THE ECOLOGY OF BIOLOGICAL INVASIONS: INTERACTIONS BETWEEN NATIVE AND INTRODUCED SALT MARSH GASTROPODS by SODY BERNAN A THESIS Presented to the Department of Biology and the Graduate School of the University of Oregon in partial fulfillment of the requirements for the degree of Master of Science June 1989 iii An Abstract of the Thesis of Jody Berman for the degree of Master of Science in the Department of Biology to be taken June 1989 Title: THE ECOLOGY OF BIOLOGICAL INVASIONS: INTERACTIONS BETWEEN NATIVE AND INTRODUCED SALT HARSH GASTROPODS Three species of gastropods are commonly found in the salt marshes of Coos Bay, Oregon. Two of these .species, Assiminea californica and Littorina subrotundata, are native, and the third, Ovatella myosotis, has been introduced from the Atlantic Ocean. Experiments were conducted in order to determine whether the introduced snail has altered the distribution or abundance of the native species. Results demonstrated that the snails show vertical zonation in the marsh. Ovatella was most abundant in the high marsh, and Assiminea and Littorina were most common in the low marsh. Results of transplant and removal experiments indicated that physical factors played a critical role in maintaining observed patterns of distribution. No evidence for competition for food or space was found amongst the three species. The success of Ovatella in the salt marshes of Coos Bay, Oregon does not appear to come at the expense of the native gastropod species. Instead, Ovatellats success appears to stem from its ability to use spatial and trophic resources in the high intertidal unused by the native species. VITA NAME OF AUTHOR: Jody Berman PLACE OF BIRTH: New York City, New York DATE OF BIRTH: December 23, 1962 GRADUATE AND UNDERGRADUATE SCHOOLS ATTENDED: University of New Hampshire University of Oregon Marlboro College Stanford University DEGREES AWARDED: Master of Science, 1989, University of Oregon Bachelor of Science with high honors, 1985, Marlboro College AREAS OF SPECIAL INTEREST: Marine Ecology PROFESSIONAL EXPERIENCE: Teaching Assistant, Department of Zoology, University of New Hampshire, Durham, 1988 - 1989 academic year. Experimental Biology Aide, Oregon Department of Fish and Wildlife, Charleston, fall 1987 through summer 1988. Teaching Assistant, Department of Biology, University of Oregon, Eugene, 1986 - 1987 academic year and summer 1988. AWARDS AND HONORS: Sigma Xi Grants-in-Aid of Research, grants 1987 and 1988. Lerner-Gray Fund for Marine Research, grant 1988 PUBLICATIONS: Berman, J. (1988). Age and growth of hybrid bass in Tenmile Lakes, Oregon. Oregon Department of Fish and Wildlife, Southwest Region, Charleston, Oregon. 24 P* I would like to express my sincerest gratitude to the following people: to Dr. James Carlton of the University of Oregon, for his help in designing and executing this research project; to the late Dr. Robert Terwilliger of the University of Oregon, Dr. Paul Reimers of the Oregon Department of Fish and Wildlife, and Dr. Larry Harris of the University of New Hampshire for their help in the editing of this mauscript. I also wish to thank Dr. Jonathan Geller for his help with editing, computers, statistics, and general moral support, Dr. Victoria Starczak for her help with statistics and her computer know-how and Ms. Carol Johnson of the South Slough National Estuarine Sanctuary for her artistry. Finally, 1 wish to thank Mr. Kelly Gestring for his never-ending field and lab assistance as well as other unmentionables. This work was supported in part by a grant from the Lerner Gray Fund for Marine Research and two grants from Sigma Xi Grants-In-Aid of Research. viii TABLE OF CONTENTS Chapter Page INTRODUCTION .............................. 11. MATERIALS AND METHODS .................... 4 Description of the Study Sites ......... 4 Description of the Study Species ....... 8 Field Studies: Observations ............ 15 Field Studies: Experiments ............. 18 Laboratory Studies: Experiments ........ 23 111. RESULTS .................................. 25 Study Site ............................. 25 Population Estimates ................... 25 Vegetation Sampling .................... 34 Growth Rates ........................... 40 Transplant Experiments ................. 42 starvation ............................. 48 Field Diets ............................. 48 Aggregative Behavior....... ............. 51 IV. DISCUSSION .............................. 57 APPENDIX A. MEASUREMENTS OF TIDAL HEIGHT OF TRANSECT LINES AT METCALF MARSH. MEASUREMENTS WERE TAKEN AT THREE METER INTERVALS ALONG THE TRANSECT LINES AND VALUES ARE GIVEN IN CM ABOVE DATUM. VALUES MARKED WITH AND ASTERISK ARE THOSE IN WHICH THE SAMPLE SIZE WAS 2, IN ALL OTHERS THE SAMPLE SIZE WAS 3 ...................... 