Hermit Crab Populations Research Articles

Shell resource partitioning as a mechanism of coexistence in two co-occurring terrestrial hermit crab species

BackgroundCoexistence is enabled by ecological differentiation of the co-occurring species. One possible mechanism thereby is resource partitioning, where each species utilizes a distinct subset of the most limited resource. This resource partitioning is difficult to investigate using empirical research in nature, as only few species are primarily limited by solely one resource, rather than a combination of multiple factors. One exception are the shell-dwelling hermit crabs, which are known to be limited under natural conditions and in suitable habitats primarily by the availability of gastropod shells. In the present study, we used two co-occurring terrestrial hermit crab species, Coenobita rugosus and C. perlatus, to investigate how resource partitioning is realized in nature and whether it could be a driver of coexistence.ResultsField sampling of eleven separated hermit crab populations showed that the two co-occurring hermit crab species inhabit the same beach habitat but utilize a distinct subset of the shell resource. Preference experiments and principal component analysis of the shell morphometric data thereby revealed that the observed utilization patterns arise out of different intrinsic preferences towards two distinct shell shapes. While C. rugosus displayed a preference towards a short and globose shell morphology, C. perlatus showed preferences towards an elongated shell morphology with narrow aperture.ConclusionThe two terrestrial hermit crab species occur in the same habitat but have evolved different preferences towards distinct subsets of the limiting shell resource. Resource partitioning might therefore be the main driver of their ecological differentiation, which ultimately allowed these co-occurring species to coexist in their environment. As the preferred shell morphology of C. rugosus maximizes reproductive output at the expense of protection, while the preferred shell morphology of C. perlatus maximizes protection against predation at the expense of reproductive output, shell resource partitioning might reflect different strategies to respond to the same set of selective pressures occurring in beach habitats. This work offers empirical support for the competitive exclusion principle-hypothesis and demonstrates that hermit crabs are an ideal model organism to investigate resource partitioning in natural populations.

Entrapment in plastic debris endangers hermit crabs

Significant quantities of plastic debris pollute nearly all the world’s ecosystems, where it persists for decades and poses a considerable threat to flora and fauna. Much of the focus has been on the marine environment, with little information on the hazard posed by debris accumulating on beaches and adjacent vegetated areas. Here we investigate the potential for beach debris to disrupt terrestrial species and ecosystems on two remote islands. The significant quantities of debris on the beaches, and throughout the coastal vegetation, create a significant barrier which strawberry hermit crabs (Coenobita perlatus) encounter during their daily activities. Around 61,000 (2.447 crabs/m2) and 508,000 crabs (1.117 crabs/m2) are estimated to become entrapped in debris and die each year on Henderson Island and the Cocos (Keeling) Islands, respectively. Globally, there is an urgent need to establish a clear link between debris interactions and population persistence, as loss of biodiversity contributes to ecosystem degradation. Our findings show accumulating debris on these islands has the potential to seriously impact hermit crab populations. This is important for countless other islands worldwide where crabs and debris overlap, as crabs play a crucial role in the maintenance of tropical ecosystems.

The Biology and Functional Morphology ofCurvemysella paula(A. Adams, 1856) (Bivalvia: Galeommatoidea: Montacutidae) Commensal withDiogenes goniochirusForest, 1956 (Crustacea: Paguridea) on China Beach, Danang, Vietnam.

The Indo-West Pacific montacutid Curvemysella paula(A. Adams, 1856) is the sole representative of its genus and the only known bivalve that is an obligate commensal of hermit crabs. As such, studies on it are accordingly very few. It lives in small groups byssally attached to the internal columella of the host's adopted shell. This paper describes the species from a wave-exposed beach in central Vietnam at Danang. Here, it was living with Diogenes goniochirus, but elsewhere in Hong Kong and Japan other taxa serve as hosts. The adult shell of C. paula is antero-ventrally long, deeply concave ventrally and so inequivalve as to appear twisted. Smaller individuals are more equivalve and equilateral and become deformed with age and growth. The hinge plate has a structure typical of the Montacutidae with the ligament ventrally formed into a lithodesma. Anatomically, C. paula is also unremarkable and interest in it focuses on reproduction. The species lives in small groups, the oldest and largest being a female, the smallest and youngest males. Intermediate sized individuals are hermaphroditic. Curvemysella paula is thus a protandric consecutive hermaphrodite. Prodissoconch morphology suggests that C. paula does not ctenidially brood fertilised eggs or, if so, only briefly. Further, it seems likely that there is subsequently an abbreviated lecithotrophic period of development perhaps undertaken close to the sea bed - thereby keeping the larvae close to established hermit crab and parental bivalve populations.

