Ecology of the Endemic Land Johngarthia malpilensis (: Brachyura: ), a Poorly Known from the Tropical Eastern Pacific1

Mateo Lo´pez-Victoria2,3,4 and Bernd Werding3

Abstract: Johngarthia malpilensis (Faxon, 1893) is the least studied of the eight American species of Gecarcinidae. This land crab is considered endemic to Mal- pelo, an oceanic island of the Colombian Pacific. Several aspects of its ecology were investigated between 2003 and 2006. We estimated its population density, distribution, daily activity, reproduction, interactions, and diet by marking and monitoring 909 individuals. During our visits we recorded of sizes from 5 to 82 mm carapace width. Johngarthia malpilensis shelters mainly in fissures and hollows between rocks. It is distributed all over the main island except in very steep sectors. An average density of 0.41 adults m2 and 0.55 juveniles m2 produced an estimated total population of 833,000. Johngarthia malpilensis showed high mobility, with crabs covering distances over 450 m in a few days on highly irregular surfaces. Activity was higher from dusk till dawn and lowest around noon. Release of larvae took place during the high tides associated with the new moon, at least during the rainy season. It is omnivorous and opportu- nistic, consuming practically every available resource. The crab is occasionally preyed upon by an endemic lizard and migratory . Its general ecology is very similar to that of J. planatus, a closely related species. As a voracious omni- vore J. malpilensis is one of the most important components of Malpelo’s food web.

Crabs of the family Gecarcinidae have a cavities and their osmotic balance. Almost all pantropical distribution and live mainly in construct , have a varied diet (from coastal environments with different types of vegetarian to omnivorous), and show sexual vegetation and soils. Although some species dimorphism, with males having larger chelae are able to survive kilometers from the coasts than females (for reviews see Tu¨rkay 1987, and over 1,000 m above sea level, all studied Burggren and McMahon 1988, Ng and Gui- species must return to the sea to release their not 2001, Hartnoll et al. 2006). larvae, which, after a period in the , Johngarthia malpilensis (Faxon, 1893), gen- return to the mainland as megalops or first erally referred to in the literature as Gecarci- crab stages (Wolcott 1988). All species are nus ( Johngarthia) malpilensis (for a revision limited by humidity levels in their branchial of its nomenclature see Tu¨rkay 1970, 1987,

1 This investigation was partially supported by the Navy. This study was supported in the field by the Co- Marine and Coastal Research Institute (INVEMAR), lombian Navy ships ARC Malpelo, ARC Valle del Cauca, the Colombian Institute for the Development of and ARC Caldas, as well as by the ship Marı´a Patricia, Science and Technology (COLCIENCIAS) (Project the ship Anita, and U.S. National Oceanic and Atmo- 2105091352703), the Department of Ecology at spheric Administration research vessel David Starr the Justus-Liebig-University of Giessen, the German Jordan. This is contribution 992 of INVEMAR. Manu- Academic Exchange Service (DAAD), the Malpelo Foun- script accepted 31 October 2007. dation, the Special Administrative Unit for the System of 2 Corresponding author (e-mail: mateo.lopez- National Natural Parks of , and the Colombian [email protected]). 3 Department of Animal Ecology, Justus-Liebig- University of Giessen, Heinrich-Buff-Ring 29, 35392, Pacific Science (2008), vol. 62, no. 4:483–493 Germany. : 2008 by University of Hawai‘i Press 4 Marine and Coastal Research Institute (INVE- All rights reserved MAR), Santa Marta, Colombia.

