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FORAGING BEHAVIOR OF THE LEATHER SEASTAR, DERMASTERIAS IMERICATA (GRUBE), IN MONTEREY BAY, CALIFORNIA A Thesis Presented to the Faculty of the Department of Biology San Jose State University In Partial Satisfaction of the Requirements for the Degree of MASTERS OF ARTS by Cynthia Ann Annett August 1982 ABSTRACT.-Foraging behavior and prey choice of masterias imbricata, from 1979 to 1981. revealed a which leather sea star, De~- investigated in the Monterey Bay area, California were stomach content analysis of diet the consisted mainly of 290 free-ranging leather stars the corallimorphian anemone, Corynactis californica. A survey of potential prey at the Monterey Coast Guard Breakwater showed that californica is the only locally abundant anemone C• which occurs in the same depth range as was found in presented found within the with a choice between c. californica regardless of previous diet. study site. However, cali£ornica and Anthopleura elegan tissima in the lab, 23 leather stars initiated first, corynactis 2 2 85% of 52 randomly placed 1/4 m quadrats and 96% of 45 1/4 m quadrats placed around D. imbricata when £. imbricata. feeding on A. elegantissima Leather stars also initiated feeding on Anthopleura xanthogrammica first when given a choice between ~. and elegantiss~a, C. californica. In single prey presentations, A. xanthogrammica xanthogrammica, and Metridium senile were all taken readily within the ~. first day; in contrast leather stars presented with C. californica initially avoided this species and 40% did not feed within 3 days. individual prey behavior~ The effects of species and differences, nematocyst sizes, and prey abundance on leather star foraging behavior are discussed. 3 LIST OF TABLES TABLE 1. Summary of prey reported in the diets of D. imbricata in the field 2. Description of ~. eleqantissima £. californica experiments 3. Number of C. caJ.ifornica found under everted stomachs of feeding Q. imbricata ~ imbricata intiating feeding on each prey species 7 16 22 4. Number of 26 5. Previous diet and subsequent prey choice of ~. imbricata when presented with £. californica and !. eleqantiss~ simultaneously 28 6. Number of anemones consumed in the laboratory during three sets of three day observation periods 7. Number of ~. imbricata initiating feeding on anemones when presented with !. xanthoqrammica and f. californica simultaneously 8. Summary of anemone behavior observed during contact with D. imbricata in the lab 30 32 36 4 LIST OF FIGURES FIGURE 1. Map of the Monterey study areas Peninsu~a and 2. Identification photograph of D. 10 ~ricata 3. Laboratory Set up 4.Prey taken by Q. 13 15 :in the fieJ.d 20 5. Percent cover of C. californica at the breakwater 25 6. Time to initiation of feeding for Q. 33 ~ricata ~ricata presented with single prey species of D. irritation 7. Reaction ~ricata to mechanical 40 5 ACKNOWLEDGMENTS I am grateful to the many persons who contributed their help to the cessful completion of this University of California Long space, without which this project. Marine project Dr. John Pearse and the staff of the Laboratory provided extensive and field work. lab the throughout Moss Landing aquaria my committee Shilo Drs. and I give my Etter, Barbara Marine Lab divers who painfully endured the Dr. Raymond Pierotti provided comments, discussions, text editing, assistance, research. on discussion and help in editing the manuscript. heart-felt thanks to my diving buddies, Ken Nicholson, Pierson, valuable could not have been accomplished. James Nybakken, John Pearse, and Michael Foster served provided SllC and emotional support which were invaluable I would like to thank my parents my studies. for thro~ghout encouragement "and My thanks to Lyn McMasters who prepared the tiona in this manuscript. Finally Dr. Ann Hurley, whose this guidance i~lustra encouragement and advice helped me to begin this project. This investigation was partially funded by a grant Lucille Packard Foundation. from the David and 6 INTRODUCTION The biology of the leather Asteroidea, order star, Spinulosida), has Dermasterias imbricata mode. emphasize three main 1857 i not been extensively studied. researchers have reported dietary information for D. imbricata. reports (Grube Several All of these characteristics of the leather star's feeding First, leather stars are capable of feeding on a variety of prey. Mauzey et al(1968) report a diet consisting of at least 15 spp. in three phyla and Rosenthal and Chess(1972) list at Second, despite thi.s varied 13 prey spp. in five phyla. diet, most leathar stars in any given area are found to be feeding on only one or leather least two prey species (Table 1). Pinally, stars feed a1most exclusively on sedentary or sessile prey, mainly in the phyla Cnidaria and Echinodermata, especially those wh~ch occur in high densities. From this information, it is unclear whether D. preference in the type of prey taken. imbricata exhibits any In any given area, leather stars may be characterized as local specialists (Fox and Morrow 198~). In fact, leather stars may be specializing more on a limited number of prey types (e.g. sessile or sedentary, dense, aggregating, etc.) rather than a limited number species. prey However, even amongst closely related prey species there may be sub tle di£ferences in behavior included of in which determine whether the species will be or excluded from the diet of the predator (see Moitoza and Phil lips 1979 for a pertinent example). My study of the predatory behavior parts. of D. imbricata consisted of two First, I conducted an investigation of the diet of the leather star in an area not previously investigated (central California). Second, a series investigations into the feeding of behavior of D. imbricata in the laboratory Table 1: Summary of pre:' renorted in the diet of D. imbricata in the field. ~---'""d ---~ ~O~ p.> "1 II :::dO Woo:J -.....JCDC't ~:J * CD '0 '~ + + • o + 11 II II II t-j () <l> :s 'l(J1I\)OcT mO(J1· P> 1 I (J1OQ ...... .....:J (J1 I CD , OU"10f\) Oc:R~mo ~ ~t-I) H) CD (1) ~O C MN p.> CDQ'Q ~Ul 3: P> UlP' N (1)'-4 e: CD (1) ~ cJ :s C C"tt-t ~ CD ~ U2 ~ ~ CD ::r: CD I-' <.OH ::rO 3 ~p.> $l) :s ~ 0 ::r (1) rn rn ct'CD ~ S»Q. ...... cT Pl :1 f-' <.0 Q) CD CO t-j ct> ~c"t ~ ~ M 0 rt ~ J-I ::s It I-' 0 ......., f\) '--' 0 0 ........, * ..... 0. •• :s I-' f\) ~ J-I 0 ~ ::1 :s 'l rt '--' c.o 0.. C o.:s '--' II t-j () t-J :s J--ooJ 0 o c: CD 0 W Q') Ul (l) to '-J Q.. ~~ J--ooJUl p.l 0 :s :sIt to ..... OQ J-I •• P> ...... tde: '-JC12 '..:I ..... ..... 0') ~~ II :s OQ . It:j ..... 0 C1 '1 0 Leucilla nuttingi 3 0 unidentified sponge }-Ie 0 P' Abietinaria spp. 0 nP' + + 0 + 0 0 0 Ptilosarcus gurneyi Eoiactis orolifera • A. ele gantissima A. xanthogramrnica 0 tolj 0 M. senile 0 ::0 t'1j to< Tealia sp. 0 0 0 Tealia coriacea en t-tJ t:J:j Q H t:tj Q 0 Tonicella lineata 0 Mopalia sp_ Q Balanus carioslls + Cue umaria lubrica 0 Psolus sp. + 0 Astrornetis sertulifera • s. 0 '~ 0 • 0 purpuratus unidentified urochodat detritus en 8 were conducted. The lab studies focused on the interaction between cata and various species were examined in detail: of anemone prey. various species of prey. 2) imbri Two aspects of this interaction 1) The effect of recent experience of on subsequent prey choice, and D. the predator the behavioral responses of the predator and 9 METHODS AND MATERIALS study Site Description Observations on predator-prey interactions, distributions of D. imbricata and their prey, and stomach contents of D. imbricata were made at two major sites, the Monterey Coast Guard Breakwater (1210 53'N, 360 36' W) and Stillwa ter Cove in Carmel (121° 57'N, 36° 34' W). Incidental observations were made in several additional areas, including Cannery Row in Monterey, the Hopkins Marine Life Refuge in Pacific Grove, and the Carmel