Intra-specific competition drives variation in the fundamental and realized niches of the hermit crab, <I>Pagurus criniticornis</I>

The difference between preferred and available resources within natural environments can be viewed as the disparity between fundamental and realized niches. We employ this concept to examine intra-specific sexual variation in the shell-size relationships of the hermit crab Pagurus criniticornis (Dana, 1852) from two treatments: (1) a natural unbiased population (i.e., realized niche); and (2) a group subjected to free-choice experiments that were able to select a preferred shell from a selection of high-quality shells (i.e., fundamental niche). Crab-shell relationships for both treatments suggest that males and females select shells proportional to their size. The relationships between crab size and preferred shell weight (i.e., fundamental niche) derived from free-choice experiments enabled the calculation of a shell adequacy index (SAI) for all individuals from both treatments. A strong interaction between SAI values across sex and treatment (♂Free choice = ♀Free choice = ♂Population > ♀Population) suggested that non-ovigerous females may experience a considerable niche disparity in their natural habitats while ovigerous females tend to inhabit shells with a greater prevalence of damaged shell apices. Results suggest a competitive hierarchy whereby males out- compete females for access to high-quality shells. Despite niche disparities, P. criniticornis typically occupied shells of good condition (low damage and encrustation), suggesting that resource limitation may not be as severe as that reported for other hermit crab populations. Our data provide insights into intra-specific competition that reflect the ability of individuals to win and hold high-quality resources within resource-limiting environments.

Yearly shifts in shell quality for the hermit crab Pagurus longicarpus in coastal Massachusetts

Global warming is expected to result in milder New England winters. In this study we monitored changes in hermit crab shell quality at Nahant, Massachusetts, USA, at intervals during 17 yr between 1997 and 2014 for a single species of hermit crab Pagurus longicarpus occupying the shells of the intertidal periwinkle Littorina littorea. The incidence of hermit crabs occupying damaged shells, shells housing the symbionts Hydractinia, Crepidula plana, and C. convexa, and showing poor shell fit varied significantly among years. Shell quality was especially bad in the summer of 2012, following one of the warmest winters on record: more than 60% of the sampled hermit crabs were found living in damaged shells and more than 50% of the shells bore symbionts. Moreover, an unusually low number (only 15%) of the hermit crabs sampled that summer were found in shells that were undamaged, without symbionts, and of adequate size, compared with 50 to 55% of hermit crabs being found in such 'perfect' shells in 1997 and 2013. We suggest that new, high-quality shells are added to hermit crab populations at our study site largely through the freeze-induced mortality of intertidal periwinkles, and that the poor shell quality documented in summer 2012 reflects reduced periwinkle mortality during the unusually warm preceding winter. If so, then P. longicarpus might serve as a coastal 'canary in the coal mine': documenting yearly shifts in the quality of shells used as shelters by coastal marine hermit crabs in New England may provide a convenient means of monitoring the impact of climate change on intertidal populations.

