Pacific Science (1984), vol. 38, no. 2 © 1984 by the University of Hawaii Press. All rights reserved

Distribution and Ecology of Shallow-Water Crinoids at Enewetak Atoll, Marshall Islands, with an Annotated Checklist of Their Symbionts!

D. L. ZMARZLy 2

ABSTRACT: Six species ofcomatulid crinoids were found to inhabit coral reefs between depths of 3 and 36 m at Enewetak Atoll , Marshall Islands. These species were Eudiocrinus tenuissimus, Dorometra nana, Comaster gracilis, Comanthus bennetti, Comanthus parvicirrus, and Comanthina schlegeli. The first four species were previously recorded from other atolls in the Marshall Islands, but Comanthus bennetti was the only species reported from Enewetak. Comanthus parvicirrus and Comanthina schlegeli have not been previously recorded for the area . Nine shallow-water species are now known from the Marshall Islands, compared to 2I species from the Palau Archipelago and 7from Guam. At Enewetak, abundance and diversity of crinoids were greatest at sites with exposure to regular current flow, and depth zonation of species was ap- . parent. Three of the species at Enewetak were polychromatic; color varieties found at Enewetak are compared to those documented for conspecifics at other Indo-Pacific locations. Spatial distribution patterns and relative abundances of the noncryptic crinoids at three sites remained nearly constant over a half-year period. No mortality or recruitment was observed in the monitored populations. Eighteen species of macro-invertebrates were found in association with the crinoids: 3 species of gastropod mollusks, 3 species of myzostomid worms, 1 species of scaleworm, 1 species of copepod, and 10 species of decapod crustaceans.

STUDIES OF THE BATHYM ETRIC and zoogeo­ Fishelson (1969), and Fishelson (1974) con­ graphic distribution of crinoids, initiated ducted in situ studies on crinoids in the Red nearly a century ago, relied on specimens ob­ Sea, but comparatively little work has focused tained by large-scale dredging (e.g., Bell 1884; on Indo-West Pacific comatulids except for Carpenter 1888; A. H. Clark 1909, 1911a, that of H. L. Clark (1915), Macurda and 1911b; H. L. Clark 1921; Hartlaub 1895, Meyer (1975, 1976), Meyer and Macurda 1912). More recently, our knowledge of (1980), and Zmarzly and Holland (1981). . species composition, bathymetry, and ecol­ These in situ studies are mainly ofshort dura­ ogy of shallow-water crinoid faunas has tion, involving observations over periods of been greatly increased by the use of skin- and days to weeks. SCUBA-diving. Extensive field studies on Longer term observations ofcrinoid popu­ the ecology and distribution of Caribbean lations inhabiting shallow tropical seas are crinoids were reported by Meyer (1971 , 1973a, lacking. In Palau, Meyer and Macurda (1980) 1973b), Macurda (1973,,1975), and Meyer and found the number of Cenometra bella Macurda (1974). Magnus (1967), Rutman and (Hartlaub) in a small area to be nearly con­ stant during visits in two consecutive years. From this observation, they suggested that C. 1 This field research was made possible by the suppor t belLa, ~ItllO_Ugh capable of active swimming , and facilities o f tne -M id ~P ii cific Research Lab oratory. maintains stable populations in favorable Manu script accepted 30 December 1983. 2 University of California, San Diego, Scripps areas. Clearly, continuous monitoring is Institution of Oceanography, A-008, La Jolla, California needed to assess parameters such as in­ 92093. dividual longevity, frequency of migration 105 106 PACIFIC SCIENCE, Volume 38, April 1984

120° 140° 160° 18 0 °

,I .J .. Pa cif ic Ocea n Hawaiian .I.slands 20° ...... 20°

Enewelak' ' " Marshall ,.••.·'::.Islands • • Palau ' . . ~ Islands

"$-. I- Bikini~ (Rongelap • - (2°N !l 0 ~ E n ew e l a k ,<1 ·Rongeri k f- .' Kwajalei~ Likiep' - .-"'\) '" • ~ f- Ma rshall 8° cl 20 0S ~ Islands " .... A rn o~ f- Jaluih

Ebon_ I 4° 162°E 166° 170 °

FIGURE I. Map of Pacific Ocean showing location of Enewetak Atoll, Marshall Islands, with inset showing distribution of atolls in the Mar shall Island s where crinoids have previously been collected.

within and between sites, and frequency of MATERIALS AND METHODS recruitment. This paper synthesizes crinoid records pre­ This investigation was carried out over a 6 viously published for the Marshall Islands month period from June through November with new data on the species composition and 1980. Abundance and distribution ofcrinoids distribution patterns of the crinoid fauna in­ at seven sites about the atoll , which differed in habiting reefs to 36 m at Enewetak Atoll topography, currents, and depth range, were (11°30' N, 162°10' E, Figure 1). Observations determined by diving with SCUBA. All on crinoid populations monitored in situ at SCUBA surveys were conducted during the intervals over a 6 month period are also day. Site locations are shown in Figure 2; presented. habitat descriptions are given in Table 1. In the course of this study, the taxonomy All sites, except site 3, where crinoid density and ecology of symbiotic organisms living on was extremely high, were surveyed by swim­ the crinoids were also investigated. Potts ming over the .study area and recording the (1915) presented observations on the as­ species, color variety, and depth ofall fully or sociates of northern Australian crinoids, with partially visible crinoids. No effort was made reference to their color resemblance to their to reveal cryptic species. For logistical rea­ host. Fishelson (1974) reported 27 associate sons, sites 1, 5, 6, and ' 7.were surveyed only species from 14crinoid species in the northern once for species present. Sites 2,3, and 4 were Red Sea. Preliminary observations on species resurveyed on a biweekly 'basis to monitor composition andother structural aspects .of changes inthe crinoidpopulationsovertime. the community of invertebrates living in as­ At site 3, abundance and bathymetric dis­ sociation with crinoids at Enewetak Atoll are tribution of noncryptic crinoids were studied reported herein. by census ofa transect area established on the

"" Shallow-Water Crinoids at Enewetak-ZMARZLY 107

Enewetak Atoll

. ~ 1 l ago on \ \ 7 0 4 Sou thwe st . ~ J Pas sa ge ~ 3,5 ... ~ 6 t 2 Deep Channel N I ( o !

