BULLETIN OF MARINE SCIENCE, 50(2): 331-341, 1992 CORAL REEF PAPER

ACCLIMAnON OF THE SHRIMP, PERICLIMENES ANTHOPHILUS, TO THE GIANT , CONDYLACTIS GIGANTEA

James A. Crawford

ABSTRACT The shrimp Periclimenes anthophilus Holthuis and Eibl-Eibesfeldt acquires protection from the tentacles of its host anemone, Condylactis gigantea, during acclimation. The shrimp is observed to acclimate to the anemone but not the anemone to the shrimp. The process of acclimation was completed in 2 h 40 min. The shrimp's body length and molt stage did not influence acclimation time. The shrimp was observed to gradually lose its protection from its host during isolation from the latter; shrimp lost their protection, became unacclimated, after 3 days 10 h of isolation. Additionally, shrimp became unacclimated when their integ- ument was wiped; it is suggested that the shrimp's protective mechanism preventing the discharge of cnidae is secretions on its epicuticle. Similarities between anemone fishes and anemone shrimps are discussed.

Marine decapods have been reported to live symbiotically with porifera (Patton, 1967), actinians (Hoffman, 1967; Smith, 1977; Ross, 1983; Bruce and Svoboda, 1984), scleractinians (Patton, 1966; Edwards and Emberton, 1980; Glynn, 1980; 1983; Bruce, 1985; Nakasone et ai., 1986), antipatharians (Davis and Cohen, 1968; Patton, 1972), echinoids (Castro, 1974; Bruce, 1986a; 1986b) and crinoids (Patton, 1967). Research efforts have focused on documenting the existence of these associations and reporting their ecological importance, but little is known about the initiation or general biology of these associations. Several species of shrimps have been documented in symbiotic associations with sea anemones. The shrimps receive protection from predators by residing among the anemone's tentacles (Bruce, 1976; Levine and Blanchard, 1980). The exoskeletons of shrimps do not appear to protect them from the anemone's nema- tocysts, and protection is thought to occur after a period of acclimation (Levine and Blanchard, 1980). The behavioral process of acclimation to anemones has gained much attention ever since the work by Davenport and Norris (1958) on the symbiosis of anemone fishes and anemones. Subsequent studies by Mariscal (1965; 1969; 1970a; 1970b; 1970c; 1971) claimed that anemone fishes became protected from the nematocysts of their hosts by altering their mucous coat during acclimation. However, Schlich- ter(1967; 1975; 1976) believed that the fish was simply coating itself with anemone mucus during acclimation, thereby camouflaging its normal, chemical stimuli from anemone detection. Most recently, Miyagawa (1989) has concluded that juvenile anemone fishes are innately protected from their natural host anemones during their first encounter. She pointed out that the earlier studies by Mariscal (1965; 1969; 1970a; 1970b; 1970c; 1971) were an exception to the rule. Mariscal (1970b; 1970c) chose to study the uncommon association of the anemone fish Amphiprion xanthurus and the anemone Stoichactis kenti, the only association that Miyagawa (1989) observed in which the fish was not protected from the anemone. In light of these new findings, it appears that there is a phase in an anemone fish's life, when it enters benthic life, in which it may associate with its natural host anemone without being harmed. Miyagawa (1989) stated, "Thus the

331 332 BULLETINOFMARINESCIENCE,VOL.50,NO.2, 1992

phase of entering benthic life is seemingly the most crucial point 10 the life of anemonefish. " Although extensive work has been conducted on the acclimation of fishes to sea anemones, little is known about the acclimation of shrimps to sea anemones. The present study aimed to analyze the acclimation phenomenon of P. anthophilus to its host anemone C. gigantea and to determine the protective mechanism involved.