483 484 PACIFIC SCIENCE . October 2008

Hartnoll et al. 2006), is an orange to pale pink provided by the sea via seabirds (Graham ; its appearance varies accord- 1975), mainly the Nazca Booby, Sula granti ing to age and molt condition: some large in- Pitman & Jehl, 1998, which has its largest dividuals are pink with pale blue green tones. breeding colony on the island (Pitman and The crab lives only on Malpelo Island, Co- Jehl 1998). The avian fauna is composed of lombia, and is the only such limited endemic 10 resident seabird species and about 50 va- of the family in the (Tu¨rkay 1970). grant and migratory species that provide the Its taxonomic status has been debated (Garth system with excrement rich in phosphate and 1948), and it has been considered a minerals and thus fertilize the scarce vegeta- of J. planatus (Stimpson, 1860) (Rathbun tion (mainly microalgae). Besides the land 1918, Prahl 1990), a species widely distrib- crab and the birds, the terrestrial fauna of uted in other islands of the tropical eastern Malpelo is composed of three endemic liz- Pacific. However, J. malpilensis is referred to ards, Anolis agassizi Stejneger, 1900; Diploglos- as a discrete species by most recent authors sus millepunctatus O’Shaughnessy, 1874; and (Tu¨rkay 1970, 1987, Ng and Guinot 2001, Phyllodactylus transversalis Huey, 1975, and Hartnoll et al. 2006), though its taxonomic ca. 60 invertebrate species (Wolda 1975, status requires further investigation. Johngar- Prahl 1990). thia malpilensis is one of the most important Observations and experiments were car- components of the island’s terrestrial fauna, ried out during eight visits between October but apart from the original description 2003 and September 2006 in the vicinity of (Faxon 1893) and some taxonomic notes five sectors selected according to their dis- (Garth 1948, Tu¨rkay 1970), only marginal tance to the sea, elevation, and accessibility commentaries have been made on the ecology (Figure 1). The Tangon sector (0–20 m of this crab in various general studies on Mal- height) is located in the mid-east of the island pelo (Prahl 1990, Brando et al. 1992). As a re- and comprises a rocky cliff of variable slope; sult of substantial recent field observations we the only access to the island is located here. present observations on the general biology, The Punta Este sector (100–140 m height) is density, distribution, daily activity, diet, and also in the mid-east of the island, with a very ecological interactions of the crab. irregular surface including many fissures and small caves. The Caban˜ as sector (110–120 m height) is on the east of Malpelo and is the Study Area only large level terrain of the island with Malpelo and the 11 neighboring islets are lo- soil. Two small houses for the Colombian cated 380 km west of Colombian mainland Navy garrison are located there. The Cerros territory and have an emerged area of @1.2 sector (260–270 m height) lies in a depression km2 (Figure 1), with a maximum elevation between the peaks of the two central hills: of 300 m (Lo´pez-Victoria and Rozo 2006). its surface is very irregular and has variable Malpelo is located in a zone of converging slope. The Sur sector (140–150 m height), in marine currents, in the confluence of trade the south, lies on a fracture zone with a mild winds from north and south forming a cloudy slope and very irregular substrate. belt known as the Intertropical Convergence Zone. Thus the island is subject to consid- materials and methods erable precipitation and humidity (Graham 1975, Prahl 1990). The majority of the island Measurements were made of carapace width surface is bare of vegetation, except for mi- (CW ) and weight for 46 adult female crabs, croalgae covering the rocks, some lichens 76 adult males, and 69 juvenile-immature in- and mosses, some isolated patches of grass, dividuals (<3.5 cm CW ). These data were and the creeping fern Pityrogramma dealbata collected in five sectors (Figure 1). Observa- (Presl, 1825). The land fauna of Malpelo is tions were made of the crab’s feeding behav- adapted to the rocky substrate and depends ior as well as of the shape and form of its on the scarce vegetation and on the nutrients refuges. For these observations individuals Figure 1. Map of Malpelo Island indicating the main sampling sites mentioned in the text and the distribution of Johngarthia malpilensis. 