Mathematical Model Reveals How Ocean Storms Reshape Entire Kelp Forest Communities

We studied California kelp forests and developed a mathematical model to understand studying California kelp forests have developed a mathematical model to understand how storm disturbance to giant kelp cascades through entire benthic communities. The study addresses a key challenge in disturbance ecology: understanding how temporally variable disturbance regimes affect foundation species and surrounding communities.

Giant kelp is unique among foundation species because it grows rapidly and shows extreme fluctuations in biomass. We built a mathematical model that simulates the kelp's three-stage life cycle and how this population responds to different storm scenarios. They then modeled how changes in kelp abundance affect competition between understory algae and sessile invertebrates for space on the seafloor.

The simulations revealed a clear pattern: severe storm regimes resulted in greater abundance of understory macroalgae and lower abundance of sessile invertebrates compared to milder regimes. The mechanism involves light availability. Dense kelp canopies can reduce the amount of light reaching the benthic community by up to 90%. When storms remove the kelp canopy, increased light availability benefits understory algae that require sufficient light to grow, while sessile invertebrates lose their competitive advantage in low-light conditions.

The model's predictions matched empirical data from 20 years of community observations from the Santa Barbara Coastal Long Term Ecological Research program. The research revealed that both the cascading effects of kelp loss and direct storm scouring of the benthos influenced competition outcomes between community members.

These findings demonstrate how disturbance-driven fluctuations in foundation species abundance can have strong consequences for community structure. The study points to the value of long-term data sets and mechanistic models for understanding the interacting effects of disturbance and foundation species in ecological communities.

Citation

Detmer, A. Raine; Miller, Robert J.; Reed, Daniel C.; Bell, Tom W.; Stier, Adrian C.; Moeller, Holly V. (2021). Variation in disturbance to a foundation species structures the dynamics of a benthic reef community. Ecology.

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