University of the Pacific Scholarly Commons University of the Pacific Theses and Dissertations Graduate School 1974 Population ecology of the littoral fringe gastropod Littorina planaxis in Northern California Russell James Schmitt University of the Pacific Follow this and additional works at: https://scholarlycommons.pacific.edu/uop_etds Part of the Biology Commons, and the Marine Biology Commons Recommended Citation Schmitt, Russell James. (1974). Population ecology of the littoral fringe gastropod Littorina planaxis in Northern California. University of the Pacific, Thesis. https://scholarlycommons.pacific.edu/uop_etds/ 1842 This Thesis is brought to you for free and open access by the Graduate School at Scholarly Commons. It has been accepted for inclusion in University of the Pacific Theses and Dissertations by an authorized administrator of Scholarly Commons. For more information, please contact [email protected]. POPULATION ECOLOGY OF THE LITTORAL FRINGE GASTROPOD LITTORINA PLANAXIS IN NORTHERN CALIFORNIA A Thesis Presented to the Faculty of the Department of Marine Sciences University of the Pacific In Partial Fulfillment of the Requirements for the Degree Master of Science by Russell James Schmitt August 19, 1974 -i;;­ Jl.CKNOHLEDGH1ENTS Dr. Steven Obrebski gave me much gu1dance, criticism, and encouragement during the twelve months of the study. I waul d 1 ike to thank Dr. Obrebski for his time and effort on my behalf, and for providing the academic stimulation that made my two year stay at the. Pacific ~1arine Station i nval uabl e. I am grateful to Dr. Tom M. Spight for his valuable sugges­ tions and criticisms during the early stages of the study, and far all his considerations subsequent to his relocation tq the east coas.t. Dr. Victor Loosanoff graciously made his extensive reprint collection available to me. In addition, Dr. Loosanoff was a con­ stant source of suggestions, encouragement, and Irish f1ist. Dis­ cussions with Dr. DNight Taylor were highly enlightening, in part due to Dr. Taylor's extensive knowledge of molluscs. Of the many membeTs of the Graduate Student Association I owe thanks to, discussions with G.L. Anderson,. D.A. Jillson, T.E. t1urray, K.A. Simon~ T.L. West, and K.B. Hest were particularly helpful. G.L. Andet~san,. L. Collins, K.A. Simon,. and D. HiTliams assisted with field co11ecttons. I would like to thank Gregory Laird J.\nderson for attempting to teach me the rudiments of micl~o-photography, how­ ever unsuccessful his attempts t-Jere. f'1Y family pt·ovi ded a constant source of mora 1, and oft times financ·ia'l:. support. Finally, I v1ould 1·ike to express my deep gratitude to Ruby f\nn Mayeda~ vtho amazingly put up with all this nonsense. -iv- POPULATION ECOLOGY OF THE LITTORAL FRINGE GASTROPOD LITTORINA PLANAXIS IN NORTHERN CALIFORNIA ABSTRACT Life history patterns of individual organisms are the result of natural selection and should be correlated with particular physical and biological characteristics of habitats in which they live. The littoral fringe is known to be the most severe physical habitat in the intertidal zone, and it is expected that organisms in it should have population characteristics associated with selective response to physical adversity rather than biological interaction. Ecological studies of populations of Littorina .R.J.MlaXi$._ were made in the Dillon Beach and Bodega Head areas. The study localities differed prin­ cipally in extent of wave exposure rather than geographical location. Abundance and population age structure data were obtained for 5 populations of L. planaxis over a 12 month period. No seasonal patterns of chang~ were observed. Recruitment was not detected at any site, and analyses of age structure indicated lack of recruit­ ment is not uncommon. A survey of all populations at Dillon Beach in July, 1974, revealed only one with a significant number of young. Gt~owth data from marked individuals indicate that L. E_lanaxis grows slowly (approx. lmm/yr) and has a long life span Ti·nc~an age: 11 yrs.). Growth was significantly reduced during the reproductive season. Sexual matur·ity was· attained at a 4.5-5 mm shell length after two to three years of growth. Br-eeding season for L J2lanaxis at Bodega Bay ·lasts ftom ~1arch to early August. A marked semilunar synchrony was observed for copulation and egg release. Laboratory studies indicated snails will sp,:wm during inter·-lunar periods aftet' conditioning by immer­ sion. A daily rhythm of oviposition corresponded with each day•s higher spring tide. Snails spawned eqg capsules with a single ovum. Fecundity was extremely high: a 13 mm snail may spavJn 114,000 eggs per season. All L. PJ.ar~~i?