71 B. MEAN NUMBER OF SNAILS OBSERVED PER QUADRAT AT EACH TIDAL HEIGHT. NUMBER OF OBSERVA- TIONS (QUADRATS) FOR TERRESTRIAL (LAND) WAS 3, FOR THE HIGH MARSH (HIGH) 16, FOR THE LOW MARSH (LOW) 6 AND FOR THE MUDFLAT (MUD) 3. STANDARD DEVIATION VALUES ARE GIVEN IN PARENTHESES ................... 72 C. MEAN NUMBER OF SNAILS PER QUADRAT EXA- MINED BY TIDAL HEIGHT AND SEASON. STANDARD DEVIATION VALUES ARE GIVEN IN PARENTHESES ......................... 75 D. COMPARISON OF ARCSINE TRANSFORMED PERCENT COVER ESTIMATES BETWEEN LARGE (1 METER) RAKES USED OUTSIDE QUADRATS AND SMALL (15 CENTIMETER) RAKES USED WITHIN SAMPLING QUADRATS AND CAGES. STANDARD DEVIATION VALUES ARE GIVEN IN PARENTHESES ............................ 76 E. PLANT SPECIES FOUND IN THE METCALF AND SOUTH SLOUGH MARSHES. IF THE PLANT DOES NOT OCCUR AT THE SITE IT IS MARKED WITH AN ASTERISK IF IT DOES OCCUR AT THE SITE IT IS WEIGHTED AS RARE (> 1 PER- CENT COVER), COMMON (1 TO 10 PERCENT COVER) OR ABUNDANT (< 10 PERCENT COVER) ................................. 77 F, TOTAL NUMBER OF LITTORINA (L), ASSIMINEA (A) AND OVATELLA (0), FOUND IN THE FIVE EXPERIMENTAL QUADRATS LOCATED IN THE HIGH ZONE OF METCALF MARSH. IN THE EXPERIMENTAL TREATMENT THE VALUES FROM JULY 9 REPRESENT THE DENSITY PRIOR TO ANY REMOVAL AND ARE NOT INCLUDED IN THE CALCULATIONS ........................... 80 LITERATURE CITED ..................................... 81 LIST OF TABLES Table Page 1. Heights Above Datum for the Four Tidal Zones at the Metcalf Marsh Study Site ........... 25 Results of Excavation Trials in Which Field Counts of Snail Density was Compared to the Numbers Obtained by Removing the Sod and Completely Dissecting it in the Laboratory. Values are Given for Littorina (L), Assiminea (A) and Ovatella (0). Lab Counts are Shown Only When They Differed From Those Obtained in the Field .......... 31 Seasonal Climatic Averages in Coos Bay, Oregon Given in Monthly Averages. Precipitation is in Inches and Temperatures are in Celsius. Data was Compiled from United States Weather Bureau Records and the National Oceanic Data CenterOs Water Temperature Guide to the Pacific Coast of North America ......................... 32 Results of the Two-way ANOVA Comparing Tidal Heiqht and Seasonal Abundance Values for Assim~nea,Littorina and Ovatella ...... 33 Results of the ANOVAs Comparing, by Season, Arcsine Transformed Large and Small Rake Estimates of Percent Cover of Bare Space at the Metcalf Marsh and South Slough Study Sites ............................... 41 Results of the Competition Experiments Conducted at South Slough, From September 13, 1987 through October 14, 1987. Data Include the Log Transformed Mean and Standard Deviation of Lip Growth in Milli- meters, as Well as the Results of Independent Paired T-Tests performed on all possible Treatment Comparisons ........ 43 Results of the Two-Way ANOVA Comparing Mean Percent Survival in the Experimental and Control Treatments of Both the Summer and Fall Reciprocal Transplant Experiments ............................... 47 8. Results of the Field Diet Analysis (Both Tidal Heights Combined) Conducted at Metcalf Marsh in October 1987. Data Presented Includes the Percentage of Assiminea (A), Littorina (L), and Ovatella (0) which Contained the Food Item as Well as an Estimate of the Item's Total Relative Abundance. For all Three Species the Sample Size was Forty ......... 49 9. Mean Percent of Individuals in Each Quadarat Found on the Soil Surface in Both Quadrats Which Contained Only Either Native or Introduced Species (Homogeneous) and Those Which Contained Bath Native and Introduced Species (Heterogeneous) ................... 51 10. Results of the Laboratory Behavioral Trials Showing the Total Number of Individuals in Each of the Group Types Formed per Treatment. In all Treatments except Ovatella Juveniles the Number of Repli- cates was 5. In the case of Ovatella Juveniles the number of Replicates was 3. In Treatments with no number of Individuals Indicated, the Number Used was 10, and in Those Treatments With no Age Indicated, the Individuals Tested Were Adults ...... 54 11. Results of Laboratory Behavioral Trial Results Showing the Number of Individuals in Each Association Type. In Treatments With no Number of Individuals Indicated, the Number Used was 10, and With No Age Indicated, the Individuals Tested Were Adults ................................... 55 12. Results of Laboratory Behavioral Trials Showing Whether One species Contributed More Individuals to the Heterogeneous Groups Observed. Groups were Designated as to Whether They Contained more Assiminea than Ovatella (A > 0), more Ovatella than ~ssimhea(0 > A) or Equal Numbers of Both Species ( A = 0). In Treatments With no Number of Individuals Indicated, the Number was 10. An asterisk