Trophic Cascades in a Formerly Cod-Dominated Ecosystem

Frank, Kenneth T.; Petrie, Brian; Choi, Jae S.; Leggett, William C.

doi:10.1126/science.1113075

Cited by 1,003 publications

(883 citation statements)

References 17 publications

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“…In Table 2 we review and summarize empirical evidence for these changes in different parts of the NWA and in the Baltic Sea. These predictions and observations corroborate the idea that the collapse of cod induces a cascade of community-wide effects (NWA: DFO, 2003;Frank et al, 2005;Baltic Sea: Alheit et al, 2005;Möllmann et al, 2005;Möllmann et al, 2008) and support the perspective of the community as a "classic" food chain with three trophic levels.…”

Section: Empirical Observationssupporting

confidence: 75%

“…These changes include direct effects of cod disappearance, such as increases in prey biomass, as well as indirect effects, such as decreased abundances of zooplankton (Carscadden et al, 2001;Casini et al, 2006) and decreased body condition of prey (Davoren and Montevecchi, 2003;Osterblom et al, 2006). For both ecosystems the collapse of cod has therefore been claimed to induce a regime or catastrophic ecosystem shift (NWA: DFO, 2003;Frank et al, 2005;Baltic Sea: Alheit et al, 2005;Möllmann et al, 2005Möllmann et al, , 2008 with community-wide effects due to cascading trophic interactions. In the context of any attempt to restore depleted cod stocks it is an important question whether the situation with high cod biomass that preceded stock collapse, and very low cod biomass afterward, represent alternative (stable) equilibrium states of the system.…”

Section: Introductionmentioning

confidence: 99%

“…The lack of cod recovery, however, suggests that the shift is irreversible and that mechanisms intrinsic to the community stabilize and maintain the system in its current state with low cod biomass. A number of studies (DFO, 2003;Choi et al, 2004;Frank et al, 2005) have ascribed the lack of recovery of NWA cod following the fishing moratorium from 1993 to changes in environmental conditions (temperature, salinity). Similarly, climate-induced changes in hydrography leading to changes in temperature and salinity have been argued to keep cod from recovering in the Baltic Sea (Alheit et al, 2005;Möllmann et al, 2005Möllmann et al, , 2008.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

How cod shapes its world

Leeuwen

Roos

Persson

2008

Journal of Sea Research

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Cod stocks in the North West Atlantic and the Baltic Sea have shown similar dynamics in recent decades with a rapid decline in abundance and a lack of stock recovery following a period of large biomass. We explore whether the lack of recovery can be ascribed to an emergent Allee effect, which is a mechanism intrinsic to the community in contrast to explanations involving environmental factors. We formulate a stage-structured biomass model for the cod-sprat interaction in the Baltic Sea, paying special attention to the size-dependent prey preference of differently sized cod. The model predicts that alternative community states can occur under the same environmental conditions, in which cod is either present or absent. In a stable equilibrium with its main prey cod has a strong effect on the prey size distribution, resulting in larger densities of preferred prey sizes for cod than in the absence of any predation. Cod thus shapes its food environment to its own benefit. Furthermore, in response to increased exploitation cod biomass and yield tend to increase unless a stock collapse is imminent. After a cod stock collapse and the consequent drop in predation the prey size distribution becomes stunted and offers insufficient food for cod to grow and recover. These results are consequences of the indirect effects of predation and harvesting, whereby increased mortality relaxes competition among surviving individuals, leading to an increase in food intake and hence increased somatic growth and reproduction. We review observed community changes following the collapse of the cod stocks in the North West Atlantic and the Baltic Sea in the light of model predictions. In line with our model predictions growth in body size of cod has slowed down after the collapse, despite high densities of prey biomass. Furthermore, estimates of total prey population fecundity in the Baltic Sea identify the emergent Allee effect as a potentially important mechanism contributing to the lack of cod recovery.

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Section: Empirical Observationssupporting

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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How cod shapes its world

Leeuwen

Roos

Persson

2008

Journal of Sea Research

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“…In particular, decreased stocks of predatory fish have generated strong increases in their prey, medium-sized or ''meso-'' predators (i.e., ''mesopredator release''), changing the interactions between higher trophic levels considerably (e.g., Myers et al 2007;Baum and Worm 2009). In some instances, there are documented cascading effects from such mesopredator increases on lower levels in the pelagic food web, including communitywide decreases of zooplankton, and increases in jellyfish and phytoplankton (e.g., Frank et al 2005;Daskalov et al 2007;Casini et al 2008).…”

Section: Introductionmentioning

confidence: 99%

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

Eriksson

Sieben

Eklöf

et al. 2011

AMBIO

111

144

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By mainly targeting larger predatory fish, commercial fisheries have indirectly promoted rapid increases in densities of their prey; smaller predatory fish like sprat, stickleback and gobies. This process, known as mesopredator release, has effectively transformed many marine offshore basins into mesopredator-dominated ecosystems. In this article, we discuss recent indications of trophic cascades on the Atlantic and Baltic coasts of Sweden, where increased abundances of mesopredatory fish are linked to increased nearshore production and biomass of ephemeral algae. Based on synthesis of monitoring data, we suggest that offshore exploitation of larger predatory fish has contributed to the increase in mesopredator fish also along the coasts, with indirect negative effects on important benthic habitats and coastal water quality. The results emphasize the need to rebuild offshore and coastal populations of larger predatory fish to levels where they regain their control over lower trophic levels and important links between offshore and coastal systems are restored.

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“…Indeed, the collapse of the stock precipitated a trophic cascade (Frank et al, 2005), and serves as a prime example of what has been termed "ecosystem overfi shing" (Tegner and Dayton, 1999); such effects on ecosystems of the removal of predatory fi sh has been well documented elsewhere (e.g., Pauly et al, 1998).…”

Section: Conclusion: Lessons For Todaymentioning

confidence: 99%