Birgus Research Articles

Growth of the coconut crab Birgus latro estimated from mark-recapture using passive integrated transponder (PIT) tags

Determination of the growth pattern of a harvested species is an important step toward a proper assessment and suitable management of the stock. Although coconut crab Birgus latro populations in most regions have been severely depleted, few reliable biological data are available. We assessed the growth of B. latro using a mark-recapture method based on the use of passive integrated transponder (PIT) tags on Hatoma Island, located southwest of Okinawa, Japan. Of 781 crabs tagged (337 males, 444 females; 14.89 to 58.03 mm thoracic length (ThL)), 17 males and 20 females were recaptured. The application of PIT tags provided field data for growth of individuals for up to 2326 d and confirmed that coconut crabs molt during the winter dry season on Hatoma Island. The curves relating ThL with age, estimated from data of 29 crabs that had spent one or multiple winter dry seasons at liberty, showed that the coconut crab is an extremely slow growing species, with males showing much higher mean asymptotic ThL (69.87 mm) than females (42.79 mm). The Brody growth coefficient (K)was 0.061 yr �1 for males and 0.091 yr �1 for females. This study is the first to provide growth estimates of wild coconut crabs based on mark- recapture over multiple years. Potentially long-lived, slow growing species such as coconut crabs may be susceptible to overharvesting, and a cautious approach is recommended to the determina- tion of resource management regimes for B. latro.

Factors influencing growth of giant terrestrial robber crab Birgus latro (Anomura: Coenobitidae) on Christmas Island

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 19:129-141 (2013) - DOI: https://doi.org/10.3354/ab00523 Factors influencing growth of giant terrestrial robber crab Birgus latro (Anomura: Coenobitidae) on Christmas Island Michelle M. Drew1,*, Michael J. Smith2, Bill S. Hansson1 1Max Planck Institute for Chemical Ecology, Hans Knoell Strasse 8, 07745 Jena, Germany 21/10 Leonora St, Como, Western Australia 6798, Australia *Email: myobatrachid@hotmail.com ABSTRACT: Birgus latro has significant conservation and socio-economic importance throughout its range, yet very little is known about its growth in its natural habitat. An extensive mark-recapture program was undertaken on Christmas Island, Australia, in which over 1440 individual crabs were uniquely identified using passive integrated transponder (PIT) tags. Over 18% of the tagged population was recaptured at least once and remeasured, providing substantial information on growth of B. latro. Our results show that in its natural setting B. latro is a very slow-growing species. Individuals commonly experience conditions that result in zero or negative growth. Sex, size, and injury all strongly influence the crab’s moult increment. Males approached zero growth at around 65 mm in thoracic length (TL), while growth in females started to plateau at around 50 mm TL. Injury frequently led to negative growth, particularly in individuals that had lost a claw and/or multiple limbs—presumably due to a loss of foraging opportunities or access to other resources and a redistribution of available energy into limb regrowth. Our study indicates that previous growth curves do not adequately describe the growth of B. latro in its natural setting and that individual crabs may live over 30 yr longer than previously predicted, with large crabs likely to be over 100 years old. This may have serious implications for the long-term conservation of the species in the face of continuing exploitation. KEY WORDS: Birgus latro · Growth · Moult increment · Mark-recapture · PIT tag · Conservation Full text in pdf format PreviousNextCite this article as: Drew MM, Smith MJ, Hansson BS (2013) Factors influencing growth of giant terrestrial robber crab Birgus latro (Anomura: Coenobitidae) on Christmas Island. Aquat Biol 19:129-141. https://doi.org/10.3354/ab00523 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 19, No. 2. Online publication date: September 24, 2013 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2013 Inter-Research.