FIGURE 2. Map showing locations of sites surveyed for crinoids at Enewetak Atoll. reef slope between 9 and 36 m depth . The crinoids. Color pattern, coupled with loca­ tran sect area was 50m long; horizontal lines tion , was used to identify individual crinoids were spaced along the reef slope 4m apart, during resurveys so that disturbance by physi­ which represented approximately 3 m depth cal tagging was avoided . The perches of 10 intervals. The total area censused covered crinoids were marked with surveyor's tape 2000m' . The area was mapped on an under­ for additional reference points . Photographs water slate, and crinoid s were counted by were taken in situ to record living position, making a single pass up one side of the tran­ substrate, and color varieties of each species. sect line and down the other side. The species, For analysis ofsymbiotic organisms, single color variety, and location of all individuals crinoids were isolated in plastic bags in the within 2 m perpendicular to each transect line field. Species, location, depth, and color were recorded. Crinoids on the border be­ variety were recorded for each individual. The tween two transects were assigned -to one of specimens were then transported to the labo­ the transects by the flip of a coin. The rnap was ratory, where they were transferred to indi­ used during subsequent resurveys to moni­ vidual containers with fresh seawater. tor changes in distribution of noncryptic Symbiotic organi sms were removed from 108 PACIFIC SCIENCE, Volume 38, April 1984

TABLE I

HABITAT D ESCRIPTIO NS OF ST UDY SIT ES SURV EYED FOR CRINOIDS AT E NEWETAK ATOLL

DEPTHS STUDY SITE HABITAT TYP E CURRENT SURVEY ED (m)

Patch reefs on gradually sloping sand bottom Generally slack . 3-10.5 within lagoon 2 Patch reefs on sand bottom within lagoon; Weak and variable 6-21 bottom steeply sloping to Deep Channel entrance 3 Steep reef slope on east side of wedge Strong daily flows 9-36 protruding into Deep Channel 4 Isolated cora l pinnacl e inside lagoon Downstream from 6-36 flow at site 3; current channeled by local reef formations 5 Steep reef slope on west side of wedge Strong daily flows 9-36 protruding into Deep Channel 6 Windward seaward reef Weak and variable 9-36 7 Leeward seaward reef Generally slack 9-30

crinoids by sealing the container, bubbling ments at Enewetak Atoll: Coman thus ben­ nitrogen gas through the water for 10-15 mi­ netti . (J. Muller), Comanthus. parvicirrus nutes to narcotize the symbionts, then agi­ (J. Muller), Comanthina schlegeli (P. H . tating the host slightly to dislodge clinging Carpenter), and Comaster gracilis (Hartlaub), organisms. Symbionts and hosts could be re­ family Comasteridae; Eudiocrinus tenuissimus vived, if desired, by transferring them to fresh Gislen, family Eudiocrinidae; and Dorometra seawater. To check the thoroughness of sym­ nana (Hartlaub), family Antendonidae. The biont removal by the nitrogen narcotization first four species were common, while E. ten­ procedure, seven randomly selected crinoids uissimus was collected only once under a ledge (approximately 10 percent of the sample on a seaward reef. Dorometra nana was not group) were fixed in 70 percent ethanol, and encountered by the author but was collected their arms were individually examined under a at Enewetak on two occasions by other work­ microscope for an y remaining symbionts. A ers (D. M. Devaney, pers. comm.). Any strictly total of two small scaleworms were found nocturnal species were probably missed since during this procedure. The cross-check was no night dives were made. performed on only one ofthe host species but The crinoid species encountered at was considered representative ofthe effective­ Enewetak were readily distinguished during ness ofthe nitrogen procedure in defaunating the daytime in the field by differences in color other crinoid species. patterns, form, and habits. Comanthus ben­ Following removal of epizoic organisms, netti and Comanthina schlegeli are relatively the digestive tract of each crinoid was ex­ large , robust, extremelymultibrachiate amined for endoparasites. Some symbiotic or ­ species. In adult Coman thus bennetti the ganisms were immediately fixed in 70 percent average number of arms was 100 (n = 37), ethanol for later analyses; others were kept with arm length about 18 em . Adult alive in flow-through containers for be­ Comanthina schlegeli averaged 130 arms havioralobservation: (n= 5) about 15 em in length-Both were non­ cryptic by habit. Coman thus bennetti was RESULTS found perching on live coral heads (mainly Six species of comatulid crinoids in three Pocillopora spp.) or dead coral outcrops ele­ families were found in shallow-water environ- vated well above the reef, with its arms ex-

' -4 Shallow-Water Crinoids at Enewetak- ZMARZLY 109

. F IGURE 3a. Comanthus bennetti , showing arc uate fil­ F IGURE 3b. Comanthus bennetti, showing arm postu re of tration fan assumed when feeding. Arm length about nonfeeding individual; depth 3 m. 18 em; depth 12 m.

tended into an arcuate filtration fan (Meyer flows which were characteristic ofits environ­ and Macurda 1980) when feeding. When the ment. Comanthina schlegeli typically had 5 to animals were not feeding, the arms were 20 short (1.8 to 2.0 em) cirri, and several ofthe curled inward over the oral disk (Figures 3a, lower arms were used in addition to the cirri 3b). Small Comanthina schlegeli often had for tethering animals to their perch. In other their oral disk wedged in a crevice or beneath areas of the Indo-West Pacific, the cirri of a soft coral, but adults were found perching Comanthina schlegeli are reported as highly underneath or on the side of ledges or out­ variable in number or altogether lacking crops or wedged between the branches of the (Clark and Rowe 1971 :pI. 1, fig. 6; Meyer coral Millepora tenera (according to Wells' and Macurda 1980). 1954 classification) (Figure 3c). The arms of Comas ter gracilis and Coman thus parvicir­ Comanthina schlegeli were typically held in a rus, with fewer arms, were only partially vis­ meridional arrangement over the oral disk. ible by day. Their oral disks and the basal The most easily detected difference between parts of their arms were generally buried Comanthus bennetti and Comanthina schlegeli within the reef, with only the tips of the arms was the number and length of cirri. emerging. The arms of Comaster gracilis were Comanthus bennetti typically possessed 30 to long and slender, with the tips often curled 35 clawlike cirri, 4.0 to 4.5 em in length , which into tendrils (Figure 3d ). The pinnules on the were used in anchorin g the animal firmly to its arms were thin and more widely spaced than perch , especially during the strong current tho se of Comanthus parvicirrus, which were 110 PACIFIC SCIENCE, Volume 38, April 1984

