Date of Award

2018

Degree Type

Thesis

Degree Name

Master of Science (Biological Sciences)

School

School of Science

First Advisor

Professor Glenn Hyndes

Second Advisor

Professor Thomas Schlacher

Third Advisor

Dr Michael Payne

Abstract

Sandy beaches make up approximately three-quarters of the world’s shorelines. They are important ecosystems, hosting abundant invertebrate macrofaunal communities that provide food resource for vertebrate predators such as shorebirds, seabirds, marine mammals and fish. Although possessing a terrestrial appearance, food input on sandy beaches is derived predominantly from the sea. Such food input includes detrital matter, mostly in the form of wrack, and has the potential to support a great diversity of species, as well as stabilising energy fluxes and dynamics of consumer populations. The movement of detritus, along with other vectors such as organisms and nutrients, across ecosystem boundaries can alter productivity and change consumers’ distribution, abundance, and growth rates at multiple trophic levels in recipient systems. Ultimately, the input of nutrients and detritus can increase primary and secondary production and alter food web structures and community dynamics in recipient ecosystems, a process termed “spatial subsidy”.

Ghost crabs (Ocypode spp.) form an important component within beach communities in several places around the world and are part of this trophic complexity. However, little is known of their densities, trophic structure and the role they play as vectors for spatial subsidies through movement of marine derived nutrients inland. The aim of this study was to determine the trophic ecology of the Golden ghost crab (Ocypode convexa) and understand what its role is in terms of marine connectivity along the Mid-West coastline of Western Australia. Using ghost crab burrows as a proxy for relative abundance, this study illustrated that Ocypode spp. are abundant and reside along beaches with minimal foot- and off-road vehicle traffic and exist in the upper intertidal zone in comparison to zones within the dune environment. In addition, from stomach content (percentage frequency (%F) and percentage volume (%V)) and stable isotope analyses (δ13C and δ15N), as well as laboratory assays, it was found that the Golden ghost crab is an omnivore that consumes a wide variety of plant and animal material. A larger proportion of its diet comprises material derived from the marine environment, compared to material derived from the terrestrial environment. These results support the importance of marine detritus as a spatial subsidy on beaches, and the important role ghost crabs are likely to play as iii consumers within sandy beach ecosystems, and as vectors for the transfer of marine material through the beach-dune food web.

Available for download on Monday, March 18, 2019

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