Date of Award

2010

Document Type

Thesis

Publisher

Edith Cowan University

Degree Name

Bachelor of Science Honours

School

School of Natural Sciences

Faculty

Faculty of Computing, Health and Science

First Supervisor

Glenn Hyndes

Second Supervisor

Dr Pippa Moore

Abstract

Marine Protected Areas (MPAs) are internationally recognised as a significant spatial management and cost-effective strategy to restore and conserve the marine ecosystems structure and function from human impact. MPAs have been declared with the aim to address a single or a set of management objectives in response to anthropogenic threats, such as fishing, which can have repercussions on biodiversity through indirect interactions or top-down control within an ecosystem or across ecosystems where consumers migrate to forage. However, this indirect impact of fishing remains poorly understood, and as a consequence, the effectiveness of MP As in conserving those ecological processes and broader biodiversity is also poorly understood. Therefore, this study investigated the potential effects of sanctuary zones (no-take MPAs) on higher-order consumers and their effects on benthic assemblage structure both on the reef and in adjacent seagrass meadows. Consumer assemblages were examined using underwater visual census (UVC) on reefs and seagrass meadows at a range of sites in sanctuary and fished zones in Marmion Marine Park (MMP) and Rottnest Island Marine Reserve (RIMP) over three seasons between July 2009 and March 2010. Epibenthic fauna and flora were also sampled using quadrats on reefs and at set distances away from reefs in adjacent Amphibolis seagrass meadows over the same period. Sanctuary zones had higher mean total abundance and biomass of fish compared to adjacent fished zones, and while not significant, there was also a trend of higher means rock lobsters abundance in sanctuary zones. However, there was a high degree of variability among sites nested in zone, and among seasons. Kingston Reefs sanctuary zone contained the highest rock lobster and fish abundance, biomass, and species richness across all seasons. In addition, there was a trend of decreasing mean abundance, biomass, and species richness of fish with increasing distance away from the reef in Amphibolis meadows. In terms of epibenthic fauna and flora assemblages, there was no significant difference in their abundances and taxa richness between zones, but as with consumers, there was high variability among sites within zone and among seasons. As sanctuary zones ii had substantially higher densities of consumers in close proximity to reefs than fished zones, it was expected that predation levels would be higher in sanctuary zones and would decrease with increasing distances away from the reef. However, there were no clear trends of decreasing epibenthic abundance and diversity with distance away from the reef. Furthermore, tethering experiments with gastropods, a major prey item for some consumer species, showed no significant differences in gastropod mortality between sites or with increasing distances away from the reef. Thus, a top-down effect caused by different abundances of consumers in sanctuary versus fished zones was not evident from the results. Much of the variability in higher-order consumers and epibenthic assemblage could be due to site-specific characteristics, including the age, size, and the geographical location of sanctuary zones, and the structural complexity of the habitat. The detection of consumers' direct influence on prey abundance, richness, and distribution could be partly masked by their feeding habits, and the level of mobility of higher-order consumers. This study highlights the level of complexity of food web structures with consideration of other environmental and biological factors. It also provides important baseline of biological data on marine ecosystems in marine parks of southwest temperate waters of W A for future assessments of those marine parks. To meet a MPAs objective of biodiversity conservation, it is crucial for managers to acknowledge all natural variations in marine ecosystems, such as the life-history traits of individuals, when setting objectives for a MPAs performance, as protection may be suitable for some species and inadequate for others.

Download

Share

 
COinS