FIGURE 3c. Comanthina schlegeli, showing large adult FIGURE 3d. Comaster gracilis, showing daytime emer­ clinging to branches of a milleporid coral; depth 24 m. gence of arm s from reef; depth 15m . longer, thicker, and more closely aligned . Polychromatism Comanthus parvicirrus was sometimes found wedged between the branches of the large With the exception of Coman thus parvicir­ shrub coral, Pocillopora eydoux i (Milne­ rus and Eudiocrinus tenuissimus, the crinoid Edwards and Haime). Comaster gracilis had species at Enewetak were polychromatic. no cirri; the cirri of Comanthus parvicirrus Comanthina schlegeli had five recurring color were short (1.0 to 1.3 em) and few in number varieties (Table 2). Varieties CSl , CS3, and (see Meyer and Macurda 1980, fig. 6g and h). CS4 were common, while CS2 and CS5 were Eudiocrinus tenuissimus was encountered comparatively rare. only once, under a ledge on the leeward sea­ Four recurring color varieties, listed in ward reef. This small species had five arms of Table 3, as well as several nonrecurring types approximately 45 mm length. The cirri were were noted for Coman thus bennetti. CB1 was well developed, about 4 mm in length, 12 to the variety most frequently encountered, en­ 15 in number, and had a distinct beaded compassing 69.5 percent of the individuals in appearance. the transect area (site 3). CB3 was found ex­ The ten-armed Dorometra nana is ofcryptic clusively at depths exceeding 2l.m. habit and was collected under coral rubble The partially cryptic Comaster gracilis had both on the windward reef and in the lagoon only three color varieties. Most commonly the (D. M. Devaney, pers. comm.). arms and pinnules were golden orange, but Shallo w-Water C rinoids a t E neweta k-Z MARZLY III

TABLE 2 COLOR VARIETIES OF Coman thina schlegeli ATENEWETAK ATOLL

DESIGNATIO N ORAL DISK CIRRI DIVISION SERIES & ARMS PINNULES

CSI Brown, often with White with Oran ge or orange-brow n; Brown with yellow tip s except white spots brown or ra ndom white varie- for variegatio ns where orange gations enco mpassi ng pin nules are white with ba nds brachials and pinnules yellow tips CS2 Or an ge-bro wn with Wh ite with Ora nge-brown with random Orange-brown with white tip s white spots o range tips white variegations except for variegatio ns where pinnu les are all white CS3 Black with white Whi te Oran ge or ora nge-brown Black with yellow tips except spots with random white for variega tio ns where variegati on s pinnules are white with yellow tips CS4 Bright yellow Bright yellow Bright yellow Bright yellow CS5 Bright yellow Bright yellow Bright yellow Blac k or brown with yellow tips; random yellow variegations

T ABLE 3 COLORVARIETIES OF Coman thus bennetti ATENEWETAK ATOLL

DESIGNATION ORAL DISK CIRRI DIVISIONSERIES & ARMS PINNULES

CBl Black with bright Same or black Black with brig ht green Black; with yellow tips in green speckli ng speckling some individuals, orange tips in others CB2 Yellow, often Black Yellow Proximally yellow, then du sted with black; with yellow tip s in black or green some individua ls, ora nge tips in others CB3 Light ora nge; some Light ora nge Light orange Oran ge darkening to brown with white distally; indi vidu als either markings on with yellow, orange, or no perimeter ofdisk tip color; sporadic white frosting on pin nules; oral pinnules white CB4 Or an ge-brown Oran ge-brown Orange, ora nge-brown, or Oran ge darken ing to brown brown distally o r brown turning to orange dist ally; individuals either with yellow, orange, or no tip co lor

some individuals were dark brown or reddish Eudiocrinus tenutsstmus. The arm s were bro wn. variegated brown and tan . Narrow maroon Although Comanthus parV1ClITUS is re­ lines flanked each side of the ambulacrum, ported to be highly variable in color at breaking up into stippling on the pinnules. Palau (Meyer and Ma curd a 1980), all in­ The anal cone was tan, with brown and white dividuals of this species at Enewetak were spots. black. No color data were available for Dorometra A single color pattern was also noted for nana.

1 _"_ , ,, _ .,,, ," , _,, ~," , ",-" ~ ' ~~'_ -'_ "' '' ' ''' '' ' " ' ' ''~ _ '' ' '' ' ' .,... __~ ." _.__._. _.. _,_.."...,".....,_..~,.,_, _ ..,._,... ~~ _...... _ . _ .~"~ ..__ ~ _ "...... _ ~..._"_....~_. ~ , ._...... _."".. ~. _ , . .J 112 PACIFIC SCIENCE, Volume 38, April 1984

