ASPECTS OF THE BIOLOGY OF ASTROSTOLE SCABRA (HUTTON, 1872) -------------_.. _.. __ ._. A thesis submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy in Zoology, in the University of Canterbury by John C. Town University of Canterbury 1979 THESlS i \ ,~ t I ':) [ -lit- ;'. CONTENTS I L r . r'l CHAPTER Page ABSTRACT x INTRODUCTION • 1 SECTION 1 1 DISTRIBUTION AND DISPERSAL OF THE GENUS ASTROSTOLE FISHER, 1923 (ECHINODERMATA: ASTEROIDEA) 3 Introduction 3 Distribution of Astrostole • 4 Distribution of Astrostole scabra •• • • 0 5 Discussion • 9 SECTION 2 2 SOME ASPECTS OF THE POPULATION DYNAMICS OF ASTROSTOLE SCABRA • 17 Introduction • • • • 17 Materials and Methods 19 Results 22 Movement 22 Size and morphology • 30 Growth, recruitment, mortality and longevity 36 Discussion • 39 SECTION 3 3 REPRODUCTIVE PERIODICITY AND SOME FACTORS AFFECTING GONAD PRODUCTION IN ASTROSTOLE SCABRA 46 Introduction • • • • . • 46 Materials and Methods 47 ii CHAPTER Page Results 48 Annual reproductive cycle • 48 Pyloric caeca indices . 51 Gonad production 51 Sex ratio • 54 Discussion • • 54 SECTION 4 4 DIETARY COMPOSITION AND SEASONAL ASPECTS OF FEEDING ACTIVITY IN ASTROSTOLE SCABRA • 59 General Study Area • 61 Study Sites 63 Materials and Methods 64 Results 68 Feeding behaviour • 68 Overall dietary composition • 69 Comparison of diet between sites 74 Seasonal aspects of feeding behaviour and dietary compositon 79 The impact of predation on the prey community • 87 5 SELECTIVE FEEDING 91 Introduction • • • • 91 Materials and Methods 92 Results 94 6 PREY ESCAPE REACTIONS 98 Introduction . • • . • . 98 Materials and Methods 103 Results 103 iii CHAPTER Page chitons • 104 Abalone • 104 Limpets, 107 Fissurellid gastropods 107 Littorinid gastropods • 108 Trochid gastropods 109 Whelks 110 Echinoderms . 110 7 SOME BIOTIC FACTORS AFFECTING DIETARY COMPOSITION IN ASTROSTOLE SCABRA • 112 Introduction . • • 112 Materials and Methods 114 Statistical methods . 115 Results 117 Effects of predator size on dietary composition and feeding frequency . 117 Effects of prey size on dietary composition 131 Effect of prey-predator spatial overlap on dietary composition 136 8 DISCUSSION . 151 Introduction . 151 Dietary composition in A. scabra . 153 Selective feeding • 155 Prey escape reactions . 160 Biotic factors and dietary composition 163 SUMMARY 173 ACKNOviLEDGENENTS 177 REFERENCES . • 178 iv LIST OF FIGURES FIGURE Page 1.1 Distribution of Astrostole and Meyenaster in the South Pacific 6 1.2 Distribution records of Astrostole scabra in New Zealand 8 1.3 Suggested routes and major current systems involved in the dispersal of Astrostole and Meyenaster 16 2.1 Site lA, a long shallow gully at the southern end of First Bay 21 2.2 Site lB, a rectangular pool at the northern end of First Bay 21 2.3 Stained, immigrant, emigrant and total A. scabra at sites lA and IB 23 2.4 Numbers of A. scabra tagged and remaining at site lA 25 2.5 Numbers of A. scabra tagged and remaining at site lB 26 2.6 Diagrammatic representations of movement of A. scabra at site lA 27 2.7 Diagrammatic representations of movement of A. scabra at site lB 28 2.8 Size frequencies of intertidal and subtidal A. scabra measured in October 1976 31 2.9 Size frequencies of intertidal A. scabra measured at monthly intervals 32 2.10 Relationship between eviscerated wet weight and radius in intertidal A. scabra 34 2.11 Relationship between eviscerated wet weight and radius in intertidal and subtidal A. scabra 35 2.12 Size frequency data subjected to paper analysis 37 2.13 Normal curves superimposed on size frequency data 38 v FIGURE Page 3.1 Monthly gonad and pyloric caeca indices 49 3.2 Monthly male and female gonad indices 50 3.3 Relationship between female gonad and pyloric caeca volumes 52 3.4 Relationship between male gonad and pyloric caeca volumes 52 3.5 Relationship between gonad volume and eviscerated wet weight in female A. scabra 53 3.6 Relationship between gonad volume and eviscerated wet weight in male A. scabra 53 4.1 Location of four sites used in the feeding study 62 4.2 Site 1, First Bay. An extensive intertidal limestone platform. site 2, a deeply indented greywacke shore platform 65 4.3 site 3 and site 4. Greywacke shore platforms 66 4.4 Quantitative distribution of prey groups of A. scabra from four sites 75 4.5 Cumulative number of prey species and feeding seastars 78 4.6 Seasonal variation in the proportion of animals feeding and the monthly variation at each site 80 4.7 Diversity and evenness of the whole diet compared with the proportion of seastars feeding 81 4.8 Number of animals feeding and the diversity of the diet at sites 1-4 82 6.1 Reactions of Haliotis