Ontogeny of sinking velocity, body density, and phototactic behaviour in larvae of the coconut crab Birgus latro: Implications for larval dispersal and recruitment in the sea

As a basis for understanding the larval dispersal and recruitment processes of the coconut crab, Birgus latro, in the sea, we examined the ontogenetic changes in the passive sinking velocity, body density, and phototactic behaviour to different light intensities and wavelengths of the zoeal and megalopal stages of laboratory-reared larvae. Six levels of light intensity, from 310μmolm−2s−1 to 0.0031μmolm−2s−1 in 10% decrements, and 14 light wavelengths in the range of 400–660nm in 20nm increments were tested. The controls were tested in the dark. The coconut crab larvae showed negative buoyancy. The mean sinking velocity was 7.5mms−1 in the first zoeal stage, which increased significantly to ~10mms−1 after the third zoeal stage. The mean body density was 1.085–1.089gcm−3 in the first to third zoeal stages; it then decreased significantly to 1.072–1.075gcm−3 in the fourth zoeal and megalopal stages. This ontogenetic pattern in body density differs from those of other decapod crustacean species and may be related to the emigration behaviour of the megalopae from the sea to the land. The coconut crab larvae were generally photopositive, with the strength of their positive phototactic behaviour decreasing at lower light intensities and with age. Higher incidences of positive phototactic behaviour were recorded at spectra of 400–660nm, 400–620nm and 400–600nm for the first, second, and third zoeal stages, respectively. The spectral sensitivity of the fourth zoeal stage showed peaks at around 400–420nm and 500–580nm, suggesting that the larval distribution in the sea changes at the fourth zoeal stage. The overall phototactic behaviour of the megalopae was weak, and the behavioural responses varied at light wavelengths above 520nm. Thus, their phototactic behaviour may have little effect on their migration to the coast.

Identification of individual coconut crabs, Birgus latro, on the basis of the pattern of grooves on the carapace

We identified individual coconut crabs, Birgus latro, on the basis of photographic matching of the grooving patterns on the carapace. The photographic matching was performed using 336 front cephalothorax photographs obtained during night searching (capture and release) from 2006 to 2012 in Ocean Expo Park, southern Japan. Grooving patterns were visually matched on the basis of the distribution, form, and number of grooves. We determined that 99 individuals were captured and photographed twice. The period between release and recapture ranged from 2 to 2224 days. The grooving pattern on the carapace was unchanged, even when there were more than 1500 days between release and capture. In addition, captive crab maintained the same grooving pattern through four molts. Therefore, photographic matching of carapace grooving patterns is a useful technique for long-term individual identification. Crabs identified using this method are safer to consume than those tagged using invasive tagging methods, including passive integrated transponder tags. Photographic matching is also a useful way to identify individuals in the harvested population.

Effects of water availability and migration timing from sea to land on survival and moulting in megalopae and juveniles of the coconut crab, Birgus latro: implications for mass production of juveniles

Populations of the coconut crab, Birgus latro (Linnaeus, 1767), have been depleted by overharvesting and environmental degradation. The aim of this study was to develop artificial propagation technologies for the restocking and conservation of this species. Coconut crabs migrate from the sea to land as megalopae, carrying gastropod shells. We examined the effects of sea-water availability and the timing of their involuntary migration from sea to land on the survival and moulting of megalopae and juveniles by culturing them individually in containers with dry “land” but with or without aquatic “sea areas.” The schedule of their involuntary migration to the land in the test containers was set at ages of 5 and 10 days after metamorphosis to the megalopal stage, and at ages between 12 and 16 days, when the megalopae walked steadily while wearing a shell. The treatments did not affect the moulting of the animals. The animals survived in the containers with seawater areas. In contrast, all those in the containers without sea areas died, and severe mortality occurred after the animals moulted to the crab stage, suggesting that water availability may protect the animals from desiccation in air during and after ecdysis. Old megalopae (10 days old) appeared to be more active than young megalopae (5 days old) in walking and manipulating shells at first landing, although the three different schedules of migration to land did not affect the survival of the animals. Our results highlight the importance of water availability in culturing coconut crab juveniles.

Crustacea Decapoda of Glorieuses Islands, with notes on the distribution of the coconut crab (Birgus latro) in the western Indian Ocean

An inventory has been made of the decapod fauna of the Glorieuses Islands, western Indian Ocean (WIO), following the BIORECIE 2 Expedition to the Islands, 5–17 December 2012. Field data are complemented by a review of taxonomic studies for these islands. Overall 157 species are now reported from the Glorieuses Islands, including 61 new records. The presence of the coconut crab, Birgus latro , is confirmed from these islands, for the first time since 1884, and the WIO distribution of this endangered species is updated, based on observations made in the region since 2006.

