether morphotypes exhibit niche segregation associated with resource and/or habitat exploitation and predator avoidance, we conducted a field survey of stickleback morphotypes, and biotic and abiotic ecosystem structure, in two habitat types within shallow coastal bays in the Baltic Sea: deeper central waters and shallow near‐shore waters. In the deeper waters, the proportion of completely plated stickleback was greater in habitats with greater biomass of two piscivorous fish: perch (Perca fluviatilis) and pike (Esox lucius). In the shallow waters, the proportion of completely plated stickleback was greater in habitats with greater coverage of habitat‐forming vegetation. Our results suggest niche segregation between morphotypes, which may contribute to the continued success of stickleback in coastal Baltic Sea habitats.

Increases of opportunistic species in response to ecosystem change: the case of the Baltic Sea three-spined stickleback

“…However, evidence from otolith microchemistry studies suggests that at least those Baltic Sea sticklebacks hatched in freshwater tend to return to their place of birth to spawn (Eesti Mereinstituut, 2017). There is also some evidence of local adaption to variation in salinity, temperature and potentially also predation pressure and pollution levels (Lind and Grahn, 2011;De-Faveri et al, 2013;Guo et al, 2015;Jakubaviči ūte et al, 2018;Eriksson et al, 2021;Yanos et al, 2021). Further, the Baltic Sea stickleback shows spatial variation in size and condition, with fish in the Bothnian Sea generally being larger than those in the Baltic Proper (Bergström et al, 2015;Jakubaviči ūte et al, 2018;Olsson et al, 2019).…”

Characterizing phenotypic diversity in marine populations of the threespine stickleback

“…Until now, evidence of local adaptation and small-scale genetic structuring in marine sticklebacks has primarily been characterized in either a single small basin (i.e. the Baltic Sea) [29][30][31] , or across very large basins (e.g. the Atlantic vs. Pacific Oceans) [32][33][34] .…”