Abstract
Construction of breakwaters provides an engineering solution for coastal protection. However, little effort has been made toward understanding the ecological impact on local coral reef ecosystems and developing engineering structures that would enhance the coral reef environment. A submerged breakwater proposed for Kahului Commercial Harbor, Hawai‘i, provided an opportunity to design a multi-purpose ‘reef structure’ to mitigate wave impacts while providing new coral reef habitat. This design involved ecological and environmental considerations alongside engineering principles, serving as a model for environmentally sound harbor development. This field study evaluated environmental conditions and reef community composition at the proposed site in a gradient extending outward from the harbor, using in situ data with multivariate analyses. Benthic and topographic features in the area were assessed using a towed drop camera system to relate to biological factors. Results that support breakwater topography should follow the natural spur and groove and depth of the adjacent reef and orient with wave direction. A deep area characterized by unconsolidated substrata and low coral cover would be replaced with the shallow, sloping hard bottom of the breakwater, and provide an exemplary area for corals to flourish while protecting the harbor from large ocean swells. Surfaces on shallow sloping hard bottoms receive higher levels of irradiance that benefits coral growth. Optimal levels of water motion facilitate sediment removal and promote coral recruitment and growth. The design of the Kahului Harbor submerged multi-purpose structure serves as a model for design of shoreline modification that enhances, rather than degrades, the local coral reef environment.
Highlights
Coastal communities in tropical and subtropical regions face multiple consequences of global climate change [1]
Our study provides an overview of reef communities and associated habitats in the vicinity of Kahului Commercial Harbor to update the interdisciplinary approach to design and engineer a submerged breakwater for both harbor protection and habitat enhancement in Hawai‘i
The proposed Kahului project provides a valuable opportunity to demonstrate the validity of an ecological engineering approach, integrating goals for harbor protection and conservation of coral reefs in Hawai‘i. This study documents and discusses what can be learned about ecological applications of artificial reefs and coastal defense structures
Summary
Coastal communities in tropical and subtropical regions face multiple consequences of global climate change [1]. Nearshore zones are hampered by intensified cyclones [2, 3], storm surges [4], and rising sea levels [5, 6]. Populated low-lying areas of many Pacific Islands are exposed to high risk of coastal erosion and flooding [7, 8], resulting in negative impacts on their economy and livelihood from destruction of property and infrastructure, loss of agricultural products and food supplies, and drinking water contamination [7, 9]. Tropical and subtropical island ecosystems rely on coral reefs as integral components of coastal communities, providing services and goods such as coastal protection and natural resources for socioeconomic activities [10].
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