Reproductive migration of the coconut crab Birgus latro

Knowledge of movement patterns is essential in tailoring spatial conservation and management measures. Although populations of the coconut crab, Birgus latro, have been severely depleted in most habitats, there have been few serious attempts to manage the resources. Recently, spatial conservation (e.g. seasonal area closure) has been suggested as an effective tool for resource management. However, relatively little is known about coconut crab movements, especially reproductive migration. To determine the dynamics of the reproductive migration of coconut crabs, we investigated both male and female migration patterns during the reproductive season in Hatoma Island, southwest of Japan. Both females and males migrated between inland and coastal areas during the reproductive season. Observed female seaward and landward migrations were temporally coincident with their reproductive activities (egg extrusion and larval hatching). Observed temporal-spatial distribution of males would be shaped by temporal variations in expected future mating opportunities within the reproductive season and male reproductive strategy in response to these variations.

LAND, MANGROVE AND FRESHWATER DECAPOD CRUSTACEANS OF MAYOTTE REGION (CRUSTACEA DECAPODA)

A documented and illustrated checklist of land, mangrove and rivers Decapoda is proposed for Mayotte region. The study area is situated between longitudes 43-48° E and latitudes 11-13°10’ S. It includes Mayotte Island, Comoros Islands, and Glorioso Islands. Records of the species are from a fieldwork at Mayotte in November 2009, complemented by a literature review. 58 species are listed including 24 new records for Mayotte region. The inventory includes 42 crabs, 11 shrimps and 5 coenobitids (Birgus latro, Coenobita spp.). Crabs Grapsoidea (Cardisoma, Geograpsus, Grapsus, Metasesarma, Metopograpsus, Neosarmatium, Pachygrapsus, Parasesarma, Perisesarma, Pseudograpsus, Pseudohelice, Ptychognathus, Sesarmops, Thalassograpsus, and Varuna) are best represented together with the Ocypodoidea (Chaenostoma, Dotilla, Macrophthalmus, Ocypode, and Uca). Shrimps belong to the genera Atyoida, Caridina, Macrobrachium, and Palaemon. Biotopes investigated include rivers, mangroves, estuaries, land, and coastal areas with a special attention paid to Malamani mangrove in the west coast of Mayotte Island. The fauna of Mayotte region is predominantly indo-west pacific in its composition (45 species). Thirteen species are distributed only in the western Indian Ocean, but only one is perhaps endemic to the region. A comparison with the fauna of the Seychelles Islands shows that at least 6 additional species, widely distributed in the Indo-West Pacific, are potentially also present in Mayotte region.

Mitigation Strategies for Harvesting-induced Body Size Miniaturization of Coconut Crab in Vanuatu

Mitigation Strategies for Harvesting-induced Body Size Miniaturization of Coconut Crab in Vanuatu

Impacts of Large Male-Selective Harvesting on Reproduction: Illustration with Large Decapod Crustacean Resources

To signal a need for caution for present large male-selective harvesting practices, negative impacts of the large male-selective harvesting on reproductive output in large decapod crustacean resources are introduced with emphasis on my own work with spiny king crab Paralithodes brevipes, coconut crab Birgus latro, and the stone crab Hapalogaster dentata. The large male-selective harvestings for several large decapod crustaceans have changed their population demographic structure by decreasing mean male size and skewing sex ratio towards females. By several field and laboratory experiments, the change of population demographic structure was anticipated to decrease female reproductive success in the resources (i.e. reproductive output of the harvested populations) through a decrease in sperm availability for females because of male size-dependent reproductive potentials and slow sperm recovery rate. Furthermore, reproductive output and stability of the large male-selective harvested resources were also anticipated to decline by a decrease in mate availability for females, attributing to combination of female mate choice for larger males with negative effects of female delayed mating and/or maternal influences. To establish the optimal management practices, the details of the mating system and reproductive ecology of each targeted species should be investigated.