MATERIALS AND METHODS

Specimens.-CoLLEcrION ANDIDENTIACATION.Periclimenes anthophilus (N = 108) and C. gigantea (N = 29) were collected together using SCUBA, at water depths of 1-7 m, from Harrington Sound, Bailey's Bay and Shelly Bay, Bermuda. Periclimenes anthophilus was positively identified using Chace's (1972) key to western Atlantic species. MAINTENANCE.Individual anemones were kept in separate glass and Fiberglass aquaria. Shrimp were isolated from one another in plastic aquaria with Fiberglass screening on top. All specimens had a separate supply of flowing sea water. Shrimp were fed TetraMin brand flake food daily and the anemones were fed frozen squid weekly. The anemones were not fed within 24 h of an experiment. Both shrimp and anemones were kept on a 12 h fluorescent light cycle (800-2000 h) and most experiments commenced at 1200 h to eliminate the possible effects of any rhythmic patterns that may have existed. TESTINGTHEANEMONE'SPREYCAPTUREABILITY.Cnidae discharge varies among individual anem- ones over time (Sandberg et aI., 1971); therefore, anemones were tested for their prey capture ability, prior to experimentation, by presenting them with a coverslip coated with saliva, which was air-dried. After the coverslip was presented to three tentacles, the cnidae present on the coverslip were stained with a 0.1 % Toluidine Blue solution and counted with a light microscope at 1,000 x magnification using immersion oil. If at least 25 discharged cnidae could be seen in anyone view, then a finger was passed through the tentacles of the anemone to check for adhesion properties. If the tentacles could be seen and felt adhering to the finger, the anemone was said to have the ability to capture prey; only these anemones were used in the experiments. Additionally, the discharged cnidae on the coverslips were analyzed and compared among different anemones. This was done by counting and averaging the number of cnidae in the densest areas of the three different traces (a group of discharged cnidae from one tentacle; after Sandberg et aI., 1971). Acclimation Experiments. - TERMINOLOGY.The following descriptions were used during the obser- vations of the acclimation behavior of P. anthophilus to C. gigantea (these descriptions refer to the shrimp-anemone association investigated here and do not necessarily apply to other shrimp-anemone partnerships or, to the more familiar, anemone fish-anemone associations): (a) Strong Contraction- a shortening or bending of an anemone's tentacle more than 1f2". (b) Capture Response-the curling or wrapping.of an anemone's tentacle around a shrimp. (c) Acclimated-when a shrimp no longer elicited a capture response or strong contraction in an anemone while contacting the distal half of an anemone's tentacle (i.e., the shrimp was free from being captured and ingested by the anemone). (d) Unacclimated-when a shrimp elicited a capture response, strong contraction, or both in an anemone while contacting the distal half of an anemone's tentacle (i.e., a shrimp in this state risked being captured and ingested by an anemone). (e) Stung-the injection of a shrimp with venom from an anemone's nematocyst. The stinging of a shrimp by an anemone has been determined by the jerking motion of the shrimp following contact with an anemone; additionally, the anemone usually contracted the tentacle that was contacted (note that "stung" is not a criterion for a shrimp that is either acclimated or unacclimated). Current investigations (by the author) are analyzing, using scanning electron mi- croscopy, the stinging phenomenon in hopes to clarify it. PROTOCOL.Prior to each experiment, shrimp were transferred to aquaria containing anemones using a glass beaker that was sterilized in 95% ETOH and rinsed in sea water. Observations during the experiments were recorded with notes, a voice-activated tape recorder, a video camera, and 35 mm photography. Individual shrimp were used only once in any given experiment, although some shrimp were used in more than one experiment. Anemones were sometimes used more than once during an experiment, in which case, they were selected at random. WHO Is ACCLIMATINGTOWHOM?Reciprocal experiments were conducted in which both acclimated and unacclimated shrimp were placed on anemones both with and without shrimp. Unacclimated shrimp and anemones without shrimp were isolated for 7 days prior to the experiments. If only the unacclimated shrimp were stung by the anemones, both with and without shrimp, this would indicate that some change had occurred in the shrimp during acclimation that resulted in their protection. Conversely, if only the anemones containing acclimated shrimp failed to sting shrimp (either acclimated eRAWFORD:ACCLIMATIONOFSHRIMPTOANEMONE 333

Table I. The different levels of protection P. anthophilus may go through during isolation from or acclimation to C. gigantea*