Hermit crab population structure and association with gastropod shells in the northern Bering Sea

Most models of the impacts of climate change on the distributions of animals have focused on limits to thermal tolerances of individual species. Such “bioclimatic envelope” models do not consider the importance of interactions among species, each of which may respond to climate change in its own way. Hermit crabs (Paguridae) cannot exist without shells produced by gastropods. Thus, their ranges are expected to depend not only on their own physiological tolerances, but also on tolerances of gastropod species that produce shells of suitable sizes for growing crabs that use successively larger shells. To assess their potential importance to range shifts of hermit crabs, we characterized these relationships over a large area of the northern Bering Sea in May to early June. Of 1539 hermit crabs collected, Pagurus rathbuni comprised 55%, Pagurus trigonocheirus 44%, and Labidochirus splendescens 1%, with only four individuals of three other Pagurus species. P. rathbuni used shells of mostly moon snails (Naticidae); only 7 to 19% used whelk shells (Buccinidae) in the first four size classes, and 34% in the largest size class. P. trigonocheirus also used shells of mainly moon snails, but its use of whelk shells ranged from 18 to 44% in the first four size classes, and 70% in the largest size class. Densities of P. rathbuni and P. trigonocheirus varied independently (r2=0.08, p=0.09, N=36 stations). Other studies suggest that hermit crabs obtain most of their shells from gastropods that have recently died, and that such empty shells are available for a relatively short period before being buried in sediments; thus, available shells should resemble the local pool among living gastropods. Correlation of P. rathbuni densities with densities of living gastropods with suitable shells was weak (r2=0.18, p<0.01, N=36 stations), while there was no correlation for P. trigonocheirus (r2<0.01, p=0.59). Density patterns of hermit crabs within the five size classes did not correspond to densities of living gastropods with suitable shells (randomization tests of independence, all p<0.002). These results suggest that at large spatial scales in the northern Bering Sea, near-term effects of climate change on hermit crab distributions will depend more strongly on factors other than concurrent effects on dispersion of gastropods.

Some ecological aspects of the land hermit crab Coenobita scaevola (Coenobitidae) at Wadi El-Gemal protected area, Red Sea

Gastropod shells can be a limiting factor in allowing hermit crab populations to increase. The impact of this factor on population size of the land crab Coenobita scaevola (Forskal, 1775) was examined. Extensive and intensive works were conducted on a sandy beach of Wadi El-Gemal island and the protected area coast (35°04’0”E, 24°42’0”N). Activity, spatial and temporal distribution, food foraging, and impact of human tourism activities for this hermit crab were discussed. A total of 365 crab individuals were collected from the sandy beach of Wadi El-Gemal island during August 2007 to July 2008, among these 137 were used for frequency measurements of occupied shells by the land hermit crabs. The hermit crabs were found occupying seventeen species of gastropod shells. A significant regression and correlation were recorded between the shell aperture and chelae. However, our data showing no significant regression values between total body weight of crabs and for each of the shell weight and internal volume. From the other angle, the correlation relationship recorded high significant value for the same relationships. This may reflect that some smaller crabs tend to occupy larger shells than the preferred ones. Moreover, the shell species occupation as a function of chelar hermit crabs size. While the negative results between body weight of crab and both shell internal volume and weight it may be due to the variations behavior of some land hermit crab individuals within population. It is logical that fit the size of chelae with aperture of shell to achieve protection from predators while some members of the population that occupied shell is greater than the size of his body to the unavailability of appropriate shells.

Invasive freshwater snails provide resource for native marine hermit crabs

Invasive species can have significant direct and indirect impacts on native biota. Here, we conducted a survey of two invasive freshwater snail species (Melanoides tuberculata and Tarebia granifera) in Tobago and assessed the effects on shell use by native marine hermit crab populations (Clibanarius tricolor and C. vittatus). Abundant in freshwater, numbers of empty shells at the mouth of a river in Charlotteville (Northeast Tobago) increased from 75 to 800 m-2 after heavy rains in the wet-season of June 2012. Subsequent sampling of a nearby rocky shore revealed that the freshwater shells were occupied by 70.2% of hermit crabs. Mimicking a flood event, the experimental planting of marked alien freshwater shells showed that 20.3% of hermit crabs exchanged their marine shell for a freshwater shell. Similarly, a laboratory shell-choice experiment showed that C. tricolor hermit crabs changed shells repeatedly, and that 22.2% occupied a freshwater shell rather than a marine shell. Overall, due to the numeric abundance of freshwater shells and the compulsive shell changing behaviour of Clibanarius spp., the ongoing invasion of freshwater gastropods in the Caribbean may change the shell use patterns and population dynamics of the native hermit crabs.