Giant Robber Crabs Monitored from Space: GPS-Based Telemetric Studies on Christmas Island (Indian Ocean)

We investigated the navigational capabilities of the world's largest land-living arthropod, the giant robber crab Birgus latro (Anomura, Coenobitidae); this crab reaches 4 kg in weight and can reach an age of up to 60 years. Populations are distributed over small Indo-Pacific islands of the tropics, including Christmas Island (Indian Ocean). Although this species has served as a crustacean model to explore anatomical, physiological, and ecological aspects of terrestrial adaptations, few behavioral analyses of it exist. We used a GPS-based telemetric system to analyze movements of freely roaming robber crabs, the first large-scale study of any arthropod using GPS technology to monitor behavior. Although female robber crabs are known to migrate to the coast for breeding, no such observations have been recorded for male animals. In total, we equipped 55 male robber crabs with GPS tags, successfully recording more than 1,500 crab days of activity, and followed some individual animals for as long as three months. Besides site fidelity with short-distance excursions, our data reveal long-distance movements (several kilometers) between the coast and the inland rainforest. These movements are likely related to mating, saltwater drinking and foraging. The tracking patterns indicate that crabs form route memories. Furthermore, translocation experiments show that robber crabs are capable of homing over large distances. We discuss if the search behavior induced in these experiments suggests path integration as another important navigation strategy.

Coconut Crabs, Birgus latro (Anomura: Coenobitidae), of Sorol Atoll, Yap, with Remarks on the Status of B. latro in the Federated States of Micronesia

Abstract: A preliminary survey of coconut crabs, Birgus latro (L.), on Sorol Atoll, Yap, during 3 weeks in June and July 2011 is only the second quantitative assessment of B. latro for any island or island group in the Federated States of Micronesia (FSM). A population density of at least 169 crabs/ha (based on 10 m and 2 m fixed-width transects combined) and as high as 354/ha (2 m fixed-width transects only) was estimated for Pigelmol Island in the atoll. The largest male measured 71.4 mm in thoracic length (TL) and weighed 2,750 g, and the largest female was 44.0 mm TL and weighed 720 g; 24 males (26% of the 91 crabs from Pigelmol) were larger than the largest female. The sex ratio did not differ significantly from 1:1. Crabs were active during the day as well as at night. Population density of B. latro on Pigelmol probably is among the highest of any island in the FSM, but a dearth of similar studies in the FSM precludes more-definitive interisland comparisons. Coconut crabs were not recorded on the tw...

Growth and morphogenesis of larvae reared at different temperatures, and mass culture of larvae in the coconut crab Birgus latro (Decapod, Coenobitidae)

Growth and morphogenesis of larvae reared at different temperatures, and mass culture of larvae in the coconut crab Birgus latro (Decapod, Coenobitidae)

First successful curative use of digoxin-specific Fab antibody fragments in a life-threatening coconut crab (Birgus latro L.) poisoning

We wish to report the first curative use of digoxin-specific Fab antibody fragments in a coconut crab Birgus latro L. poisoning in New Caledonia. The female patient, aged sixty-three with a previous history of cardiovascular and metabolic dysfunctions, showed marked first-degree atrio-ventricular block and several atrial pauses, and was given 760 mg of digoxin-specific Fab antibody fragments. Shortly after the perfusion her electrocardiogram returned to close to normal with only slight first-degree atrio-ventricular block and no more atrial pauses. Neriifolin LC-MS/MS tests performed on the patient's serum and urine samples confirmed cardenolide poisoning. Another, younger patient, with high neriifolin levels in her serum and urine samples only experienced gastro-intestinal symptoms and was discharged without specific treatment. The consumption of coconut crab in New Caledonia should be avoided even though the first of the two cases reported suggests that digoxin-specific Fab antibody fragments can be effective in the treatment of life-threatening poisoning caused by the ingestion of this crustacean.

