Maximising positive outcomes for threatened species from coastal infrastructure upgrades

Lea T. Mamo

doi:10.25918/thesis.146

Protective infrastructure in coastal areas, such as breakwaters, is critical due to the rapid expansion of coastal settlements. However, climate change impacts, such as sea-level rise and storm surge intensification, threaten their integrity. Consequently, protective infrastructure will need to be upgraded to withstand additional water levels and wave loading. While it is common knowledge that existing infrastructure can impact adjacent ecosystems, little is known about the effects of infrastructure design upgrades on biodiversity. To fill this knowledge gap, I utilised the upgrade of the Coffs Harbour (NSW, Australia) breakwater as a case study, comparing benthic assemblages on the infrastructure before and after it underwent major upgrade works. A three-year Before-After Control-Impact (BACI) study showed that the upgrade significantly changed community structure. Where possible, the use of more sustainable coastal adaption strategies is recommended in the future. The breakwater upgrade was subject to unique constraints because it was believed to be the only place globally where the critically endangered seaweed Nereia lophocladia (hereafter called Nereia) occurs. The interdisciplinary processes associated with balancing engineering standards and impact avoidance to the Nereia population during the breakwater upgrade were investigated. Furthermore, the incorporation of ecologically engineered boulder habitat, as a mitigation strategy to enhance the habitat availability for Nereia and other benthic taxa living on the breakwater, was evaluated. While Nereia has yet to recruit to these eco-engineered habitats, incorporating different rock sizes (i.e. small and large) and types (i.e. top and bottom of greywacke and granite boulders) attracted diverse assemblages. To ensure the long-term persistence of Nereia , additional conservation strategies were explored, guided by high-priority actions in the species' recovery statement. Despite its listing as critically endangered, it was evident that data on Nereia was limited or anecdotal. Regular targeted surveys along the breakwater and adjacent reefs revealed that the species could be observed almost all year round (i.e. June - February). Furthermore, surveys 150 km north and south of Coffs Harbour revealed that Nereia occurs at a minimum of six more locations, significantly expanding its distribution. However, genomic analysis based on SNP data showed that these populations have low genetic diversity and are highly inbred, suggesting limited gene flow and a decreased ability to adapt to environmental changes. In combination with future studies on the biology and ecology of Nereia , an ongoing monitoring program will help inform conservation measures and secure the species' long-term survival. Such targeted conservation approaches, together with mitigating eco-engineering measures, can reduce the ecological footprint of climate change associated upgrades to protective infrastructure until alternative approaches to coastal adaption become best practice.

Maximising positive outcomes for threatened species from coastal infrastructure upgrades

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Maximising positive outcomes for threatened species from coastal infrastructure upgrades

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