Species Of Fiddler Crabs Research Articles

Population genetics of two sibling species of fiddler crabs (Decapoda, Ocypodidae): Brazilian homogeneity and West Atlantic heterogeneity

Abstract Fiddler crabs are a widespread group of marine invertebrates. Their wide distribution is due to the great capacity of their larvae to disperse among estuarine and shelf waters. Therefore, it is expected that all populations along their distribution show molecular similarities due to extensive gene flow. Thus, we assessed the intra- and interspecific genetic divergence of two sibling species of fiddler crabs, Minuca panema and Minuca mordax, based on COI mtDNA sequences. The molecular data resulted in a highly mixed haplotype network for M. panema, while M. mordax sequences were clustered in two groups, one with Brazilian and other with Costa Rican haplotypes. The highest variance in M. panema was found within populations, while in M. mordax it was between groups and populations. The analyses of nucleotide divergence showed small genetic variance within populations of both species and between Brazilian populations, and higher variance between Brazilian and Costa Rican populations of M. mordax. The highest genetic divergence was found between the two species. Thereby, our results show an intense gene flow along the Brazilian coast, while there is a clear divergence among Brazil and Costa Rica, which may be a result of the great distance between these populations.

Confirming the occurrence of two fiddler crabs, Tubuca dussumieri (H. Milne Edwards, 1852) and T. coarctata (H. Milne Edwards, 1852) (Crustacea: Decapoda: Ocypodidae), in Hong Kong by DNA barcoding and morphology

The Indo-West Pacific region has a rich fiddler crab fauna. In East Asia, some species of fiddler crabs, such as Tubuca coarctata (H. Milne Edwards, 1852) and T. dussumieri (H. Milne Edwards, 1852), are considered insular, being present in the Philippines, Taiwan, and Ryukyus, but with no consistent record on continental China. Although T. dussumieri has been previously recorded in continental China, these records were considered dubious or misidentified. The nature of the Kuroshio Current and the colder waters of the China Coastal Current, compared to the currents along the eastern coasts of the Philippines and Taiwan, are considered barriers to the entrance of larvae of these species into the region. Nonetheless, using the cytochrome oxidase subunit I (COI) gene and morphological evidence, we present the first record of T. coarctata and show the presence of a T. dussumieri population in Hong Kong SAR, China. We hypothesize that the newly found T. coarctata in Hong Kong may be related to water temperature increases due to anthropogenic climate change, which allows its larvae to survive in this region and develop into adult crabs. Furthermore, our findings corroborate previous records of T. dussumieri in continental China. The restricted distribution of T. dussumieri in China and the smaller size of individuals, however, may indicate suboptimal habitats for arriving larvae. The limited presence of the two crabs on Chinese shores indicates that the intense coastal development in the country, such as in Hong Kong, may destroy suitable habitats and render these species susceptible to local extinction.

Caught in transition: changes in brachyuran diversity following mangrove encroachment into saltmarshes at a southern distribution limit

Mangroves are expanding polewards due to global change, often encroaching into adjacent temperate saltmarshes. In both vegetated ecosystems, brachyurans are responsible for ecological processes and functions such as nutrient cycling and sediment bioturbation. South African mangroves occur at a latitudinal limit and are establishing further south due to past planting events and global change, making these ideal study systems for the effects of mangrove expansion and encroachment. Here, we investigated the effect of mangrove encroachment on brachyuran community composition at two saltmarsh sites with planted mangrove stands of different ages. Transects were laid perpendicular to each estuary where three habitat types were demarcated (mangrove, ecotone, saltmarsh). Sediment samples were collected for analyses and quadrats were used to measure pneumatophore density, saltmarsh cover, and brachyuran abundance and diversity. We found that brachyuran community structure at each site has significantly changed over seven years, with two mangrove-associated fiddler crab species, Tubuca urvillei and Paraleptuca chlorophthalmus, now recorded at the younger planted site, indicating a new southern distributional limit. Community structure was also significantly different amongst habitat types (p < 0.05) with Parasesarma catenatum dominating saltmarshes while Danielella edwardsii was more prominent in mangroves. However, community composition did not differ significantly between the two (differently aged) sites (p > 0.05). Pneumatophore density had a proportional relationship with crab abundance, diversity and richness, while saltmarsh cover had an inversely proportional relationship with crab abundance, diversity and richness. It is likely that as mangroves continue to expand into saltmarshes, more mangrove-associated species will move into saltmarshes, potentially altering ecosystem processes in this unique habitat.