Lev.lt Anemone's response to contact by the shrimp; Unacclimated 8 -tentacles quickly (duration < I sec) wrapped around the shrimp upon every contact 7 -tentacles wrapped around the shrimp upon every contact (duration> I sec) 6 -tentacles wrapped around the shrimp upon majority (> 50% but < 100%) of contacts 5 - tentacles wrapped around the shrimp upon 10-50% of the contacts 4 -tentacles rarely wrapped around the shrimp upon contact « 10%), but moved >1/2" within 0.5 sec upon majority (> 50% but < 100%) of contacts Acclimated 3 - tentacles moved < 1/2"upon majority (> 50% but < 100%) of contacts 2 -tentacles moved <'!4" upon majority (> 50% but < 100%) of contacts I -tentacles rarely «10%) moved upon contact o -no tentacle response upon contact by the shrimp

• Each level of protection was described in terms of the anemone's response to contact by the shrimp because this was more uniform than the response of the shrimp. t The m~in difference between unacclirnated and acclimated is the wrapping of tentacles around the shrimp (see text for further explanatIOn). :I: The anemone's response refers to contact of the distal half of the tentach;s by the shrimp; contact elsewhere elicited a weaker response or no response at all in the anemone.

or unacclimated), this would indicate that some change had occurred in the anemone during accli- mation, which resulted in the shrimp's protection. LEVELSOF PROTECTION.The shrimp's protection from the anemones changed during isolation, as well as during acclimation. The different levels of protection of shrimp to anemones were categorized for comparison purposes based on the anemone's response to contact by the shrimp (Table I), because the anemone's response was more uniform than the shrimp's throughout acclimation. The anemone's response to a shrimp was divided into nine increasingly intense responses. Each response was assigned a numeric level; the levels ranged from zero to eight, with zero being no response and eight being the greatest response of the anemone. Shrimp at levels 0-3 were considered to be acclimated, and those at levels 4-8, unacclimated. Unacclimated shrimp were obtained for acclimation experiments by isolating the shrimp from the anemones for at least 3 days 12 h; all of these shrimp were at level five or higher at the initiation of the experiments. There was no significant correlation (r = 0.066) between isolation time and acclimation time for shrimp that were isolated greater than 3 days 12 h (N = 54). Loss OF PROTECTION.Acclimated shrimp lose their protection from anemones if isolated from the latter. The isolation time required was determined by isolating acclimated shrimp for varying time periods between 30 min to 15 days. Acclimated shrimp, of at least 24 h to ensure complete acclimation, were removed from their anemones, using a sterile glass beaker, and placed in individual aquaria. Following the completion of their isolation periods, the shrimp were returned to their previous anem- ones and checked to see if they were still protected. DURATIONOFTHEACCLIi,IATIONPROCESS.To determine the time required for acclimation, shrimp were observed for 4-min periods at 15-min intervals starting when the shrimp first contacted the anemones. The acclimation experiments were completed when the shrimp reached a level of protection at which they remained for I h. The time of acclimation was recorded when the shrimp first reached its final acclimated level. All shrimp completed acclimation within 9 h 30 min. MONITORINGMOLTING.The molt cycle of each shrimp was monitored by checking ecdysis to determine if changes in the shrimp's exoskeleton, caused by molting, had any effect on the shrimp's acclimation time. In previous experiments the shrimp were never observed to feed upon their exuviae; therefore, aquaria were inspected for exuviae twice a day at approximately 0800 and 2000 h. ALTERINGTHESHRIMP'SINTEGUMENT.An experiment was conducted to investigate the role of the shrimp's integument in protection from the anemone's cnidae. For this experiment, the shrimp's integument was gently wiped with a moist foam sponge. During this procedure, the shrimp was carefully placed onto a Fiberglass screen, which was sterilized in 95% ETOH and rinsed three times in sea water, and then the shrimp was gently wiped with a moist foam sponge, also sterilized and rinsed. Both sides of the shrimp were wiped three times, which resulted in an unprotected shrimp. Acclimated and unacclimated shrimp were treated in the same manner and then allowed to reacclimate to their previous anemone. Their acclimation times were compared to the acclimation times of other shrimp that were placed on Fiberglass screening but not wiped. If acclimated shrimp lost their protection from the 334 BULLETINOFMARINESCIENCE,VOL.50,NO.2, 1992

