The Effect of Predator Netting on Clam Recruitment in Baynes Sound, Bc with a Special Focus on the Response of the Manila Clam (Venerupis Philippinarum)
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THE EFFECT OF PREDATOR NETTING ON CLAM RECRUITMENT IN BAYNES SOUND, BC WITH A SPECIAL FOCUS ON THE RESPONSE OF THE MANILA CLAM (VENERUPIS PHILIPPINARUM) by DAPHNE MARIE MUNROE B.Sc.Hons., Simon Fraser University, 2000 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Animal Science) THE UNIVERSITY OF BRITISH COLUMBIA SEPTEMBER 2006 © Daphne Marie Munroe, 2006 Abstract Passive and active forces determine the patterns of settlement of invertebrate larvae. Research efforts into larval settlement have been dominated by attached and conspicuous species in hard substrate environments. Here, data on early recruitment patterns of a mobile bivalve species from a soft-sediment habitat is provided. In particular, how intertidal clam aquaculture netting influences the distribution of settling pediveliger larvae was investigated. Early recruitment patterns of Manila clam larvae (Venerupis philippinarum) were examined in relation to predator netting used in farming clams in British Columbia. A method for sampling recent settlers from intertidal sediments was developed, proven effective and employed to sample settled clams (<600 um shell length) from four sites in Baynes Sound, on the eastern side of Vancouver Island, B.C. in 2003 and 2004. Paired netted and non-netted plots were compared for number of early recruits. Plots with the netting and high density of adult clams experienced lower levels of settlement. Settlement varied annually with 2003 experienceing an order of magnitude less recruitment than 2004. In addition, laboratory tests were run using flumes to examine the retention of competent clam larvae within flumes with netting on the bottom. No difference in the retention of clam larvae was observed due to netting or sediment treatments. Sediment properties (sediment grain size, organic carbon and inorganic carbon) were also compared between netted and non-netted plots. No difference was seen in the sediment properties measured except for slightly higher levels of organic carbon beneath nets; this was likely due to the higher number of adult clams beneath the nets. The netting buffers temperature at the sediment surface during tidal exposure by up to 3°C, the biological relevance of this remains untested. No increase in sedimentation was measured beneath netting; however, decreased bivalve settlement beneath netting was observed but only in the year when overall settlement was high. This decrease in recruitment was not supported by the flume trials; however these were run at ii one velocity. Trials at different velocities may produce different results. These field observations are an important contribution to understanding larval settlement of mobile species in a soft-sediment habitat. Table of Contents ABSTRACT H TABLE OF CONTENTS IV LIST OF TABLES VI LIST OF FIGURES VH ACKNOWLEDGEMENTS XI DEDICATION Xffl CHAPTER 1: INTRODUCTION 1 INTRODUCTION 1 LARVAL BIOLOGY 2 Spawning and Fertilization 2 Larval Development 4 Settlement and Metamorphosis 7 JUVENILE DISPERSAL .10 LARVAL ECOLOGY 17 History 17 Factors Influencing Settlement Patterns 19 Biological Factors 19 Chemical Factors 22 Physical Factors 26 FLUID MOTION 28 Benthic Boundary Layer 28 Reynolds Number 30 Turbulence 31 SHELLFISH AQUACULTURE 32 Manila Clam Aquaculture 33 Clam Culture in British Columbia 35 Predator Netting 36 THESIS OUTLINE 38 REFERENCES 40 CHAPTER 2: SAMPLING RECENTLY SETTLED CLAMS FROM SEDIMENTS 56 INTRODUCTION 56 MATERIALS AND METHODS 57 RESULTS 59 DISCUSSION 61 CONCLUSIONS 63 REFERENCES 64 CHAPTER 3: THE EFFECT OF NETTING ON ESTERTIDAL SEDIMENTATION 66 INTRODUCTION 66 MATERIALS AND METHODS 68 Site 68 Clam Populations. 70 Sediment Grain Size 70 Carbon 72 Temperature 72 RESULTS 73 Clam Populations. 73 Sediment Grain Size 75 Carbon 76 iv Temperature 77 DISCUSSION 79 Clam Populations. 79 Sediment Grain Size 80 Carbon 81 Temperature 81 CONCLUSIONS 82 REFERENCES 83 CHAPTER 4: BIVALVE RECRUITMENT TO CULTURE PLOTS 86 INTRODUCTION 86 MATERIALS AND METHODS 89 RESULTS 91 DISCUSSION 97 CONCLUSIONS 102 REFERENCES 104 CHAPTER 5: SETTLEMENT OF LARVAE IN EXPERIMENTAL FLUMES Ill INTRODUCTION Ill MATERIALS AND METHODS 113 RESULTS 117 DISCUSSION 120 CONCLUSIONS 123 REFERENCES A 124 CHAPTER 6: CONCLUSIONS AND GENERAL DISCUSSION 128 APPENDIX 1: SUMMARY TABLE OF JUVENILE BIVALVE DISPERSAL RESEARCH 131 REFERENCES APPENDLX 1 134 APPENDIX 2: COMPARISON OF METHODS FOR THE DETERMINATION OF CARBON ES ENTERTEDAL SEDIMENTS 137 INTRODUCTION 137 MATERIALS AND METHODS 139 Sample Collection and Preparation: 139 Acid-Burn: 140 LOI: 141 CHN: 142 RESULTS 143 DISCUSSION 148 CONCLUSIONS 149 REFERENCES APPENDLX 2 150 APPENDLX 3: LARVAL SETTLEMENT DATA FROM 2002 152 APPENDIX 4: FIELD SITE VELOCITY MEASUREMENTS 156 APPENDIX 5: CONSIDERATION OF TURBULENCE IN CALIBRATION OF PLASTER BLOCKS USED FOR FLOW MEASUREMENT 158 INTRODUCTION 158 MATERIALS AND METHODS 