THE SIGNIFICANCE OF SARGASSUM ON SINGAPORES REEFS

SARGASSUM ON SINGAPORE'S REEFS LOW KIM YEW JEFFREY M.Sc. National University of Singapore A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF BIOLOGICAL SCIENCES NATIONAL UNIVERSITY OF SINGAPORE 2015 DECLARATION I hereby declare that this thesis is my original work and it has been written by me in its entirety. I have duly acknowledged all the sources of information which have been used in the thesis. This thesis has also not been submitted for any degree in any university previously. LOW KIM YEW JEFFREY Jan 2015 ACKNOWLEDGEMENTS Many thanks and much gratitude to the following people, without whom none of this would have been possible: First and foremost, to my wife, Eunice, who has been a source of inspiration and continuous support. She's been my buddy not only in the countless dives in my field trips, but also in life's journey; Prof Chou, for taking me under your wing all those years ago, and your guidance throughout my years as a researcher; The people from the Reef Ecology and the Experimental Marine Ecology Laboratories: many thanks for your companionship, discussions (heated, frivolous and otherwise), and help on numerous occasions. A special shout out to Li Jinghan, for her invaluable work on the epifaunal studies; To the team from the Marine Ecology Research Group, Nanyang Technological University, past and present: Dr Peter Steinberg (headhoncho); Dr Bryan Wilson (DNA sequencing and analysis); Dr David Feary (fish communities); Dr Adriana Verges (herbivory); Dr Alexandra Campbell (epifaunal studies); Dr Andrew Bauman (coral settlement); Dr James Guest and Rick Leong (coral-algae interaction studies); To National Parks Board (NParks), for supporting me in my studies; To my colleagues at NParks, who helped take the weight of the workload during the times of my absence; special shout-out to Rachel for her help with the maps; My many dive buddies, especially Chay Hoon, Debby, Ben, Vincent, Kee Seng. Thanks for taking the time to accompany me in my field work! Last but not least, I would like to thank my parents for their continuous support of me and my aspirations. They are much loved. i TABLE OF CONTENTS ACKNOWLEDGEMENTS I SUMMARY IV LIST OF TABLES VII LIST OF FIGURES IX CHAPTER 1. INTRODUCTION 1.1. Brief profile of Singapore 1.2. Coral reef studies in Singapore 1.3 Importance of algae 1.4. About Sargassum 1.5. Sargassum species as a foundation species 1.6. Sargassum as an invasive species 1.7. Sargassum studies in Singapore 1.8. Sargassum as a study subject 1.9. Research objectives 10 11 13 CHAPTER 2. STATUS OF SARGASSUM IN SINGAPORE: IDENTIFICATION AND 14 14 17 17 18 19 19 20 22 22 30 33 36 41 41 42 43 44 MORPHOLOGY 2.1. 2.2. Introduction Materials and methods 2.2.1 2.2.2. 2.2.3. 2.2.4. 2.2.5. Examination of herbarium records Sampling sites Collection for morphological study Collection for DNA analysis DNA extraction, PCR and sequencing 2.3.1. 2.3.2. 2.3.3. 2.3.4. Updating the Sargassum species list for Singapore Locality details from herbarium specimens Morphological analysis DNA analysis 2.4.1. 2.4.2. 2.4.3. DNA and morphology Analysis of archived material Species lost, or misapplied species names? 2.3. 2.4. 2.5. Results Discussion Summary CHAPTER 3. DISTRIBUTION AND ANNUAL VARIATION OF SARGASSUM ISLANDS SOUTH OF SINGAPORE 3.1. Introduction 3.2. Materials and Method 3.2.1 Sampling sites 3.2.2. Sargassum distribution 3.2.3. Growth 3.2.4. Biomass of Sargassum on Singapore reefs 3.2.5. A retrospective analysis of occurrence of Sargassum 3.3. Results 3.3.1. Description of reefs surveyed 3.3.2. Density of Sargassum 3.3.3. Annual growth cycles 3.3.4. Biomass of Sargassum 3.3.5. Proportion of “MA” comprising Sargassum IN THE 3.3.6. Distribution of Sargassum inferred from coral reef surveys 3.4. 3.5. Discussion Summary CHAPTER 4. MACROGRAZERS OF SARGASSUM SINGAPORE: STUDIES ON 76 76 HERBIVORY 4.1. IN 45 45 47 47 48 50 51 51 52 52 56 57 62 65 65 69 75 Introduction ii 4.2. Materials and methods 4.2.1. 4.2.2. Herbivorous fish assessment Herbivory pressure 4.3.1. 4.3.2. Herbivorous fish assessment Herbivory pressure 4.3. 4.4. 