anemone's cnidae following the wiping of their integument, this would suggest that cuticular secretions on the surface of the epicuticle provided the shrimp with protection. POSSIBLEANEMONESTIMULI.Shrimp were exposed to anemone mucus for 3 h prior to acclimation to determine if association with anemone mucus would decrease their acclimation times. Anemone mucus was collected by suspending an anemone over a sterile glass beaker using Fiberglass screening. If the shrimp were simply coating themselves with anemone mucus, the acclimation times of these shrimp should be significantly lower than average. Additionally, shrimp were placed in cages made of Fiberglass screening and suspended in aquaria containing anemones, prior to acclimation. The cages were placed out of the anemone's reach. If the shrimp were using visual or chemical cues from the anemone or its environment to acclimate, the acclimation times of these shrimp should be significantly lower than average.

RESULTS Acclimation Experiments. - WHO Is ACCLIMATINGTO WHOM?In all reciprocal experiments, in which acclimated and unacclimated shrimp were placed on anem- ones with and without shrimp, the acclimated shrimp was not stung and the unacclimated shrimp was stung by the anemone regardless of the state of the anemone (Table 2). Thus, the shrimp were acclimating to the anemones, Loss OFPROTECTION.The shrimp's level of protection was demonstrated during isolation experiments in which acclimated shrimp were isolated from their anem- ones for time periods ranging from 30 min to 15 days (Fig. 1). It was observed that 100% of the shrimp that were isolated from anemones greater than 3 days II h (N = 39) lost their protection (> level 3). Of the shrimp that were isolated less than 3 days 11 h (N = 38), their protection significantly decreased as isolation time from their anemone increased (r = 0.703). After 3 days 11 h of isolation, there was no significant change in the shrimp's protection level (r = 0.233). ACCLIMATIONBEHAVIOROFSHRIMP.The behavior of the shrimp during accli- mation was observed (in its entirety) for 12 specimens. Upon introduction into an aquarium with C. gigantea, the unacclimated shrimp swam directly towards the anemone contacting the anemone's tentacles with its antennae, pereiopods, or both. Usually the shrimp was stung and jerked backwards upon the first few contacts (Fig. 2). Occasionally, an appendage of the shrimp (usually an antenna, pereiopod, or uropod) would adhere to a tentacle and the shrimp would pull itself free, Once on the anemone (during the first 10 min), if the shrimp remained motionless, the anemone usually did not respond to its presence. As soon as the shrimp moved, the anemone usually responded by contractions of the tentacles, and the shrimp was occasionally stung. Some anemones responded to the shrimp's contact so quickly that several tentacles wrapped around the shrimp at one time (level eight). In this case, the shrimp quickly jerked or swam away occasionally settling elsewhere on the anemone. The shrimp were stung many times (> 5) during the initiation of acclimation but were rarely stung towards the end. Mostly, the shrimp avoided the anemone's capture response by walking away from the contracting tentacles (Fig. 3) or by migrating to the proximal region of the tentacles (during the first 15 min) where the capture response was less pro- nounced or nonexistent, In this proximal region, the shrimp scurried around the base ofthe tentacles picking at the anemone and overlying mucus with its chelae. When the shrimp encountered a ring of anemone mucus around a tentacle (Fig. 2), it occasionally cut off pieces of mucus using the chelae of its chelipeds. Pre- sumably, the shrimp was feeding on the mucus or food particles contained within it. White clumps, which appeared to be mucus, were also seen adhering to the shrimp's appendages (especially after tentacle adhesion), mostly the antennae and pereiopods (Fig. 3). The shrimp cleaned off these white clumps during its frequent grooming. Scanning electron micrographs revealed that these white clumps, which CRAWFORD: ACCLIMATION OF SHRIMP TO ANEMONE 335