Feeding hermit crabs to shrimp broodstock increases their risk of WSSV infection

White spot syndrome virus (WSSV) is a serious shrimp pathogen that has spread globally to all major shrimp farming areas, causing enormous economic losses. Here we investigate the role of hermit crabs in transmitting WSSV to Penaeus monodon brooders used in hatcheries in Vietnam. WSSV-free brooders became PCR-positive for WSSV within 2 to 14 d, and the source of infection was traced to hermit crabs being used as live feed. Challenging hermit crabs with WSSV confirmed their susceptibility to infection, but they remained tolerant to disease even at virus loads equivalent to those causing acute disease in shrimp. As PCR screening also suggests that WSSV infection occurs commonly in hermit crab populations in both Vietnam and Taiwan, their use as live feed for shrimp brooders is not recommended.

Symbiosis of sea anemones and hermit crabs: different resource utilization patterns in the Aegean Sea

The small-scale distribution and resource utilization patterns of hermit crabs living in symbiosis with sea anemones were investigated in the Aegean Sea. Four hermit crab species, occupying shells of nine gastropod species, were found in symbiosis with the sea anemone Calliactis parasitica. Shell resource utilization patterns varied among hermit crabs, with Dardanus species utilizing a wide variety of shells. The size structure of hermit crab populations also affected shell resource utilization, with small-sized individuals inhabiting a larger variety of shells. Sea anemone utilization patterns varied both among hermit crab species and among residence shells, with larger crabs and shells hosting an increased abundance and biomass of C. parasitica. The examined biometric relationships suggested that small-sized crabs carry, proportionally to their weight, heavier shells and increased anemone biomass than larger ones. Exceptions to the above patterns are related either to local resource availability or to other environmental factors.

Shelter association between the hermit crab Sympagurus dimorphus and the zoanthid Epizoanthus paguricola in the southwestern Atlantic Ocean

Schejter, L. and Mantelatto, F.L. 2011. Shelter association between the hermit crab Sympagurus dimorphus and the zoanthid Epizoanthus paguricola in the southwestern Atlantic Ocean. —Acta Zoologica (Stockholm) 92: 141–149. The available literature on zoanthid–hermit crab associations deals only with records of this phenomenon, providing no detailed information. We describe, for the first time, the shell-like colonies of Epizoanthus paguricola associated with the hermit crab Sympagurus dimorphus from benthic samples taken in the Argentine Sea, between 85 and 131 m depth, and provide information about morphometric relationships between the hermits and the zoanthids. In total, 260 specimens (137 males and 123 females) of S. dimorphus were collected, 240 (92.3%) of which were living in symbiosis with E. paguricola. The remaining 20 (7.7%) were living inside gastropod shells. As the initial structure of the pseudoshell, 12 different gastropod species were found (all were almost totally covered with colonies of E. paguricola). The hermit crab lives in the spiral cavity inside the soft colony, which seemed to be slightly different depending on the initial gastropod. Aperture pseudoshell morphology did not seem to be related to the sex of the hermit crab host, although males showed larger apertures for a given colony size. This fact is probably related to a larger size of male’s cheliped (sexual dimorphic character) used like a gastropod operculum and that may serve as a template for the growing of the aperture pseudoshell edge. The number of epizoanthid polyps per colony increased in relation to the weight of the colony and to the size of the hermit crab. A process of selection of the initial shell was evident, because species of Naticidae were not the most common gastropods in this benthic community, but were those most used by hermit crabs (>60%). The puzzling association between hermit crab, shell and zoanthid presumably occurs during the hermit juvenile phase, when the crab occupies a small shell, and a zoanthid larva settles on it. Given the close relationship between S. dimorphus and E. paguricola found in this region, we support the idea that due to the low availability of adequate gastropod shells for hermit life cycle, this association allows the establishment and the continuity of the hermit crab population in the studied area.