486 PACIFIC SCIENCE . October 2008 were followed for several minutes on differ- for duration, locality, and whether the female ent days and at different hours. All the aver- was ovigerous. Release of larvae and presence age values are followed by G1 standard error of ovigerous females near the sea were exam- (SE). ined with respect to moon phase, in particular To estimate abundance, population size, around periods of new moon, based on ob- and distribution of Johngarthia malpilensis, its servations conducted throughout a month be- presence or absence was recorded during a tween May and June 2006. survey of the island and some of the islets. We made detailed observations on the in- To estimate the average adult density, 29 teractions between the crabs and the tetra- square plots (10 by 10 m) were established at pods in Malpelo, as well as the interactions dusk in different sectors on the eastern side of among crabs. and competition for the island. To estimate average juvenile den- food were recorded through marking and fol- sity, eight band transects (20 by 2 m) were lowing crabs over various time intervals. To censused at night. All squares and band tran- examine the relationship between crabs and sects were conducted in similar areas; because breeding Nazca Boobies, 30 chicken of of the lack of higher vegetation the island’s size, weight, and color similar to those of the habitat was considered uniform for these pur- seabird were placed as follows: 21 in empty poses. Population size was estimated by ex- nests and nine between nests. Behaviors trapolating the average density data to the during the crabs’ examination of eggs, eat- total distribution area established for the ing by the crabs, and interactions with li- crabs in the island, using a Digital Elevation zards and birds during this process were Model (see Lo´pez-Victoria and Rozo 2006). recorded. To evaluate mobility and site fidelity, dis- placement of 125 adult crabs marked with results a number on the carapace was followed (25 crabs on each of the five sectors), as well Average weight of adult females was 64.5 g as the displacement of another 784 crabs ðG1:8Þ, and of adult males 94.0 g ðG4:2Þ. marked with letters according to the sectors. Maximum CW and body weight for females Recaptured crabs were marked again, adding were 65.6 mm and 93.1 g, respectively, and the letter of the place where they were found for males 82.1 mm and 180.0 g. The smallest again. crab was 5.5 mm CW and weighed less than The daily activity pattern was evaluated on 0.2 g. A comparative analysis between females two fixed sites of 4 by 4 m, where total num- and males with similar CW (average width ber of individuals was already known. The difference less than 2%) showed differences observations were conducted during seven in the average body weight of near 13%. day-night cycles almost around the clock. Such differences are attributable to the chelae Measures were taken at 1- to 2-hr intervals. size being much larger in males. Data on relative humidity (% RH; accuracy Johngarthia malpilensis cannot swim, but it G 2.5) and temperature (C; accuracy G 0.8) can walk on the bottom of small ponds for were measured using an electronic meter short distances and times. Several individuals (Volkraft HT-200), placing the sensor 3 cm were observed scraping and eating green al- above the soil (external measure) or at the gae, semisubmerged or fully submerged in bottom of the crab’s shelter (internal mea- natural freshwater puddles: this may be im- sure). Activity was expressed as the number portant in replenishing body fluid level in of individuals out of their shelters and mov- preparation for molting. ing in the sites. Correlations and polynomial Few areas of Malpelo are covered with regressions were made between time of day, soil, and most of its surface is naked basaltic crab activity, humidity, and temperature. rock. Johngarthia malpilensis uses fissures and Ovigerous females were monitored in the hollows between rocks as shelters, although Tangon sector. All copulations were recorded it also digs burrows in the few places where The Land Crab of Malpelo . Lo´pez-Victoria and Werding 487 the soil is deep enough. The galleries are in- Caban˜ as (distance: 420 m). However, some terconnected and may be used by several in- individuals (especially from Caban˜ as sector) dividuals at the same time. showed substantial fidelity to a sector and Johngarthia malpilensis is distributed over were marked and recaptured there several almost the entire island except some very times over 60 consecutive days. steep sectors or cliffs (Figure 1). Both adults Adults’ daily activity peaked at dusk, dur- and juveniles were found everywhere, from ing the night, and in the early morning, with sea level up to the highest peaks. Despite an a drastic decrease at noon and the early