4.5 80 80 82 Results 87 87 91 Discussion Summary 99 104 CHAPTER 5. EPIFAUNAL DISTRIBUTION AND SINGAPORE 5.1. Introduction 5.2. Materials and methods 5.2.1 Study sites 5.2.2. Environmental parameters 5.2.3. Algal sample collection 5.2.4. Epifauna composition and density 5.2.5. Epifauna classification 5.2.6. Analysis of data 5.3. Results 5.3.1. Environmental variables 5.3.2. Variation of epifauna within Sargassum 5.3.3. Epifaunal assemblage 5.3.4 Spatial variation of epifauna 5.3.5. Temporal variation 5.3.6. Between-algae variation 5.4. Discussion 5.4.1. Lack of mesograzers 5.4.2. The "refuge quality" of an algal host 5.4.3. Seasonality of the algal hosts VARIATION ON 5.5. Summary SARGASSUM IN 105 105 109 109 110 110 111 112 113 114 114 115 118 120 122 125 131 131 132 135 136 CHAPTER 6. CONCLUDING REMARKS AND FUTURE WORK 6.1. Sargassum morphology and DNA 6.2. Emphasis on macroalgae 6.3. Alga-herbivore interaction 6.4. Alga-coral interaction 6.5. Protection of marine habitats in Singapore 6.6. Leveraging on citizen scientists 6.7. Novel uses of macroalgae 6.8. Future work 138 138 139 141 142 143 144 145 146 REFERENCES 148 iii SUMMARY This thesis presents the first quantitative studies on the macroalgae Sargassum, which has long been known to comprise a major component on Singapore's coral reefs, but was never fully studied. It comprises chapters that reviewed its classification, quantified its distribution and seasonal variation, and investigated the effects of herbivory within Singapore's reef system. Forty-one valid species were documented from both the Singapore Herbarium (at the Singapore Botanic Gardens) and the Herbarium, Lee Kong Chian Natural History Museum. Morphological and DNA analyses of fresh specimens, however, confirmed the presence of only five species in the field, namely, S. ilicifolium, S. granuliferum, S. aquifolium and S. swartzii, which are subtidal, while the fifth species, S. polycystum, was intertidal. The occurrence and distribution of the other 36 species are currently unknown. Sargassum was found to be distributed throughout the islands south of Singapore, with long term reef monitoring data documenting its occurrence for over two and a half decades. Sargassum was persistent on the reefs (the basal portions are perennial), with higher densities on the reef flat than the reef crest. The densities on the reef crest ranged between 15 ± 11.9 m-2 and 30.2 ± 9.4 m-2, and on the reef flat, between 57.4 ± 20.5 m-2 and 93.8 ± 28.4 m-2. All species showed iv cyclical growth and die-back, which coincided with the Northeast Monsoon (between August and March) and the Southwest Monsoon (between April and July) respectively. Peak average length and biomass for S. ilicifolium were 219 ± 35 cm and 18.5 kg/m2 wet weight (WW), while for S. aquifolium were 88 ± 14 cm and 465.6 g/m2 WW. The biomass for S. ilicifolium was 5-40 times that reported elsewhere. Not enough data could be collected for the other two subtidal species. Herbivory pressure was measured in terms of bite rates using underwater video, and was many magnitudes lower than reported elsewhere, at just 0.24 bites/h. Consumption rates using macroalgal bioassays were also low, estimated at 0.125 cm/h. An indirect measure of herbivory, using bite marks on leaves, showed marginally higher fish bites at the outer reefs. This result was supported by fish surveys which showed non-signifcant differences between sites for herbivorous fish, which were more abundant in the outer islands. The macroherivores on local reefs comprised two fish genera, Scarus and Siganus, and the sea urchin, Diadema setosum. Both their abundances were low, with maximum densities of 0.203 individuals/m2 and 0.205 individuals/m2 respectively. Similarly, herbivory by epifauna was low, despite showing similar community structure with studies elsewhere. Only about 30% of the fauna observed were herbivores, and occurred in abundances of no more than individual/g WW of algae. This was to 32 times lower v than reported for substantial effects on macroalgal cover to be observed. No spatial variation could be seen in epifaunal communities on Sargassum, nor on Hypnea and Bryopsis which were used for comparative studies. There were, however, distinct differences in the epifaunal communities between Hypnea and Bryopsis, with the assemblage from Sargassum overlapping both. vi LIST OF TABLES Table 2.1. The current classification of Sargassum, based on Trono (1997), Mattio and Payri (2010) and Guiry and Guiry (2014). Table 2.2. Morphotypes collected from seven sites in the southern islands of Singapore (total 72 samples from seven morphotypes