Habitat enhancement to support invertebrate biodiversity: Comparing gabions to seawalls in an urbanised estuary.

Abstract

Urbanisation is a major driver of biodiversity loss in coastal ecosystems. Artificial structures, such as seawalls, often support lower biodiversity than their complex natural counterparts due to their smooth, featureless surfaces. Ecological engineering aims to enhance biodiversity and ecological functioning on these structures by incorporating nature-based designs and promoting habitat creation. Gabions, wire mesh baskets filled with rocks, are increasingly used in estuarine and sheltered areas, offering greater habitat complexity than traditional seawalls. However, their impacts on biodiversity and potential as an eco-engineering solution remain poorly studied. This 12-month study compared colonising benthic organisms on gabions to that on vertical concrete seawall controls in Knysna Estuary, South Africa. Gabions supported greater species richness compared to seawalls at some timesteps, whilst control seawalls supported higher functional diversity. Gabions and seawalls hosted significantly different communities with gabions hosting important habitat-forming species. This study adds to the limited but growing evidence base on the ecological role of gabions in urbanised estuaries and highlights the need for further research across broader spatial and temporal scales.