Combating biodiversity decline in coastal waters with intertidal eco-engineering and Green Gravel : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Biological Science at Massey University, Albany, New Zealand

Abstract

Biodiversity generates a multitude of benefits for humanity, such as food provision, maintenance of clean air and water, climate regulation, and soil erosion prevention. Widespread human activities in the oceans continue to cause declines in species diversity and abundance, threatening ecosystem services and ecological stability. The persistence of biogenic habitats emerges as a critical countermeasure against biodiversity loss and the preservation of ecosystem health. This thesis examines the effects of engineered coastal structures for rockpool biodiversity and a kelp forest restoration technique termed Green Gravel. In Chapter Two, I analysed differences in the biodiversity of natural and artificial rockpools, including riprap and concrete structures. Riprap and concrete exhibited comparable taxa richness and functional group prevalence to natural substrates; however disturbances, particularly smothering, significantly reduced taxa richness in all habitats. Distinct taxa associations emerged in response to disturbance and habitat type with encrusting algae and grazers favouring riprap habitats with normal pool conditions, and surprisingly, artificial structures showed resistance to nonindigenous species. This chapter underscores the importance of microhabitat diversity in supporting species and ecosystem health on artificial structures, guiding eco-engineering strategies to optimize their ecological value while accommodating inevitable urbanization. In Chapter Three, I explore the efficacy of different Green Gravel methodologies for restoring collapsed Ecklonia radiata forests and investigate the impact of environmental conditions on gravel retention and sporophyte length. Gluing gravel to the substrate significantly improved gravel retention, and interestingly sporophyte lengths varied between attachment methods, with sporophytes on placed gravel initially being 100mm shorter than sporophytes on glued Green Gravel. Notably, these initial differences in sporophyte length between placed and glued Green Gravel disappeared by the end of the experiment indicating that placed Green Gravel experienced greater growth toward the end of the experiment. Despite having 40% lower retention than glued Green Gravel, 20% of placed Green Gravel were still present after 14-months offering significant restoration potential, especially for resource-restricted community groups. Due to the relative ease of implementation, Green Gravel offers promise as a tool for community-led active marine restoration and ameliorating some of the challenges our declining kelp forests face. Addressing these biodiversity declines requires immediate and collective endeavors to facilitate transformative changes that foster nature conservation, restoration, and sustainable resource utilization, all while striving to achieve overarching global societal objectives.