Distribution ofCrinoids all co-occurred and reached peak abundance at sites 3 and 5; where regular, strong currents The lagoon at Enewetak reaches a max­ flowed. Under these favorable conditions, an imum depth . of 62 m. There are three average density of 0.129 crinoids per m 2 was passages into the lagoon, all in the southern measured. Because the two sites were very halfofthe atoll: the Southwest Passage , which similar, a quantitative survey was carried out . is less than 2 m in depth; the Deep Channel, only at site 3. which is less than 2 km wide but reaches a At site 3, Comaster gracilis and Comanthus depth of58 m; and the Wide Passage, which is parvicirrus, of semicryptic habit by da y, were nearly 10km in width and 11 to 22 m deep. the only species present on the reef flat at One major current stream moves through depths of 9 m and less where the water was these latter two passes, affecting less than a often turbulent. Comaster gracilis was present quarter of the lagoon area. Maximal tidal at all transect depths, but reached peak abun­ flow has been measured at 2 kn in the Deep dance at 21 m. Comanthus parvicirrus was Channel and 1kn in the Wide Passage. Inside most abundant at 24m, its lower limit of the lagoon, a wedge-shaped reef (sites 3 and distribution at site 3 (Figure 4). Densities of 5) protrudes into the Deep Channel from the Comaster gracilis and Comanthus parvicirrus north and receives good expo sure to these in the transect area (2000 m2) were low, 0.017 tidal currents (Emery, Tracey, and Ladd and 0.011 per m", respectively: 1954). Elsewhere, the lagoon bottom ispre­ Mixed aggregations of Coman thus bennetti dominantly sandy and is dotted by patch reefs and Comanthina schlegeli covered promon­ of variable size (sitesl and 2) and coral pin­ tories which projected into current channels nacles (site 4) which rise to within 10m ofthe at this site, especially at depths exceeding surface (see Figure 2 for site locations). While 18m. Otherwise, crinoids typically occurred Comanthus bennetti was the most common as isolated individuals, with the minimum dis­ crinoid at Enewetak, different species domi­ tance between individuals determined by nated the crinoid fauna at different sites. the presence of .suitable substrate. Coman­ Six crinoids were encountered on the small thus bennetti first occurred at 12m and patch reefs within site 1. Five of these were Comanthina schlegeli first occurred at 15m. Comanthus bennetti, with the shallowest oc­ Both species were observed deeper than the currence at 3 m. The . other was a large last transect line at 36 m. Comanthus bennetti Comanthina schlegeli, also at 3 m. was more abundant than Comanthina At site 2, which ranged in depth from 6 to schlegeli at all transect depths where they oc­ 21 m, Comanthina schlegeli was more abun­ curred, but depth zonation of the two species dant than Comanthus bennetti, but the was evident (Figure 5). Peak abundance was Comanthina schlegeli individuals were much reached by Comanthus bennetti between 18 smaller than those encountered elsewhere. · and 24 m, while the abundance ofComanthina Currents at this site were weak and unpre­ schlegeli was greatest between 27 and 33 m. dictable. On two occasions, large particles of Densities of Coman thus bennetti and flocculent material were observed both in the Comanthina schlegeli in the transect area were 2 water column and clinging to the benthic 0.086 and 0.015 per m , respectively. fauna. Maximum densities can be calculated by con­ At site 4, which ranged in depth from 6 to sidering only the number of crinoids in the 36 m, 10 Coman thus bennetti were found in a zone ofpeak abundance, an area of600 rrr' in wedge between 10 and 18 m where local reef both cases. These maximum densities are ap­ formations concentrated current flow. Two proximately two times the overall densities, or Comaster gracilis were also present at this site, . 0.203 . per m ~ for Comanthusbennetti and but Comanthina schlegeli and Comanthus par­ 0.028 per m 2 for Comanthina schlegeli. vicirrus were absent. On the windward seaward reef (site 6), the Coman thus benneiti , C. parvtctrrus, reef sloped gradually to depth, and stony Comanthina schlegeli, and Comaster gracilis corals were not very well developed.

li ...... 24441 ,"'... lJl; iII M t ' n:::m: ; .;g,:; G·.;:" tljii , . 4, j&et!.i, Mi" Shallow-Water Crinoids at Enewetak-ZMARZLY 11 3

10 10 -0 0 --Ci) ::J 8 8 . ~ ·S :-::: .<-> <-> s..... ~ Cl3 tl) C4 6 6 ..... Ci) ~ ::J Ci) is Cl3 E: s 4 0 E: 4 <.J 0 <.J 0 -....0 0 Q) -.... 2 2 ..a Q) E ..a 1\°7- :J . E . 0 - 0-0/ Z :J Z 0 0 9 12 15 18 21 24 27 30 . 33 36

Depth (rn)

FIGURE 4. Depth distribution of Comanthus parvicirrus and Comaster gracilis in transect area, site 3, Enewetak lagoon.

80 10 - 70 ---• • 8 ~ --'i::; ...... 60 tl) Cl) ~ t:: -c t:: <-> Cl) 50 Ci) 6 -Q Cl3 Ci) I e ::J ·s is 40 / "\ / is . / t:: t:: . Cl3 4 30 E: 0E 0 <.J / e " <.J 20 e\ " 0 ....0 2 -.... - Q) Q) ..a 10 .o E .--.---.~ E :J - ~~ / :J Z 0 0 Z 9 12 15 18 21 24 27 30 33 36

Depth (m)

FIGURE 5.Depth distribution of Comanthus bennetti and Comanthina schlegeli in tra nsect area, site 3, Enewetak lagoon. 114 PACIFIC SCIENCE, Volume 38, April 1984

