A cross-scale trophic cascade from large predatory fish to algae in coastal ecosystems

Coastal hypoxia is increasing worldwide in response to human‐caused changes in global climate and biogeochemical cycles. In this paper, we view anthropogenic trends in coastal hypoxia through the lens of disturbance ecology and complexity theory. Complexity theory provides a framework for describing how estuaries and other coastal aquatic ecosystems respond to hypoxia by understanding feedback loops. Can it also be valuable in understanding how these ecosystems behave under shifting (i.e., unnatural) disturbance regimes? When viewed as a disturbance regime, shifts in the spatial (areal extent and fragmentation) and temporal (frequency and duration of events) characteristics of coastal hypoxia can be used to track changes into a non‐stationary future. Here, we consider options for increasing the resilience of coastal aquatic ecosystems to future, unnatural hypoxic regimes. To start, we define desirable states as ecosystems with long trophic chains and slow nutrient and carbon dynamics that produce many ecosystem services. We then work backward to describe circumstances dominated by positive feedbacks that can lead ecosystems toward an undesirable state (i.e., depauperate communities and chemically reduced sediments). Processes of degradation and recovery can be understood in the context of island biogeography whereby species diversity in habitats fragmented by hypoxia is determined by the balance between rapid local extinction, slow recolonization from the edges of hypoxic patches, and opportunities for ecological succession during between disturbance events. We review potential future changes associated with changing global climate and highlight ways to enhance coastal resilience. In addition to efforts to slow climate change, potential interventions include reduced nutrient and carbon loadings from rivers, restoration of aquatic vegetation, and managing for key species, including those that promote sediment oxygenation, that enhance water clarity, or that promote grazing on epiphytic algae through top‐down control.

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“…A similar decoupling of nutrient effects has also been reported for ecosystems gaining piscivorous predators (Donadi et al. ).…”

Section: Introductionsupporting

confidence: 80%

Unnatural hypoxic regimes

et al. 2018

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“…The decline of pike has been attributed to increased interspecific resource competition during early life stages, habitat exploitation and high fishing pressure (Larsson et al., ; Ljunggren et al., ). Sticklebacks have consequently been favoured by predator release partly constituted by declining pike populations (Bergström et al., , ; Donadi et al., ; Sieben, Ljunggren, Bergström, & Eriksson, ). Many efforts, including fisheries regulation and habitat restoration, have been directed towards remediating the underlying causes for the decline, aid the recovery of pike and ultimately improve the coastal ecosystem (Engstedt, Nilsson, & Larsson, ; Nilsson, Engstedt, & Larsson, ).…”

Section: Introductionmentioning

confidence: 99%

Predator–prey role reversal may impair the recovery of declining pike populations

Nilsson

Flink

Tibblin

2019

Journal of Animal Ecology

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Many fish populations have experienced declines in recent decades due to anthropogenic disturbances, such as overfishing and habitat exploitation. Despite management actions, many populations show a limited capacity to recover. This may be attributed to reversal of predator–prey roles, yet empirical evidence to that effect remains scarce. Here, we combine field and laboratory studies to investigate the interaction between pike (Esox lucius), a large keystone top predatory fish, and the small‐bodied mesopredatory threespine stickleback (Gasterosteus aculeatus) in the Baltic Sea where pike populations have declined. Our data suggest that stickleback predation on pike larvae depletes a large proportion of the recruitment and influences the size distribution through size‐selective predation, which is corroborated by a gape‐limitation experiment and diet analysis of wild‐captured sticklebacks. The effects of stickleback predation are present across several populations and years, and our data suggest that early arrival of sticklebacks has stronger effects on juvenile pike survival. Finally, we use data on pike gape‐limitation and the size distribution of sticklebacks to illustrate the process of role reversal. These findings suggest that mesopredator behaviour can reduce recruitment of a top predator species and impair the capacity of populations to recover. This emphasizes predator–prey role reversal as an important ecological and evolutionary driver that influences the outcome of restoration and management actions.

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“…, Donadi et al. ). Both of these feedbacks should result in that epiphytic algae biomass decreases with increased plant density.…”

Section: Discussionmentioning

confidence: 99%

“…Recently, these effects have also been shown to affect aquatic vegetation (Donadi et al. ). Declines of large predators can also interact with other stressors such as eutrophication (Halpern et al.…”

Section: Introductionmentioning

confidence: 99%

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Density‐dependent positive feedbacks buffer aquatic plants from interactive effects of eutrophication and predator loss

Donadi

Austin

Svartgren

et al. 2018

Ecology

Self Cite

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Self‐facilitation allows populations to persist under disturbance by ameliorating experienced stress. In coastal ecosystems, eutrophication and declines of large predatory fish are two common disturbances that can synergistically impact habitat‐forming plants by benefitting ephemeral algae. In theory, density‐dependent intraspecific plant facilitation could weaken such effects by ameliorating the amount of experienced stress. Here, we tested whether and how shoot density of a common aquatic plant (Myriophyllum spicatum) alters the response of individual plants to eutrophication and exclusion of large predatory fish, using a 12‐week cage experiment in the field. Results showed that high plant density benefitted individual plant performance, but only when the two stressors were combined. Epiphytic algal biomass per plant more than doubled in cages that excluded large predatory fish, indicative of a trophic cascade. Moreover, in this treatment, individual shoot biomass, as well as number of branches, increased with density when nutrients were added, but decreased with density at ambient nutrient levels. In contrast, in open cages that large predatory fish could access, epiphytic algal biomass was low and individual plant biomass and number of branches were unaffected by plant density and eutrophication. Plant performance generally decreased under fertilization, suggesting stressful conditions. Together, these results suggest that intraspecific plant facilitation occurred only when large fish exclusion (causing high epiphyte load) was accompanied by fertilization, and that intraspecific competition instead prevailed when no nutrients were added. As coastal ecosystems are increasingly exposed to multiple and often interacting stressors such as eutrophication and declines of large predatory fish, maintaining high plant density is important for ecosystem‐based management.

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A cross-scale trophic cascade from large predatory fish to algae in coastal ecosystems

Cited by 65 publications

References 73 publications

Unnatural hypoxic regimes

Unnatural hypoxic regimes

Predator–prey role reversal may impair the recovery of declining pike populations

Density‐dependent positive feedbacks buffer aquatic plants from interactive effects of eutrophication and predator loss

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