Trait Plasticity and Warming Vulnerability in a Structurally Diverse Seagrass Ecosystem

Area of Science:

• Marine ecology
• Plant science
• Conservation biology

Background:

• Seagrass ecosystems provide vital ecological functions but are threatened by climate change and local stressors.
• Temperate lagoon seagrasses are influenced by thermal stress, turbidity, and tidal exposure.
• Zostera capensis morphology and density were investigated in Langebaan Lagoon, South Africa.

Purpose of the Study:

• To investigate spatial and seasonal variability in Zostera capensis morphology and density.
• To identify key environmental predictors of seagrass density.
• To assess the vulnerability of Zostera capensis morphotypes to thermal stress and predict future impacts.

Main Methods:

• Field surveys and environmental monitoring of seagrass meadows.
• Analysis of spatial and seasonal variations in seagrass morphology and density.
• Generalised additive mixed models to determine environmental drivers of seagrass density.
• Experimental assessments of thermal thresholds for different morphotypes.

Main Results:

• Strong spatial contrasts observed: shallow sites had high shoot density/low biomass (small-leaved), deep sites had low density/high biomass (large-leaved).
• Temperature, turbidity, and tidal exposure were primary drivers of seagrass density, explaining over 80% of variation.
• Both morphotypes declined above 26°C, indicating vulnerability to warming; morphological plasticity offered limited acclimation.
• Large-leaved morphotypes supported greater epiphyte loads and faunal associations.

Conclusions:

• Zostera capensis exhibits significant morphological plasticity in response to environmental conditions.
• Seagrass meadows are vulnerable to projected climate warming, with potential loss of structurally complex beds.
• Conservation strategies must address local stressors and preserve thermal refugia to enhance seagrass resilience and biodiversity.