Numerous large tables of A cropora sp. were chaeta (Polynoidae and Myzostomidae), and broken and turned over as a result of storm Crustacea (Copepoda and Decapoda, Caridea damage in 1979 (M. V. DeGruy, pers. and Anomura), were found in association with comm.). No crinoids were found during a four crinoid species at Enewetak Atoll. Sym­ survey between 9 and 36 m. biont species, along with the host species on In contrast, the seaward reefon the leeward which they were found, are listed in Table 4. side ofthe atoll showed a sharp break in slope Eudiocrinus tenuissimus was excluded from at 12m. Corals and other sessile benthic in­ symbiont studies due to its small size and vertebrates were well developed at site 7. Four infrequent occurrence. Over half of the sym­ crinoid species occurred at the site investi­ biont species were associated with a single gated to depths of 30 m: Comanthus bennetti, host species. Only the scaleworm, Paradyte C. parvicirrus, Comanthina schlegeli, and crinoidicola, utilized all four host species. Eudiocrinus tenuissimus. ASSOCIATES OF Comanthus bennetti: Speci­ Persistence ofObserved Crinoid Distribution mens of Comanthus bennetti were collected Patterns from a variety of lagoonal habitats between 3.5 and 36 m depth, in order to makeas broad The distribution ofComanthus bennettiand a survey as possible. Comanthina schlegeli at three lagoonal sites The anomuran crab, Allogalathea (for­ (2, 3, and 4) monitored at biweekly intervals merly Galath ea) elegans, is thought to be ex­ remained nearly constant throughout the 6 tremely common on crinoids across the Indo­ month period. No recruitment, mortality, or Pacific to Japan and South Africa and into the emigration out of the area was observed. At Red Sea (Baba 1969, Haig 1973, Lewinsohn site 3, two Comanthus bennetti moved into the 1969). However, the taxonomy of this species 18 m transect zone in November from some is currently in question (see Baba 1969), and point outside of the transect area itself. This any zoogeographic data reported for A. was considered to be a case of immigration (Galathea) elegans may have to be recon­ rather than recruitment since the animals sidered. At Enewetak, only 23 percent of the were of adult size. The other crinoids re­ Comanthus bennetti sampled were occupied mained on their original perches over the 6 by the crab, although crabs occurred over a months. Random removal of individuals wide depth range from 8 to 36 m. On 50 per­ from monitored populations did not affect the cent ofhosts, A. elegans occurred as a hetero­ established distribution patterns. sexual pair. In the remainder of cases, hosts Another instance of migration was ob­ were occupied by single individuals, generally served at site I, which was not mapped or males. As figured by Fishelson (1974), these resurveyed. During one dive, a single crabs were typically found clinging to the Comanthus bennetti was encountered in tran­ aboral side of the bases of the host's arms, sit. Its imprint in the sand could be followed to with their large chelae pointing outward. a small patch reef about 3 m away. This in­ Allogalathea elegans was also found on an dividual, recognizable by its distinct colora­ alternate host, Comanthina schlegeli, with tion, was found stationary on a nearby patch greater frequency (54 percent). reef the next day. The following day, the same Periclimenes amboinensis and Araiopontonia crinoid was again observed actively crawling odontorhyn cha were the largest of the pon­ over the sand, approximately 8 m from its toniine shrimps associated with Comanthus previous site. bennetti. The two species were similar in size and shape, had robust chelae, and were found exclusIVelyon~C .- -b(m ni?ltCrn botIl species ,-a Fauna Associated with Crinoids at Enewetak single heterosexual pair of shrimp occupied Atoll a host. In addition to their morphological A total of 18 species of macro-invertebrates, similarity and association with the same host representing Mollusca (Gastropoda), Poly- species, both species occupied the oral disk

h' Shallow-Water Crinoids at Enewetak-ZMARZLY 11 5

TA BLE 4

P ERCENT O CCURRENCE OF S YMBIOTIC ORGA NI SMS ON F OUR C RINOID H OST SP ECIES AT E NEWETAK ATOLL

HOST CRINOIDS

Comanthina Comanthus Comanthus Comaster SYM BIONT schlegeli bennetti parvicirrus gracilis SPECIES n = 13 n = 73 11 =7 n = 4

Crusta cea, Decap od a Ga latheida e Allogalathea elegans (Ada ms .& Wh ite) 54 23 Palaemonidae, Pontoni inae Araiopontonia odontorhyn cha F ujino & M iyake 14 Palaemonella pottsi (Borradaile) 46 * 43 50 Periclimenes amboinensis (DeMan) 49 P. commensalis Bor radaile 54 70 P. pilipes Bruce & Zmarzly 46 P . tenuis Bruce 18 Ponton iopsis comanthi Borrad aile t 71 Alpheidae Synalpheus carinatus (De Ma n) 92 29 S. stimpsoni (De Ma n) 71 100 Crustacea, Co pepoda Pseudanthessius comanthi Humes Annelida, Polych aeta Polynoidae Parady te crinoidicola (Potts) 46 48 14 25 Myzostom idae Myzostoma Leuckart sp. I 31 M . sp. 2 t M . sp. 3 15 Mollusca, Gastro po da Unidentified sp. 08 03 Calliostoma Swai nson sp. 08 07 14 Clanculus atropurpureus Gou ld 15

•Only one juvenile P. puttsi was encountered on Comanthus benneIIi. t P. coman thi was fou nd on Comanthus bennetti only once, on a host with no other symbiotic organisms. t Specimens were collected from severa l hosts for taxonomic analysis but presence was not quantitat ively assessed.

of the crinoid. The two species were never 1983). Araiopon tonia odontorhyncha was pre­ found to co-occur, except in a single case viously known only from its type locality in where a juvenile A . odontorhyncha was found the Ryukyu Islands, Japan (Fujino and on a host already occupied by a pair of P. Miyake 1970), until its discovery at Enewetak -amboinensis. Atoll. Araiopontonia odontorhyncha, a rare The small Periclimenes commensalis was species, was encountered on only 14 percent found on 70 percent of the hosts examined, of the Coman thus bennetti examined and was from 3.5 to 36 m depth. P. commensalis is restricted in its occurrence to depths between commonly reported on crinoids throughout 7 and 27 m. Periclimenes amb oinensis, which the Indo-Pacific, from the east coast ofAfr ica was found over the entire depth ran ge sam­ to Hong Kong, New Caledonia, and Australia pled, occurred 3.5 times more often than A. (Bruce 1971 , 1980, 1982). Typically at Ene­ odontorhyncha. wetak, two to three pairso f adults in addition Periclimenes amboinensis, ofwhich the type to several juveniles occurred together on a material from Ambon, Indonesia (DeM an host. These shrimp appeared to occupy the 1888), is no longer extant, has since been re­ distal parts of the arms of the crinoid and ported from Heron Island , Australia (Bruce were frequ ently observed darting between 116 PACIFIC SCIENCE, Volume 38, April 1984

