Weaving Indigenous Knowledge Systems with ecological engineering to enhance the functionality and biodiversity of urbanised ecosystems along the southeast coast of South AfricaOcean Sprawl

Nobuhle Mpanza^{1, 2}, Francesca Porri^{1, 2}, Paula Pattrick³

¹South African Institute for Aquatic Biodiversity (SAIAB), South Africa - ²Rhodes University, South Africa - ³South African Environmental Observation Network (SAEON), South Africa

Ocean sprawl is accelerating globally, driven by increasing human migration to coastal regions and exacerbated by climate change-induced sea level rise. This shift has led to the transformation of natural shorelines into artificial infrastructure, which, despite its societal benefits, alters the complexity of natural coastal ecosystems. These structural modifications disrupt essential ecological functions supported by complex natural substrates, including spawning grounds, refugia, and nursery habitats. To mitigate these impacts, ecological engineering approaches are increasingly considered to rehabilitate urbanised coastal ecosystems across the globe. No studies have however yet incorporated Indigenous Knowledge Systems in their designs. As such, this research weaves ecological engineering techniques with Indigenous Knowledge and practices to innovatively co-create nature-based prototypes. The study aimed to assess the installation longevity, seeded mussel survival and growth, and biological succession of two nature-based prototypes (Imizi – Cyperus textilis material, and Soilsaver – jute fibre material) in marine coastal environments along the southeast coast of South Africa. Three treatments (control, flat and seeded) were assigned to each prototype and monitored monthly for 12 months. Results showed significant differences in longevity, with Imizi prototypes outlasting Soilsaver configurations. All Soilsaver prototypes at natural rocky shore sites were lost within two weeks, precluding the deployment of Imizi at natural sites. Mussel-seeded treatments exhibited greater longevity than flat treatments for both prototypes. The Imizi nature-based prototype supported higher sessile/sedentary species richness and abundance than the Soilsaver prototype, while mussel-seeded and control treatments had higher richness than flat treatments. These findings hold potential for upscaling rehabilitation initiatives of urban coastlines using Imizi mussel-seeded nature-based solutions to durably enhance habitat complexity and biodiversity.