River Beach (Figure 1). Twenty hours of underwater observations were conducted using at gear the Monterey Coast Guard Breakwater (henceforth referred to as "the break water") between September and December 1981. half way The main study area was located along the breakwater on the seaward side (Figure 1) and was identi fied on the surface from landmarks on the breakwater itself. was SCUBA The study area a loosely defined 50 meter area extending from the surface to the base of the rocks at about 10 meters depth where the boulders and cobbles ended in a sand plain. Fifteen hours of underwater observations Cove between April and July of the cliffs in Stillwater Dermasterias imbricata were found in three (2 to ~). the 10 Each of these areas were characterized by either meters in height) or large boulders, and were strictly subtidal. Dermasterias imbricata were relatively rare in other of the cove. in cove, and 3) at the base of a washrock located at the seaward edge of the cove (Figure vertical conducted 1) Arrowhead Point, 2) on a large table mount areas within the cove: center ~980. were areas Figure 1: Map of the Monterey Peninsula showing the location of the study areas. II stomach Contents Survey In order to determine the prey species consumed by Q. imbricata in the area the stomach contents of leather stars found in my study areas were examined. ~l D. Imbricata found during an extensive search of the study Monterey areas were checked for prey. If the leather star's stomach was was usually the case) the stomach and substratum directly below checked for the presence of partially digested prey. were eve~ed the (as stomach If the stomach was not everted, I forced the stomach and any prey out through the mouth by gently pressing on the aboral surface near the anus. found, as well as the size and location of the The identity of any prey so leather star, were then recorded on a plastic slate. Prey Distribution The percent cover of subtidal anemones was estimated at the breakwater in order to stars. determine the type and abundance of prey available to the leather The percent cover of anemones occurring in 1/4 square quadrats was visually estimated and recorded on plastic slates. were placed in one of two ways, either randomly or around D. locations of random~y random distance along a horizont~ vertica~ study area. Quadrats placed around leather ~uminum The quadrats imbricata. The placed quadrats were determined by placing them at ran domly chosen distances along a a meter star was in the center. D. meter tape which had been placed at meter tape located at the center of the imbricata were placed Quadrats were placed around found within the study area during one day of diving. ~l so that the D. imbricata Individual }~rking and J.2 ~easurement Organisms were brought into the laboratory for more detailed observa A total of 46 Q. imbricata (Appendix I) were collected from the break tions. water and kept in aquaria at the University of California Joseph the aboral surface from the center of the disc to the end of each was then photographed and (1972) leather star. length of Each was modified from Rosenthal and of attaching small colored plastic beads to the A heavy duty embroidery needle was used to a insert short 12 lb. test monofilament fishing line under the epidermis near the madreporite. ously consisted arm. (Figure 2) and tagged for identification. The method used for tagging leather stars Chess Long The leather stars were measured with a flexible meter tape along Laboratory. individual M. The colored fishi~g small line was then tied in a loop near the base and vari plastic craft beads were held in place by a second beads were strung on the two ends. kno.~ tied in the end of the line. The In this way, the leather stars were individually identified by their unique color combination (see Figure 2 for an example). the leather stars in any way. I These tags did not appear to never found any wounds around the tags, any obvious changes in the leather stars' behavior, or any behavioral between tagged leather harm differences stars and the five individually recognizable leather stars used as controls. Anemone prey were collected at several with Corynactis californica locations. Small rocks covered were collected at the breakwater (Appendix II). Anthopleura elegantissima were collected from the Moss Landing Harbor, Terrace Point ( Santa Cruz) , and Davenport Landing (Santa Cruz County). xanthogrammica were collected off mussels gathered Cruz County). at Panther Anthopleura Beach (santa Metridium senile were obtained from a holding tank and had been kept in the lab for an unknown period of time. The oral disc diameters of all anemones except ured. Because were measured. of the large number £. The oral disc diameters f. californica were meas californica used, only 40 individuals (exclusive of tentacles) of fUlly expanded anemones were measured underwater with a small plastic ruler. elegantissima, A. xanthogrammica, and by a number floor. ~l written a with ~. senile were individually All A. identified grease pencil near their bases on the aquaria c. californica on each rock were counted at the beginning and end of each experiment. Individual rocks were identified by numbered plastic tags attached by a short length of monofilament. The wet weight for six six groups biomasses. ~. elegantissima (1.0 em oral disc diameter) and of five C. californica were measured as an indication of relative Anemones were carefully removed from rocks and scraped clean of all adhering debris, then blotted dry before weighing. Laboratory Observations To determine behavior, D. the effects imbricata were of recent dietary experience on feeding kept in the lab for two weeks and then divided into three groups maintained on restricted diets before experiments were ducted. Indiv~dua~s was placed in a tained were c~rcular random~y ~~ocated tank (1.5 meter diameter by 60 em on a diet of chopped bait squid. depth) One group and This group of leather stars referred to as "squid tank") were kept away from all anemones for six weeks. The other two groups, consisting of seven leather stars each, put main Approximately 500 grams of squid was placed in the bottom of the tank every week. (henceforth into the treatments. con were in each half of another circular tank which had been divided with a plas tic screen (Figure 3a). The leather stars in one half of this tank were main Figure 3: Laboratory set up. A. Anthopleura and Corynactis tank. Note the plastic screen in the center which acted as a divider. B. Water table containinq C. californica and A. eleqantissima. c.~ Divided water table used for con~rolled prey presentations. 15 tained on tank n while the leather stars in ), a elegantissima diet of C. californica (henceforth referred to as "corynactis (henceforth the referred other to as half were maintained "Anthopleura tank"). on A. Both the anemone and squid tank were provided with flowing coarsely filtered sea water c. at 15° After being kept in the circular tanks on restricted diets for six weeks, 24 imbricata were used in a series of experiments on prey choice. D. these leather stars had been collected at the same time same manner. and treated All of in the Dermasterias imbricata used in later experiments were collected at different times and maintained on sqUid diets for one to two weeks prior to to experimental observations (Appendices I and III). Prey choice experiments were conducted in a water table (2m x ~ x 20 em deep) equipped with running sea water and a constant light cycle (12 hrs light 12 hrs dark; Figure 3b). A. elegantissima as Three replicates were run using C. prey (Table 2). In each exper~ent, californica and leather stars were chosen from the circular tanks by assigning a random number to each individual and allocating table. them according to the listing obtained from