Edith Cowan University Research Online Theses: Doctorates and Masters Theses 2006 Detached macrophyte accumulations in surf zones: Significance of macrophyte type and volume in supporting secondary production Karen Ruth Crawley Edith Cowan University Follow this and additional works at: https://ro.ecu.edu.au/theses Part of the Marine Biology Commons Recommended Citation Crawley, K. R. (2006). Detached macrophyte accumulations in surf zones: Significance of macrophyte type and volume in supporting secondary production. https://ro.ecu.edu.au/theses/1744 This Thesis is posted at Research Online. https://ro.ecu.edu.au/theses/1744 Edith Cowan University Copyright Warning You may print or download ONE copy of this document for the purpose of your own research or study. The University does not authorize you to copy, communicate or otherwise make available electronically to any other person any copyright material contained on this site. 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DETACHED MACROPHYTE ACCUMULATIONS IN SURF ZONES: SIGNIFICANCE OF MACROPHYTE TYPE AND VOLUME IN SUPPORTING SECONDARY PRODUCTION EDITH COWAN UNIVERSITY Karen Ruth Crawley B. Se. (Hons) University of Western Australia This thesis is presented in fulfilment of the requirements for the degree of Doctor of Philosophy at Edith Cowan University School ofNatural Sciences Faculty of Computing, Health and Science Edith Cowan University January 2006 USE OF THESIS The Use of Thesis statement is not included in this version of the thesis. Abstract Detached macrophytes (sea grass and macroalgae) are transported from more offshore areas and accumulate in large volumes in surf zones, where they are commonly called wrack. In coastal regions in other parts of the world, wrack transported from one habitat to a second habitat can be considered as a "spatial subsidy" for the recipient habitat with significant consequences for community dynamics and food webs. The primary aim of this study was to determine the significance of the different components of wrack (i.e. sea grass and brown, red and green algae) as a direct and indirect food source and habitat for invertebrates and fish in surf zones of south-western Australia. The importance of different volumes of surf zone wrack to determining fish abundance and composition was also investigated. These aims w:ere achieved by examining the food and habitat preference of invertebrates and the habitat preference of fish through laboratory trials and field experiments. Gut content analysis was used to examine the importance of wrack-associated invertebrates as a food source for fish, while stable isotope analysis (carbon, nitrogen and sulfur) and lipid analysis (lipid class and fatty acid composition) were conducted on macrophytes, amphipods and fish to determine the source of nutrients and energy. The composition of surf zone wrack in the region comprises large quantities of seagrass, then brown and red algae, with negligible quantities of green <1;lgae. Allorchestes compressa, the dominant macroinvertebrate in surf zone wrack, showed a preference for consuming brown algae over other macrophyte types. Similarly, stable isotope analysis from some locations and fatty acid analyses indicated that A. compressa assimilates nutrients predominantly from brown algae. The influence of brown algae on secondary production extends to second-order consumers. Allorchestes compressa was the major prey of juveniles of the cobbler Cnidoglanis macrocephalus and the sea trumpeter Pelsartia humeralis, the main fish species in surf zone wrack accumulations in the region. Detached brown algae therefore contributes most to the detached macrophyte - amphipod - fish trophic pathway in the surf zones, and thus drives secondary production in these regions and provides a crucial link between coastal ecosystems. Detached macrophytes also provide an important, but transient, habitat for invertebrates and fish in south-western Australia. Under laboratory conditions, Allorchestes compressa showed a. strong preference for inhabiting seagrasses over macroalgae, iii however in situ caging experiments showed that A. compressa has a strong preference for brown algae, red algae or a mixture of macrophytes, but tended to avoid seagrass. Therefore, A. compressa showed a clear preference for different types of detached macrophytes as a habitat, with seagrass ranking below other types of macrophyte under field conditions. In contrast, neither Cnidoglanis macrocephalus or Pelsartia humeralis showed a preference for inhabiting different types of detached macrophytes as a habitat, but showed a strong positive influence by increasing volumes of wrack The species composition, densities and biomass of fish, which were dominated by juveniles, were strongly influenced by increasing volume of wrack in surf zones of south-western Australia. This study has shown that both the type and volume of detached macrophytes transported from more offshore regions subsidizes consumers and plays a crucial role in supporting secondary production in less productive surf-zone habitats of south-western Australia. The removal of large amounts of wrack from nearshore areas could have a detrimental impact on the biodiversity or abundance of macroinvertebrate and fish populations, which rely on wrack for food and shelter. / iv Declaration I certify that this thesis does not, to the best of my knowledge and belief: (i) incorporate without acknowledgment any material previously submitted for a degree or diploma in any institution of higher education. (ii) contain any material previously published or written by another person except where due reference is made in the text; or (iii) contain any defamatory material. I also grant permission for the Library at Edith Cowan University to make duplicate copies of my thesis as required. Signature: Date: .... '3 ./.4-. ./. O.G ............... V Acknowledgements First, I would like to say a huge thank-you to Glenn Hyndes for being a fantastic supervisor! Thank you for all that you taught me, for encouraging and pushing me when I needed it. Thank you also for your support and advice and for keeping up so well with reading drafts. I'm sure you'll be as relieved as I am that it's now finished! My thanks also go to a number of others who have been involved in this project at various stages. I am very grateful to Mat Vanderklift for your advice and help with practical details of the experiments, discussions and reading draft chapters. My thanks also go to Andy Revill and Peter Nichols for your patience in teaching me about the whole new world of lipid chemistry. I have greatly valued your help and involvement and the opportunity to carry out lipid analysis. Thanks to Suzy Ayvazian for your valuable input regarding 'fishy' aspects of this project. Thank you to Julia Philips for your willing help and encouragement in various ways. There are many people at Edith Cowan University who helped during the course of my PhD and to whom I am extremely grateful. Thanks to Jason Tranter for running the mass spec and your great optimism that everything would work out fine. I am very grateful to Danielle Brady for statistical advice. Thank you to all of the administrative and technical staff at the School of Natural Sciences and the ECU library staff for their assistance, which was freely given and much appreciated! A big thank-you goes to everyone who assisted with field-work, particularly Jason How, Grey Coupland, Rebecca Ince and Michael Burt- seining in wrack was a nightmare! Thanks to Gordon Lymn from the Department of Fisheries for providing a seine net for sampling. Thanks to everyone in the marine group and my ECU office room-mates for their encouragement and support. For financial support, I am extremely thankful to The Centre for Ecosystem Management and The School of Natural Sciences at Edith Cowan University, as well as the CSIRO Strategic Research Fund for the Marine Environment (SRFME) project. Thank you to The Karrakatta Club, who in conjunction with Edith Cowan University, provided funding for this project through the Dame Mary Gilmore Student award, and The Australian Society of Fish Biology through the John Glover Travel Fund. vi Finally I would like to acknowledge and thank my wonderful friends and family for their help in so many ways to enable me to reach this point. In particular I thank my parents for their constant support and sacrifices over the years, without which this would not have been possible. This is dedicated to you. vii Publications The publications listed below form the basis for parts of this thesis. Crawley, K.R., Hyndes, G.A. and Ayvazian, S.G. (in press). The influence of different volumes and types of detached macrophytes on fish community structure