after- intensive search in the islets, not a single noon. This general pattern was positively crab was found there. An average density of correlated with the relative humidity of the 0.46 G 0.07 individuals m2 was estimated air (correlation r ¼ 0.621, P < .01), which for adult crabs, whereas for juvenile crabs the was always higher within the crabs’ shelters average density was estimated at 0.55 G 0.10 than outside, and negatively correlated with individuals m2. The great variation in the temperature (r ¼ –0.645, P < .01). Conse- density of individuals is attributable to the quently, during and shortly after showers, great crab concentration occurring in even on overall warm days, crab activity in- the Caban˜ as sector, where one of the squares creased. On the contrary, during very sunny showed a density of 2 individuals m2, com- and dry days, very few active crabs were ob- pared with other sectors where the lowest served, and the majority of those resting in density was 0.1 individual m2. Extrapolating their lairs had their eyes and legs completely the average density values (0.41 G 0.04 in- folded against their bodies (fully asleep). In dividuals m2; excluding the highest value the late afternoon, and before and at dusk, around the Caban˜ as sector) to the island sur- greater crab activity was observed coinciding face occupied or visited by crabs (obtained with the return to the colony of hundreds of from the Digital Elevation Model [see Figure Nazca Boobies coming back from their fish- 1]), the adult crab population actually living ing activities. This increase in crab activity in Malpelo is nearly 350,000, and the juvenile could be related to the birds’ arrival and, crab population (less than 35 mm CW ) is therefore, to the increase of the excrement approximately 483,000. Both densities are input to the system. Juvenile crabs were seen underestimates because when the counts outside crevices only during the night. were made (at dusk), although the crabs Two forms of mating were observed. One showed great activity, it was not possible to occurred everywhere, not associated with ensure that the total population was out of shelters, and comprised the union of an adult the shelters. The same situation is applicable nonovigerous female and a male. The female to the juvenile crab population because, al- was briefly courted by the male, who uses his though they are very active at night, they chelae to make rapid touches and rubbing may hide in fissures without being detected of short duration on the female’s carapace. by the observer. The male seized the female 1 or 2 min after Marking and recapture indicated that J. initial contact. Once they were face to face, malpilensis shows high mobility, even when they made contact with their walking legs, not in the breeding season. The most extreme then the male covered the female’s carapace cases, assuming a straight-line displacement with his chelae and then with his walking between sectors, were observed in those in- legs. When the couple was facing, the abdo- dividuals marked in Cerros sector and re- mens were unfolded, and the male inserted captured in Caban˜ as and later in Tangon his gonopods in the gonopores of the female. sectors, covering distances of 450 m in 14 The couple remained joined for up to an days, over an irregular and very steep terrain. hour or more (Figure 2). During that time Other extreme cases were observed in indi- the male frequently rubbed the female’s cara- viduals marked in Caban˜ as, recaptured in pace while she remained static, her chelae Tangon some days later, and seen again in folded against her body and her eyes sunk 488 PACIFIC SCIENCE . October 2008

Figure 2. Johngarthia malpilensis mating: the male above, the female (not having eggs) embraced by the male’s chelae below. in the orbits. On the contrary the male re- washed the cliff, staying at the limit of maxi- mained alert, with his eyes outside the orbits. mum high tide level. At this point females When other crabs or lizards came close to the waited for the highest wave’s cycle and were couple, the male displayed his chelae in a immersed three or four times while shaking challenging attitude, driving off the intruder. their abdomens, releasing larvae into the sea. The other form of copulation followed a After releasing larvae females rapidly climbed similar pattern but was limited to the zone the cliff back to the supratidal zone. Twice near the sea (first 10 to 15 m of the cliffs) during the May 2006 release of larvae, fe- and involved very large males and ovigerous males were observed being swept away by females. No