Burrow morphology of three species of fiddler crab (Uca) along the coast of Pakistan

Burrowing by crabs is an important component of their functional role in mangrove biotopes. The Fiddler crab (Uca) is one of the more conspicuous burrowing organisms in the mangrove areas of Pakistan. To evaluate interspecific differences in burrowing behaviour between three species of Uca (U. annulipes, U. chlorophthalmus and U. sindensis), we compared vegetation cover, sediment composition and burrow morphology by using plaster of Paris casts. Five burrow morphology characters were measured (burrow number, depth, length, volume, and diameter of the burrow openings). Nearly all the morphological characters of the burrows differed significantly between species. The burrow morphology variations were correlated with the tidal level (distance from the water mark during low tide), porosity, percent organic matter, vegetation cover and structure of the sediments. The species-specific differences in the burrows cautions against generalizing regarding the functional role of fiddler crabs along the coast of Pakistan.

Goliath is not the enemy: Fiddler crab species of similar size are stronger competitors than their larger adversaries in the climate change context

Many intertidal species are expanding their distribution limits towards the poles as a consequence of increased temperature due to climate change. At the same time, some intertidal habitats have been reduced due to rising sea levels. Fiddler crabs inhabit mangroves, and different species occupy well-established zones. Due to the restricted mangrove areas and consequent latitudinal expansion of the species, the distribution and density of fiddler crabs may be subject to change. The overlap forces several species to cohabit in a smaller territorial space. Fiddler crab species can vary in size, which could decisively affect territorial competition. Using Leptuca urguayensis as a reference, we tested how competing species of different sizes (larger size: L. thayeri and Minucapanema; similar size: L. cumulanta and L. leptodactyla) might interact in future climate change scenarios. First, we showed that within the territory of L. uruguayensis, the species L. cumulanta and L. thayeri occurred mainly in the lower mesolittoral zone, while L. leptodactyla and M.panema predominated in the upper mesolittoral zone. In a laboratory experiment, we evaluated whether the density and size of the heterospecific competitors could alter the agonistic behavior of Leptuca uruguayensis. Our results indicated that increasing the density can increase the agonistic behavior of L. uruguayensis with a greater intensity against species of a similar size. In a second field experiment, we demonstrated that the presence of a burrow enhances the intensity of agonistic interactions between L. uruguayensis and species of similar size. Therefore, in a scenario of territorial expansion of fiddler crabs due to climate change, it is expected that similarly sized species represent a greater competitive threat to populations of L. uruguayensis.

Comparing the effect of larval dispersal strategies on morphological versus genetic differentiation in two neotropical fiddler crabs

AbstractThe dispersal mode of estuarine invertebrates has a strong effect on genetic variability and phenotypic expression, potentially maintaining gene flow among widely separated populations or limiting connectivity among close ones. Understanding the dispersal strategies effects can support adequate strategies for environment management and understand the evolutionary history of the studied species. A comparative study on the effect of larval dispersal strategies (export vs retention) along the overall geographic distribution ranges of adult populations of two co‐distributed fiddler crab species was performed. Geometric morphometric techniques were used to evaluate morphological differentiation in the shape of the carapace and major cheliped propodus in 10 populations of Minuca mordax and five populations of Leptuca leptodactyla. Potential genetic differentiation was assessed using DNA sequence data from up to 170 fiddler crab specimens, corresponding to the mitochondrial gene cytochrome c oxidase subunit 1 (COX1). Patterns of genetic and morphological characteristics diverged among populations of both species. In terms of morphology, populations of both species showed intraspecific variation in the shape of the carapace and, to a lesser extent, in the major cheliped propodus. This observed intraspecific variation followed a clear geographic pattern of morphometric differentiation, in which the geographic origin is associated with a phenotypic response to the environmental diversity along the extended Brazilian coast. In contrast, there are shared haplotypes in populations separated by more than 4000 km, but with significant ΦST values among most populations of L. leptodactyla and M. mordax, suggesting a moderate to high level of gene flow. Therefore, it can be concluded that the split of the Central South Equatorial Current has not acted as an efficient long‐term barrier to the dispersal of larvae in both species. In M. mordax, a slight limitation of genetic exchange can be observed between the southernmost populations and the remaining ones. This first evidence of genetic structuring within this widely distributed species is consistent with its documented strategy to retain larvae in the estuarine environments. However, occasional transport of larvae to more open coastal waters seems to maintain stepwise gene flow between neighboring populations. Overall, our results still provide evidence of more pronounced genetic homogeneity in a species with a larval export strategy (L. leptodactyla) compared to a species with a larval retention strategy (M. mordax). This suggests that larval dispersal strategies, coupled with the microhabitat in which the respective species occur, have a noticeable effect on the degree of gene flow. Most likely, these biological aspects are further influenced by the estuarine and coastline geomorphology.