a random numbers A similar technique was used to allocate individuals to rando~y chosen parts of the water table at the beginning of each experiment. Observations were made continuously for experiment and first two hours of each then for at least one hour a day until the termination of the experiment. Since the leather stars usually feeding inactivity or the after the settled into long periods of first two hours, constant observation was deemed unnecessary, and instead the position and actiVity of all leather stars and prey were recorded at one to twelve hour intervals throughout the experi ments. In total 25 hours of continuous observation and 28 periodic checks Table 2: Description of ~.elegantissima/f. californica choice experiments Experiment # 2a 21:> 10/25/81-10/30/81 10/31/81-11/3/81 1 date 10/14/81-10/16/81 number of leather stars diet) diet) 15 (12 from #2a 3 from squid tank) X radius 9.52 em (sd=1.S4cm) 9.22 em (sd=1.26cm) (sd=1.13cm) number of A. elegantissima 21 39 26 X oral disc diameter 1.9 em (sd=1.14 em) 2.1 (sd=O.78 em) 3.0 em (sd=O.71 em) number of californica 863 on 12 rocks 586 on 10 rocks 696 on 12 rocks X oral disc 0.55 em (sd=O.22) 0.55(sd=O.22 em) 0.55 (sd=O.22 em) 9 (3 from each 12 (4 from each 9.23 em c. 1.7 were made during the I I days of these experiments. Further experiments on predator-prey interactions were conducted on Q. imbricata presented with a variety of anemone prey. lated vations the water table was f~erglass inserting screen (Figure 3C). allowed to divided p~itions or interact Small M. senile (X-l.8 em sd=1.15 em) dividing 30 cm 2 elegantissima, either~. either sd~O.27 alone comp~ments comp~ment comp~ment. ~. by and The prey xanthogrammica, M. or in combination (Appendix III). em) and small A. xanthogrammica (X-1..94 em were used so that their size range was similar to that of the A. elegantissima used in the experiments (x-2 ..5 em sd-l.23 em). the For these obser these with strips of plastic with and feed on the prey in the californica, C. and fifteen One D. imbricata was introduced into each used in these experiments were senile into iso activity of the Observations on leather stars were made at five to lS minute intervals from the time the leather star was introduced until until three hours elapsed. it settled on prey or Periodic checks were made at one to 12 hour inter vals from this time until the termination of the experiment. Mechanical Irritation To determine the effects of tocysts) on to pinching mechanica~ irritation (e.g. stinging by nema the behavior of the leather stars the reactions of leather stars were observed. Individua~s were placed in a plastic screen box which was carefully rotated so that they were suspended upside down on the top and I was able to view their oral surfaces while pinching them with metal for ceps ( similar to Barnes et al 1970). One tube foot on each arm was pinched. Then a piece of squid was placed on the screen near the mouth, and the leather stars were allowed to evert their stomachs on the squid. At this time the tube 18 feet were again pinched, as well as the stomach lobes. dermis and In addition, the epi dermal papillae of leather stars in the squid tank which were not used in feeding experiments were pinched. 19 RESULTS stomach Contents of Dermasterias in the field A total of 109 different leather stars were examined at and 134 different leather stars at the breakwater. at each location. cora~limorphian The most commonly taken prey Stillwater Of these, 66% were feeding at both corynactis californica (Figure 4). locations feeding on C. californica. ~. (~, too far. prey item. determine the californica leave no hard parts) a rough estimate can be calculated from the few stomachs in which progressed the imbricata examined at Stillwater Cove were Although it was often difficult to number of anemones in the stomach was At the breakwater, 84% of the 92 feeding leather stars contained C. californica as the main Similarly, 62% of the 73 feeding Cove The median number of C. digestion had not californica eaten per D. imbri cata was 10 at the breakwater (range - 5-44) and 5.5 at stillwater cove (range = (Table 1-22) 3). This difference in meal size may be due in part to the smaller size of the leather stars at Stillwater Cove and to the lower density of C. californica (pers. obs.). A number of other prey species were At the breakwater the D. imbricata ate A. a~so taken at each site elegantiss~a (Figure (5\ of observations), hydroids (3% of observations), bryozoans (3% of observations), and ous A. items such as crab molts or barnacles (totaling 4\ This clone was located on the top of a boulder in a area and had five leather stars feeding within it. mainly Aglaophenia sp. and Abietinaria ap. miscel~ane of observations). The elegantissima were all in the same c10ne found just outside study area. 4). of the main very shallow The hydroids consumed were These hydroids were found as the main prey in a few stomachs. in the However, they were also found in small of many of the leather stars that were eating stomachs amounts califor ~. nica. Since these hydroids grew in amongst the f. eaten exclusively, and made up a very small percentage of the biomass of prey in the stomachs, californica, seldom were they were not considered an important prey item. The bryo zoans consumed were mainly epiphytic on red algae. Minor prey species consumed at Stillwater Cove were basically similar but showed a few important differences. of the washrock fed mainly on centrotus purpuratus). f. These Dermasterias imbricata found at the base californica and purple urchins were trapped in sions, preventing their escape from the leather stars. of the washrock urchins (Strongylo sh~low rock depres On the shoreward side at a depth of 15 meters the depressions (approx±Mately 3 em deep and 5 em across) are so numerous that they cover the bottom, found feeding edge to edge. Leather stars at Stillwater Cove were also on bryozoans of observations), the sponge Tethya aurantia (5% of observations), arti (10% culated coralline algae (14% of observations), chitons (1% of observations), and miscellaneous items such as crab claws and dead scyphozoan medusae (total ing 4% of observations). Several dives were made during the fall of 1979 and early in number of different locations to compare the diet of D. Monterey Peninsula. found feeding on f. During september ~979, twenty of californica on large rocks off 2~ ~ricata leather f. californica, the rest were not feeding. found three leather stars feeding on C. at a around the stars were Cannery Row in Monterey. One of seven leather stars examined at Carmel River Beach in was feeding on 1980 californica A at November, ~979, few days later, I the washrock in Table 3: Number of C. californica under the everted stomachs of feeding Q. imbricata Monterey Coast Guard Breakwater radius of longest arm (em) number of £. californica in stomach 6 5 8 6 9 10 10 10 10 25 10 44 stillwater Cove radius of longest arm (em) ~ number of C. californica in stomach 4 1 6 4 6 5 6 6 6 7 7 l. 7 5 7 ~2 9 6 10 1.2 23 stillwater Cove (2~ meters depth) and one which was not feeding. In January, 1980, I made another dive at the breakwater and found imbricata feeding on £. californica and one not feeding. made two dives in the Hopkins Marine Life Refuge in stars are rare l~ During May, 2980, Pacific Grove. D. I Leather in this area, and I was only able to find four D. imbricata. These were at the base of a large rock covered with C. but were interacting with ca~ifornica, not feeding. Behavioral Observations in the Field Dermasterias imbricata were observed prey on several occasions. approaching Three leather stars were seen moving away from partially digested C. californica at the breakwater. stars and Each was lifting at least one arm away from neighboring £. had attached extruded mesenterial filaments to the leather face. I group of its c. also observed a of these californica which stars' oral sur leather star at Stillwater Cove approach a small f. californica, contact the tentacles of the anemones, arm leather rapidly lif~ and change directions, thereby avoiding any further contact with the californica. The solitary coral, Balanophyllia elegans, response in leather stars in the field. stars encounter arms and ~. alter also elicited elegans at the washrock, and each time quickly their avoidance On two occasions I observed leather movements to leave the area. ~so, imbricata in areas of high coral abundance and did not find corals. an lift their I seldom found D. them feeding on On four occasions when I surveyed the distr1bution of D. imbricata at the table mount in stillwater Cove I found only one or two leather the on the upper three lower three meters of the vertical face, but 20-~8 stars on 24 meters. Those leather stars on the upper portion were feeding mainly on C. californica which were absent from the lower portion. few encounters between Q. imbricata and purple urchins were observed at A the washrock. diameter urchin. 