precopulation display or visual the waves and did not return to land. Most recognition was observed before mating, and hatching occurred on the 2 days following mating was not associated with shelters in new moon, and then the number decreased any case. No preferences on timings for cop- nightly as the level of the maximum high ulations were recognized. tide decreased. All ovigerous females had old Larval release was associated with the high carapaces of pale color. Large males, appar- tides of the days before, during, and after the ently seeking to mate, joined the releasing fe- new moon. Ovigerous females stayed in fis- males in fissures and hollows. sures and hollows close to the sea waiting for Johngarthia malpilensis is omnivorous and the high tide at dusk (in May–June 2006 opportunist and will eat everything available, between 1830 and 1930 hr local time). Once but its regular diet consists of microalgae the high tide was close or at its maximum, that it scrapes from the rocky surfaces, females walked slowly to where the waves excrement and feathers, and, seasonally, eggs, The Land Crab of Malpelo . Lo´pez-Victoria and Werding 489 chicks, and juveniles of the Nazca Booby. ‘‘new’’ object in the surroundings. The crab This crab has a reliable access to the second recognized an immediately on contact chick of the Nazca Booby because this species with walking legs or chelae: it changed from practices siblicide, so that although it lays two regular random movement to a concentrated eggs, the first chick expels the second from manipulation of the egg. In every case the the nest and it invariably dies. This food crab raised the egg with its chelae and tried, source was frequently used during the months in vain, to bite it with its mouthparts; then it of high nesting activity, from June to No- started moving the egg from the site. Eggs vember. were not opened by the crab using its chelae, On all our visits up to nine crabs were seen but breakage resulted from transport over the constantly harassing each of the active nests rough ground or, on some occasions, during of Nazca Booby. Nevertheless, on only three a dispute with another crab. When two or occasions did we observe a crab successfully more crabs fought over an egg, the bigger stealing an egg. This was always followed by crab (having bigger chelae) always kept the abandonment of the nest by the birds. Spo- egg. Once the egg was broken, the crab radically, the crabs fed on carcasses of other started eating the contents and shell, which , particularly dead birds. Fresh car- often attracted other crabs and lizards (D. casses were fully eaten within 24 hr. Marking millepunctatus) that came to steal part of the studies showed that an initial group of 30 to contents. 50 feeding crabs was replaced in a few hours Individuals of all sizes of J. malpilensis are by others once the first are satiated. Finally occasionally devoured by D. millepunctatus. only a few hard remains of the bird were rec- Juveniles are swallowed whole, whereas adult ognizable, such as parts of the pelvic girdle crabs, after removal of the walking legs and and the rachis of the primary feathers and chelae, are opened from the rear; the abdo- retrices. Following marked individuals indi- men raised and the carapace removed. Inte- cated that more than 400 crabs may feed rior soft parts are then eaten and sometimes from a single carcass of an adult Nazca also the appendages. Juvenile crabs are also Booby. preyed upon by A. agassizi (which swallows The crab sporadically cannibalizes juve- the crab in pieces) and by some migratory niles by hunting at night among the rocks. It birds (i.e., herons, turnstones, and plovers). occasionally captures lizards or insects, and Although D. millepunctatus preys upon the when near the shore it may feed in the inter- crab, when competing for food, as with a tidal zone on invertebrates and fleshy algae carcass of a Nazca Booby, for example, during low tides. They also feed on the only crabs repel the lizards by exceeding them in higher plant (the creeping fern Pityrogramma number. dealbata) on the eastern side of the island. Around the barracks of the Colombian Navy discussion Station crabs eat leftovers and garbage dumped by marines and visitors. The appearance, size, and general biology of Thirty chicken eggs were located experi- Johngarthia malpilensis is very similar to those mentally in or among Nazca Booby nests: six of J. planatus (a closely related sibling spe- were broken and expelled from the nest by a cies), except that the latter has on many is- returning male before any crab located them. lands of the tropical eastern Pacific a more Five other eggs ended up exclusively as food intense red orange color (R. Pitman, pers. for lizards (D. millepunctatus) or shared with comm.; M.L.