iris and H. australis 106 7.1 Feeding frequency indices of A. scabra of various size classes 118 7.2 Qualitative changes in dietary composition with increase in predator size 119 7.3 Per cent inclusion of M. aethiops and M. dilatatus in the whole diet according to seastar size 121 vi FIGURE Page 7.4 Per cent inclusion of I. maorianus, O. neglectus and A. glaucus in the whole diet according to seastar size 121 7.5 Indices of prey species diversity and similarity 123 7.6 Relationship between mean size of chitons and spiral-shelled gastropods consumed and seastar size 124 7.7 Difference in mean size of spiral-shelled gastropods consumed by A. scabra of given size classes 127 7.8 Difference in mean size of prey chi tons consumed by A. scabra of given size classes 127 7.9 Relationship between shell length and dry weight of foot and viscera in I. rnaorianus, O. neglectus and A. glaucus 128 7.10 Relationship between shell height and dry weight of foot and viscera in M. aethiops and T. smaragdus 129 7.11 Mean prey per meal consumed by A. scabra of different size classes 130 7.12 Mean annual freeding frequency of different A. scabra size classes 130 7.13 Relationship between prey size and predator size for M. aethiops and T. smaragdus 132 7.14 Relationship between prey size and predator size for I. maorianus 133 7.15 Size refuge and attractiveness threshold limits for three major chiton prey species 135 7.16 Vertical distribution and mean density patterns of major prey species at site 1 138 7.17 Vertical distribution and mean density patterns of major prey species at site 3 139 7.18 Vertical distribution and mean density patterns of major prey species at site 4 140 7.19 Size discriminant predation pattern for T. smaragdus 144 vii FIGURE Page 7.20 Size discriminant predation pattern for R. varia 145 7.21 Size discriminant predation pattern for M. aethiops 146 7.22 Size discriminant predation pattern for M. dilatatus 147 7.23 Size di ser iminant predation pattern for I. maorianus 148 7.24 Size discriminant predation pattern for o. neglectus 149 7.25 Size discriminant predation pattern for A~ glaucus 150 viii LIST OF TABLES TABLE Page 1.1 The known distribution and bathymetric range of Astrostole and Meyenaster 11 2.1 Net distances moved by resident A. scabra 29 2.2 Numbers of A. scabra regenerating lost rays 33 2.3 Year classes derived from analysis of size frequency data 33 2.4 Estimates of asteroid longevity 43 2.5 Estimates of age at first maturity in various asteroids 44 4.1 Prey species and their frequency in the diet of A. scabra at four sites 71 4.2 Dietary proportion in total meals of major prey species 76 4.3 Number of observations and diet characteristics at four study sites 76 4.4 Monthly composition of the diet at site 1 83 4.5 Monthly composition of the diet at site 2 84 4.6 Monthly composition of the diet at site 3 85 4.7 Monthly composition of the diet at site 4 86 4.8 Number of prey consumed/m2/year 89 4.9 Mean, range and standard deviation of prey density, and percentage removal rates 89 5.1 Range of prey sizes offered in selective feeding experiments 95 5.2 Percentage inclusion of species in the natural diet 95 5.3 Results of prey choice experiments 1 and 2 97 7.1 Difference in mean size of prey chitons and spiral­ shelled gastropods consumed by A. scabra of single size classes 126 ix TABLE Page 7.2 Size related prey characteristics compared with prey density, escape reactions and predator preferences 126 ABSTRACT The known geographical distributions of the genus Astrostole and the New Zealand species A. scabra are modified extensively by new records presented here. The supposed dispersal agency, West Wind Drift, is shown to have been incapable of producing the present pattern, and interaction, between a west to east current north of the sub-tropical convergence, an eastern Pacific surface gyre and the Peru Coastal Current is suggested as the dispersal mechanism. Studies conducted at Kaikoura (420 ,25'8, l73°,42'E) showed that intertidal A. scabra were not site specific, and were heavier, smaller, immature, and regenerated more rays than subtidal ones. Longevity in A. scabra exceeds six years and sexual maturity is achieved during the fourth year of life, after seastars have migrated to depths of 20-146m. During three years of study, spawning in subtidal A. scabra occurred once per year in late August -early September. The volume of gonad produced by individual seastars was reduced by ray damage, and a few, large intertidal seastars developed small gonads. A. scabra is a food generalist and scavenger with a diet composed chiefly of mollUSCs and crustaceans belonging to more than sixty genera.