Can multitrophic interactions and ocean warming influence large-scale kelp recovery?

Area of Science:

• Marine Ecology
• Climate Change Biology
• Ecosystem Dynamics

Background:

• Northeastern Atlantic coastlines are experiencing shifts from sea urchin barrens to kelp forests.
• These changes coincide with altered sea temperatures and predator abundances, offering insights into climate change impacts.
• Understanding multitrophic interactions is crucial for predicting kelp forest recovery.

Purpose of the Study:

• To explore the influence of climate change and multitrophic interactions on kelp forest recovery along the Norwegian coast.
• To identify regional patterns in kelp recovery and sea urchin recruitment.
• To relate these patterns to abiotic (temperature) and biotic (predator abundance, habitat complexity) factors.

Main Methods:

• Compiled data from over 1,500 km of Norwegian coastline.
• Analyzed regional patterns of kelp recovery and sea urchin recruitment.
• Assessed the population dynamics of sea urchin predators (Cancer pagurus, Paralithodes camtschaticus) and a potential crab predator (Gadus morhua) across a latitudinal gradient.

Main Results:

• Kelp recovery and sea urchin recruitment were low in the southernmost, warmest region, despite local sea urchin abundance.
• Sea urchin barrens dominated further north with high juvenile densities.
• Kelp forests recovered in the northernmost, coldest region, with sea urchins restricted to refugia and kelp on open bedrock, coinciding with increased crab abundance and decreased coastal cod populations.

Conclusions:

• Ocean warming, increased crab populations (edible and invasive red king crab), and declining coastal cod may drive observed kelp recovery and sea urchin distribution changes.
• A conceptual model is proposed to explain the roles of key species (kelp, sea urchins, cod, crabs) in structuring these coastal communities.
• Habitat complexity (refugia) plays a critical role in sea urchin distribution and kelp recovery.