-V., unpubl. data). This might the crabs. The remaining 19 eggs were eaten be because those locations have substantial by one or more crabs, which seemed to find vegetation covers, and the intense coloration the eggs inadvertently. Rather than an active derives from the plants’ pigments. Alterna- search motivated by visual or olfactory clues, tively, dense vegetation cover may protect the crabs responded to the presence of a the crab from discoloration produced by sun- 490 PACIFIC SCIENCE . October 2008 light. Both species have similar diet and living There are no previous studies on the den- conditions, although on many islands of the sity of J. malpilensis. Environmental condi- tropical eastern Pacific (i.e., Clipperton, So- tions differ, but in comparison with densities corro, Cocos, Gorgona) Johngarthia planatus of J. planatus in Socorro Island (Pe´rez-Chi burrows actively due to areas of soft soil that 2005) average values in Malpelo are greater: are easy to excavate (Ehrhardt and Niaussat 1.1 m2 (adults and juveniles) versus @0.08 1970, Pe´rez-Chi 2005; R. Pitman, pers. m2, respectively. However, density is lower comm.; M.L.-V., unpubl. data). In size J. than @6m2 on Clipperton (Ehrhardt and malpilensis is intermediate among American Niaussat 1970). With respect to G. ruricola, gecarcinids, compared with the larger Cardi- another typical island species in the Carib- soma guanhumi Latreille, 1825 (maximum bean, in Santa Catalina Island (very similar CW @ 130 mm), and C. crassum Smith, 1870 in emerged surface to Malpelo, though with (maximum CW @ 130 mm), and the smaller a substantial vegetation cover) Hartnoll et al. quadratus de Saussure, 1853 (@60 (2006) found average values of 0.4 adults m2. mm). It is smaller than the maximum size of This is very close to the adult density of 0.41 J. planatus (82 versus 100 mm, respectively), m2 on Malpelo. However the juvenile den- but an active search for the largest crabs on sity on Malpelo appears to be greater than Malpelo was not initiated (maximum sizes those found in Santa Catalina and Providen- taken from Tu¨rkay [1970] and Fischer et al. cia for G. ruricola, where recruitment has [1995]). been suggested as sporadic (Hartnoll and Size and weight differences between sexes Clark 2006; R. Hartnoll, pers. comm.). in J. malpilensis are due to the larger CW In contrast to other gecarcinids that and chelae in males, typical of other species show moderate fidelity to their burrows, par- of land crabs (Hartnoll 1982, 1988). This ticularly during the breeding season (e.g., size difference between sexes could result guanhumi [Henning 1975]), J. mal- from the high risk for females during release pilensis appears to be highly peregrine and not of larvae so that they never reach potential dependent on a fixed refuge. Nevertheless, maximum size. Herreid (1967) and Henning the distances we recorded for J. malpilensis (1975) suggested that the smaller size of the are not comparable with the many kilometers adult females of C. guanhumi (with respect to that some other gecarcinids may travel during males) is due to a lesser longevity associated their massive breeding migrations (e.g., Ge- with the risks implied in the migration and carcoidea natalis [Hicks 1985]); of course, the subsequent release of larvae of that species. islands where other gecarcinids live are much Similarly, Hartnoll et al. (2006) suggested larger than Malpelo, which makes compari- that the smaller size of females of Gecarcinus sons difficult. ruricola (Linnaeus, 1758) might be attributed Distribution in Malpelo is not homoge- to the risks associated with migration. Our neous, due to the regular food source in the observations during release of larvae of J. Caban˜ as sector that raises density compared malpilensis, when some females were swept with the rest of the island. Also, during re- away by the waves, suggest that at least some lease of larvae, the crab density in the supra- females are lost. However the frequency of tidal zone is greater than usual, because such losses has not been estimated. In addi- hundreds of ovigerous females and males tion it is believed that the energy costs for re- seeking copulation concentrate there. In oth- production are higher for females than for er islands of the tropical eastern Pacific J. pla- males, and therefore females are limited to natus also has a patchy distribution, but the smaller sizes due to slower