The Composition and Variation of Epiphytic Communities on Sydney Seaweeds and the Differing Approaches of Mitigation by Two Species of Macroalga
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The composition and variation of epiphytic communities on Sydney seaweeds and the differing approaches of mitigation by two species of macroalga Jacinta Green A thesis in fulfilment of the requirements for the degree of Doctor of Philosophy School of Biological Earth and Environmental Sciences Faculty of Science June 2016 THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet Surname or Family name: Green First name: Jacinta Other name/s: Kathryn Abbreviation for degree as given in the University calendar: Ph.D School: Biological Earth and Environmental Faculty:Science Sciences Title: The composition and variation of epiphytic communities on Sydney seaweeds and the differing approaches of mitigation by two species of macroalgae Abstract 350 words maximum: (PLEASE TYPE) Macroalgal epiphytic communities are critical components of marine ecosystems and can drive increased biodiversity. Understanding the epiphytic communities on macroalgae and the mechanisms that algae to mitigate the impact of epiphytes adds to understanding of the evolution and ecology of these communities. The interaction between the communities and the host also informs our understanding of life history traits, growth and resource allocation strategies of the host algae. I assessed the epiphytic communities on a range of macroalgae across several sites around the Sydney, NSW region. The type of algal host was the most significant factor in determining both fouling load and epiphytic community composition. The green alga Caulerpa filiformis J.Agardh and the brown alga Dilophus marginatus J.Agardh were selected for further study. Unexpectedly I recorded a decrease in fouling coverage on both D. marginatus and C. filiformis over the period of this study. A decrease in fouling coverage was correlated with warmer local temperatures for D. marginatus, but the inverse was true for C. filiformis. I found that juvenile sporophyte fronds of the heavily fouled D. marginatus were chemically defended against fouling. The efficacy of these defences was significantly less on extracts from fronds with visible sporangia. The in- situ coverage of epiphytic communities on juvenile and reproductive fronds was reflected in the efficacy of the surface extracts, highlighting the importance of ontogeny. Compounds from juvenile D. marginatus fronds should be further investigated as a source of anti-fouling compounds. C. filiformis is heavily defended against herbivory, but I found little evidence that this alga had any chemical defences against fouling. The strong relationship between damage and fouling and the observation of empty fronds adjacent to abscission zones suggests that epiphyte growth is mitigated by blade abandonment. This is the second recorded case of blade abandonment suggests that C. filiformis may engage in protoplasm resorption to recycle resources. This thesis has demonstrated that in situ fouling is a remarkably poor predictor of the presence of chemical defences. Ontogeny and morphology should be considered in designing bioassays to reveal complex defence strategies. FOR OFFICE USE ONLY Date of completion of requirements for Award: ii ORIGINALITY STATEMENT ‘I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged.’ Signed …………………………………………….............. Date …………………………………………….............. COPYRIGHT STATEMENT ‘I hereby grant the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstract International (this is applicable to doctoral theses only). I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation.' Signed ……………………………………………........................... Date ……………………………………………........................... AUTHENTICITY STATEMENT ‘I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format.’ Signed ……………………………………………........................... Date ……………………………………………........................... Acknowledgments Greg Davis, its done! Thanks for the belief in me Time for the next phase Angela Moles An inspiring arsekicker Saviour at the end Paul Adam, mentor Always there, never missing Thanks is not enough Peter Steinberg, well! Thanks for having me this long And keeping the faith My medical team I am alive and healthy You got me this far The skills and lessons Once learnt will not be wasted Science campaigning iv Table of Contents Chapter 1 Introduction 1 Chapter 2 Composition and coverage factors of 15 fouling communities on macroalgae in the Sydney region Chapter 3 Methodological considerations of 59 settlement assays Chapter 4 Variation in defence against fouling in the 83 brown alga Dilophus marginatus as a function of age, size, and reproductive status. Chapter 5 Defence against epibiois in the green alga 123 Caulerpa filiformis Chapter 6 Discussion 177 v vi Introduction Figure 1.1: Solieria robusta (Greville) Kylin, and its epibionts. (Image: J.Green). 1 Introduction Algal assemblages are critical components of marine communities (Sellheim et al. 2010). They are simultaneously habitats, refuges, nutrient sources and substrates for a myriad of species from amphipods to urchins (Andrew 1993; Duffy and Hay 1991; Parker et al. 2001; Poore 1994). Sessile members of these communities, attached to the host macroalga, are known as epiphytes (Smith 1996). Epiphytes can provide valuable ecosystem services in their own right. For example, one of the most common examples, the oyster, can filter and clean the water column (Ehrich and Harris 2015). Epiphytic communities on macroalga, (which are too soft to host oysters), are also valuable to the wider ecosystem into which they are incorporated. The epiphytes can host their own microbial communities (Toth and Pavia 2002; Verges et al. 2011). They can facilitate the presence of larger members of the ecosystem (Gunnill 1982; Hall and Bell 1988), e.g. by providing food for the small crustaceans that support fish communities (Aumack et al. 2011). However, whether they have value to their hosts or whether they are detrimental is not so clear cut (Barea-Arco et al. 2001; Brawley and Adey 1981; Bulthuis and Woelkerling 1983; Dixon et al. 1981; Karez et al. 2000; Nylund et al. 2013; Sand-Jensen 1977; Wahl and Hay 1995). Without the host alga, the epiphytes have limited surfaces on which to establish, but excessive growth can damage or kill the host. The epiphyte/host balance therefore helps shape the larger ecosystem, particularly for habitat-forming species (Connell and Glasby 1999; Dayton 1985; Kennelly 1987). 2 Introduction There are potential economic benefits of an increased understanding of the interactions between hosts and their epiphytes. Manmade structures such as fishing nets (Dubost et al. 1996), and ships (Bienen 2004) are under constant pressure from epiphytes. Fouling on ships also aids the dispersal of invasive species (Smale and Childs 2012). There is potential to identify, imitate and exploit the antifouling mechanisms of algae to reduce detrimental fouling in marine systems (Frankovich and Fourqurean 1997; Harms and Anger 1983; Howard and Short 1986; Irlandi et al. 2004; Lebret et al. 2009; Orth and Vanmontfrans 1984; Venugopalan 1990; Wahl 1989; Wahl 2009). Fouling has been well studied on sea grass hosts (Apostolaki et al. 2011; Balata et al. 2007; Castejon-Silvo and Terrados 2012; Dunn et al. 2008; Frankovich and Fourqurean 1997; Frankovich and Zieman 2005; Giovannetti et al. 2010; Horner 1987; Lavery and Vanderklift 2002; Nesti et al. 2009; Piazzi et al. 2007; Trautman and Borowitzka 1999). On seagrasses epiphytes have been identified as playing a positive role, such as nitrogen fixation (Goering and Parker 1972) and protection against desiccation (Orth and Vanmontfrans 1984). Epiphytes also negatively impact seagrasses through shading (Alcoverro et al. 2004), drag (Andrew and Viejo 1998), and co-consumption (Strong et al. 2009). However, macroalgae have a higher growth rate than do seagrasses, in addition to a different suite of chemical and physical defences, and so pose different challenges for successful epiphytic growth.