arms. P. commensalis also occurred frequently SYMBIONT SPECIES ON OTHER HOSTS: A pair on another host, Comanthina schlegeli. of alpheid shrimp was generally found Periclimenes tenuis, a smaii and slender on the oral disk of crinoids other than species, often co-occurred on Comanthus ben­ Comanthus bennetti. Comanthina schlegeli netti with P. commensalis, with which it was exclusively occupied by Synalpheus cari­ shared the distal parts ofthe arms ofthe host. natus, with 92 percent of the hosts examined Twelve to ·15 P. tenuis per host was common, inhabited by this shrimp. A closely related with up to half being juveniles. This species species, S. stimpsoni, was the only alpheid was comparatively rare, occurring on only 18 found on Comaster gracilis. Although only a percent ofthe hosts examined. While P. tenuis small number of this host species could be was found between 12 and 36 m, its incidence examined, all were found to carry a pair of S. of occurrence markedly increased to 43 per­ stimpsoni. Comanthusparvicirrus was an alter­ cent on hosts from depths exceeding 18m. In nate host for both alpheid species, although addition, P. tenuis occurred on 100 percent of they were never found to co-occur on a single the hosts of color variety CB3, found only at host. Synalpheus stimpsoni occurred more depths exceeding 21 m. Periclimenes tenuis frequently than S. carinatus in the C. parvicir­ was first described from East Africa (Bruce rus samples. A third species, S. demani,was 1969) and has since been reported from the reported from crinoids at Enewetak by northern Red Sea (Fishelson 1974)and Heron Banner and Banner (1968), but the host de­ Island , Australia (Bruce 1983). termination as Comanthus bennetti is believed Two species of gastropods were occasion­ to be in error. S. demani was 116t collected ally found in association with Comanthus ben­ during the present study and is it compara­ netti. An unidentified parasitic species (sp. 1) tively rare species. Was attached to the host. Snails tentatively Several other pontoniine shrimps were col­ identified as Calliostoma sp. were generally lected from Enewetak crinoids. The recently found in groups of three to six individuals, described Periclimenes pilipes (Bruce and clustered on the substrate under the cirri of Zmarzly 1983) was specific to Comanthina the crinoid, When the crinoid was removed, schlegeli. .Pontoniopsis comanthi was found the snails quickly scattered to the neare st once in association with Coman thus bennetti, cover. This species appeared to be a faculta­ on a host with no other symbionts, but more tive associate at best, but it was frequently commonly occurred on Comanthus parvicir­ encountered. It was also found to shelter rus. Similarly, a juvenile Palaemonella pottsi under Comanthina schlegeli and Comanthus was obtained once from C. bennetti, but parvicirrus. mated pairs of this shrimp were routinely en­ . The polynoid scaleworm, Paradyte cri­ countered on C. parvicirrus, Comaster graci­ noidicola, was found to inhabit Comanthus lis, and Comanthina schlegeli. Neither P. co­ bennetti, in addition to the other three host manthi nor P. pottsi is felt to be a significant species examined. These scaleworms roamed associate of Comanthus bennetti at Enewetak. the arm s of their host , generall y orienting lon­ A comparatively rare myzost omid species, gitudinally in the ambulacrum. Of the C. Myzostoma sp. 3, was epizoic on Comanthina bennetti examined, 50 percent had at least one schlegeli. It was found wrapped around in­ to a maximum of four scaleworms. dividual pinnules, which it mimicked in color­ Two species of myzostomid worms, ation, on the arms of its host. specialized parasites of crinoids and a few The gastropod Clanculus atropurpureus was other echinoderms, occurred on Coman thus found to shelter under the cirri of Comanthina bennetti , one endozoic and the other epizoic. schlegeli in a manner similar to that described Myzostoma sp. 1 typically occurred as a pair, [01' Calliostof11 iL ~P' i n th~ previous secti~n . just inside the mouth ofits host. Occasionally one or two juveniles would also be found. An DISCUSSION epizoic species in the same genus (sp. 2) was ubiquitous on the host specimens examined, Table 5 gives all records of crinoid species with up to 30 individuals on a single host. from atolls in the Marshall Islands. Although

.. ~ , + , :: :: q ¢ t: :e t*j#jU i ,. = i# TABLE 5

R ECORDS OF MARSHALL ISLAND CRINOIDEA

ATOLLS AND COORD INATES WHERE COLLECTED

ENEWETAK BIKINI RONGELAP RONGERIK LIKIEP KWAJALEIN ARNO JALUIT EBON 11°30' N 11°40' N 11°10' N 1I°15'N 10°00' N 9°00' N 7°05' N 6°00' N 4°35' N CRINOID SPECIES 162°10' E 165°25' E 166°30' E 167°40' E 169°10' E 167°40' E 171°45' E 169°30' E 168°45' E

Comasteridae Comanthus bennett ! (J. Muller) Comanthus parvicirrus (1. Mu ller)" Comanthina schlegeli (P. H. Carpenter) Comaster gracilis (Hartlaub) Mariametridae Lamprometra palmata (1. Muller) 3 2*, 3 St ephanometra indica protectus (Liitkenj/ S. indica indica (Smith) 3 21, 3,4* Eudiocrinidae . Eudiocrinus tenuissimus Gislen 3 Colo bometr idae Cenometra bella (Har tlaub) as C. bella var. magnifica 3 Antedonidae Dorometra nana (Hartlaub) + 3 .3

K EY: I = Specimens hou sed in the reference collection of the Mid-Pacific Research Laboratory . 2 = Hartl aub 1912. *(as Antedon brevicuneata ; see A. H. Clark 1952 :303). ' (as Antedon monacantha; synonymized by Gislen 1940: II ). 3 = Gis len 1940. 4 = A. H. Clark 1952. "(as Him erometra heliaster in A. H. Clark 1908; see Clark 1952:303) 5 = Holthui s 1953. 6 = A. H. Clark 1954 (additional record s on p. 263 for Arno Atoll not tabul ated here; see text for explanation). 7 = Banner 1959. 8 = Banner and Banner 1968 (the crinoid host listed as Comanthus bennetti may have been incorrectly identified). 9 = Humes 1972. 10 = Bartolini, Erdman, and Scheuer 1973. + = Present collection. 118 PACIFIC SCIENCE, Volume 38, April 1984