5 . J. em humped imbricata unsuccessfully attack a The leather star climbed on top the of urchin and up the center of its body so that it could surround the urchin without touching it. its I watched a 12 em radius D. spines During five minutes of observation I watched the urchin and repeatedly leather star's oral surface. stomach and withdrew reach out with its pedicellaria and pinch the The leather star did not attempt without feeding. flatten to evert its I found several D. imbricata in this area with detached urchin pedicellaria attached to their oral surfaces, indi eating that encounters with urchins may be fairly common. Size Distribution of Dermasterias The leather stars examined at the breakwater than those at stillwater Cove t-test). (p=O.OO~i were significantly The mean length of the long est arm of 60 leather stars measured at the breakwater was em) with a range of 3.3-12.5 em. 8 . 75 em em). However, the range ( sd=-~. 52 In contrast, the mean arm length of the longest arm of 45 leather stars measured in Stillwater Cove was only (sd~1.98 larger in sizes was s~lar 6.91 em to the breakwater leather stars (4.0-13.0 em). Prey Distribution Corynactis californica was the only commonly found both .. study • 1 p~acea ~ areas. subtidal anemone corynactis californica occurred in 44 of the 52 m-? quadrats at the breakwater (Figure 5). Almost half (21 in rando~y 25 quadrats) of these had over 25% cover. not found in any of the quadrats. The A. at By comparison, elegantiss~a elegantissima were ~. in the intertidal zone the breakwater usually occurred on the flat tops of boulders and were spa tially separated from the C. californica, which generally were found on verti cal surfaces, by a band of barren rock, green algae, and barnacles. Several large (at least lS em oral disc diameter) A. xanthogrammica were found in study the area only but were not found in quadrats. anemones found in the the Corynactis californica were also quadrats placed around D. Corynactis californica were found in 43 of 45 of these quadrats. per cent cover of C. californica in these quadrats did not imbricata. .However, the differ signifi cantly from the randomly placed quadrats. Corynactis californica were also the Stillwater Cove. Large most commonly found anemones elegans However, £. imbricata stomachs . Solitary corals ( Balanophyllia and paraeyathis stearnsi) were also found in small numbers within the study areas. and Cove. generally larger than 10 em oral disc diameter and were were not found as prey in only Only a few P. stearnsi were found in quadrats at the breakwater, one small group of ~. elegans were found near the study area. contrast, B. elegans were more common in the Stillwater Cove study areas, usually in A. xanthgrammica were found subtida.l.ly at Arrowhead Point, and Tealia spp. were found at all sites in Stillwater these anemones on lower portions of the rock walls than ·were occupied by ~. In but imbri cata. Feeding Behavior and Prey Choice in the Laboratory When given a choice between two or more species of anemones in the leather stars consistently chose certain species over others. the lab, When the 27 choice was between A. elegantissima and and f. Q. 2b) 22 of 23 f. californica imbricata initiated feeding on (experiments ~. elegantissima, none on californica, and one did not feed in 72 hours (Table 4). as elegantiss~a the first prey The choice of and Corynactis separated from the on a diet of ~. tanks). diets (squid, It is obvious from the data that being elegantissima for six weeks and having squid A. consumed was consistent between the three groups of leather stars which had been maintained on different Anthopleura, 2a, 1, been maintained or C. californica did not alter the prey choice of the leather stars (Table 5). After settling on and consuming their first prey item, most of remained in the same area feeding on neighboring anemones. imbricata the D. I care fully mapped the movements of the leather stars in the second experiment and checked their stomach contents on the second day (Appendix IV b). 12 leather stars observed, seven fed on A. elegantissima together. These leather stars ate two to five A. on A. elegantissima and then on neighboring contac~ imbricata had been in tiss~a ing on f. californica. from elegantiss~a first ~. other anemones. table, Three £. leather ~. californica. this latter fed These D. !. elegan elegantissma before initiating feed elegantiss~a which were Both of these leather stars consumed the A. and then moved to another part of the water table, elegantiss~a grouped stars californica while feeding on Two D. imbricata fed on A. which they encountered. feed during these observations. water c. and did not contact any other isolated the with were Of 'the elegantissima in succession before moving to another part of the water table. first which (2a) settling One leather star did not Por the first day, after being placed in leather star encountered only other D. imbricata already settled on prey. on f. It then moved to the californica or the corner of 29 the table near the drain and ceased moving for the rest of the experi water ment. The high rate of feeding by the D. obvious from data elegantissima and C. on number of ca~ifornica, imbricata prey consumed. A. elegantissima is When given a choice of A. the D. imbricata consumed all available and very few of the C. tiss~a on A. californica (Table 6). elegan Many of the leather stars fed on more than one A. elegantissima at the same time (Appendix IVb). The feeding rate of the D. imbricata was consistently low for nica ( 0 . 27-0 . 33 anemones/leather star/day). the size and density of the C. imbricata in more Meal sizes at a time. In the lab, they typically ate However, in the lab, no more than 14 £. The diameter=O.55 em, 9 A. wet weight of a single s.d.=O.22 s.d.