Table 2. Experiments in which P. anthophilus. acclimated and unacclimated, were presented to C. gigantea. with and without shrimp. Numbers represent the number of shrimp that were tested in each experiment. Unacclimated shrimp and anemones without shrimp were isolated for 7 days prior to the experiments. The data show that none of the acclimated shrimp were stung and all of the unac- climated shrimp were stung (N = 51)

Anemone

With shrimp Without shrimp

Shrimp Stung Not stung Stung Not stung Acclimated o 10 o 15 Unacclimated 12 o 14 o were visible to the naked eye, consisted of 100's or 1,000's of discharged nema- tocysts adhering to the shrimp's integument (pers. obs.). As acclimation progressed (at least 30 min from the start), the shrimp moved to the distal portion of the tentacles, picking at the tips of the tentacles with its chelae (Fig. 4). During the latter part of the acclimation process, the tentacles responded to the shrimp's contact but the capture response was subdued. As time passed (at least I h from the start), the tentacles responded less and less to the shrimp's presence and the shrimp moved about the anemone more quickly. At the end of acclimation, the tentacles no longer curled to the shrimp's contact but usually contracted or wavered slightly. Additionally, no tentacles were observed adhering to the shrimp. The acclimation experiment was completed

••

7

.-& •• 4 j- a:0 5 -0 4

! 3 o- f 2

o 3 6 7 8 11 13 15 Time of IeoIatian for Shrimp (dayel Figure J. The levels of protection (Table I) of acclimated shrimp following their isolation from anemones. The lower the level the greater the protection. The shrimp's protection significantly de- creased as isolation time increased up to about day 4 (r = 0.703), with no significant difference after day 4 (r = 0.233). Plots are the means for each day. Bars indicate 1 SD; values to the right indicate the sample size for that day (N = 77). 336 BULLETIN OF MARINE SCIENCE, VOL. 50, NO.2, 1992

Figure 2. An unacclimated shrimp, P. anthophilus, is stung by a tentacle (T) of the sea anemone C gigantea during the beginning of acclimation. Note that the tail is flexed anteriorly as the shrimp jerks, or swims, away from the contracting tentacle (T). Also, note the ring of mucus (M) surrounding a tentacle. when the shrimp dropped below level four and remained at the same level for five observations (i.e., 1 h to ensure that the shrimp was no longer acclimating). DURATIONOF THEACCLIMATIONPROCESS.The mean acclimation time for P. anthophilus to C. gigantea was 2 h 40 min (SD ± 1.28, N = 54). The acclimation times of shrimp to different anemones were compared (Fig. 5; N = 43). The acclimation times of shrimp to anemone #5 were significantly higher than the rest (Wilcoxon Rank Sum, P = 0.05). Shrimp acclimating to anemone #5 were stung more frequently and left the anemone more often. Analysis of cnidae discharge from anemone #5 onto coverslips showed no significant difference in density or number when compared to the other anemones (Kruskal Wallis, P = 0.05). Ad- ditionally, there was no significant correlation (r = 0.078) between previous ac- climation experience, the number of times previously acclimated, and subsequent acclimation times (N = 58). MOLTINGOFACCLIMATEDSHRIMP.Acclimated shrimp were still protected im- mediately following ecdysis with no difference in their level of protection (N = 4). Exuviae from recently molted shrimp [0-12 h; acclimated (N = 3), and un- acclimated (N = 9)], which were picked up using a sterilized glass pipette and then released above the tentacles of anemones, caused capture responses in anem- ones upon contact with their tentacles. These exuviae were always released by the anemone a few seconds later and not ingested (possibly due to a lack of mechanical stimulation). Shrimp in various stages of molting (determined by time since last molt) were used in experiments of acclimation. The mean molt cycle for P. anthophilus lasted 11.0 days (SD ± 4.1, N = 61) in water 25-28°C. There was no significant cor- CRAWFORD: ACCLIMATION OF SHRIMP TO ANEMONE 337