growth rates factors affecting such distribution are also (Herreid 1967, Hartnoll 1988, Hartnoll et al. related to the presence of substantial vegeta- 2006). Nevertheless, slower growth rates may tion covers on those islands (e.g., Clipperton imply a delay in reaching a maximum size but [Ehrhardt and Niaussat 1970] and Socorro not necessarily the impossibility of reaching Island [ Jime´nez et al. 1994]). it. The behavior of J. malpilensis follows what The Land Crab of Malpelo . Lo´pez-Victoria and Werding 491 in other land crab species has been described and even adult crabs, whereas when adult it as a circadian rhythm (see Burggren and is an opportunist , , and McMahon 1988). The crab is much more recycler of organic material. Except for the active at dusk, night, and dawn than in day- lizard D. millepunctatus, which on some occa- light. However, contrary to J. planatus in So- sions is even preyed upon by the crab, J. corro and Gorgona islands (Pe´rez-Chi 2005; malpilensis has no other important natural M.L.-V., unpubl. data), it might not be con- predators. sider a nocturnal crab in a strict sense but On the basis of average density and weight rather a partially diurnal species with higher and distribution of crabs, the estimated total nocturnal activity. biomass of J. malpilensis on the island is Johngarthia malpilensis reproduces during a nearly 30 tons. By removing the algal cover major portion of the year, at least during the and eating, in practice, every type of organ- rainy season (from May to December), but ism, the Malpelo crab is the major trans- without concentrated mass migrations. It dif- former as a recycler of organic matter in the fers from some other gecarcinids that have trophic network of the island. Its contribu- marked seasonal reproductive behavior, often tion in excrement must form an important with massive migrations: examples are G. ru- component of the scarce soils of Malpelo, ricola in Providence Island, Colombia (Hart- and its persistent grazing keeps this soil al- noll and Clark 2006); natalis in most totally free of higher vegetation, in the Cristmas Island, Australia (Hicks 1985); and same way that other land crab species control Gecarcinus lateralis in , USA, and Ber- the seedling recruitment in tropical forests muda (Bliss et al. 1978). Nevertheless, the (e.g., Gecarcoidea natalis in general scheme of larval release into the sea [Green et al. 1997], in during the days of highest tides of the lunar Costa Rica [Sherman 2002]). These charac- cycle matches that found in several other teristics make J. malpilensis one of the main gecarcinids (e.g., G. lateralis [Klaassen 1975, constituents (perhaps the most important) Bliss et al. 1978], C. guanhumi [Henning within the trophic network of Malpelo. 1975]). Based on growth estimations from mega- lops of G. ruricola recruited in Providence Is- acknowledgments land (Hartnoll and Clark 2006, Hartnoll et al. We are grateful to M. Rodrı´guez, P. Herro´n, 2006) and on a megalop maximum size of 3 S. Garcı´a, F. A. Estela, J. C. Botello, and J. mm for J. planatus reared in the laboratory Zamudio for assistance in the field. R. Pitman (Cuesta et al. 2007), juveniles with a CW of kindly shared his observations on land crabs less than 6 mm should not be older than 6 of several islands in the tropical eastern Pa- months. This renders it probable that over a cific. The manuscript was improved based on good portion of the year, except perhaps in comments and suggestions from R. Hartnoll the dry season (from the end of December and two anonymous reviewers. M. Mendoza to April), recruitment of J. malpilensis occurs and S. Graham helped to improve a prelimi- on Malpelo. This is reassuring, because larval nary English version. dispersal in the plankton is at the mercy of wind and currents and could make return to Malpelo uncertain. Literature Cited In contrast to J. planatus on Socorro Is- land, which is regularly preyed upon by land Bliss, D. E., J. Van Montfrans, M. Van Mont- birds (Rodrı´guez-Estrella et al. 1996), J. mal- frans, and J. R. Boyer. 1978. Behaviour pilensis is only preyed on sporadically by small and growth of the land crab Gecarcinus lat- numbers of migratory birds. Its role within eralis (Freminville) in southern Florida. the Malpelo trophic network is multiple and Bull. Am. Mus. Nat. Hist. 160:113–151. depends on its stage of development. When Brando, A., H. von Prahl, and J. R. Cantera. juvenile it is a prey of lizards, migratory birds, 1992. Malpelo: Isla ocea´nica de Colombia. 492 PACIFIC SCIENCE . October 2008

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