Turning riprap into reefs: Integrating oyster shells into shoreline armouring

Area of Science:

• Marine biology
• Coastal ecology
• Habitat restoration

Background:

• Boulder seawalls with granite riprap offer limited habitat complexity, resulting in reduced marine biodiversity compared to natural rocky shores.
• Artificial coastal structures often fail to support diverse marine ecosystems.

Purpose of the Study:

• To assess the effectiveness of oyster shell additions to riprap structures for enhancing marine biodiversity and ecosystem functioning.
• To determine if artificial reefs made of oyster shells can mimic natural rocky shore conditions.

Main Methods:

• Oyster shell baskets and shell strings on concrete blocks were deployed on riprap structures in Hong Kong.
• Marine taxa inhabiting the structures were monitored for 18 months.
• Ex-situ biofiltration capacity of the developed communities was measured.

Main Results:

• Oyster shell structures supported significantly higher marine biodiversity, averaging 3.8 times that of control riprap.
• These enhanced habitats hosted diverse taxa, including suspension feeders, herbivores, and carnivores, which were scarce on control sites.
• Increased microhabitat availability on shell structures was identified as the primary driver of enhanced epibiota diversity.

Conclusions:

• Oyster shell additions are a viable method for increasing biodiversity and ecological function on artificial riprap shorelines.
• The creation of complex microhabitats using oyster shells can effectively restore marine biodiversity on degraded coastal structures.
• Restored oyster shell habitats demonstrate potential for improving ecosystem services in coastal zones.