and one out-group). Distinguishing characters for Sargassum derived from the morphological study. (H2: Pulau Hantu; TPT: Terumbu Pempang Tengah; S4: Pulau Semakau; J1: Pulau Jong; PSD1: Sisters’ Islands; SJn: St John’s north; and Tk: Pulau Tekukor). Table 2.3. Sargassum species documented from Singapore. Species with specimens lodged at the Singapore Herbarium and the Herbarium, Lee Kong Chian Natural History Museum are in bold typeface, and marked *1 and *2 respectively. Validity of the species names checked against AlgaeBase (Guiry and Guiry, 2014) unless otherwise stated. All locality sources also include Pham et al. (2011) and Low and Chou (2013) unless otherwise indicated. Table 2.4. Locations from which Sargassum had been collected, compiled from herbarium records from Singapore Herbarium and the Herbarium, Lee Kong Chian Natural History Museum. Species in bold were observed in field in this study. Online catalogues were not used, because the accuracy of the lists was in doubt. Table 2.5. Habitats from which Sargassum had been collected, compiled from herbarium records of Singapore Herbarium and the Herbarium, Lee Kong Chian Natural History Museum. Species in bold were observed in field in this study. Online catalogues were not used, because the accuracy of the lists was in doubt. Table 2.6a. Characters for Sargassum morphotypes in Singapore waters (seeAjisaka, Noro and Yoshida, 1995; Phang, Noro and Yoshida, 1995; Tseng and Lu, 1995; Noiraksar, Ajisaka & Ogawa, 2007; Noiraksar and Ajisaka, 2008; Mattio & Payri, 2009). Table 2.6b. Characters for Sargassum morphotypes in Singapore waters (seeAjisaka, Noro and Yoshida, 1995; Phang, Noro and Yoshida, 1995; Tseng and Lu, 1995; Noiraksar, Ajisaka & Ogawa, 2007; Noiraksar and Ajisaka, 2008; Mattio & Payri, 2009). Table 3.1. A list of the sampling sites and what types of surveys were carried out. Table 3.2. Qualitative descriptions of the reefs, observed during swim-through surveys. Si = S. ilicifolium; Sa = S. aquifolium; Ss = S. swartzi; Sg = S. granuliferum; Sp = S. polycystum. Table 3.3. Results for Two-Way Crossed Analysis using ANOSIM in PRIMER on growth data of S. ilicifolium from seven sites, in the islands south of Singapore, from August 2012 to December 2012. Figures indicate Global R statistics, those in parenthesis are significance levels. Cells in bold show significant differences. (a) Pairwise test between sites, (b) Pairwise tests between sampling times, (c) Monthon-month comparisons between years. Table 3.4. Global R statistics and their significance levels from a Two-Way Crossed Analysis using ANOSIM in PRIMER on growth data of S. aquifolium (4 sites), S. swartzii (4 sites) and S. granuliferum (2 sites), in the islands south of Singapore, from August 2012 to December 2012. Table 3.5. Percentage of Sargassum compared to other macroalgae making up the lifeform category "MA". Values derived from line intercept transects carried out in vii the islands south of Singapore between 2010 and 2012. (Legend: "DICT" = Dictyoca; "CCA" = crustose coralline algae; "GREEN" = all green algae; "RED" = all other red algae; "SARG" = Sargassum). Table 3.6. Growth cycles for three species of Sargassum. Peak length data for S. ilicifolium / cristaefolium was extracted from Trono and Luisma, 1990; Aterweberhan et al., 2005, 2006, 2008; and this study. S. cristaefolium is a synonym of S. ilicifolium. Data for S. siliquosum from Ang (1985) and Low and Chou (2013) were also included. Peak length data for S. aquifolium / binderi was extracted from Wong and Phang (2004) and Yeong and Wong (2013). S. binderi is a synonym for S. aquifolium. MCR = Cape Rachado, Malaysia; MPD = Port Dickson, Malaysia; PB = Bolinao, Philippines; RS = Sheik Said Island, Red Sea; S = Singapore Table 4.1. Fish survey sites and sampling times between 1987 and 2012. Table 4.2. Time and locations for the mobile invertebrate surveys under the Reef Friends programme. Table 4.3. ANOSIM results for bite marks at seven sites in the islands south of Singapore, between Decemebr 2011 and March 2013. Global R between sites: 0.403; p[...]