Conservation needs of the coconut crab Birgus latro on the Nicobar Islands, India

AbstractWe describe the distribution of the coconut crab Birgus latro, categorized as Data Deficient on the IUCN Red List, local perspectives towards the species, and its conservation needs on the Nicobar Islands in the eastern Indian Ocean. The species is threatened with extinction across most of its range and in India it is found only on a few islands in the Andaman and Nicobar archipelagoes. We carried out informal discussions with Nicobari communities to examine issues regarding conservation of the species and conducted timed searches in areas where coconut crabs were likely to be found. The discussions revealed that there are social taboos against hunting the coconut crab on most of the Nicobar Islands. However, on some islands these taboos are not being followed and community members may hunt the crab for consumption. Athough the coconut crab is legally protected under the Indian Wildlife Protection Act none of the villagers were aware of this. Of the six islands surveyed we recorded the presence of 17 and 14 crabs on two islands, respectively. On four islands villagers reported the presence of the crab prior to the tsunami of 2004, and on two of these islands the species may now be locally extinct. A small population size and a fragmented distribution in areas of coconut plantations suggest that the species is threatened. We recommend monitoring and detailed research on the ecology and genetics of the coconut crab, along with community-based conservation initiatives to conserve the species and its habitat.

Reefs and islands of the Chagos Archipelago, Indian Ocean: why it is the world's largest no-take marine protected area.

The Chagos Archipelago was designated a no-take marine protected area (MPA) in 2010; it covers 550 000 km2, with more than 60 000 km2 shallow limestone platform and reefs. This has doubled the global cover of such MPAs.It contains 25-50% of the Indian Ocean reef area remaining in excellent condition, as well as the world's largest contiguous undamaged reef area. It has suffered from warming episodes, but after the most severe mortality event of 1998, coral cover was restored after 10 years.Coral reef fishes are orders of magnitude more abundant than in other Indian Ocean locations, regardless of whether the latter are fished or protected.Coral diseases are extremely low, and no invasive marine species are known.Genetically, Chagos marine species are part of the Western Indian Ocean, and Chagos serves as a 'stepping-stone' in the ocean.The no-take MPA extends to the 200 nm boundary, and. includes 86 unfished seamounts and 243 deep knolls as well as encompassing important pelagic species.On the larger islands, native plants, coconut crabs, bird and turtle colonies were largely destroyed in plantation times, but several smaller islands are in relatively undamaged state.There are now 10 'important bird areas', coconut crab density is high and numbers of green and hawksbill turtles are recovering.Diego Garcia atoll contains a military facility; this atoll contains one Ramsar site and several 'strict nature reserves'. Pollutant monitoring shows it to be the least polluted inhabited atoll in the world. Today, strict environmental regulations are enforced.Shoreline erosion is significant in many places. Its economic cost in the inhabited part of Diego Garcia is very high, but all islands are vulnerable.Chagos is ideally situated for several monitoring programmes, and use is increasingly being made of the archipelago for this purpose.

An improved mark-recapture method using passive integrated transponder (PIT) tags in Birgus latro (Linnaeus, 1767) (Decapoda, Anomura)

The effectiveness of Passive Integrated Transponders (PIT tags) was investigated in the robber or coconut crab, Birgus latro. A pilot study was conducted in Chumbe Island, Zanzibar, and a definitive study on Christmas Island, Indian Ocean. No mortality or adverse behaviour was recorded as a result of PIT tagging. On Christmas Island 1150 crabs were tagged in 2009 and 2010. In the period to April 2011, 169 crabs were recaptured, some up to four times. Of these, 67 had moulted before recapture. Approximately equal numbers of each sex were marked, and recaptured. Tag loss was estimated at ~5%. Alternative sampling protocols using grid and transect searches were tested. They produced different results in terms of sampling efficiency and sex ratio: sampling protocol must be considered when interpreting data.PIT tagging in Birgus is a promising method for long term population studies. It promises low tag loss and good recapture rates in comparison with previous studies.