Crustacean parasites associated with hermit crabs from the western Mediterranean Sea, with first documentation of egg predation by the burrowing barnacle Trypetesa lampas (Cirripedia: Acrothoracica: Trypetesidae)

Parasitic isopods (family Bopyridae) and burrowing barnacles (family Trypetesidae) infesting hermit crabs were investigated from shallow subtidal collections made along the southeastern coast of Spain in 2009. A total of 713 specimens of Clibanarius erythropus (Latreille, 1818) and 82 Calcinus tubularis (L., 1767) were examined. Gastropod shells and worm tubes inhabited by hermit crabs were collected by hand while snorkeling and were cracked to determine host species, size, sex and presence of eggs. Two species of bopyrid isopods were found on C. erythropus: the branchial parasite Bopyrissa fraiseii (Carayon, 1943) and the abdominal parasite Parathelges cardonae Codreanu and Codreanu in Codreanu, 1968. Among all C. erythropus examined, Bopyrissa fraiseii was found on 0.6% of hermit crabs and P. cardonae was found on 0.3%. A redescription of P. cardonae is provided and the species is documented with light and scanning electron microscopy for the first time. No Calcinus tubularis harbored parasitic isopods, but one specimen was parasitized by an unidentified rhizocephalan barnacle of the genus Septosaccus (1.2%). The burrowing barnacle Trypetesa lampas (Hancock, 1849) was found associated with both hermit crab species and evidence of predation on host eggs by this barnacle is shown for the first time. Trypetesa lampas was found in 4.2% of the shells collected. The present study expands our knowledge of the parasite fauna of hermit crabs from the Mediterranean Sea and indicates that additional research is needed to determine the impact of trypetesid egg predators on hermit crab populations.

Bio-ecological aspects of the hermit crab Paguristes calliopsis (Crustacea, Diogenidae) from Anchieta Island, Brazil

In southern Atlantic studies on hermit crab biology are scanty considering the local biodiversity. In this way, some population features of Paguristes calliopsis Forest and Saint Laurent, 1968 such as size frequency distribution, sex ratio and shell occupation in the natural environment were studied. Specimens were collected by means of scuba methods in the infralittoral area of the Anchieta Island. A total of 116 individuals were analyzed. Size measurements (minimum; maximum; mean shield length +/- sd, respectively) were 0.8; 4.5; 2.76 +/- 0.79 mm for males and 2.28 +/- 0.36 mm for females. The sex ratio was 1.47:1 in favor of males which prevailed in the largest size classes. The hermit crabs occupied shells from eleven gastropod species and Cerithium atratum (Born 1778) was significantly the most occupied one (75.86%). Significant correlations were not obtained in all regression analysis, demonstrating sexual differences on fitting of the occupied shells. In the studied area P. calliopsis population is small if compared with the other hermit crab populations. The shell utilization varies as a function of shell availability and hermit crabs interspecific competition, in relation to the other coexistent species.

Habitat bottlenecks in stage-structured species: hermit crabs as a model system

The availability of habitat at one stage of a species' life history may limit the ultimate population size of that species. In particular, species that use distinct juvenile habitats may experi- ence bottlenecks at an early life stage that have important and potentially unexpected consequences for adult population sizes. I used intertidal hermit crabs Pagurus samuelis and P. hirsuitisculus as a model system to test experimentally the effect of increasing juvenile and adult habitat (snail shells, Littorina sp. and Tegula funebralis) availability on adult population size. Despite strong evidence from these experiments that juvenile hermit crab population size was limited by juvenile habitat availability, adult population size was not. Instead, results indicated that adult populations were probably limited by recruitment and adult habitat availability. Consequently, these results (1) demon- strate that identifying true habitat bottlenecks can be challenging, (2) show that identifying true bottlenecks requires one to evaluate the effect of bottlenecks on adult population size, and (3) offer a rigorous empirical test of the assumption that hermit crab populations are limited by the availability of large shells. These results also highlight how conservation and management strategies designed to protect species with stage-structured life histories must consider the actual role different habitats play in controlling adult population size if they are to be most effective.