=O.059). size class of s.d. s O.09). average em) ~. C. cali. only necessarily c. californica (x oral disc 0.03 g (x of six groups of In contrast, the average wet weight of the smallest elegantissima A large was five elegantissima, (Table 2) and so a meal of the same number of individuals from each species is not five~O.166, D. ca.lifornica were Also, the size range of the was much smaller than that of the A. equival~nt. of the field indicate that leather stars are capable of feeding on consumed during a three day interval. fornica califor This is especially evident when californica is considered. as many as 44 anemones in a single meal. or f. was elegantiss~a 0.47 9 (l.O em diameter, x-O.47 9 can weigh much more than this (51 and 67 for two 6.0 em diameter individuals). The feeding rate of D. imbricata on and O. 97 anemones per star per day. ~. elegantissima varied between 0.48 The variability is due in part to the differences in the number of anemones available in relation to the number of D. imbricata in the water table, and differences in the sizes of A. to elegantissima used (Table 2). When given a choice between A. xanthogrammica results were similar. Eight none on C. californica. tained a on diet of D. ~ricata Of these eight f. and C. californica settled on A. xanthogrammica and Q. imbricata, three had elegantissima, and two on a diet of nothing but over (Appendix III). Since weeks from which these had not been main californica, three had been maintained on a diet of squid and then A. four ~. squid encountered this species this, all eight settled on A. for xanthogrammica is rare in the area imbricata had been collected, i t is very likely that ~. the in the field before collection. xanthogrammica during the first day, they Despite seven of these settled within the first hour (Table 7). When presented with A. xanthogrammica, three californica, and ~. senile, all O. imbricata settled on the A. xanthogrammica rather than the other two species. ments £. These D. because ~ricata they differed from the others used in previous experi were collected from Arrowhead Point in Stillwater Cove a week before this experiment was conducted. However, their behavior was ident ical to the sea stars collected from the breakwater. For a week chitons (Mopalia mucosa) and snails also added to aquaria containing 14 O. ~ricata. (Calliostoma No D. spp.) ~ricata were were ever observed attempting to feed on any of these molluscs. When individuals were introduced into compartments containing only a sin gle species of anemone the behavior of the D. depending on the species of anemone prey. tissima, M. senile, and ~ricata varied considerably All sea stars settled on ~. elegan A. xanthogrammica shortly after encountering these species (Figure 6). The median time to the initiation of feeding for five D. 34 imbricata fed M. senile was 60 xanthogrammica was under 60 minutes leather stars. The median time minutes (range=15-120 minutes) and for (range~60 to first imbricata fed A. elegantissima was higher minutes-120 minutes) for ~. six settlement on prey for five Q. (median a 120 minutes; range~15-480 minutes) . This is similar to the length of time to the initiation of feeding of the seven imbricata D. originally introduced to the Anthopleura tank. Five of these D. imbricata settled on A. elegantissima in the circular tank within the first hour, and all seven began feeding on A. elegantiss~a during the first 12 hours. This behavior differed from that of D. imbricata presented with fornica as the only available prey (Figure 6). f. cali The median time to first set tlement on prey for six of ten leather stars presented with C. ca2ifornica was 48 hours with a range of 10-72 hours. Pour D. imbricata did not settle in three days and so were not included in these calculations. The D. imbricata in these experiments usually moved around the compartment several t1mes, often encountering the c. californica and obviously avoiding any prolonged contact with them. The behavior of the seven D. imbricata Corynactis tank was essentially the same. origina~ly introduced C. californica for four weeks of observation. were consistently found on the walls of the When tank, These three D. away from placed on the bottom, each one climbed back up on the tling on prey. the No leather star settled on C. cali fornica during the first day and three of the seven were not observed on into the wa~ls feeding imbricata anemones. without set 35 Predator-Prey Interactions in the Laboratory The defense behaviors used by each species of anemone differed in several aspects. The most obvious differences were in senile, which is the only species tested that has these use of mesenterial filaments by c. californica. ~. the use of acontia by structures, and the other observed differences in response included whether anemones retracted their tentacles or remained expanded, and whether anemones released from the substratum after contact with D. imbricata (Table 8). I observed four attacks by the senile M. retracted £. their imbricata on M. senile. tentacles columns as the D. imbricata began to attacks, the D. settle and On each occasion extruded acontia from their on them. In three of these imbricata touched the anemone's tentacles first, lifted their arms up, and then proceeded forward with raised arms and settled. contac~ fourth attack, the leather star tolerated prolonged In the with the tentacles before settling on the anemone (at which time the anemone retracted its tenta cles). Leather stars were never observed to avoid Twenty-eight of 32 ~. contac~ with the acontia. xanthogrammica were seen to contract by leather stars, while only four remained expanded. when touched The leather stars almost always settled on !. xanthogrammica shortly after first encountering them. eight the occasions leather star moved directly on top of the anemones, and only four of the 12 observed from the On £. imbricata were seen to lift their arms up away anemones before settling. substratum after being touched by a Pour A. leather xanthogrammica-~ star and released from the floated upside down tentacles when because of their inflated bases. Anthropleura elegantissima touched and often remained did not always retract their expanded for several hours while underneath the 37 .. stars, which were settled on neighboring anemones. tissima were observed to On 15 occasions A. elegan remain expanded after being attacked by a leather star, and several remained open for an hour or more after On seven occasions the A. elegantissima retracted being their settled on. tentacles when touched. Q. Eight imbricata were observed elegantissima without settling, encountering the anemone. to while move away after encountering A. 16 were seen to settle minutes after The anemones which were successful in repelling attacks usually remained open and were able to touch the leather stars' aboral surface with their tentacles. leather disc fashion. leather caused the rapid contraction of the stars' dermal papillae and often the withdrawal of the leather stars' arm from contact. oral This One!. elegantissima which was exceptionally large (9. 0 diameter) was particularly successful at avoiding attack in this On numerous occasions over a two month stars to contact surface by the anemone, ClI\ period I observed various the base of this anemone, get stung on the aboral and withdraw without settling. The anemone was finally eaten by a leather star which approached it from above by moving off a neighboring rock and on top of the anemone. several centimeters above the The leather star was suspended floor for several minutes before the anemone contracted its body. When I examined the stomach contents of the leather stars at the experiments I often star (Appendix IV). the substratum and found two or more A. Usua~ly been of elegantissima in a single leather one or more of these had apparently released from carried away by the leather star. digested anemones were covered in mucus and often had an ynx. end These partially everted actinophar 38 The greatest number of encounters observed were between D. c. californica. This resulted because c. During one experiment, I placed four A. patches of C. californica imbricata and californica were often encountered elegantissima on rocks within and allowed them to attach to the rock. These A. elegantissima were the last to be ea~en by leather stars. However, these were eaten before the C. californica. On six different occasions I saw leather stars lift their arms away c. californica which had extruded mesenterial filaments. appeared to penetrate the epidermis and remained attached moved. from These filaments when the arm was In each case the leather star had been feeding on neighboring anemones for