... noted that most of the collections of old were from the reef flat areas 12 1.9 Research objectives The overall objective of this study is to fill in the gaps on our knowledge about Sargassum on Singapore reefs In summary, the studies examined the classification of the local genera through morphological and DNA analyses (Chapter 2); quantifying the extent the species and their seasonality of growth (Chapter... distribution or zonation have been made, save a detailed assessment of their zonation for one island (Chou and Wong, 1984) There is little knowledge as to whether these functions are the result of a single species or a mixed group complex It is for these reasons that the taxonomy of local Sargassum species be 16 clarified, as an important first step before effective conservation and management actions can be... stems from the expression of its variable morphology, which can be dependent on not only the environmental factors, but also on the age of the alga and its reproductive state (Kilar et al., 1992) It expresses this variability either between populations, within the same population, or even within one individual The ranks were originally developed based on differences in the size and shape of the leaves,... 2005), the study of their ecology becomes paramount to understanding the interactions on local reefs Secondly, there was recognition that there were other habitats adjacent to the coral reefs that were very much understudied This realisation arose from a mini "renaissance" for marine biodiversity and ecology in Singapore, with the infusion of new research laboratories in both the National University of. .. broader geographical scale, there is also the threat of biological invasion, particularly to other coasts, exemplified by the spread of S muticum on the Pacific coast of northern America and on 9 the Atlantic coast of Europe (Critchley et al 1990) The proliferation of Sargassum has also been linked to environmental changes, particularly in relation to enhanced siltation and nutrient loads (McCook 1999; Schaffelke... compilation of existing records (Pham et al., 2011) Other work on Sargassum was sparse, despite Sargassum beds constituting a key coastal habitat and providing significant shelter for biodiversity (Mukai, 1971; Rossier and Kulbicki, 2000; Tanaka and Leite, 2003) The only known quantitative study on algae zonation on a Singapore reef (Chou and Wong, 1984) reported the zonal distribution of 8 species of macroalgae... investigating the roles of both macrograzers (fish and urchins, Chapter 4) and mesograzers (epifauna, Chapter 5) in regulating the distribution of the dominant Sargassum species Data were collected through methods devised for the study, and also recalled reef monitoring data collected over the years, providing a retrospective look at Sargassum on our reefs The final chapter (6) encapsulates the conclusions of the. .. dependent on not only the environmental factors, but also on the age of the alga and its reproductive state (Kilar et al., 1992) This variability can be expressed either between populations, within the same population, or even within one individual Additionally, the ranks ascribed to this genus are very complex (see Table 1), and were developed based on differences in the size and shape of the leaves,... Sargassaceae Genus Sargassum Subgenus Sargassum (one of 5) Section Sargassum Section Zygocarpicae Section Polycestae Section Ilicifoliae Section Binderianae Section Johnstonii Section Lapazaenum Section Sinicola (Section Sargassum now incorporates the older sections Malacocarpicae and Acanthocarpicae, as proposed by Mattio and Payri, 2010) Recent attempts to standardise the characters... Figure 5.5 MDS plot of epifauna on Sargassum, Hypnea and Bryopsis at seven sites in the islands south of Singapore, July to December 2012 Stress is an indication of fit of data on a two-dimensional plane; any value below 0.2 is considered a good fit (Clarke and Warwick, 2001) The overlay shows correlation of environmental parameters (Pearson’s correlation > 0.2) to the epifaunal data (a) Sargassum; (b) . Biomass of Sargassum on Singapore reefs 51 3.2.5. A retrospective analysis of occurrence of Sargassum 51 3.3. Results 52 3.3.1. Description of reefs surveyed 52 3.3.2. Density of Sargassum. and a half decades. Sargassum was persistent on the reefs (the basal portions are perennial), with higher densities on the reef flat than the reef crest. The densities on the reef crest ranged. Reef Survey and Conservation Project (RSCP), which contributed to the development of the "Blue Plan" mentioned earlier. The Blue Plan advocated the conservation of marine biodiversity