Transient dynamics during kelp forest recovery from fishing across multiple trophic levels

Abstract

Outcomes of management efforts to recover or restore populations of harvested species can be highly dependent on environmental and community context. Predator–prey interactions can alter recovery trajectories, and the timing of management actions within multi‐trophic level harvest scenarios may influence the dynamics of recovery and lead to management trade‐offs. Recent work using a generalist predator–prey model suggests that management promoting synchronized recovery of predators and prey leads to faster and less variable recovery trajectories than sequential recovery (predator or prey first). However, more complex communities may require different management actions to minimize recovery time and variability. Here, we use a tri‐trophic level rocky reef community dynamics model with size‐structure and fisheries at multiple trophic levels to investigate the importance of three ecological processes to recovery of fished communities: (1) size‐structured predation, (2) non‐consumptive effects of predators on prey behavior, and (3) varying levels of recruitment. We also test the effects of initiating recovery from community states associated with varying degrees of fishery‐induced degradation and develop a simulation in which the basal resource (kelp) is harvested. In this system, a predator‐first closure generally leads to the least volatile and quickest recovery, whether from a kelp forest, urchin barren, or intermediate community state. The benefits gained by selecting this strategy are magnified when recovering from the degraded community, the urchin barren, because initial conditions in the degraded state lead to lengthy recovery times. However, the shape of the size‐structured predation relationship can strongly affect recovery volatility, where the differences between alternate management strategies are negated with size‐independent predation. External recruitment reduces return times by bolstering the predatory lobster population. These results show that in a tightly linked tri‐trophic level food web with top‐down control, a predator‐first fishery closure can be the most effective strategy to reduce volatility and shorten recovery, particularly when the system is starting from the degraded community state. Given the ubiquity of top predator loss across many ecosystems, we highlight the value of incorporating insights from community ecology into ecosystem management.

Variation in body size drives spatial and temporal variation in lobster–urchin interaction strength

“…In marine protected areas where lobsters are protected from fishing, lobster size and density are greater than in fished areas (Kay et al, 2012; Peters et al, 2019). With a relatively high density of large lobsters our results suggest that there could be substantial predation pressure on urchins, which is consistent with recent modelling work that highlights the importance of size‐selective predation on the recovery of kelp communities under different management strategies (Dunn et al, 2021). Alternatively, our foraging trials demonstrate that even small lobsters can be effective predators of small urchins.…”

No‐take marine protected areas enhance the benefits of kelp‐forest restoration for fish but not fisheries

“…Transient dynamics from our model provide only a guide for comparison among scenarios: the true recovery time and nature of the transients are likely to differ and be influenced by the mechanisms linking fished species to their habitat (which we do not explicitly model). For example, the shape of a size‐structured relationship between predators and prey has shown to affect community volatility (degree of variability in transients) and recovery time, with volatility and recovery increasing when smaller prey are more susceptible to predation (Dunn et al, 2021).…”

Changes in kelp forest communities off Washington, USA, during and after the 2014-2016 marine heatwave and sea star wasting syndrome

“…kelp forests) to sea urchindominated (urchin barrens) habitat (Ling et al 2015, Beas-Luna et al 2020, which poses a risk to the wide range of the valuable ecosystem functions provided by kelp forests (Smith et al 2021, Smith & Fox 2022. These state changes can be precipitated by climate and oceanographic variability (Pearse & Hines 1987, Pfister et al 2018, Smale 2020, or by trophic dynamics triggered by shifts in populations and behaviors of key consumers (Ling et al 2009, Watson & Estes 2011, Feehan & Scheibling 2014, Ling et al 2015, Shelton et al 2018, Dunn et al 2021. The distribution of kelps is strongly related to ocean temperature (Breeman 1990, Smale 2020) making them vulnerable to both long-term ocean warming and the more temporally discrete effects of marine heatwaves (MHWs, prolonged but defined periods of anomalously warm water; Hobday et al 2016).…”