Dynamic and context-dependent keystone species effects in kelp forests

Area of Science:

• Marine ecology
• Keystone species dynamics
• Trophic cascades

Background:

• Sea otters are keystone predators crucial for kelp forest health.
• Their impact on kelp forests varies geographically.
• Previous studies highlight sea otter roles in maintaining kelp ecosystems.

Purpose of the Study:

• To analyze long-term datasets on kelp forest communities during sea otter reintroduction.
• To compare the effects of sea otters on kelp forests in different regions (Vancouver Island and San Nicolas Island).
• To understand how dynamic species interactions influence community trajectories.

Main Methods:

• Analyzed two 30-year datasets on kelp forest communities.
• Developed a community model to estimate dynamic species interaction rates.
• Compared sea otter impacts on sea urchins and subsequent kelp recovery in two distinct locations.

Main Results:

• A classic trophic cascade (urchin depletion, kelp recovery) occurred off Vancouver Island following otter arrival.
• This cascade was muted around San Nicolas Island, with coexistence of otters, urchins, and kelp.
• Differences were attributed to initial strong otter impacts in Vancouver Island and indirect competitive interactions in San Nicolas Island, highlighting dynamic interaction strengths.

Conclusions:

• Dynamic interaction strengths, rather than average interaction strength, are key to explaining differing community trajectories.
• Interspecific interactions can significantly alter keystone species function across various community contexts.
• Considering dynamic interaction strengths improves predictions of community change.