First Record of a Pearlfish, mourlani, Inhabiting the Aplysiid Opisthobranch Mollusc Dolabella auricularia1

Peter W. Glynn,2,3 Ian C. Enochs,3 John E. McCosker,4 and Abigail N. Graefe5

Abstract: Adult individuals of the pearlfish Carapus mourlani (Petit, 1934) occur commonly in the mantle cavity of the opisthobranch mollusc Dolabella auricu- laria (Lightfoot, 1786) in shallow marine waters of the Gulf of Chiriquı´, Pacific Panama´. Nearly 30% of the molluscan hosts collected during the day on a reef contained one or two fish. Feeding observations of a captive fish as well as the intact condition of the host’s ctenidium and other internal organs suggest that C. mourlani is an commensal and not parasitic. Fish curl around the ctenidium during the day and capture microcrustaceans when the fish emerge from their host at night to feed. From low-light infrared video record- ings, Carapus was observed to accurately grasp rapidly swimming amphipods in nearly total darkness and ingest them. This symbiotic relationship appears to benefit Carapus by allowing the fish to avoid predators during the day and to forage at night.

Carapid pearlfishes are free-living, com- ates that shelter within (but not inside the mensal or parasitic (Trott 1981, body cavity of ) the host. Some carapid spe- Parmentier and Vandewalle 2005). Those cies enter the coelom of their hosts, but this that are inquiline commensals are reported was not observed in Carapus mourlani in our to occupy holothurians, sea stars, or bivalve study. molluscs (Trott 1970, Markle and Olney It has also been suggested, but not demon- 1990, Paredes-Rios and Balart 1999). The strated, that some carapids facultatively oc- terminology adopted herein follows Castro cupy polychaete worm tubes (Williams and (1988). is defined as a close hetero- Shipp 1982) and sponges (Ayling and Cox specific association irrespective of harm or 1982). Many possess a propen- benefit to the partners. Commensals are sym- sity for finding shelter in a variety of inani- bionts with no metabolic dependency (e.g., mate substrates and as such their hiding food, growth factors) between the members behavior in a particular host can be described of the association. Inquilines refer to associ- as facultative rather than obligate (Svetovidov 1961, Markle and Olney 1990). This is the first report of a pearlfish, Carapus mourlani 1 Support was provided by U.S. National Science (Petit, 1934), inhabiting the mantle cavity Foundation grant OCE-0526361 and earlier awards. of a large opisthobranch mollusc, Dolabella Manuscript accepted 26 October 2007. 2 Corresponding author (e-mail: pglynn@rsmas auricularia (Lightfoot, 1786), in the Gulf of .miami.edu). Chiriquı´, Panama´. 3 Division of Marine Biology and Fisheries, Rosen- Four of carapids are recognized stiel School of Marine and Atmospheric Science, Uni- from the eastern tropical Pacific (Markle and versity of Miami, 4600 Rickenbacker Causeway, Miami, Olney 1990, Parmentier et al. 2006). They Florida 33149-1098. 4 California Academy of Sciences, San Francisco, Cal- are exilium (Rosenblatt, 1961), which ifornia 94118-4599. are free-living as adults; Carapus dubius (Put- 5 Marine and Atmospheric Science Program, Univer- nam, 1874), which inhabits bivalve molluscs; sity of Miami, Coral Gables, Florida 33124-0411. Carapus mourlani, an associate of sea stars and holothurians (Markle and Olney 1990); Pacific Science (2008), vol. 62, no. 4:593–601 and vermicularis (Muller, 1842), : 2008 by University of Hawai‘i Press an obligate parasite of the holothurian Actino- All rights reserved pyga lubrica (Sluiter).

