Edge effects reverse facilitation by a widespread foundation species.

Area of Science:

• Marine ecology
• Interspecific interactions
• Biogenic habitat structure

Background:

• Foundation species often buffer environmental extremes for associated organisms.
• Previous research focused on comparing conditions inside vs. outside biogenic habitats.
• Environmental gradients within habitat patches are less understood.

Purpose of the Study:

• Investigate how edge effects within a single habitat patch alter ecological interactions.
• Determine if habitat-forming species can exacerbate environmental stresses.
• Examine thermal stress gradients in California mussel (Mytilus californianus) beds.

Main Methods:

• Quantified temperature differences between mussel bed interiors, surfaces, and adjacent bedrock.
• Assessed thermal stress and mortality risk for juvenile mussels across these gradients.
• Utilized Mytilus californianus as a model foundation species.

Main Results:

• Mussel beds exhibited complex thermal modification, decreasing temperatures in the interior and increasing them at the surface.
• Peak temperatures varied by up to 25°C across a 6-10 cm gradient from bed interior to surface.
• Juvenile mussels experienced higher thermal stress and mortality risk at the bed surface compared to the interior.

Conclusions:

• Environmental gradients within biogenic habitats significantly alter ecological interactions.
• Habitat-forming species can create conditions that exacerbate stress for some associated organisms.
• Understanding microhabitat heterogeneity is crucial for predicting species interactions and survival.