Factors Affecting the Abundance of Paracyathus Stearns!! on Subtidal Rock Walls
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MLML / M8~RllIBR;jRY 8272 MOSS LANDING RD. MOSS LANDING, CA 95039 FACTORS AFFECTING THE ABUNDANCE OF PARACYATHUS STEARNS!! ON SUBTIDAL ROCK WALLS by Mark Pranger A thesis submitted in partial fulfillment ofthe requirements for the degree of Master ofScience in Marine Science in the School ofNatural Sciences California State University, Fresno August 1999 ACKNOWLEDGMENTS I would like to thank the members of my graduate advisory committee for their advice and guidance during this process. Dr. James Nybakken for his interest and education in invertebrate biology and for allowing me to help in the teaching of others. For the insights and humor of Dr. Mike Foster, that helped improve this study and my education. For the help of Dr. Stephen Ervin who in the last hours help me through all CSU Fresno's paper work and deadlines. I am grateful to the staff at the Pollution Studies Lab at Granite Canyon for their help during experiments and for allowing me the use of their working space. I am indebted to the staff at Moss Landing Marine Labs that kept all the equipment working and operational, and to the Dr. Earl and Ethel Myers Oceanographic and Marine Biology Trust for helping to fund this project. Most of all, thanks goes to the many students at Moss Landing. Without their help this study would not have been completed. Special thanks goes to; Mat Edwards for being a faithful dive buddy, to Torno Eguchi, Michelle White, Bryn Phillips, Cassandra Roberts, Michelle Lander, and Lara Lovera for their help on statistics and editing of early drafts, and especially to Michele Jacobi for her help in all aspects of this study and her constant encouragement for me to finish. I also would like to thank my family and friends for their love and encouragement and the joy they bring to each day. ABSTRACT FACTORS AFFECTING THE ABUNDANCE OF PARACYATHUS STEARNSII ON SUBTIDAL ROCK WALLS The distribution and abundance ofParacyathus stearnsii, a scleractinian ahermatypic solitary coral, is primarily limited to the lower edge ofrock walls and areas ofhigh sand scour on the central California coast. I attempted to determine how competition, predation, and settlement affected P. stearnsii distribution near the upper edge ofsubtidal rock walls. Survival rates ofP. stearnsii polyps were reduced when transplanted within COIynactis californica aggregations, but were not significantly different from controls. Potential predators did not consume adult P. stearnsii. Paracyathus stearnsii spawned between March and May of three consecutive years, but an insufficient number oflarvae were collected to test for settlement preferences. Biological effects examined in this study had limited influence on the adult population, suggesting patterns ofdistribution and abundance may be set in larval and juvenile stages. Mark Pranger August 1999 TABLE OF CONTENTS Page LIST OF TABLES. VI LIST OF FIGURES Vll INTRODUCTION 1 METHODS 3 Patterns ofSpatial Distribution . 3 Laboratory Competition Experiment 5 Field Competition Experiment 6 Predation Experiment 7 Reproduction/Settlement 8 Growth Rates . 9 RESULTS 11 Patterns ofSpatial Distribution . 11 Laboratory Competition Experiment 12 Field Competition Experiment 12 Predation Experiment 13 Reproduction . 13 Settlement 14 Growth Rates . 14 DISCUSSION 16 LITERATURE CITED . 22 LIST OF TABLES Table Page I. Mean abundance per zone. 11 2. Feeding test design and percentage of items at least partially eaten. 13 LIST OF FIGURES Figure Page 1. Map of study area 4 2. Percent increase in size after 6 months, based on initial surface area of top of calyx. 15 INTRODUCTION Three ahermatypic scleractinian corals and one corallimorpharian compete for resources along the coast of central California (Chadwick 1991). These species are usually separated into three horizontal zones at the upper and lower edges of subtidal rock walls (Pequegnat 1964, Morris et al. 1980, Chadwick 1987). At a site in Monterey bay, Chadwick (1991) found that the corallimorpharian Carynactis califarnica Carlgren 1936 was most abundant (53.5 % cover) near the upper edge, upper zone, where it can form large aggregations by asexual reproduction. Carynactis califarnica occurred only sporadically in the middle zone and never in the lower zone (Morris et al. 1980, Chadwick 1987, 1991, Patton et. al. 1991). The coral Astrangia lajallaensis (Durham 1947) was most abundant in the lower zone (30 % cover) where it forms encrusting colonies (Fadlallah 1982, Chadwick 1991). It was rarely found in the middle or upper zone. The cup corals Balanaphyllia elegans (Verrill 1864) and Paracyathus stearnsii (Verrill 1869) were found in all zones, but were most abundant in the lower zone (7.5 % cover for B. elegans and 0.8 % cover for P. stearnsii, Morris et al. 1980, Fadlallah 1983, Chadwick 1991). Competition among these species is thought to be one of the factors that influences the distribution and relative abundances of these species (Chadwick 1991). In field and laboratory experiments, Chadwick (1991) studied the hierarchical