Shell condition and adequacy of three sympatric intertidal hermit crab populations

Shell use in relation to size adequacy and presence of physical damage and encrustation was evaluated and compared among and within three co-existing species of intertidal hermit crab (Clibanarius antillensis, C. sclopetarius and C. vittatus) in the intertidal region of Pernambuco Islet, São Sebastião Channel, south-eastern Brazil. Comparisons of shell utilization patterns among species and sexes were made with respect to physical damage (perforations and breakage in aperture and apex), encrustation by other organisms and shell size adequacy. Two adequacy indices were calculated. The visual adequacy index (VAI) was based on the degree of hermit crab retraction into the shells (1 = crab totally retracted and 6 = shield exposed). The shell adequacy index (SAI) was calculated through a comparison of the weight of the used versus the preferred shell. A relationship was found between VAI and SAI with crabs assigned as VAI = 3 occupying optimal shells (SAI = 1), i.e. crabs that could retract and those that could not retract the whole body into shells were in relatively heavier and lighter shells than the preferred ones, respectively. Shells utilized by the hermit crabs were generally undamaged and highly encrusted (except for C. antillensis) by oysters, barnacles and green algae, features that may reduce the risks of desiccation and predation. The frequent damage to the shell apertures was associated with a high abundance of shell-crushing predators in the studied area. The degree of encrustation as well as the shell adequacy (VAI and SAI) showed intra- and interspecific variation, while the presence of damage differed only among sexes (reproductive classes). In general, the smallest individuals in the populations used relatively heavier shells. Fecundity of the crabs of this assemblage is thought not to be limited by shell use once ovigerous females are occupying optimal shells.

Hermit crab population ecology on a shallow coral reef (Bailey’s Cay, Roatan, Honduras): octopus predation and hermit crab shell use

Gilchrist, S.L. 2003. Hermit crab population ecology on a shallow coral reef (Bailey’s Cay, Roatan, Honduras): octopus predation and hermit crab shell use. In: Lemaitre, R., and Tudge, C.C. (eds), Biology of the Anomura. Proceedings of a symposium at the Fifth International Crustacean Congress, Melbourne, Australia, 9‐13 July 2001. Memoirs of Museum Victoria 60(1): 35‐44. Shells can be a limiting factor in allowing hermit crab populations to increase. Predators of gastropod molluscs and of hermit crabs release shells into reef environments where hermit crabs find and cycle them within their populations. Predators also play a role in distributing shells among hermit crab species. To highlight how octopuses influence shell availability to hermit crabs, observations were made on members of Octopus vulgaris Cuvier, 1797 and O. briareus Robson, 1929 at Bailey’s Cay Reef (Roatan, Honduras) during July and August each of three years, 1999‐2001. In addition to feeding while foraging, Octopus vulgaris and O. briareus individuals create shell and debris middens outside of their temporary dens. These middens concentrate shells and food for hermit crabs in the reef environment where locating an empty shell could be difficult. However, because hermit crabs are prey items for octopuses, hermit crabs using the middens risk predation from the den occupant. Relatively small hermit crab species such as Pagurus brevidactylus (Stimpson, 1858) and P. criniticornis (Dana, 1852) were found commonly in dens and among middens, opening the possibility that the den functions as a refugium for some species as well.

Shell utilization patterns of a tropical intertidal hermit crab assemblage

The shell selection and utilization patterns of three sympatric hermit crab populations (Clibanarius antillensis, C. sclopetarius, and C. vittatus) and shell availability were studied in a tropical intertidal low energy area. Shell availability (except for C. antillensis) was low and the hermit crabs showed overlap in size (mainly C. sclopetarius and C. vittatus). The influence of shell availability and selection on shell use was dependent on crab species. Clibanarius antillensis used mainly shells of Cerithium atratum, the most available shell species, while Clibanarius sclopetarius and C. vittatus occupied shells with lower availability in the studied area such as Chicoreus senegalensis, Stramonita haemastoma, Leucozonia nassa and Cymatium parthenopeum. The three species selected different gastropod shells with only Clibanarius antillensis using almost exclusively its preferred shell species in nature. The relationship between shield length and the weight of the used shell was not dependent on crab species or shell species, indicating that the size (not species) of the shells defines what size (not species) of crabs will occupy them.