Figure 3. A clump of anemone mucus and nematocysts (C) adheres to the antennule of an unaccli- mated shrimp, P. anthophilus, as it walks away from a contracting tentacle (T) of the anemone C. gigantea. relation (r = 0.033) between the acclimation time of shrimp and time since last molt. SHRIMP LENGTH. There was a slight correlation (r = 0.250) between shrimp length and acclimation time (N = 71, Fig. 6); shorter shrimp acclimated in less time. Shrimp length was measured from the eyes to the base of the telson and rounded to the nearest mm. Shrimp used in this study measured from 6-12 mm in length. ALTERINGTHESHRIMP'SINTEGUMENT.Acclimated shrimp lost their protection from anemones after their integument was gently wiped (N = 7), following which the shrimp had to reacclimate to the anemone. The reacclimation times of these wiped shrimp ranged from 1.5-72.0 h (N = 6). All but one shrimp acclimated in less than 20 h. The longer acclimation time may have been the result ofa damaged exoskeleton. None of the control shrimp, which were gently placed onto a Fiber- glass screen, had to reacclimate in order to move about the anemone unimpeded. Furthermore, the sterile foam sponge did not elicit a response from the anemone. Three unacclimated shrimp that had their integument wiped, in the same man- ner, were released above separate anemones. One shrimp was caught and ingested by the anemone 55 sec after the initial contact; it had just molted within the past 12 h. The other two shrimp had acclimation times of 2 hand 19 h. POSSIBLEANEMONESTIMULI.The acclimation times of the eight shrimp exposed to anemone mucus prior to acclimation and the acclimation times of the seven shrimp caged in aquaria containing anemones prior to acclimation were not sig- nificantly different from those of the other shrimp (r = 0.045 and r = 0.059, respectively). 338 BULLETIN OF MARINE SCIENCE, VOL. 50, NO.2, 1992

Figure 4. An acclimating shrimp, P. anthophilus, picks off a piece of mucus (M) from the tip of a tentacle (T) from the anemone C. gigantea. The shrimp had been acclimating for 50 min.

DISCUSSION In the only report on shrimp acclimation, Levine and Blanchard (1980) observed variation in the acclimation times of P. anthophilus to C. gigantea (1-5 h ± 25 min). They speculated its cause to be either an insufficient isolation time (24 h) for their shrimp prior to acclimation or variations in the shrimp's exoskeletons due to their molting cycle. This study showed that there was no significant dif- ference in the acclimation times caused by the molting cycle, but an isolation time of 24 h was indeed insufficient to render all the shrimp unacclimated. The acclimation times in this study were 2 h 40 min, SD ± 1.28, for shrimp isolated longer than 3.5 days (N = 54). Factors that may have contributed to this variation are the health of each shrimp and anemone during the experiments, and the variation in cnidae discharge of the anemones. Similar variation in the acclimation times of the anemone fish Amphiprion clarkii to the anemone Macrodactyla do- reensis was reported by Brooks and Mariscal (1984). During shrimp acclimation, Levine and Blanchard (1980) observed shrimp exhibiting defensive behaviors to avoid capture by the anemone. Clear mucus was observed adhering to the shrimp's appendages, presumably from the anemone, which the shrimps appeared to clean off while grooming. In this present study, white clumps of material on the integument of the shrimp were identified as numerous discharged nematocysts. Similar findings have been reported for anem- one fishes (Miyagawa, 1989). Holthuis and Eibl-Eibesfeldt (1964) briefly described some behaviors of P. anthophilus on C. gigantea. They stated that the anemone reacted to the presence of a shrimp walking on the tentacles by slow contractions, especially when the anemone was not inhabited for several days. The results of the present study show no variation in anemone response with respect to isolation time from shrimp CRAWFORD: ACCLIMATION OF SHRIMP TO ANEMONE 339 ,-~

] ~ j "Ii i J

~_~_~I.~~_ -L-_-l.. SIm1IIongth inmI Figure 5 (left). The mean acclimation times of shrimp that were acclimated to six different anemones. The acclimation times to anemone #5 are significantly different from the rest (Wilcoxon Rank Sum, P = 0.05). Bars indicate I SD; values to the right indicate the sample size for that anemone (N = 43). Figure 6 (right). The acclimation times of shrimp according to their body length. Shrimp length was measured from the eyes to the base of the telson and rounded to the nearest mm. There was a significant, but slight, correlation between shrimp length and acclimation time (r = 0.250). Bars indicate I SD; values to the right indicate the sample size (N = 7I).