Pushing the Envelope in Paradise: A Novel Approach to Rat Eradication at Palmyra Atoll

Palmyra Atoll National Wildlife Refuge is a moist Central Pacific atoll that supports one of the best remaining tropical forest ecosystems in the region, including 10 species of breeding seabirds and a robust population of the world’s largest terrestrial invertebrate, the coconut crab. Despite these riches, the atoll’s ecosystem has been modified by introduced black rats that were inadvertently brought to Palmyra during WWII. Between June 1 and 30, 2011, a partnership between the U.S. Fish and Wildlife Service, The Nature Conservancy, and Island Conservation successfully implemented a project to remove rats from Palmyra. Independent monitoring of bait application and its environmental effects was undertaken by the USDA. Over the 28-day operation, a team of 41 people from 5 countries utilized 2 helicopters, 10 slingshots, 148 bait stations, and hand spreading to strategically apply 38,561 kg of rodent bait containing the anticoagulant brodifacoum (25 ppm) to Palmyra’s 235 hectares of emergent land. Palmyra’s challenging eradication environment demanded the development of a novel approach, such as broadcast application rates between 75 and 85 kg/ha and the use of “bolas” to bait coastal forest canopy to minimize bait drift into the marine environment. Initial findings show minimal non-target impacts as a result of the project, and post-eradication monitoring has failed to detect rats. Increased recruitment by at least 2 native tree species has been observed. By removing rats from Palmyra, the partnership aims to safeguard the atoll’s indigenous flora and fauna, encourage the reestablishment of extirpated seabird species, and create an ecological refuge for species within the Central Pacific region that are at risk of extinction. This project is a conservation milestone for the Refuge, and it has established a benchmark for eradication campaigns on other tropical islands.

Plausible causes for sperm-store variations in the coconut crab Birgus latro under large male‑selective harvesting

In populations subjected to size-selective harvesting of large males, remaining males are small and participate in more matings than in pristine populations. The reproductive rate of such harvested populations can be restricted due to sperm limitation, because the numbers of sperm passed to females decrease with decreasing male size and increasing male mating frequency. Japa - nese populations of the coconut crab Birgus latro are typical examples of populations that are subject to selective harvesting of large males. Reproductive output of the population may have declined via sperm limitation. However, there is no evidence that males exhaust sperm reserves through succes- sive matings, and little is known about the factors causing variations in the number of sperm retained by females in the harvested population. Using field investigations and laboratory experiments, I examined (1) whether males exhaust sperm reserves and (2) what factors cause variations in the number of sperm retained by females. About half of the males had exhausted sperm reserves by the end of the mating season. These males were found to be incapable of further mating or of ejaculating larger numbers of sperm, which was inferred from laboratory experiments. The size of individuals of both sexes participating in mating decreased as the mating season progressed, and males did not adjust ejaculate size in response to female size. Thus, variations in the number of sperm retained by females may have mainly been due to a decline in the male ability to ejaculate large numbers of sperm, due both to increased male mating frequency and decreased male size.

Emigration behaviour during sea-to-land transition of the coconut crab Birgus latro: Effects of gastropod shells, substrata, shelters and humidity

Populations of the coconut crab, Birgus latro, have been severely depleted on most inhabited islands throughout the Indo-Pacific because of over-harvesting and environmental degradation. Coconut crabs emigrate from the sea as megalopae carrying gastropod shells. Better knowledge of emigration behaviour can assist in conservation of coconut crab populations through understanding and protecting the habitats indispensable for completing their life cycle. We examined the behaviour of coconut crabs during sea-to-land transition by culturing megalopae and juveniles in containers that hold sea-water and hard substrate simulating an intertidal microhabitat in nature. The test environmental factors were availability of gastropod shells and substrata (small and coarse coral sands) including shelters on land, and humidity (relative humidity, 76% and 98%). Megalopae matured their nature for acquiring shells and emigration from the sea in around 10 days. Humidity and shell availability affected animal behaviour. Low humidity decreased the proportion of animals on land, and burrowing behaviour was stimulated in low humidity and shell-less conditions. Animals in low humidity had a low survival rate. Shelters and shells stimulated the proportion of animals on land at low humidity, and animals concentrated under the shelters on land. Shells, burrows and shelters should act to protect animals from desiccation by keeping microclimates around animals on high humidity. Thus, coconut crab megalopae and juveniles preferred a humid environment, and high-humidity conditions stimulated emigration from the sea. Our findings highlight the importance of a humid environment around the seashore in sustaining the recruits for coconut crab populations.