several hours. On only one occasion did I observe a leather elegantissima and C. californica simultaneously star to contact both A. and then settle on the C. 39 . . r californica. feeding on This leather star had recently a neighboring~. elegantissima. consumed C. californica while Ten leather stars settled on A. elegantissima after encountering both species simultaneously and two others moved away without settling. Response to Mechanical Irritation When the dermal papillae were pinched, five ~ediately out of five D. imbricata withdrew patches of dermal papillae directly around the area that was stimulated. This was similar to the response seen in D. imbricata con tacted on the dermal papillae by other sea stars or by anemones. When a single tube foot was pinched on the leading arm of moving stars in the holding tank, two ... £. leather imbricata lifted their arms off the substra tum and one continued moving without lifting the arm. When a tube foot was pinched on each arm within of the screen cage, four responses were noted. non-feeding D. imbricata Three of the nine leather stars lifted one or two arms off the substratum away from the source of tation. irri Three leather stars did not move their arms but instead retracted all of the tube feet on the arm and closed the opening to the ambulacral groove so that no tube feet were exposed (Figure 7). of these three, two exhibited this reaction with only one of their five arms, and one exh~ited the reaction with two of their five arms. Seven D. imbricata withdrew the tube feet tube foot that arms, adjacent to the was pinched, but did not retract the tube feet on the arm on either side of the irritation. '~ ~ediately Of these, one exhibited this reaction on three three on four arms, and three on all five arms. to react to this pinching. No leather star failed In comparison, after the stomach was everted over squid, only one leather star retracted all of the tube feet on the arm, and then only responded this way with one of its five arms. However, seven of the nine D. imbricata retracted tube feet in the local area of irritation. When the stomach lobes' were pinched, four D. imbricata withdrew the at least partially, while five gave no response at all. dermis was pinched, none of the D. is significant lobe When the aboral epi imbricata gave a noticeable response. that none of the nine It Q. imbricata moved away from the squid, even when the tube feet or stomach was pinched. The reaction instead was to retract the irritated body parts and continue feeding. Another interesting observation was that five of the nine which .. s~ilar anemones. These to that observed in leather stars Q. imbricata feeding retracted the food. After a a body parts in urchins and cavity was formed period of five to 15 minutes, the leather stars everted their stomachs so that the stomach lobes filled the only on the tube feet located around the mouth, and elevated the center of their bodies so that the imbricata were fed squid in this experiment humped their bodies up over the squid in a manner around D. contac~ cavity and were with the food. Also, the tube feet were never used to manipulate the stomach lobes. 42 DISCUSSION Two major patterns are evident from the data. First, Q. non-random a which does not appear to be dependent solely on prey availa diet The consistently low preference for f. californica as compare to bility. other imbricata has anemones indicates food items by the ~. the all anemones are not perceived as equivalent that Second, Q. imbricata react in consistent imbricata. and obviously different ways depending on the species of prey encountered. The non-random diet observed in the laboratory appears to interpret in relation to the feeding data from the field (Figure 4). There is an obvious inconsistency between the high frequency of feeding on C. califor nica observed at the breakwater, Stillwater Cove, and other areas around the Monterey Bay, and the hesitancy of D. imbricata to feed on C. ,.., difficult the (Tables lab 4, 5 and 7 and Figure 6). not (e.g. ~. commonly found in of anemones habitats where they occur in central light ~970, Porter 1972, ~974, Ormond et al 1973, 1976, Using caging and transplantation that A. elegantiss~a interpreted exper~ents, Col~ins Sebens et a~ ~970, 1974). (~977) demonstrated are capable of surviving in the subtidal zone if they are protected from predation. to C~ifornia of studies by Sebens (1977,1981) on Anthopleura sp. and by a number of researchers on Acanthaster planci-coral interactions (Barnes Vine which elegantiss~a). These inconsistancies are only apparent, however, and can be in in It also appears unusual that D. imbricata preferentially feed on species and size classes are californica However, when leather stars were allowed access the transplants, either because they were introduced into the cages or the transplants were not caged, the leather stars rapidly consumed tissima. In addition, Sebens found D. the~. elegan imbricata feeding on A. elegantissima 43 on the lower edges of the anemone clones in his study areas. tions led Sebens to (1977) lower distribution of ~ suggest that These observa Q. imbricata predation limits the elegantissima in some areas. This is similar to the in the effects of P. ochraceus predation on mussel distribution (Paine 1974). No large anemones were found in the field, although species apparently or ~une individuals diameter)~. imbricata Because of this, and the in elegantissima aquaria, my from D. imbricata predation. ~unity. First, imbricata are ~. usually by anemones which can use tentacular nematocyts to sting the leather stars' aboral surfaces. tracted, that the D. while feeding. leather D. of anemones may reach a size at which they are Two factors contribute to this repelled of they did occur in the study areas. long survival of the large (9 em some stomachs star Second, some anemones are so large, when con imbricata cannot touch the substratum with its tube feet Since tube feet are never used would even to hold onto anemones, the be vulnerable to being washed off the anemone by wave or surge action in this situation. Another factor which is response of Anthopleura ~portant to However, is that of may be very effective in this case would be to remove (and possibly kill) the anemones exper~ents, release until after the D. imbricata had settled on them. for The end result from clones, have the same affect as predation on the anemone population. not all Anthopleura individuals released during my not in unsuitable reattachment (e.g. the sand plain surrounding the breakwater). may escape in many areas, by employing such behavior the anemone might well be washed away from the clone, and possibly into an area which the spp. Releasing from the substratum and inflation of the base was ineffective in the aquaria but field. consider and ~so, many did These anemones 44 were often carried off, allowing the leather stars to feed on individual simultaneously. some of the experiments. more than one This contributed to the high feeding rate seen in In these cases, the escape behavior of the anemone actually increased the predation rate. The sharp boundary on the lower edge of A. elegantissima clones by Sebens (1977) is similar to what I observed at the breakwater. observed The break water has an unusually steep slope, changing from high intertidal to 10 meters of depth in only about 50 meters of horizontal distance. fairly protected from wave action. move between As a result, D. This area is imbricata can a~so probably the lower intertidal and the subtidal zone and does not have to pass over extensive areas of sand or an active wave zone which may act as bar riers to It is very l1kely that in a situation such as this, leather stars. ~portant D. imbricata could be very elegantissima distribution. in asexual reproduction enlarge during this