593 594 PACIFIC SCIENCE . October 2008

Carapus mourlani was first reported from from the reef framework. Collections were the eastern Pacific on the basis of specimens made from 2002 to 2005, the first 6 months found to inhabit the Isostichopus after emplacement of the rubble bags, then fuscus (Ludwig) off the Ecuador coast (Par- at yearly intervals thereafter. Dolabella and mentier et al. 2006). Twelve C. mourlani Carapus were also collected at 4–6 m depth were found within the coelomic cavity, respi- along the south shore of the Uva Island ratory tree, or digestive tracts of the 4,345 embayment when the opisthobranch host (0.28%) I. fuscus that were collected between emerged at night. The presence of Carapus depths of 5 and 60 m and examined. Carapus inhabiting Dolabella was determined when mourlani is widely distributed in the tropical the oxygen concentration declined and the Indo-Pacific from East Africa to Hawai‘i and fish exited the host. The emerging fish were throughout Micronesia. In the central to then quickly revived with frequent water western Indo-Pacific it is known to inhabit changes and aeration. Symbionts employed the asteroids novaeguineae Mu¨ller & in long-term observations were reintroduced Troschel, Pentaceraster cumingi (Gray), Cho- to their hosts and maintained in flow-through riaster granulatus Lu¨tken, and Acanthaster aquariums until shortly before departure to planci (Linnaeus) and the holothurians Sticho- Miami, Florida. About 4 hr before the flight, pus variegatus Semper, Stichopus chloronotus symbiont-host pairs were placed in polyethyl- Brandt, argus Ja¨ger, Actinophya ene bags containing approximately 1 liter of muritiana (Quoy & Gaimard), and filtered seawater and 2 liters of 100% oxygen. scabra Jaeger (see Markle and Olney 1990). Bagged specimens were placed inside a large cooler and transported as cargo aboard a materials and methods flight to Miami. Upon arrival, the symbionts were immediately moved to flow-through Dolabella auricularia, a member of the opis- aquariums at the Rosenstiel Marine School, thobranch family Aplysiidae, is an uncom- University of Miami. monly large sea slug easily recognized by its were maintained in powder- truncated posterior border, which forms a coated, metal screen–covered (to prevent es- sloping, disklike shield with elongated simple cape) 40-liter aquariums supplied with sea- papillae covering the dorsum (Camacho- water from Biscayne Bay. Aquariums were Garcı´a et al. 2005). Dolabella is the largest sea kept in subdued lighting during the day and hare present in the tropical Indian and Pacific in darkness at night. Large rocks were placed , reaching 0.5 m in length. It is widely in each aquarium to provide shelter for the distributed from the Red Sea to the tropical cryptic habit of the molluscan hosts. The eastern Pacific, including the Hawaiian and hosts were fed several times a week with Gala´pagos islands (Gosliner et al. 1996). Car- green filamentous (Derbesia sp.) and brown apus mourlani, family Carapidae, is a common Stypopodium zonale algae. The algae were col- species and differs from other carapids in its lected from Biscayne Bay and contained dentition, swimbladder morphology, and col- abundant associated microfauna. oration. It reaches 17 cm in total length Observations on the exit and entrance be- (Markle and Olney 1990). havior of several fish were conducted during The majority of the symbionts were cap- the day and night. Behavioral observations tured during the day in 25- to 30-liter- in aquariums were obtained with a remote, volume mesh bags of Pocillopora spp. coral night-vision, digital video recorder (DVR). rubble anchored at 3–6 m depth on the sea- An infrared (IR) LED (light-emitting diode) ward side of the Uva Island coral reef. The illuminator was positioned over an aquarium coral reef is on the west side (07 49 0 N, 81 and programmed to turn on automatically at 46 0 W ) of Uva Island in the Gulf of Chiri- low light levels, beginning before sundown quı´, Pacific Panama´ (Figure 1). The bundles and ending after sunrise. A low-light IR- of rubble were located about 5 m downslope sensitive bullet camera was connected to a Pearlfish Inhabits an Opisthobranch Mollusc . Glynn et al. 595

Figure 1. Dolabella auricularia collection sites in the Gulf of Chiriquı´, Panama´. 1, Uva Island coral reef; 2, south shore of Uva Island embayment; 3, Canal de Afuera Island; 4, north shore of Coiba Island; 5, Jicarita Island; 6, coral reef on unnamed island in the Secas Islands group.

DVR (Archos 504) and was positioned to re- and other organs, and gut contents, respec- cord the symbionts. An aquarium divider was tively. All of these specimens were living to- used to constrain the symbionts within the gether. Two of the opisthobranch hosts were field of view. Video files were later uploaded from field-collected (March 2005) specimens. to a computer and symbiont activity was sub- The remaining two hosts and four fish sym- sequently observed. bionts were collected 18–22 March 2006 at The total body lengths (TL) of Carapus Uva Island and remained together in aquari- preserved in 70% ethanol were measured to ums for about 3 months. Specimens of C. the nearest millimeter. Live body lengths mourlani are deposited in the Ichthyology and weights of 27 specimens of Dolabella Department of the California Academy of were obtained within a few hours after cap- Sciences (cas), San Francisco, California, and ture. Length measurements were taken from the Virginia Institute of Marine Sciences naturally relaxed individuals and weights (vims), Glouster Point, Virginia. Included from animals blotted for about 30 sec with are cas 225463 (85 mm TL); cas 225464 absorbent paper towel. A least squares regres- (84 mm TL); cas 225465 (85 mm TL); cas sion analysis was performed on these 27 indi- 225466 (68 mm TL); cas 225467 (77 mm viduals. The weights of nine individuals were TL); cas 225468 (73 mm TL); cas 225469 estimated from their lengths according to the (82 mm TL); cas 225471 (87 mm TL); cas regression relationship noted. 225472 (76 mm TL); cas 225473 (87 mm Four individuals each of Dolabella and Car- TL); vims 12001 (TL not measurable); vims apus preserved in 70% ethanol were dissected 12002 (71 mm TL); vims 12003 (74 mm to determine the condition of the ctenidia TL); and vims 12004 (71 mm TL). 596 PACIFIC SCIENCE . October 2008

