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Temporal Variability in the Fatty Acid Composition Of TEMPORAL VARIABILITY IN THE FATTY ACID COMPOSITION OF SUSPENSION-FEEDERS AND GRAZERS ON A SOUTH AFRICAN ROCKY SHORE Submitted in Fulfilment of the Requirements for the Degree of MASTER OF SCIENCE Rhodes University By Rachel Tintswalo Ndhlovu February 2013 Abstract ABSTRACT Numerous ecological studies have used lipids to determine trophic pathways in aquatic systems, as fatty acid profiles provide time-integrated information on an organism’s assimilated diet. Many of these studies have, however, been based on sample collections with a limited temporal scale. The trophic ecology of pelagic systems has been studied intensively using fatty acid analyses, but very little work has been directed toward benthic communities, with the intertidal being especially neglected. The investigation of trophic pathways within rocky shore communities will help us to better understand system responses to environmental changes. The determination of long term temporal variation of the food web within a community could reveal the type, magnitude, duration and frequency of highly seasonal productivity. Changes in fatty acid profiles through time in primary consumers of intertidal rocky shores are poorly understood, but represent an important step towards a more comprehensive understanding of rocky shore food webs, compared with those derived from snapshot or short-term studies. The aim of this thesis was to clarify the temporal variability in the diets of rocky shore intertidal suspension-feeders (the brown mussels Perna perna and the Cape reef worm, Gunnarea gaimardi) and grazers (the Cape sea urchin Parencinus angulosus and the Goat-eye limpet, Cymbulus oculus) on the south east coast of South Africa using fatty acid profiles, and to investigate the effects of life style (e.g. feeding mode) and life cycle on temporal variations in tissue fatty acid profiles. I had three hypotheses: firstly, that suspension-feeders experience high levels of variability in their diets through time because water quality has the potential to change quickly and drastically, whereas grazers experience less variability in their diets over time since their food sources are more constant. Secondly, the reproductive cycles of the suspension-feeder P. perna and the grazer P. angulosus affect the fatty acid composition of their gonads, with temporal variations in lipid composition reflecting changes in reproduction investment. Thirdly, the total amount of energetic reserves available for reproduction are different for each gender (females allocate more energy to egg production than males allocate to gamete production). To address these aims, fatty acid profiles of suspension-feeders and grazers were investigated over a period of twelve months ii Abstract (from July 2010 to June 2011) at a single site on the south east coast of South Africa. The results showed high variability in the fatty acid composition of both the suspension-feeders strongly related with changes in their food source (suspended particulate material). Furthermore, similar temporal changes in fatty acid profiles of the two suspension-feeders were observed over time, reflecting their common diet and life style. There were some inter- specific differences in the suspension-feeders, likely originating from differences in their particle capturing mechanisms. Grazers showed less variability through time compared with the suspension-feeders, with the limpets being more consistent than the sea urchins. The temporal variability in the sea urchin diets may have resulted from the highly diverse and heterogeneous food sources available to them, whereas limpets may be more selective and have a limited range of diet items. Differences between the two grazer species may have arose from differences in their feeding strategies and intertidal zonation. The fatty acid compositions of gonad tissues in both P. perna and P. angulosus showed temporal variability strongly related to reproductive cycle. Differences in the fatty acid values between females and males were apparent, with females richer in total and polyunsaturated fatty acids than males. Spawning and gametogenesis influenced the variability of fatty acids through time in both species, suggesting the importance of considering the reproductive cycle when studying lipids in rocky shore species. Little evidence of lipid transfer between muscles and gonads was seen, suggesting the importance of direct lipid storage into the reproductive tissues. The influence of diet and life history of intertidal consumers on the temporal variability of their fatty acid compositions is important to understand, as it provides us with a better understanding of the functioning of rocky shore systems. There is an enormous potential for future research in this field of study. iii Table of Contents TABLE OF CONTENTS ABSTRACT…………………………………………………………………………………..ii TABLE OF CONTENTS........................................................................................................iv LIST OF TABLES ………………………………………………………………………….vi LIST OF FIGURES …………………………………………………………………………x ACKNOWLEDGEMENTS ................................................................................................ xvi DEDICATION ……………………………………………………………………………xviii DECLARATION …………………………………………………………………………..xix CHAPTER 1: GENERAL INTRODUCTION ..................................................................... 1 1.1. The coastal environment ................................................................................................. 1 1.2. The South African coastline ............................................................................................ 1 1.3. Rocky intertidal zone ..................................................................................................... 2 1.4. Rocky shore food webs .................................................................................................. 2 1.4.1. Primary producers and feeding modes of rocky intertidal organisms ...................... 3 1.4.2. Study species ........................................................................................................... 6 1.5. Trophic biomarkers ........................................................................................................ 7 1.6. Thesis overview ............................................................................................................... 8 CHAPTER 2: GENERAL METHODS .............................................................................. .10 2.1. Sample collection ....................................................................................................... ..10 2.2. Sample treatment .................................................................................................. …….13 2.3. Fatty acid analysis ........................................................................................................ 14 CHAPTER 3: TEMPORAL VARIABILITY IN DIET AND LIPID COMPOSITION OF SUSPENSION-FEEDERS AND GRAZERS ON A SOUTH AFRICAN ROCKY SHORE .................................................................... 16 iv Table of Contents 3.1. INTRODUCTION ....................................................................................................... .16 3.2. METHODS ................................................................................................................. ..19 3.2.1. Study area, sample collection and treatment ........................................................ .19 3.2.2. Trophic and dietary fatty acid markers……………………………………….......19 3.2.3. Data analysis……………………………………………………………………...20 3.3. RESULTS ...................................................................................................................... 21 3.3.1. Temperature ............................................................................................................ 21 3.3.2. Primary producers .................................................................................................. 22 3.3.3. Suspension-feeders and grazers .............................................................................. 31 3.3.4. Diets of suspension-feeders and grazers using target fatty acids ........................... 32 3.4. DISCUSSION ............................................................................................................... 48 3.5. CONCLUSION ............................................................................................................. 55 CHAPTER 4: LIFE HISTORY RELATED VARIATIONS IN THE FATTY COMPOSITION OF ROCKY SHORE CONSUMERS ........................... 56 4.1. INTRODUCTION ......................................................................................................... 56 4.2. METHODS .................................................................................................................... 59 4.2.1. Study area, sample collection and treatment .......................................................... 59 .2.2. Sample collection and treatment .............................................................................. 60 4.2.3. Data analysis ........................................................................................................... 60 4.3. RESULTS ...................................................................................................................... 61 4.3.1. Environmental variables ......................................................................................... 61 4.3.2. Temporal variations in fatty acid proportional composition of gonads ................
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