From kelp forests to turf reefs: Patterns, drivers, and impacts to functional diversity

Area of Science:

• Marine Ecology
• Climate Change Biology
• Oceanography

Background:

• Kelp forests are declining globally due to ocean warming and human activities.
• In warming regions like the Gulf of Maine, kelp forests are being replaced by turf algae.
• The drivers and consequences of this kelp-to-turf transition are not fully understood.

Purpose of the Study:

• To investigate the continuation of kelp forest collapse and turf algae expansion in Maine.
• To identify the environmental drivers influencing the shift from kelp forests to turf algae dominance.
• To assess the ecological consequences of this ecosystem state shift.

Main Methods:

• Conducted field surveys across 32 sites in Maine from 2018-2023.
• Utilized a structural equation model integrating benthic cover data and environmental variables.
• Analyzed seaweed traits, including growth rates, surface-area-to-volume ratios, and canopy height.

Main Results:

• Confirmed ongoing kelp forest decline and northward expansion of turf algae along the Maine coast.
• Ocean warming and reduced wave disturbance directly promoted turf algae, while kelp loss indirectly benefited turf algae.
• The kelp-to-turf shift resulted in seaweed assemblages with reduced canopy height, impacting habitat provision and carbon storage.

Conclusions:

• Climate change is accelerating the degradation of temperate reef ecosystems.
• The transition to turf algae represents a significant state shift with ecological consequences.
• Urgent action is needed to mitigate further kelp forest loss and its associated vital services.