(Table 2). They also reported that when a shrimp was contacted by a tentacle from above, the shrimp shook its antennae and the tentacle moved away. In this study, that behavior was never observed; the shrimp either moved out of the way or was carried with the tentacle. Some of the observations of Holthuis and Eibl- Eibesfeldt could have resulted from their unspecified handling techniques. During the early part of acclimation, P. anthophilus moved about the anemone slowly, apparently making fewer contacts with the anemone than in the later part of acclimation. Lubbock (1981) observed a similar slow movement of the anemone fish A. clarkii during its acclimation to the anemone Stoichactis haddoni. This behavior may not only reduce the number of cnidae discharged onto the shrimp but may also reduce the level of stimulation provided by excitatory substances on the shrimp's body. It has been shown that the ability of a compound to incite cnidae discharge increases with mechanical stimulation (Lubbock, 1979; Thor- ington and Hessinger, 1988; Watson and Hessinger, 1989). This may also explain why the shorter, and smaller, shrimp acclimated in shorter time periods (Fig. 6). An interesting observation was that acclimated shrimp lost their protection when their integument was wiped, as occurred in anemone fishes (Mariscal, 1970a; 1971), but retained their protection following ecdysis. This suggests that the shrimp was not merely coating itself with anemone mucus, as was suggested by Levine and Blanchard (1980) and as Schlichter (1967; 1975; 1976) believed was the case with anemone fishes, but may have altered its chemical secretions to acquire protection. One hypothesis is as follows: when a shrimp is wiped, chemical pro- tectants are removed exposing the exoskeleton to cnidocyte receptors. When a shrimp molts, chemical protectants, which are secreted along with the new cuticle prior to ecdysis, protect the shrimp from the anemone. The ability of anemones to detect recently shed exuviae could be due either to the rapid breakdown of the exuviae's chemical protectants, or to the release of stimulants from the exposed underside of the exuviae, or both. This study also showed that unacclimated shrimp whose integument was wiped risked a greater chance of being caught by an anemone's tentacles, suggesting that cuticular secretions provided a mechanical, or chemical, barrier to firing cnidae. Lubbock (1980a; 1980b) reported anemone fishes to have a mucous coat 3-4 x thicker than related non-symbionts. If so, this thicker coat may help protect an unacclimated fish during acclimation. 340 BULLETIN OF MARINE SCIENCE, VOL. 50, NO.2. 1992

There are other similarities between anemone shrimps and anemone fishes, These symbiotic shrimps and fishes usually are not found away from their host anemones in nature. Presumably, they use their hosts as a means of protection from predators. Host anemones are usually occupied by more than one individual ofthe same species, and on occasion, different species may occupy the same host. Although similarities exist between acclimating shrimps and fishes, it is not known if their mechanism of acclimation is the same. In light of recent reports on chemical mixture interactions and chemical inhibition at receptor sites (Derby et aI., 1985; Arbas et aI., 1988), it is suggested that these events could be involved in the acclimation of shrimps and fishes to anemones. Symbionts, upon detection of their host, may secrete a chemical that either acts on its own or combines with an anemone derived substance and inhibits cnidae discharge by binding to a receptor site of the cnidocyte [i.e., contact inhibition, see Thorington and Hes- singer (1988) for information on cnidocyte chemoreceptors]. On the other hand, the symbionts may simply camouflage themselves from anemone detection by picking up anemone mucus on their integument, although the results from this study do not support this hypothesis. Comparative studies need to be conducted on the physical and chemical properties of the integument of anemone shrimp, and the mucus from anemone fish and anemones.

ACKNOWLEDGMENT

This study was supported, in part, by the Visiting Graduate Intern program of the Bermuda Biological Station for Research, Inc. (BBSR). This is contribution No. 1291 from BBSR.

LITERATURE CITED

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DATEACCEPTED: April 30, 1991.

ADDRESS: Department ojBiology. West Georgia College, Carrollton. Georgia 30118.