Recruitment failure of coastal predatory fish in the Baltic Sea coincident with an offshore ecosystem regime shift

Abstract

Ljunggren, L., Sandström, A., Bergström, U., Mattila, J., Lappalainen, A., Johansson, G., Sundblad, G., Casini, M., Kaljuste, O., and Eriksson, B. K. 2010. Recruitment failure of coastal predatory fish in the Baltic Sea coincident with an offshore ecosystem regime shift. – ICES Journal of Marine Science, 67: 1587–1595. The dominant coastal predatory fish in the southwestern Baltic Sea, perch and pike, have decreased markedly in abundance during the past decade. An investigation into their recruitment at 135 coastal sites showed that both species suffered from recruitment failures, mainly in open coastal areas. A detailed study of 15 sites showed that areas with recruitment problems were also notable for mortality of early-stage larvae at the onset of exogenous food-intake. At those sites, zooplankton abundance predicted 83 and 34% of the variation in young of the year perch and pike, respectively, suggesting that the declines were caused by recruitment failure attributable to zooplankton food limitation. Incidences of recruitment failure match in time an offshore trophic cascade that generated massive increases in planktivorous sprat and decreases in zooplankton biomass in the early 1990s. Therefore, sprat biomass explained 53% of the variation in perch recruitment from 1994 to 2007 at an open coastal site, where three-spined stickleback also increased exponentially after 2002. The results indicate that the dramatic change in the offshore ecosystem may have propagated to the coast causing declines of the dominating coastal predators perch and pike followed by an increase in the abundance of small-bodied fish.

Effects of Altered Offshore Food Webs on Coastal Ecosystems Emphasize the Need for Cross-Ecosystem Management

“…This is confirmed by small-scale experimental exclusion of larger fish and grazers, showing that declines in larger predators-by inducing a four level trophic cascade-increase filamentous algal growth with rates comparable to those caused by nutrient enrichment alone Sieben et al 2011b). Food competition and egg predation by the high abundances of stickleback may now even contribute to decreased recruitment success of perch and pike (Nilsson 2006;Ljunggren et al 2010), and potentially ''lock'' the coastal food web in an alternative, mesopredator-dominated regime. Thus, overfishing of offshore cod populations may have contributed to a shift in nearshore food web structure.…”

“…Full pike data is presented in Sect. 1 in the electronic supplement to Ljunggren et al (2010). Estimates of high, low and no recruitment of perch and pike are also based on Ljunggren et al (2010) restore significant migrations between offshore and coastal habitats (Fig.…”

“…Recently, offshore abundances of stickleback have increased exponentially ( Fig. 4a; Ljunggren et al 2010), suggesting a dramatic increase of this mesopredator also in the coastal habitat. Coastal monitoring of migrating fish is poor, but a combination of unique data from an open archipelago of the Swedish Baltic coast (the Kalmar sound) indicates that the changes in fish community structure in the open Baltic Sea have also affected nearshore areas.…”

“…Interestingly, these cascading effects seem dependent on offshore-inshore migrations of mesopredators, combined with changes in interspecific competition, as well as release in predation pressure (Ljunggren et al 2010). On the Swedish coast of the central Baltic Sea, juvenile three-spined stickleback (Gasterosteus aculeatus)-a smaller predatory fish feeding on crustacean and gastropod mesograzers Sieben et al 2011b)-completely dominate many sheltered coastal communities in early summer Ljunggren et al 2010). Stickleback changes distribution over the ontogeny, and after their first summer the majority migrate offshore (unpublished data).…”

Biomass and number of fish impinged at a nuclear power plant by the Baltic Sea

“…This species has also been dominant and increasing in numbers during recent years in a wider range of waters surrounding the Forsmark plant (Karås et al 2010;. The increase has raised concern since an increasing number of three-spined stickleback may, through an increased competition for zooplankton, hamper the recruitment of larger predatory fish such as pike and perch in coastal waters of the Baltic Sea (Ljunggren et al 2010). It is therefore possible that the impingement of three-spined stickleback at Forsmark decreases its abundance and is beneficial for pike and perch recruitment by decreasing the predation pressure on zooplankton.…”