Research themes: Disturbance and resilience

Nearly all ecosystems experience disturbances that change the physical environment and disrupt ecosystem structure. A major focus of our research is on understanding the consequences of such environmental disruptions for populations of habitat-forming foundation species, such as kelps, seagrasses, and oysters, that are the hallmark of many coastal ecosystems. Additionally, our work is revealing how the loss and recovery of foundation species cascades to structure biodiversity and ecosystem function.

Key findings

Canopy disturbance and habitat quality control kelp forest productivity

  • Disturbances often impact net primary productivity (NPP) by causing disproportionate losses from certain vegetation layers, such as the forest canopy. However, such disturbance-driven changes may be mediated by environmental conditions that affect habitat quality and species interactions.
  • In giant kelp forests, habitat quality (herbivory and substrate) can mediate the effects of intensified disturbance on NPP by changing both the amount of canopy vegetation removed by disturbance and the compensation of lost canopy productivity by understory macroalgae (Castorani et al. 2021). 

Resistance and resilience to marine heatwaves are geographically variable

  • Ocean heatwaves are increasing in frequency and duration in response to global climate trends.
  • The loss and subsequent recovery of giant kelp populations under extreme ocean warming vary strongly across space (Cavanaugh et al. 2019). Regions experiencing longer, hotter heatwaves are more susceptible to catastrophic declines, but recovery is unrelated to temperature.

Repeated loss of foundation species can outweigh the influence of less-frequent but severe disturbances for biodiversity

  • Disturbance regimes vary in both their frequency and severity, however investigations have often been incapable of disentangling the effects of these disturbance attributes. 

  • Disturbance frequency outweighs severity in structuring kelp forest communities (Castorani et al. 2018). Frequent loss of giant kelp strongly alters community guilds in a manner consistent with their reliance on physical, trophic, and habitat resources. 

  • In contrast, variation in disturbance severity has the strongest effects on highly mobile consumers capable of migrating to more suitable habitat.

Connectivity is key for local and regional metapopulation dynamics

  • Ecological theory indicates that dispersal and connectivity among spatially structured populations can strongly influence the dynamics of both local populations and the overall population network, or metapopulation.
  • In metapopulations of giant kelp, increasing connectivity diminishes the risk of local extinction and improves the likelihood of subsequent colonization, and patch area mediates this effect (Castorani et al. 2015). 

  • Ignoring fluctuations in population fecundity can lead to overestimation of connectivity and persistence because fluctuations in fecundity, rather than dispersal, are the dominant driver of demographic connectivity and a key determinant of local extinctions and colonizations of giant kelp (Castorani et al. 2017). 

Disturbance maintains spatial coexistence through a competition-colonization trade-off

  • Ecological theory predicts that disturbance can facilitate coexistence between species competing for limited resources.

  • In field surveys and experiments, disturbance to competitively-dominant, short-dispersing seagrass enhances spatial coexistence with competitively-inferior, broad-dispersing burrowing shrimp (Castorani et al. 2014).
  • In population models, disturbance size and frequency interact to structure coexistence through the spatial storage effect (Castorani & Baskett 2020). Supporting theory, intermediate disturbance enhances biodiversity.
  •  Hence, disturbance size, frequency, and their interaction can mediate landscape-scale biodiversity by altering the duration of time over which inferior competitors can escape competitive exclusion.

Related publications:

  • Smith, R.S., S.L. Chengand M.C.N. CastoraniIn press. Meta-analysis of ecosystem services associated with oyster restoration. Conservation Biology.
  • Smith, R.S., B. Lusk, and M.C.N. Castorani. 2022. Restored oyster reefs match multiple functions of natural reefs within a decade. Conservation Letters 15(4):e12883. [PDF]
  • Castorani, M.C.N., T.W. Bell, J.A. Walter, D.C. Reuman, K.C. Cavanaugh, and L.W. Sheppard. 2022. Disturbance and nutrients synchronise kelp forests across scales through interacting Moran effects. Ecology Letters 25(8):1854–1868. [PDF]
  • Walter, J.A., M.C.N. Castorani, T.W. Bell, L.W. Sheppard, K.C. Cavanaugh, and D.C. Reuman. 2022. Tail-dependent spatial synchrony arises from nonlinear driver-response relationships. Ecology Letters 25(5):1189–1201. [PDF]
  • Shoemaker, L.G., L.M. Hallett, L. Zhao, D.C. Reuman, S. Wang, K.L. Cottingham, R.J. Hobbs, M.C.N. Castorani, A.L. Downing, J.C. Dudney, S.B. Fey, L.A. Gherardi, N.K. Lany, C. Portales-Reyes, A.L. Rypel, L.W. Sheppard, J.A. Walter, and K.N. Suding. 2022. The long and the short of it: mechanisms of synchronous and compensatory dynamics across temporal scales. Ecology 103(4):e3650[PDF]
  • Castorani, M.C.N., S.L. Harrer, R.J. Miller, and D.C. Reed. 2021. Disturbance structures canopy and understory productivity along an environmental gradient. Ecology Letters 24(10):2192–2206. [PDF]
  • Zhao, L., S. Wang, L.M. Hallett, A.L. Rypel, L.W. Sheppard, M.C.N. Castorani, L.G. Shoemaker, K.L. Cottingham, K. Suding, and D.C. Reuman. 2020. A new variance ratio metric to detect the timescale of compensatory dynamics. Ecosphere 11(5):e03114. [PDF]
  • Gaiser, E.E., D.M. Bell, M.C.N. Castorani, D.L. Childers, P.M. Groffman, C.R. Jackson, J.S. Kominoski, D.P.C. Peters, S.T.A. Pickett, J. Ripplinger, and J.C. Zinnert. 2020. Long term ecological research and evolving frameworks of disturbance ecology. BioScience 70(2):141–156. [PDF]
  • Castorani, M.C.N. and M.L. Baskett. 2020. Disturbance size and frequency mediate the coexistence of benthic spatial competitors. Ecology 101(1):e02904[PDF]
  • Cavanaugh, K.C., D.C. Reed, T.W. Bell, M.C.N. Castorani, and R. Beas-Luna. 2019. Spatial variability in the resistance and resilience of giant kelp in southern and Baja California to a multiyear heatwave. Frontiers in Marine Science 6:413. [PDF]
  • Castorani, M.C.N., D.C. Reed, and R.J. Miller. 2018. Loss of foundation species: disturbance frequency outweighs severity in structuring kelp forest communities. Ecology 99(11):2442–2454. [PDF]
  • Castorani, M.C.N., D.C. Reed, P.T. Raimondi, F. Alberto, T.W. Bell, K.C. Cavanaugh, D.A. Siegel, and R.D. Simons. 2017. Fluctuations in population fecundity drive variation in demographic connectivity and metapopulation dynamics. Proceedings of the Royal Society B: Biological Sciences 284(1847):20162086. [PDF]
  • Castorani, M.C.N., D.C. Reed, F. Alberto, T.W. Bell, R.D. Simons, K.C. Cavanaugh, D.A. Siegel, and P.T. Raimondi. 2015. Connectivity structures local populations dynamics: a long-term empirical test in a large metapopulation system. Ecology 96(12):3141–3152. [PDF]
  • Castorani, M.C.N., K.A. Hovel, S.L. Williams, and M.L. Baskett. 2014. Disturbance facilitates the coexistence of antagonistic ecosystem engineers in California estuariesEcology 95(8):2277–2288. [PDF]