only one species, Comanthus bennetti, was occur at Enewetak but were overlooked. The previously reported from Enewetak (Banner third species, Cenometra bella, is reported to and Banner 1968, Bartolini, Erdman, and perch on certain antipatharians and gor­ Scheuer 1973, Humes 1972), seven species of gonians (Meyer and Macurda 1980), which comatulid crinoids in five families had been were uncommon at the sites investigated; recorded for the Marshall Islands, excluding therefore C. bella may be restricted in occur­ the record of Antedon sp. from Arno Atoll rence by sub strate requirements. (Banner 1957) which is most likely incorrect. The decrease in diversity from 21 shallow­ Specimens of Comanthus parvicirrus and water species in four families in the Palau Comanthus samoanus are erroneously listed Islands to 9 species in five families in the by Clark (1954: 263) from Arno Atoll, M . I. Marshall Islands is consistent with the general but are confirmed to have been collected at attenuation of species which occurs with dis­ Onotoa Atoll, Gilbert Islands (as indicated in tance from the Indo-Pacific center of dis­ Clark 1954: 249) in the records of the U .S. tribution (Clark and Rowe 1971). With the National Museum (Smithsonian Institution), exception of Eudiocrinus tenuissimus, a small where the specimens were deposited (M. E. and cryptic species which may easily be over­ Downey, pers. comm.). Two species, looked, the crinoid fauna of the Marshall Comanthus bennetti and Comaster gracilis, Islands is a subset of that in Palauan waters. were present in the reference collection of the The seven comatulid species found in Guam Mid-Pacific Research Laboratory (MPRL) at are also a subset of the Palauan fauna, yet the time of this work. Comanthina schlegeli Guam and the Marshall Islands have only and Comanthus parvicirrus were not known four species in common (see Meyer and from the Marshall Islands, the closest pre­ Macurda 1980 for species lists from Palau and vious records being the Mortlock Islands in Guam). With some minor variations, the the eastern Caroline group (Meyer and species found at Enewetak conform well to Macurda 1980) and Onotoa Atoll, Gilbert the species descriptions, based on specimens Islands (Clark 1954), respectively. However, a from other areas of the Indo-Pacific, in A. H. specimen of Comanthina schlegeli was present Clark's (1931) monograph. in the MPRL reference collection, incorrectly The three most abundant crinoid species at determined as Comanthus bennetti. Six species Enewetak were polychromatic. The pigments in three families are now known from of Indo-Pacific comatulids have been studied Enewetak, and a total of nine species, rep­ in detail (Sutherland and Wells 1967, Powell, resenting five families, is now recorded for the Sutherland, and Wells 1967, Smith and Marshall Islands (see also short review on this Sutherland 1971, Bartolini, Erdman, and subject by Devaney, in press). Scheuer 1973), but the functional significance, Although onl y six of the nine species now if any, of crinoid polychromism is unknown. known to occur in the Marshalls were found While polychromism is prevalent among at Enewetak, this is the maximum number so shallow-water crinoids, it is lacking below far recorded for any of the individual atolls. 100m, where illumination ceases (D. B. Because it is reasonable to expect that the Macurda, pers. comm.) At Enewetak, the total number ofspecies present in a local area trend appeared to be for individuals of the will be less than that recorded for the region more exposed species to be the most variable defined by a set of islands, it is possible that in color, while individuals ofthe more cryptic the three species not found during the survey species showed little or no variation in color. at Enewetak do not occur there. However, This trend requires further testing on both two of the three missing species are reported larger numbers ofconspecific individuals and to be highly cryptic within the .reefinfrastruc­ larger numbers of species grollR~(LQY liyLng ture by day and perhaps are only nocturnally position and behavior. The results of this active (Meyer and Macurda 1980). Since no study, compared with other published ac­ night collections were made during this counts of crinoid coloration, confirm that survey, it is also possible that these species do there are intraspecific differences in color pat-

.I SS Shallow-Water Crinoids at Enewetak-ZMARZLY 119

terns between regional populations. Some crinoid species; (2) occurrence of some sym­ varieties, like CB I , are conserved between re­ biont species appeared to be correlated with gions. Meyer and Macurda (1980) reported a host depth; (3) occurrence and organization color variety of Comanthus bennetti found ex­ ofsymbionts on individual hosts seemed to be clusively at depths exceeding 15m, similar to related to partitioning of host space and per­ CB3 at Enewetak. haps, although not directly assessable , to The distribution and abundance of interspecific competition for preferred sites. shallow-water crinoids around Enewetak This idea is supported by the mutually exclu­ Atoll were highly variable. As indicated by sive occurrence of species which inhabit the their increase in abundance at sites with daily same site on a host (for example, Periclimenes current flow, Coman thus bennetti, C. parvicir­ amboinensis and Araiopontonia odonto ­ rus, Comanthina schlegeli, and Comaster gra­ rhyncha). The occurrence, in several species, cilis are rheophilic species. These species all of a single pair of individuals per host is exhibit mechanical or behavioral adaptations probably indicative of active defense of host which enable them to inhabit environments space against invasion by conspecifics. with strong currents. Comanthus bennetti has Predator-prey relationships between sym­ extremely robust clawlike cirri which grasp biont species, although possible, were not coral substrates; Comanthina schlegeli has observed but may also play an important reduced cirri and occurs on coral sub­ role in the structure of these symbiont strates with smaller diameter branches which microcommunities. the cirri can grasp firmly. This species does not perch high above the substrate like Comanthus bennetti, but lowers itself between ACKNOWLEDGM ENTS the coral branches on which it is perching or sits on the protected side of the substrate, I am extremely grateful to D. M. Devaney tethered by several arms. Comanthus parvicir­ for his enthusiastic encouragement of ·this rus has similarly reduced cirri but fewer arms work and for his critical reading of an earlier and occurs in protected crevices or well within draft of the manuscript; this paper is dedi­ the protection of a coral head. Comaster gra­ cated to his memory. Thanks are due A. cilis, with no cirri and long , slender arms, Fielding for sharing her field knowledge ofthe occurs exclusively within the reef with only problem and for providing invaluable advice, its arms emerging. Perhaps because of their and C. Arneson for his infinite patience cryptic habits, the latter 2 species can in­ underwater. I would also like to thank the vade shallow turbulent areas from which following experts for confirming or providing Comanthus bennetti and Comanthina schlegeli species identifications: D. M. Banner, A. J. are excluded. Bruce , R. Hanley, E. A. Kay, and D . L. The results of the present study suggest Meyer. The manuscript was improved by that over this half-year period, migration, re­ comments from D. B. Macurda, Jr. and from cruitment, and mortality were not significant members of my doctoral committee, espe­ factors in population regulation. Individual cially W. A. Newman and P. K. Dayton. longevit y may figure prominently in the per­ sistence ofcrinoid populations over time, but data on longevity, reproductive periodicity, REFERENCES CITED and juvenile settling are needed before such constancy can be assessed. BABA, K. 1969. Four new genera with their Our knowledge ofstructural and functional representatives and six new species of the aspects of crinoid symbiotic associations is Galatheidae in the collection of the still extremely limited, but the following Zoological Laboratory, Kyushu Univer­ points regarding structure are stated in sum­ sity, with the redefinition of the genus mary: (I) a pool ofpotential colonizers, based Galathea. OHMU, Kyushu University on host specificities, was identified for each 2(1) : 1-32. 120 PACIFIC SCIENCE, Volume 38, April 1984