Factors selecting for avoidance of drilled shells by the hermit crab Pagurus longicarpus

Periwinkle shells ( Littorina littorea) that have been drilled by moon snails are abundant at Nahant, MA, and yet hermit crabs ( Pagurus longicarpus) are rarely found living in them. In the laboratory, hermit crabs will occupy drilled shells only if no other options are provided to them; they will, in fact, choose intact shells that are too small for them over drilled shells of appropriate size. This paper documents the selective forces that might account for this marked avoidance of drilled shells by hermit crabs. We show that drilled shells increase the vulnerability of the hermit crabs to decapod predators (e.g., the green crab, Carcinus maenas), in part by allowing predators to enlarge the drill hole and also by reducing the force needed for predators to crack the shells open. Living in drilled shells also made the hermit crabs in our study more vulnerable to eviction by conspecifics and more vulnerable to low-salinity stress. Thus, moon snail predation on periwinkles, rather than supplying the Nahant hermit crab population with suitable empty snail shells, actually serves to destroy a potential resource for the hermit crabs and apparently to heighten competition among hermit crabs for intact shells.

Population biology and growth of three sympatric species of intertidal hermit crabs in south-eastern Brazil

Hermit crab populations have been described in different habitats and latitudes but few studies focused on coexisting populations. Such information is especially important to evaluate the effect of coexistence in the population biology of such organisms. This study was done in the intertidal region of Pernambuco Islet, São Sebastião Channel, south-eastern Brazil. Random samples of crabs were taken monthly during one year to evaluate their size and sex. The three coexisting Clibanarius populations (C. antillensis, C. sclopetarius, and C. vittatus) showed similar patterns of sex ratio (skewed for females), sexual dimorphism (males larger than females), recruitment (February to June) and population growth but differed in size structure (Cs&gt;Cv&gt;Ca) and reproductive activity over the year. Population growth was estimated using the von Bertalanffy growth function (VBGF) and revealed that the growth of these three populations was strongly reduced from August to January and that longevity varied from 42 to 48 months. Clibanarius antillensis showed continuous reproduction with high frequency of ovigerous females over the year while C. sclopetarius and C. vittatus had a reproductive peak in April and absence of ovigerous females in August/September. Coexistence seemed to influence population biology of these hermit crabs, given the relationship of their reproductive periods and growth patterns to the shell adequacy to the crabs. The overlap in reproductive peaks and recruitment periods may strengthen competition for shells. Comparisons of the reproductive patterns of the hermit crab populations recorded to date emphasize that reproduction and, consequently, life strategies of hermit crabs are not directly dependent on taxonomic or geographical proximity, but on their evolutionary histories and on local processes acting on each assemblage or population.

The Survival Crisis Faced by Coastal Ecosystems In Tropical and Subtropical Areas

In tropical and subtropical coastal areas, there are unique ecosystems in which the land hermit crab plays an important roll. Recent land developments have forced them into a survival crisis, particularly around the Okinawan islands in southern Japan.The islands of Okinawa used to be surrounded by cobalt color reef seas and abundant ecosystems, of which the land hermit crabs were at the heart. While still dominant, most of them are now being destroyed by the construction of artificial barriers such as sea walls for roads, and land development.Field surveys have revealed that coastal ecosystems in subtropical seas are facing a survival crisis. The main results can be summarized as follows:(1) The numbers of land hermit crabs that live on coasts with artificial eco-barriers are far less than the numbers living on natural coasts with no artificial eco-barriers.(2) On a coast that contains artificial barriers, the distribution of the land hermit crab population in different age groups does not follow the normal distribution pattern as seen in natural coasts. The natural coast shows a distribution that has the maximum number at breeding age and follows a pattern similar to the Gauss's distribution function.(3) One more important thing that this research has shown is that in developing countries, there are very few small coastal animals, such as land hermit crabs and beach crabs. This is almost certainly due to land development, as almost all of the resort island coasts are now taken up by resort hotels and affluent residences. Their ecosystems may also be facing a crisis similar to that in Okinawa.