159 RESULTS 161 DISCUSSION 162 REFERENCES APPENDLX 5 163 v List of Tables Table 1-1. Current velocities reported to cause byssal drift in post metamorphic bivalves 15 Table 2-1. Grain size components, percentage by dry weight, of each sediment type. The size category >2000um contains both granule+ and broken shell 59 Table 3-1. Site characteristics (tidal height is reported at meters above chart datum) 69 Table 3-2. Results of tests of assumptions for paired T-test. Normality tested on the distribution of the difference between pairs, correlation calculated for linear regression of pairs 71 Table 4-1. Results of ANOVA test of factors influencing Venerupis philippinarum settlement 93 Table 4-2. Results of linear regression of Venerupis philippinarum biomass versus larval settlement 94 Table 5-1. Lengths of Venerupis philippinarum larvae (nm ± SD) used for each trial and source batch; n = 20 for each measure 115 Table 5- 2. Summary statistics from ANOVA test for percentage of Venerupis philippinarum larvae leaving the system during the trial 117 Table 5-3. Summary statistics from ANOVA test for proportion of Venerupis philippinarum larvae leaving in the last 30 minutes of the trial 120 Table Al-1. Summary of research on juvenile bivalve dispersal 131- Table A2-1. Means and standard errors for each test for carbon analysis method and each value measured 145 Table A2-2. Significance values for multiple comparisons of means for each comparison of test type for organic carbon values 146 Table A2-3. Significance values for multiple comparisons of means for each comparison of test type for inorganic carbon values 147 List of Figures Figure 1-1. The general life cycle of marine bivalves 3 Figure 1-2. General diagram of the trochophore and veliger larvae of marine bivalves. (A) trochophore larva; (B) veliger larva with velum extended. Not drawn to scale 5 Figure 1-3. Modes of post-larval dispersal. A. Byssus drift; long byssus threads carry the bivalve through the water column. B. Climbing (from Yankson, 1986); the animal uses its ciliated foot and strong byssus to climb walls. Side branches of byssus are used to hold the animal while it probes with its foot. C. Drifting by foot protrusion (from Sorlin, 1988); the animal begins in a normal feeding position, works its way to the surface then protrudes its foot to act as a sail 13 Figure 1-4. Graphic representation of the flows in the Benthic Boundary Layer. Longer arrows represent faster flows; grey at the bottom represents the surface. Flow increases with distance from the surface and eventually reaches a rate equivalent to the free-stream 29 Figure 1-5. Annual production of mollusc aquaculture by mass shown with open squares and on left axis. Number of molluscan species in production worldwide shown with solid grey circles and on right axis. Data from FAO 2005 32 Figure 1-6. Global molluscan production by mass contribution by country. Country labels are listed on the right. For each year shown, the top eight countries are graphed, the rest of the countries for that year are pooled in "rest of world" category. Data from FAO 2005 34 Figure 1- 7. Comparison of Manila clam (Venerupis philippinarum) production from capture fishery versus aquaculture. Capture fishery is shown with grey bars and aquaculture shown in black. Data from FAO 2005 35 Figure 1-8. Location of Baynes Sound on Vancouver Island, Canada. Inset left shows location of Vancouver Island in relation to Canada 38 Figure 2-1. Means and standard deviation for numbers of clams (Venerupis philippinarum) per sample for the three sediment types. The dashed line indicates the expected number of clams per sample (58.8) based on number of larvae placed in each tank. N = 3 for each treatment 60 Figure 3-1. Map of beach sampling sites within Baynes Sound. Each beach is marked with number and labelled with site name. Inset top right: Location of Vancouver Island within Canada. Inset bottom left: Location of Baynes Sound on Vancouver Island, British Columbia, Canada 69 Figure 3-2. Length frequencies (count) of Venerupis philippinarum (>5mm) from each site, 2003 in left column and 2004 in right. Clams measured from netted plots represented by black bars, clams from non-netted plots represented by open bars. Shell length in mm plotted along the horizontal axis, frequency on the vertical axis 74 Figure 3-3. Mean number of Venerupis philippinarum (>5mm shell length) per m2 from sites in 2003 (left) and 2004 (right). Netted samples represented with hatched bars, non-netted plots represented with grey bars. Error bars represent 95% confidence interval. For each bar, n=16 75 Figure 3-4. Mean number of Nuttalia obscurata (>5mm shell length) per m2 from sites in 2003 (left) and 2004 (right). Netted samples represented with hatched bars, non-netted plots represented with grey bars. Error bars represent 95% confidence interval. For each bar, n=16 75 Figure 3-5. Percent silt (<0.063 mm grain size) content of samples from each site and plot. Data from 2003 shown in left panel, 2004 shown in right panel.