elegantiss~a, In addition,~. and it may be to elegantissima, small predation Chess 1972). g. missed ~.xanthogrammica, al have been reported as prey in different areas (Mauzey et and that they extend into areas frequented by Therefore there may be a seasonal component study. of A. Also Sebens (1977) reports a distinct seasonality in~. t~e at determining the lower boundary as clones imbricata. during my and M. senile 1968, Rosentha~ Thus the apparent paradox of preferring prey which were not found to occur in the study area is not a paradox at all. The other part of the paradox can also be explained. C . californica is frequently eaten in the field (Figure 4), but is also extremely abundant (Fig ure 5). The observaton that a predator may feed heavi~y on a secondarily pre ferred prey (Sensu Paine 1969) if it is very abundant while the primarily pre ferred prey species is scarce has been made by many researchers (e.g. P. 45 ochraceus, Feder 1959). Since the diet of D. imbricata in other areas con sists mainly of one or two species of very abundant prey, this observation is not wholly unexpected. The variability in the behavior of D. imbricata when encountering prey is of interest, and may help to explain the observed feeding preferences. major differences observed in species occur Q. imbricata behavior toward four prey in the time to first settlement on prey (Figure 6) and in prey choice when presented with more than one species (Tables 4 observations the The of the D. and 7). Carefu~ imbricata during the period of initial contact with prey confirmed that most of the sea stars contacted C. californica as fre quently or more often than they did other prey species presented in the exper iments. As a result, these encounters. Indeed, D. t~es differences are not due imbricata often encountered C. to non-random prey californica several without settling before encountering and settling on Anthopleura spp. The main reason for the differences in feeding behavior appears to be due to an active aviodance of contact with C. californica by Approaching leather stars repeatedly withdrew from contact californica, but seldo~y from other difference in behaviors might be that the anemones. One g. with ~. imbricata. expanded C. explanation for this imbricata are reacting to irrita tion caused by the discharge of nematocysts by the anemones. Three lines of reasoning support this hypothesis. First, it is very likely that the anemones are using nematocysts as defense since these are well known as a mechanism used by cnidarians in defense. tures Some anemones have struc such as acontia and mesentarial filaments which contain nematocysts and have been reported to be used in interspecific aggressive encounters 2973, (waters Choa 1975) and were observed to be used against the leather stars in my 46 experiments (even acrohagi were occasionally used elegantissima). by~. The anemones would not be everting, inflating, or extruding these structures after contact by the leather star other than for their use in defense. c. Finally, tocysts than 1955a and b). to C. californica has much larger and perhaps more irritating nema the other anemone species used in these exper~ents (Hand 1954, This is consistent with the stronger reaction of leather stars californica. Dermasterias imbricata appears to have well developed morphological and behavioral mechanisms which allow them to avoid contact between sensitive body parts and discharging nematocysts. For example, leather fully derm~ retract their tube feet and after contact with anemones. papillae in ~so, the nudibranch loc~ized able to areas rapidly s~liar to papillosa (waters ~973). Aeolidia be they are covered with a mucus layer which may entrap discharging nematocysts in a manner of are Their stomach and epidermis do not appear to sensitive to mechanical irritation. defense stars imbricata often approached prey with uplifted arms, and the mucus Dermasterias assumed a domelike posture over the prey by humping their bodies and contracting their tube feet. By doing this, the leather star presumably aviods any contact with the prey. These behaviors and dation on cnidarians morphologica~ because they characteristics may be related to are similar to those found in other asteroids with similar diets but are not necessarily found in those that prey on molluscs. Por example, A. Pisaster giganteus depend heavi~y asteroids planci avoids using the tube feet when mounting a coral head (Barnes et al 1970) while pycnopodia and pre helianthoides upon their tube feet for prey capture. This may help to explain why Pisaster spp. and other asteroids won't climb ~ pilings which are ringed at the base by c. californica (Wolfson et al 1979) 47 while Patiria minata (which is very similar in many ways to leather stars) and D. imbricata are often found amongst f. californica (pers. obs.). Finally, leather stars encountering expanded anemones reacted in the same way as those that had been pinched with metal forceps. In both cases the leather stars retracted tube feet and dermal papillae, often only in localized areas around the source of irritation, and sometimes raised arms away from the stimulus. stars However, similar reactions were also occasionally used encountering leather bait squid or conspecifics, and it is di£icult to explain As these latter observations in terms of mechanical irritation. explanation by a possible for this odd behavior, it may be that since most prey items eaten by leather stars in nature have defense mechanisms capable of irritating sitive sen tube feet that these leather stars use a similar, stereotypic, reponse to all encounters. Mechanical irritation by nematocysts does at least partially explain avoidance of C. californica by Q. D. ~ricata were unavailable. behaviors Hence (e.g. I ~. planci (Ormond et al which c~ifornica (~976) nature ~976). Also, I did not found that see ~ricata in the lab. ~. planci kept in aquaria The frequency of the arm lifting response no different in these experienced ~. it is was planci, but they appeared much more capa ble of overcoming their initial avoidance However, in were initially avoided would accept them at a much higher rate in prey preference tests. coral. californica reduced arm lifting) which suggested that D. In comparison, Ormond et al corals C. Unfortunately have no idea whether this behavior is a learned became insensitive to contact with C. with in the laboratory. which had not previously encountered response, as it may be in any ~ricata the and settling on the unpreferred significant to note that these researchers were not 58 Appendix IV Number and size of anemones found in the stomaes of D. imbricata during laborabory experiments. Dermasterias tag sequence anemone species number and size of anemones time (hours from beginning to stomach examination) A. xanthogrammica (1 ) 8 em 48 hours (radius in em) goowb (7.7) gowbb (7.3) go099 (6.7) gobog (7.7) ggogg (7.8) ( 2 ) 5 em ( 1 ) 2 em ( 5 ) 1 em ( 3 ) 2 em ( 2 ) 2cm (7 ) 1.5 em gbgbo (6.2) gooob (9.2) bbb (9.0) A. elegantissima ( 1 ) 1 em (3 ) 2 (1) 2 em oobb (9.8) bbbo (7.5) em II ( 2 ) 3 em (1) 4 em bwo (10.S) (1) 1.5 em ( 3 ) 2cm (1) 2.5 em bwb (10.5) ( 2 ) 1.5 em ( 1 ) 2.5 em (1) 4 cm gowb (8.5) (1) 1.5 em (1) 2.0 x 5.5 em oob (8.2) (1 ) 4cm ( 2 ) 1.5 em b (10.2) (1) 3cm s-tip 0000 (1~.2) (8.0) .. (1) 1cm (1) 2.5 em (1) 2 cm 26 hours 48 able to reduce the acceptance rate of preferred corals, even by feeding the A. planci other prey for two months. While mechanical irritation alone may explain some of my observations, it is ~portant known to be to remember that chemical substances liberated by the prey are ~portant asteroids (Collins in inducing or inhibiting ~974, Ormond et al 1976). feeding responses other in While nothing is yet known about the influences of chemicals on the feeding behavior of imbricata, D. this cannot be