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EMERY, K. 0., J. I. TRACEY, Jr., and H . S. the East Indies. Geol. Soc . Amer. Abstracts LADD. 1954. Geology of Bikini and nearby with Prog. 7(7): 1184. atolls. U.S . Geol. Surv . Prof. Pap. 260­ --- . 1976. The ecology and zoogeography A: 1-265 + 64 pis. of the crinoids of the Indian Ocean. Geol. FISHELSON, L. 1974. Ecology of the northern Soc. Amer. Abstracts with Prog. 8(6): 992. Red Sea crinoids and their epi- and en­ MAGNUS, D. B. E. 1967. Ecological and etho­ dozoic fauna. Mar. BioI. 26: 183-192. logical studies and experiments on the echi­ F UJI NO, T., and S. MIYAKE. 1970. Araio­ noderms of the Red Sea. Stud. Trop. pontonia odontorhyncha gen. et sp. nov ., Oceanogr., Miami 5: 635-664. a new shrimp from the Ryukyu Islands, MEY ER, D. L. 1971. Functional morphology Japan (Decapoda, Palaemonidae, Pon­ and autecology of the shallow-water un­ toniinae). OHMU, Kyushu University stalked crinoids (Echinodermata) of the 3(1) : 1-10. Caribbean Sea. Doctoral Dissertation, GISL EN, T. 1940. A collection of crinoids Yale University. from the South Sea Islands. K. svenska - - - . 1973a. Distribution and living habits Vetenskakad. Handl., ser. 3, 18(10) : of comatulid crinoids near Discovery Bay, 1-16 + 3 pis. Jamaica. Bull. Mar. Sci. 23 :244- 259. HAIG, J. 1973. Galatheidea (Crustacea, --- . 1973b. Feeding behavior and ecology Decapoda, Anomura) collected by the of shallow-water unstalked crinoids F.I.S. "Endeavour." Rec. Aust. Mus. (Echinodermata) in the Caribbean Sea. 28(14) :269-289. Mar. BioI. 22 : 105-129. HARTLAUB, C. 1895. Reports on the dredging MEYER, D. L., and D. B. MACURDA, Jr. 1974. operations . .. carried on by the "Albatross" The zoogeography of Caribbean crinoids: during 1981. XVIII. Die Comatuliden. Bull. A model for paleontological interpretation. Mus. Compo Zool. , Harvard 27(4): 127­ Geol. Soc. Amer. Abstracts with Prog. 152 + 4 pis. 6(7): 868. --.1912. Report on the results of dredg­ - -- . 1980. Ecology and distribution ofthe ing . . . by the U.S. Coast Survey Steamer shallow-water crinoids ofPalau and Guam. "Blake" . XLV. Die Comatuliden. Mem. Micronesica 16:59-99. Mus. Compo Zool., Harvard 27(4): POTTS, F. A. 1915. The fauna associated with 275-491 + 18 pis. the crinoids of a tropical coral reef: with HOLTHUIS, L. B. 1953. Enumeration of the especial reference to its color variations. decapod and stomatopod Crustacea from Pap. Dept. Mar. BioI. Carnegie Inst. Wash. Pacific coral islands. Atoll Res. Bull. 8: 71-96 + 1 pI. 24 : 1-66. POWELL, V. H. , M . D. SUTHERLAND, and J. W. HUM ES , A. G. 1972. Pseudanthessius comanthi WELLS . 1967. Pigments of marine animals. n. sp. (Copepoda, Cyclopoida) associated V. Rubrocomatulin monomethyl ether, with a crinoid at Eniwetok Atoll. Pac. Sci. an anthraquinoid pigment of the Comatula 26 :373-380. genus of crinoids. Aust. J. Chern. 20(3) : LEWINSOHN, C. 1969. Die Anomuren Des 535-540. Roten Meeres (Crustacea Decapoda: RUTMAN, J., and L. FISHELSON. 1969. Food Paguridea, Galatheidea, Hippidea). Zool. composition and feeding behavior of Verh ., Leiden 104: 1-213 + 2 pis. shallow-water crinoids a t Eilat (Red Sea). MACURDA, D. B., Jr. 1973. Ecology of coma­ Mar. BioI. 3 :46-57. tulid crinoids at Grand Bahama Island. SMITH, I. R., and M. D. SUTH ERLA ND. 1971. Hydro-Lab Jour. 2 :9-24. Pigments of marine animals. XI. Angular - - - . 1975. The bathymetry and zoogeog­ naphthopyrones from the crinoid raphy of shallow-water crinoids in the Comanthus parvicirrus tim orensis. Aust. J. Bahama Islands. H ydro-Lab Jour. 3: 5­ Chern. 24: 1487-1499. 24. SUTHERLAND, M. D., and J. W. WELLS. 1967. MACURDA, D. R , Jr., and D. L. M EY ER. 1975. Pigments of marine animals. IV. The an­ The behavior and ecology ofthe crinoids of thraquinoid pigments of the crinoids, 122 PACIFIC SCIENCE, Volume 38, April 1984

Comatula pectinata L. and C. cratera A. H. ZMARZLY, D. L., and N. D. HOLLAND. 1981. Clark. Aust. J. Chern. 20(3):515-533. Rates of food transport down the ambu­ W ELLS, J. W . 1954. Recent corals of the lacral grooves and through the gut of Marshall Islands: Bikini and nearby atolls. Comanthus bennetti (Echinodermata: Part 2. Oceanography (Biologic). Geol. Crinoidea) observed in situ. Mar. Ecol. Surv. Prof. Papers 260-1: 385-486 + pls. Prog. Ser. 6(2) :229-230. 94-185.