Investigation of Bara-Baruga (mangrove) ecosystem recovery after a hail storm in Boambee Creek, Gumbaynggirr, NSW

Abstract

Context: Understanding the causes of decline in mangrove forests requires on-ground investigations, which are best conducted in collaboration with Traditional Knowledge Holders. Aims: To compare the ecological communities and contaminants in an unhealthy and healthy mangrove forest in Boambee Creek. Methods: Nearmap Imagery identified the timing of mangrove die-back. On-site surveys included quadrat counts of pneumatophores, seeds and seedlings, timed searches and benthic cores for invertebrates. Samples were collected for nutrient analysis of water, elemental analysis of sediment and gas chromatography-mass spectrometry for volatile contaminants in pneumatophores. Results: A hail storm in 2021 coincided with the mangrove die-back. Chemical analysis showed ongoing eutrophication, and high concentrations of sediment mercury, carbon disulfide and toxic hydrocarbons in pneumatophores at the unhealthy site. Invertebrate species richness and density of pneumatophores, seeds and seedlings were significantly lower at the unhealthy site. Infauna richness decreased at the unhealthy site compared with an historical baseline in 2006, but did not change at the healthy site. Conclusions: These surveys confirmed contamination and a loss of ecological integrity at the unhealthy mangrove site. Implications: Intervention may be required at the unhealthy site to assist natural recovery and restoration of mangrove ecosystem services.