discounted, especially since their anemone prey are known to release biologically active chemicals into the water (Martin 1968). The feeding behavior of D. imbricata is similar in many ways to the predatory nudibranch Aeolidia papillosa waters (1973) reported that .. A. xanthogrammica, but (~ater to avoid C. for D. effectiveness of caused part to the species, repelling nudibranchs. a~ ~ricata and size of the and Prey defensive result reported papillosa would not con greater Whereas acontia did not they became entangled in the nudibranchs' cerata obvious damage and irritation. sma~l ~. the of ~974). elegantissima senile in the lab. This seemed to be due to the acontia obviously damage Q. and Unlike imbricata, waters (1973) found that sistently feed on M. on~. californica. behavior was used to explain these preferences. here 1973, Edmunds et al !. papillosa fed readily tended that ~. However, my results may be due in senile used, the the low density of this prey used. sma~l sample sizes for That D. this imbricata can sus tain damage after contact with some species of anemones is evident from obser vations made in the field by R. Cohen (pers. comm.). In summary, I have found in this investigation that in the Monterey area, the leather star (Dermasterias imbricata) feeds mainly on C. californica. 49 Corynactis californica is a small, extremely abundant anemone which has a depth range which overlaps extensively with that of the leather star. However, when other species of anemones are made equally accessible in the lab, leather stars consistently choose A. elegantissima,~. xanthogrammica, and M. senile over C. californica. Dermasterias imbricata do not appear to lose their preference for pleura spp. when kept on alternate diets for up to s~ weeks (see Landenberger 1968, Murdoch 1969, and Ormond et al 1976 for other examples of exhibiting strong preferences which ~. it implies that whenever leather stars encounter xanthogrammica they would feed on them preferentially nica. invertebrates do not switch to secondarily preferred This is prey until the preferred prey are completely unavailable). because Antho ~. ~portant elegantiss~a or over the C. califor This may reduce the ability of these anemones to extend the lower lim its of their distributions into areas frequented by D. imbricata ( Sebens 1977) . Also, it is small anemones. l~ely that ~. imbricata are limited to feeding on relatively No large anemones were found in their diet, and the leather stars in the lab had difficulty capturing large individuals. few reports of them There particularly also preying on large anemones and some species may have an escape in size similar to that reported by Paine (1976) for mussels. a are appealing hypothesis This is since it helps to explain, at least in part, the scarcity of small anemones and the persistence of larger individuals of the A. xanthogrammica were absent from the subtidal zone in washington, but abundant same species in the subtidal zone. Sebens (1981) observed that small in the intertidal zone on mussles. ever, adult A. xanthogrammica migrate into the very As they reach larger sizes, how low intertidal and subtidal 50 zones which, imbricata. important. in at least some areas, overlaps with the distribution of D. 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Sere 1: 81-89. 53 Appendix I: Description of individual £. imbricata and treatments tag color sequence 9 0 g09 gbgbo ~~ bwb gog orange gowbo gowob go099 ggg go gg g obo 9 bgg ggogg gooob 'Wob bbbb gowbb gowb gb 00 wbo wwb bb 000 boo bo booo bbo oob six arm bwbb owb bbbo collection date 9/81 9/8~ 9/8/81 11/11/81 11/1~/81 9/81 9/81 9/81 11/11/81 11/11/81 11/11/81 9/81 9/16/81 9/81 9/81 9/8/81 9/8/81 9/°81 9/16/81 11/11/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 arm radius x (sd) em 8.2 6.1 10.~ 10.5 7.1 7.8 6.5 6.6 7.1 8.7 7.1 7.7 6.3 7.8 9.2 10.4 10.3 7.3 7.9 8.2 10.2 12.1 9.3 10.5 8.1 8.1 8.1 7.9 8.2 8.1 8.4 9.0 9.1 7.2 ( 0 .27 ) (0. 3~ ) (0. 40 ) ( 0.50 ) ( O. 30 ) ( 0.23 ) ( 0 . 37 ) ( 0.23 ) ( 0.30 ) ( O. 43 ) ( 0 . 36 ) ( o. 87 ) (0.31) (0.34) ( 0 . 37 ) ( 0.27 ) (0. 2S ) (0.24) ( O. 43 ) (0.47 ) ( 0.28 ) ( 0 . 42 ) ( 0.15 ) (1.0) (0.29) (0.15 ) ( 0 .13 ) ( O. 36 ) (0.31 ) (0 .1~ ) ( 0.33 ) ( 0.22 ) (0.44 ) (0.25 ) (continued next page) radius of longest arm-- ( em ) *treatments 8.5 6.5 10.5 11.0 7.6 8.0 6.9 7.0 7.4 9.2 7.5 8.5 6.7 8.2 9.5 10.7 10.5 7.6 8.5 8.9 10.5 12.5 9.5 10.7 8.5 8.3 8.3 8.3 8.6 8.2 8.9 9.4 9.6 7.5 5,3 s,3 s, 2a, 21:>, 3 s,3 s,3 s,3 5,3 s,3 s,3 s,3 s,3 9,3 9,3 9,3 s,3 s,3 s,3 s,3 s,2a,2b,3 s,3 s,l e,l a,l s,l e,l a,l s,l e,l a,l c,2a,2.b s,2b s,2b s,2.b s,2a,2b S4 tag color collection date sequence b 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 9/8/81 10/81 oobb bbb bwo I-tip 0 s.a.I.m. ob 0000 orange arm goowb arm radius x (sd) em. 9.6 9.2 8.5 9.7 10.5 9.4 7.0 8.8 7.8 8.9 7.7 (0.45 ) (0.39) ( 0.30 ) ( 0 . 66 ) ( O. 46 ) ( 0 . 36 ) ( 1.03 ) radius of longest arm (em) ( 0 . 33 ) 10.2 9.8 9.0 10.5 11.2 9.7 7.6 9.1 8.0 ( O. 81 ) 9.4 (0.19) ( a .35 ) 8.1 '*'treatments a, 2a, 2.b s,2a,2b a, 2a, 21:> a, 2a, 21:> c,2a,2b c,2a,2b s,2a,2b s, ,2b c,2a,2.b s 9,3 *treatments; s=squid tank a=Anthopleura elegantissima tank c=Corynactis californica tank l-first replicate of paired ~. elegantissima/f. californica choice experiment 2a=second replicate of paired !. elegantissima/f. californica choice experiment 2b=modified !. elegantissima/£. californica choice experiment 3=single and multiple prey choice experiment (see appendix 2 for details of prey composition) 55 Appendix II: Description of £. californica used in experiments Collection dates: 9/8/81, 9/16/81, 1~/ll/81 oral disc diameter: X=O.55 sd=O.22cm X n (measured)=40 Corynactis Rock dimensions (em) width length 30- 34 34 5 22 5 6 29 31 34 38 87 75 27 46 26 27 38 27 36 54 61 42 19 74 22~ 44 178 34 24 26 53 36 132 42 28 28 129 24 ~ Number of Corynactis per rock 21 24 32 16 17 28 x=27.9 em 52 36 p37.0 em 64 94 86 39 48 50 81 x=80 corynactis per rock sd=12.6 sd=14.5 sd-55 56 APpendix III: Description of Single Prey Species Presentation leather star tag color sequence gowbb *prey species squid Ax/CC 9gog9 squid Ms Ax/Cc Cc gobog squid Ms Ax/Cc Cc go squid Cc Cc gooob gbgbo gb squid Ae Ae 9/81-21/23/81 11/23/81-11/27/81 22/11/81-12/13/81 12/4/81-12/7/81 11/11/81-11/23/81 12/23/81-11/27/81 12/3/81-12/5/81 squid 11/11/81-12/4/81 12/4/81-12/7/81 squid squid Ae/cc squid squid Cc Cc bwb 9/81-11/23/81 11/23/81-11/27/81 12/11/81-12/13j81 12/4/81-12/7/81 9/81-11/23/81 11/23/81-11/27/81 11/27/81-12/4/81 Cc gowbo 9/81-12/11/81 12/11/81-12/13/81 squid Ae Ae Cc orange exper~ent Ax/Cc Cc gowb duration of 9/81-11/23/81 11/23/81-11/27/81 11/27/81-12/4/81 12/11/81-12/13/81 Cc gog presented squid Ae/Cc 11/11/81-12/4/81 12/4/81-12/7/81 9/16/81-10/25/81 10/25/81-11/4/81 12/4/81-12/7/81 11/11/81-12/4/81 12/4/81-12/7/81 9/81-11/23/81 11/23/81-11/27/81 12/3/81-1.2/5/81 9/8/81-10/25/81. 10/25/81-11/4/81 57 Ms Cc gogog goowb squid 9/8~-1~/23/8l Ae Ax/Cc 11/23/81-11/27/81 12/11/81-12/13/81 squid 12/3/81-12/5/81 11/23/81-11/27/81 12/11/81-12/13/81 Cc Ax/Cc squid/ms ggg Ms Cc gg gowob 11/11/81-11/23/81 11/23/81-11/27/81 12/4/81-12/7/81 squid 11/1~/81-11/23/81 Ae Cc 11/23/81-11/27/81 12/7/81 squid Cc 9/81-11/23/81 11/23/81-11/27/81 12/3/81-12/5/81 Cc squid googg 11/23/81-11/27/81 12/4/81-12/7/81 Ms Ax/Cc Cc 9/81-11/23/81 11/23/81-11/27/81 12/11/81-12/13/81 12/4/81-12/7/81 .~ squid wob bbbb small #1 small #2 Ae 9/8/81-11/23/81 11/23/81-11/27/81 squid Cc Cc 9/8/81-11/23/81 11/23/81-11/27/81 12/3/81-12/5/81 squid Ax/Cc 12/6/81-12/7/81 squid A:x/Cc 12/6/81-12/7/81 * treatments; squid~squid tank Ae=!:. elegantissima Ax=~. xanthogrammica Cc~£. californica Ms=M. senile Ax/CC=~. xanthogrammic and f. californica presented simultaneously Ae/Cc=~. elegantissima and £. californica presented simultaneously previous experiment (see text) in