Abstract
Aquaculture, defined as the cultivation of aquatic organisms, continues to be the fastest-growing protein production sector in the world. As wild-capture fisheries stagnate and decline, the expansion of aquaculture is necessary to meet the demands no longer possible or practical for wild populations. With the continued expansion of aquaculture in New Zealand, it is imperative that the industry is managed with sustainability at the forefront to reduce negative environmental impacts and ensure the preservation of native ecosystems.
Aquaculture species can be divided into subgroups based on the intensity of required inputs: ‘intensive’ species, which require feed inputs, and ‘extensive’ species, which require no feed inputs. By understanding the interactions between multiple trophic levels of aquaculture species, Integrated Multi-Trophic Aquaculture systems (IMTAs) can be created to utilize the wastes of one species to fuel the production of another in polyculture array systems, increasing overall efficiency. Suspension feeders and macroalgae are both ‘extensive’ species that are good candidates for IMTAs due to their high global demand, nutritional profiles, and wide range of applications. The production of metabolic wastes from suspension feeders allows for an exciting opportunity for macroalgae co-culture that can utilize a previously wasted resource for increased growth. In turn, detrital material produced by macroalgae continues to be a well-supported contributing source of organic matter to suspension feeder diets globally.
While the appeal for IMTAs is growing globally, our understanding of the biochemical and ecological nuanced interactions between suspension feeders and bivalves remains convoluted. As such, the present thesis aimed to apply biochemical and ecological scientific approaches to increase our understanding on the exchange of organic and inorganic matter between dominant temperate large-brown macroalgae and the green-lipped mussel (Perna canaliculus) in New Zealand. Further, the work considers how changes in macroalgae community composition will likely impact the availability of macroalgae-derived detrital material (MDOM) to suspension feeders and how variability in biochemical, nutritional, and trace elemental profiles may impact the overall health of marine and human food webs.
The findings demonstrate that temperate New Zealand macroalgae offer a wide range in total phenolic concentrations, presenting exciting novel uses for large-brown macroalgae for bio-extracts in IMTAs (chapter two). In addition, the thesis presents evidence from both lab-based experiments (chapter three) and field observations (chapter four) to suggest MDOM is an important component of the diet of P. canaliculus in the Otago Harbour Region. Also, the work outlines the potential bioremediation capacity of three economically promising kelp species for the alleviation of metabolic wastes produced by P. canaliculus (chapter five). And finally, this thesis is among the first studies to consider the utilization of trace element profiles alongside stable isotopic values to increase the discriminatory capacity between macroalgae species within the Phaeophyceae class and also to consider the potential hazards heavy metals in macroalgae may present for use in the food sector (chapter six). Overall, the thesis presents new perspectives on the application of biochemical and ecological interactions between suspension feeders and macroalgae that can be used to best inform the implementation of ecosystem-based management practices in the aquaculture sector of New Zealand in the pursuit of the establishment of IMTAs.