TABLE 1 Numbers of Carapus mourlani Found in Association with Dolabella auricularia Collected from Rubble Bags at 4–6 m Depth on the Seaward Front of the Uva Island Coral Reef, 2002–2005

Location on Reefa Date No. Dolabella No. Carapus Car./Dol.b Mean Prevalence

North 19 Sept. 02 1 0 — 10— 7 Mar. 04 8 1 1 9 Mar. 05 1 0 — 10 Mar. 05 4 0 — 0.067 Center 4 Mar. 03 1 1 1 411 30— 15 Sept. 03 2 0 — 10 Mar. 05 1 2 2 11 Mar. 05 4 1 1 12 Mar. 05 4 0 — 0.263 South 17 Sept. 02 5 1 1 9 Mar. 03 10 2 1 14 Sept. 03 1 1 1 13 Mar. 04 6 5 1, 2, 2 15 Mar. 05 2 0 — 7 4 ? 0.419 Overall mean prevalence 0.292

a North, center, and south sectors of reef. b Denotes number of Carapus per host when inquiline was present.

results liner at Isla Jicarita in 2003 (Figure 1, site 5). The presence of Carapus was determined by On the Uva Island coral reef, the overall introducing Quinate (active ingredient qui- mean prevalence of adult Carapus mourlani naldine) to the mantle cavity. Six adult C. with Dolabella auricularia was 0.292 (Table 1; mourlani were found by Robertson inhabiting Figure 1, site 1). The prevalence of the sym- D. auricularia collected from under rock scree biosis was highest at the south end of the reef with a prevalence of @0.01. Finally, 22 Dola- (0.419) compared with the north (0.067) and bella were collected in March 2003 from un- central (0.263) reef sectors. Most Dolabella der coral blocks at 1 m depth on a reef flat ðn ¼ 8Þ hosted single individuals, but three in the Secas Islands (Figure 1, site 6), but different hosts contained two fish each. Dola- none of these contained the inquiline. Only bella collected at night (March 2005, 0100– two tenuis-stage larvae were found over the 0200 hours; March 2006, 2100–2200 hours) course of this study. They were collected while grazing along the coral/rock bottom of from Dolabella in rubble bags on March 2003 the south shore embayment (Figure 1, site 2) from central and south Uva reef locations. exhibited a prevalence of 0.22 (4 Carapus/18 Euapta godeffroyi (Semper), the only other Dolabella). Three C. mourlani were associated large abundant holothurian at the study site, with nine Dolabella (prevalence ¼ 0.33) col- did not host C. mourlani. Examination of lected during the day from under pocilloporid 60 individuals of E. godeffroyi collected from blocks along the leeward side of Uva reef. rubble bags across the reef front during The carapid inquiline was also found inhabit- 2002–2005 did not reveal associated carapids. ing D. auricularia by D. R. Robertson (pers. Numerous specimens of Acanthaster planci, comm.) in 2003 at Canal de Afuera Island another potential host, were examined and and along the north shore of Coiba Island dissected at the Uva reef and from other lo- (Figure 1, sites 3, 4), and by Terence M. Gos- calities in the Gulf of Chiriquı´ from 1970 to Pearlfish Inhabits an Opisthobranch Mollusc . Glynn et al. 597

Figure 2. Head of Carapus mourlani protruding from inhalant siphon of Dolabella auricularia (arrow) recently collected at the Uva Island coral reef, March 2004.

