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

Abstract

Under rapid environmental change, opportunistic species may exhibit dramatic increases in response to the altered conditions, and can in turn have large impacts on the ecosystem. One such species is the three-spined stickleback (Gasterosteus aculeatus), which has shown substantial increases in several aquatic systems in recent decades. Here, we review the population development of the stickleback in the Baltic Sea, a large brackish water ecosystem subject to rapid environmental change. Current evidence points to predatory release being the central driver of the population increases observed in some areas, while both eutrophication and climate change have likely contributed to creating more favourable conditions for the stickleback. The increasing stickleback densities have had profound effects on coastal ecosystem function by impairing the recruitment of piscivorous fish and enhancing the effects of eutrophication through promoting the production of filamentous algae. The increase poses a challenge for both environmental management and fisheries, where a substantial interest from the pelagic fisheries fleet in exploiting the species calls for urgent attention. While significant knowledge gaps remain, we suggest that the case of the Baltic Sea stickleback increase provides generalisable lessons of value for understanding and managing other coastal ecosystems under rapid change.

The role of chemical communication in the predator-prey role reversal of northern pike (Esox lucius) and three-spined stickleback (Gasterosteus aculeatus)

“…For example, sticklebacks from turbid environments have been shown to discriminate among stickleback populations based on olfactory cues (Hiermes et al, 2015) whereas benthic sticklebacks used olfaction to discriminate between con-and heterospecific potential mates (Rafferty and Boughman, 2006), while the same ability was not found in sticklebacks inhabiting habitats with higher visibility (Mobley et al, 2016). This could potentially explain why we did not detect any general effect of treatment since the Baltic Sea sticklebacks spend a majority of their life-cycle in the offshore pelagic habitat with generally high visibility and may thus predominantly rely on visual cues (Olin et al, 2022).…”

“…Multiple reasons have been linked to the decline, among them habitat degradation (Sundblad and Bergström, 2014), fisheries (Bergström et al, 2019), eutrophication (Bergström et al, 2016;Lehtonen et al, 2009), and increased predation pressure by seals (Halichoerus grypus) (Bergström et al, 2022;Hansson et al, 2018) and cormorants (Phalacrocorax carbo sinensis) (Heikinheimo et al, 2021;Östman et al, 2012). Recently, there has also been increasing support to the hypothesis that rapidly increasing abundances of the three-spined stickleback (Gasterosteus aculeatus, hereafter stickleback) negatively impact the abundances of pike and perch, which in sub-adult and adult life-stages are main predators on sticklebacks in the coastal habitat, both by resource competition and direct predation on their young (Bergström et al, 2015;Eklöf et al, 2020;Nilsson et al, 2019;Olin et al, 2022).…”

“…Sticklebacks migrate in spring from their offshore foraging habitat into coastal areas for spawning, coinciding with the recruitment period of pike and perch (Byström et al, 2015;Hall et al, 2021;Nilsson et al, 2019;Olin et al, 2022). Sticklebacks commonly aggregate in areas used by pike and perch for reproduction (shallow brackish bays, river mouths, and streams) and intensively predate on the early life-stages of predators until they outgrow the stickleback predation window at lengths of about 33 mm and 25 mm for pike and perch respectively (Byström et al, 2015;Nilsson et al, 2019).…”

Species‐ and origin‐specific susceptibility to bird predation among juvenile salmonids

“…Second, as the availability of alternative prey for cormorants has been shown to affect predation risk for juvenile salmonids (Good et al, 2022), differences in availability of alternative prey between the two time periods may have contributed to the difference. For example, in 2005-2006 it was generally more herring (a common prey in the diet of cormorants; Boström et al, 2012;Östman et al, 2013) in the area than in 2017-2021 (Olin et al, 2022). As herring assemble in coastal areas for spawning during the same time of the year as salmonids migrate to the sea (late spring-early summer), cormorants may have assembled to forage in areas with large schools of herring to a larger extent in 2005-2006 than during the most recent years (2017)(2018)(2019)(2020)(2021).…”

Small but voracious: invasive generalist consumes more zooplankton in winter than native planktivore

“…To date, few reports have investigated sticklebacks invading the pelagic zone and interacting with other pelagic fish or zooplankton. The exception is the Baltic Sea, where numerous studies tried to reveal the causes and consequences of stickleback increase (Olin et al 2022). One study showed that sticklebacks are potential competitors for herring and sprat due to similar diets and prey selection (Jakubavičiute et al 2016), whereas others showed that sticklebacks suppress native fish by preying on their larvae (Ljunggren et al 2010;Byström et al 2015;Eklöf et al 2020).…”