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Abstract
Netted swimming enclosures in Sydney Harbour offer an important habitat for local seahorse populations. While this artificial habitat appears attractive to seahorses, it has been suggested that a dependence on these alternative habitats may be caused by the disturbance and loss of natural habitat such as seagrass within the estuary. Previous studies have found that permanent (year round) swimming enclosure nets have an established community of fouling sessile epibiota which attract and support a greater density of seahorses than nets installed seasonally. This study aims to examine the role of habitat complexity (via natural fouling and artificial structures) in determining the distributions of seahorses and their prey. In Chapter 1, I look at the relationship between different levels of net fouling and potential seahorse prey, and show that cleaning nets by reducing sessile epibiota has an effect on the amount of small mobile invertebrates inhabiting nets. Chapter 2 assesses the differences in fouling mass and mobile epifauna between three net types deployed in the field for twelve months. Net types varied in the mass of fouling, with implications for management of nets to reduce cleaning requirements. In Chapter 3, nets were manipulated to add additional structure with the aim of enhancing the abundance of mobile epifauna, and testing habitat associations by seahorses. High habitat complexity was a strong determinant of epifauna abundance and seahorse distribution. This thesis presents research that will serve to inform managers of swimming net enclosures on the merits of using certain net materials and suggests ways in which suitable, permanent, and productive artificial habitat could be used to benefit local seahorse populations.