2006. Carapus was not found in that species after sunset and enter the exhalant siphon either. headfirst after varying times of free- Field observations of recently captured swimming activity. The times outside the fish showed them to enter the host’s mantle host varied from 24 to 587 (9.8 hr) min. On cavity headfirst through the anteriorly located two occasions, fish exited and entered its inhalant siphon. However, on several occa- host twice. During 10 nocturnal video rec- sions fish explored the inhalant siphon area ords over a 2.5-month period, Carapus failed headfirst then quickly inserted their tails and to emerge from its host. backed in to the mantle cavity tail first. This Fifteen C. mourlani collected from Dola- tail-first entry was executed quickly, in from bella in rubble bags over the period 10–15 2to@25 seconds, by vigorous body wriggling March 2005 had ethanol-preserved mean (1 (Figure 2). A few fish were observed to exit sd) lengths and wet weights, respectively, of their hosts headfirst from the exhalant siphon. 81.3 (6.9) mm and 0.83 (0.32) g. Total lengths In no instance did the activities of Carapus ranged from 68 to 97 mm and weights cause Dolabella to contract or release ink. from 0.315 to 1.534 g. The Dolabella length- Video records (n ¼ 13, @12 hr nocturnal weight relationship for 27 individuals (Figure observations each) over a 4-month period 3) is expressed as the power function y ¼ (November–March) showed a hidden fish to 0:040X 3:271 ðr 2 ¼ 0:893Þ. Nine individuals emerge headfirst from the inhalant siphon with known lengths only are also plotted in 598 PACIFIC SCIENCE . October 2008

Figure 3. Body length and mass relationship of live Dolabella auricularia collected at the Uva Island coral reef ðn ¼ 36Þ. Solid symbols denote Dolabella hosts with Carapus mourlani. The number 2 identifies hosts that contained two fish symbionts.

Figure 3. Carapids occurred with Dolabella covered with the brown alga Stypopodium zo- over a wide range of host sizes, from 10 to nale. Amphipods, 4–6 mm in body length, 20 cm in length. The smallest and largest Do- were captured as they swam rapidly upward labella hosts contained two and one C. mour- from the algal substrate. The carapid quickly lani, respectively. The two tenuis larvae were sensed the location of the amphipod in nearly 143 and 153 mm in length. Their specific total darkness, from distances of 2 to 4 cm. In hosts could not be identified. some instances, detection seemed to involve Upon visual inspection of four dissected the swimming motion of the prey because Dolabella that hosted carapids, none revealed the fish was oriented in the opposite direc- damage to tissues lining the mantle cavity or tion. Adult carapids such as C. mourlani have damage to the ctenidium, digestive gland, a moderately developed lateral line and ce- gonad, and kidney (Figure 4). Another indi- phalic pore system that would allow the de- cation that the host’s gonads were not im- tection of such prey movements. The fish paired is from reproductively active Dolabella grasped each amphipod and crushed and harboring the fish inquilines. On 13 March swallowed body parts. On a few occasions, 2004, six Dolabella hosting five carapids at the amphipods were captured, momentarily south end of Uva reef were aggregated and chewed, and then rejected. Other swimming laying large masses of eggs. crustaceans (ostracods and mysids) also were On several consecutive nights (4–13 detected, captured, and ingested. Multiple March 2007), the infrared video recordings feedings per night were observed. One night showed C. mourlani feeding on swimming a carapid captured and ingested five crusta- crustaceans that had emerged from a rock ceans. Pearlfish Inhabits an Opisthobranch Mollusc . Glynn et al. 599

Figure 4. Dissected mantle cavity of Dolabella showing exposed, undamaged ctenidium. A Carapus sheltered in this aquarium-confined host for about 3 months.