dominance of these species. She found that adult B. elegans suffered tissue damage from all other species, and C. califarnica killed the crawling larvae of B. elegans. Survival rates ofA. lajallaensis were reduced in the presence of C. califal7lica and P. stearnsii. In laboratory tests, P. stearnsii displaced C. 2 californica by one tentacle distance, but no tissue damage was seen on either species. Chadwick (1991) indicated that C. califomica was the dominant space competitor over B. elegans and A. lajollaensis, and co-dominant with P. stea17lsii. When C. califomica was removed from the upper zone both B. elegans and A. lajollaensis were able to survive. Chadwick (1991) therorized that C. cal!fomica's competitive dominance was the primary factor limiting the abundance of B. elegans and A. lajollaensis within the upper zone. This reasoning does not hold true for P. stea17lsii. Paracyathus steamsii's apparent ability to displace C. califo17lica should have allowed it to be equally abundant within all zones. The objective of this study was to examine factors that potentially limit the abundance of P. stea17lsii within the upper zone. Rock walls were sampled to quantify the distribution of P. steal7lsii within Stillwater cove. Laboratory and field competition experiments were conducted to test Chadwick's (1991) results of co-dominance between P. steal7lsii and C. califomica. Feeding tests were conducted to determine the effect of predation on P. steamsii distribution. Larval stages were collected to test for settlement cues or preferences. METHODS Field studies were conducted at Stillwater Cove, Pebble Beach, California (36 0 34' N, 121 0 56' W, Fig. 1). The cove opens to the southeast, which dampens storms from the north and west. The outer half of the cove contains many outcroppings of sandstone and conglomerate rock that provided vertical surfaces for field manipulations. Patterns of Spatial Distribution Sites within Stillwater Cove were chosen haphazardly to quantify the distribution and abundance of Paracyathus stem-nsii, Corynactis califomica, Balanophyllia elegans and their potential predators. A zodiac was driven seaward from Pescadero Rock (Fig_ 1) on randomly determined compass headings for random lengths of time. Divers using self-contained breathing apparatus (SCUBA) swam approximately 10 m away from the anchor line of the sampling vessel on a randomly chosen compass heading. Divers circled counterclockwise around the anchor line, and the first vertical wall greater than 5 m in height which contained P. steamsii and C. califomica was sampled. Based on pilot studies, it was determined that proximity to the upper or lower edges of rock walls had a more significant effect on the distribution and abundance of species than water depth. To compensate for this edge effect and reduce variances, all walls were divided into three zones: I) upper, 0-2 m from the upper edge; 2) middle, in between the upper and lower zones, 2-5 m in height; and 3) lower, 0-2 m from the bottom. Transect tapes were laid horizontally and vertically within each zone and four 0.25 m" quadrats were placed at random distances along the tapes. A 0.25 m" quadrat was large enough to adequately 4 ------------- ---._--_._------ .._-----------"--/ , , i . i I StilhvaterCove Carmel Bay i! 0 Sites N ** Pescadero t Rocks 5 sample P. steamsii and C. califomica (pilot study). The number of P. steamsii and B. elegans, percent cover of C. californica, depth, height from the bottom, compass heading of supporting wall, and number of potential predators were recorded for each quadrat. Percent cover was estimated from a grid of 36 fixed points within each quadrat. Potential predators were defined as animals known to eat cnidarians and other sessile invertebrates, including: Sun Stars (Pycnopodia lzeliantllOides), Masking Crabs (Loxorhynchlls crispatlls), Bat Stars (Asterina miniata), Leather Stars (Demzasterias imbricata), and Rainbow Stars (Ortlzasterias koehleri). After a site was sampled, or if no vertical wall was found, divers surfaced and a new heading and time length were chosen from that point. Percent cover data for C. califomica was arcsin transformed because of non normal distributions. Differences in mean abundances were analyzed using a two factor ANOVA (site and zone). Differences among levels were analyzed using the a posteriori Bonferoni method or two-sample t-test. Laboratory Competition Experiment To test the effect of competition for space, C. califomica and P. steamsii were transplanted into aquaria at Moss Landing Marine Laboratories, Moss Landing, California. Corynactis califomica were transported on small pieces of shell or debris, whereas P. steamsii were chipped off rocks using a knife. Species were held in separate aquaria supplied with filtered seawater until needed. Small pieces of shell containing a single polyp of C. californica were glued to glass slides and distributed among four trays with flowing seawater. Paracyathus steamsii polyps were glued directly to glass slides and randomly placed among the C. californica polyps. Six polyps from each species were placed randomly in two rows within each tray.