_ popu1 ati on~; showEd extreme stabi 1ity in abun­ dance, age structure, growth, and recruitment. The virtual lack of recruitment rt?flects the physical sev1~rity of the environment to the ,iuveni ·1 es ·in terms of access to su·i tab 1e substrate by sett1 i ng larvae and subsequent early survival. ·The data val ida ted t~urphy•s (1968) predictions based on theoretical considerations that long life, late sexual matu·rity, and iteropadty are associated w"ith habitats inhospitable to juvenne sutvival. The ·inapplicabil'ity of r- and K- selection concepts to the populations studied are dis­ cussed. -v- Available data on the reproductive characteristics of the genus Littorina were obtained from published literature and analysed to · discover cOi~relations among life history parameters. It was found that littorinids have 4 major reproductive strategies associated with position in the intertidal zone. Major differences between high and low intertidal species were in 1) mode of development, 2) size of the ovum, 3) fecundity, and 4) type of pelagic capsule. High intertidal species tended to have planktotrophic or ovoviviparous development, egg capsules containing a single small ovum, and high fecundity. Initial hypotheses about the adaptive significance of these correla- tions are: · 1) High intertidal species must produce planktotrophic larvae, otherwise the energetic cost of benthic egg production is too high because of the severe envir­ onment and the necessity to protect the ova. Ovovi­ viparity achieves the same end by protecting the de­ veloping juvenile wi·thin the adult body. 2) High fecundities are imperative in situations where juvenile survival is low if adult population stability is to be maintained. 3) The significance of differences in number of eggs per pelagic capsule is not known, but it is suspected that. it is related to conditions in the environment of.the larvae and the adult. -vi- TABLE OF CONTENTS PAGE ACKNOWLEDGEr~ENTS • . iii ABSTRACT • • •• iv LIST OF FIGURES . viii LIST OF TABLES . xi INTRODUCTION • • 1 CHARACTERISTICS OF THE LITTORAL FRINGE • . 4 POPULATION DYNAMICS 10 Study Sites 11 ~~lethods • . .. 14 Abundance •.• 16 Mean Size of Snail 24 s·i ze-Frequency Dis tr·i buti on: Recru.i tment 33 GROWTH • • • 43 Methods • 43 Results 43 REPRODUCTION 49 r~ethods • 49 Copulation 50 Size at Sexual Maturity 51 Sex Ratio .••.•• . .. 51 Egg Capsules and Mass 52 Development . 53 Spa,.. mi ng . 53 -vi·i- TABLE OF CONTENTS PAGE Oviposition ..•.••••••• 53 Seasonality of Spawning . 54 Lunar/Tidal Synchrony of Spawning . 55 Daily Tidal Rhythm of Spawning •••. 57 Size-Specific Fecundities • . 59 EVOLUTION OF REPRODUCTIVE STRATEGIES 73 An Initial Inquiry 73 Results • 75 Classification of.Reproductive Strategies. 76 Discussion·. 78 DISCUSSION 91 SUMMARY •• 99 BIBLIOGRAPHY . 103 -viii- LIST OF FIGURES FIGURE PAGE 1. Mean monthly maximum and minimum air temperatures at the Pacific Marine Station, Dillon Beach, Cal .••.•••••••••• 7 2. Mean monthly inches of precipitation at the Pacific Marine Station, Dillon Beach, Cal •.•.....•.•....••••••••••• 8 3. Mean monthly surf temperature at the Pacific Marine Station, Dillon Beach, Cal •...••.•••...••..•.••...••••••••• 9 4. General view of Littorina planaxis sampling areas •••••.•.••• 12 5. L.ittorina Q}_Qnaxis sampling areas at Bodega Head and Dillon Beach ............................................... 13 6. Graphic illustration of monthly sampling procedure ..•...•.•. 15 7. Estimates of population abundance for Dillon Beach Si te 1. • . • . .. .. • . • . • . • . • • . • • . • . • . • • • • • . • . • . • • • 18 8. Estimates of population abundance for Dillon Beach S i te 2 . .. .. .. 19 9. Estimates of population abundance for Dillon Beach s; te 3 . ... .. 20 10. Estimates of popu.lation abundance for Bodega Head Site 1 ................................................. ~~~ .... 21 11. Estimates of population abundance for Bodega Head Si·te 2 .: ............. , .................................... 22 12. Monthly mean shell length for snails at· Dillon Beach Site 1 ....................... " ... ~· .............................. 26 13. Monthly mean shell length for snails at Dillon Beach Si te 2 ...................................... ., ........ , . 27 14. Monthly mean shell length for snails at Dillon Beach s 'i ·te 3 II' e • e • • • • • • • e •• , ... 11 " • • • ' • • • • • • • 1 • 1 • • • • • • • • e e ••• • ••• e • 1 28 15. Monthly mean shell length for sn~ils at Bodega Head Si te 1 ••••....•....•... > ........ II • • • • • • • • • • • • • • • • • • • • • • • • • • 29 16. Monthly mean shell length for snails at Bodcqa Head $ i te 2 . ~. , .. .. .. .. .. 30 -ix- FIGURE PAGE 17. Size-frequency distributions of Littorina E}?naxis at Dillon Beach Site 1 ....................................... 37 18. Size-frequency distributions of Littorina planaxis at Dillon