Examination of the adult buccal cavity re- stant supply of inhalant water that irrigates vealed well-developed dentition with numer- the single ctenidium, over which Carapus is ous backward-directed, needlelike teeth on coiled, ensures a sufficiently oxygenated me- the upper and lower jaws. The two or three dium. Besides benefiting from the shelter teeth anteriorly on the vomer are stout and provided by Dolabella, it is possible that the large, and located along the midline of the host’s grazing activities on algal substrates roof of the mouth. The same arrangement expose mobile microfauna that can then be of teeth was present but less well developed more readily detected and consumed by the in the tenuis larval stage. pearlfish. This would be ecologically equiva- lent to hamlets that follow parrotfish and discussion surgeonfish schools, feeding on and fishes flushed from algal turfs by the The presence of two fish per host is not un- grazing (Ogden and Buckman common among carapid symbioses. As many 1973). Meyer-Rochow (1979) suggested that as 15 and 19 Carapus mourlani, respectively, some hosts of C. mourlani may offer a source were reported in single individuals of a holo- of prey. For example, the cushion sea star thurian and an asteroid species (Meyer- Culcita, a common host of pearlfish in the Rochow 1977). At least one of the fish was central and West Pacific, generally shelters present in the holothurian’s coelom. It is like- shrimp that may be consumed by Carapus. ly that the paired C. mourlani found in Dola- No commensals were observed bella in our study were of the opposite sex, on Dolabella. although this was not verified (Trott 1981). Another possible advantage of Carapus The relatively large and nearly totally en- sheltering in Dolabella is the ability of this closed mantle cavity of Dolabella renders this host to sequester noxious second- a suitable resting space for Carapus. The con- ary metabolites from its algal diet. The con- 600 PACIFIC SCIENCE . October 2008 centration of unpalatable chemicals would froyi, due to the presence of anchor ossicles, likely render Dolabella less likely to be con- would offer an entanglement hazard to Cara- sumed by potential reef predators. Pennings pus. et al. (1999) demonstrated from feeding as- The ability of Carapus mourlani to feed says on reefs at Guam that the skin, eggs, under subdued light conditions demonstrates and digestive glands of D. auricularia were a capacity to detect and capture rapidly mov- unpalatable to reef fishes. The opistho- ing prey at night. Meyer-Rochow and Tiang branch’s ink also likely plays a role in chemi- (1978) showed that the eyes of C. mourlani cal defense, due to the concentration of a are fully functional and concluded (p. 583) dietary-derived red algal pigment (aplysiovio- ‘‘that the eye of C. mourlani is basically a lin). The unpalatable nature of the host’s tis- photoreceptor designed for vision in a dark sues might also discourage feeding by the fish environment characterized by high sensitivity symbiont. and poor resolution, but that its visual perfor- A study conducted in the South Moluccan mance drops with age.’’ It is also possible that Sea, based on gut analyses of adult C. mour- the swimming activities and pressure changes lani associated with (asteroids generated by potential prey serve to alert C. and holothurians), demonstrated that de- mourlani of a feeding opportunity. capod crustaceans, probably polychaetous an- Considering the nocturnal feeding behav- nelid worms, and small fishes were consumed ior, visual sensitivity under low-light condi- by the symbiont (Meyer-Rochow 1979). An- tions (Meyer-Rochow and Tiang 1978), and other line of evidence, from the stable isoto- the adaptations of the buccal apparatus for pic composition of adult muscle tissue of C. feeding, it is likely that the diurnal association mourlani living in the coelomic cavity of a of Carapus mourlani with a variety of hosts cushion sea star in French Polynesia, supports evolved in response to avoid visual preda- the earlier findings of a nonparasitic associa- tors. Based on the structural and behavioral tion (Parmentier and Das 2004). Our results, specializations in feeding, adult C. mourlani of nocturnal feeding on crustaceans and no can be justifiably placed among grasping apparent damage to the opisthobranch host’s hunters. internal organs, also support those studies. Two tenuis-stage larvae were found with Do- acknowledgments labella, but we were not able to determine their feeding habits. Jangoux (1974) noted John E. Olney kindly identified the carapid that the young stages of C. homei (Richard- species. We thank Tyler B. Smith and Juan son) are more inclined to than L. Mate´ for photographic help, and C. M. adults, consuming the gonadal tissues of their Eakin, Vincent Flynn, Peggy Fong, Gena asteroid hosts. This claim is suspect, however, Hockensmith, Derek Manzello, and Matt because his description of the fish is incor- Whartian for field and laboratory assistance. rect, and C. homei does not inhabit asteroids The feeding and maintenance of animals was and is not parasitic. performed by Tara Dolan, Carla Ferna´ndez, Acanthaster planci occurs at the Uva reef, Tally Holcombe, Daniel Holstein, Lindsay sometimes at relatively high population den- Jones, Margarita Kruyff, Megan Porter, and sities (25–30 individuals ha1) but has not Erin Reilly. Jonathan Walkenstein (Non- been observed hosting C. mourlani as in the linear Dynamics Laboratory, University of western Pacific (Cheney 1973). On Guam, A. Miami) and Aaron Jozsef offered technical planci is probably not a major host of Carapus advice on the IR illuminator and camera de- because only around 1% of 450 sea stars sign. Information on Carapus mourlani collec- contained the inquiline. The only large holo- tions from Panama´ were provided by D. R. thurian present at the Uva reef is Euapta god- Robertson and Terence M. Gosliner. Permis- effroyi, but C. mourlani has not been found to sion to work and collect specimens in the inhabit this species either. It is possible that Coiba National Park was authorized by the the sticky body wall and tentacles of E. godef- Autoridad Nacional del Ambiente (ANAM), Pearlfish Inhabits an Opisthobranch Mollusc . Glynn et al. 601

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