Sharing is living: The role of habitat heterogeneity in the coexistence of closely related species.

In biologically diverse ecosystems, an essential process to support competing species to coexist is ecological differentiation. Habitat heterogeneity is, hence, important in establishing species abundance and richness, favoring the coexistence of species due to habitat partition. In this context, shading and species thermal tolerance can be good factors to elucidate the role of habitat heterogeneity in the habitat partition among closely related species. Herein, we study shading effects in microhabitat selection, behavior, and physiological limitation on two species of fiddler crabs (Leptuca leptodactyla and Leptuca uruguayensis). Indeed, shading conditions influenced fiddler crabs species proportion over time, with L.leptodactyla more associated with nonshaded/warmer areas while the L.uruguayensis to shaded/cooler ones. They also adjusted their behavior differently from each other to deal with thermal stress. Finally, we have demonstrated that these effects are related to species' physiological limitations. We conclude that biologically diverse ecosystems, such as intertidal regions from estuaries (e.g., mudflats and mangroves), support the coexistence between closely related species by reducing competition due to habitat partition.

Genetic Structure of the Endemic Fiddler Crab Uca (Xeruca) formosensis on the West Coast of Taiwan.

Xeruca formosensis is the only endemic species of fiddler crab on the west coast of Taiwan. However, its natural habitats and populations have been compromised by excessive anthropogenic activities and improper land use over the past four decades. In light of these changes, we sought to evaluate the genetic diversity and gene flow of the species by examining the genetic variation of X. formosensis at different sampling locations. To this end, we performed molecular analyses of three endonuclease-amplified fragment length polymorphisms (TE-AFLP) and the cytochrome oxidase subunit I (COI) marker from leg muscle samples. We found that the genetic variation within sampling locations was higher than that among sampling locations, and the expected heterozygosity of genetic diversity (Hj) was 0.152 for TE-AFLP data. Meanwhile, the COI marker showed high haplotype diversity (h = 0.976 ± 0.008) and a low genetic differentiation level (FST = 0.021) in X. formosensis populations. Importantly, the genetic connectivity of X. formosensis may be influenced by larval-stage crabs drifting between coastal and marine habitats. As such, crab gene flow is promoted among populations by larval exchange via nearshore currents. Although X. formosensis has high gene flow, the species could undergo an extinction crisis if the population sizes continue to decline, as with most endangered species. In order to maintain the natural habitats and population size of X. formosensis, long-term monitoring and investigation will be necessary.

Body colourations affect predation risk from fish in fiddler crabs

Many animals show conspicuous colour patterns that inform potential predators about their unprofitability due to their toxicity or unpalatability (aposematism). However, no systematic work has evaluated the colouration of crabs in terms of aposematism, even though many species exhibit conspicuous colouration. We conducted a laboratory study to compare predation risk from a fish predator, the barred mudskipper (Periophthalmus argentilineatus), in two sympatric fiddler crab species with different body colour patterns: Austruca perplexa with brownish-white colourations and Paraleptuca crassipes with red-and-black colour patterns. Fiddler crabs and mudskippers are active on tidal flats during low tides. A predation trial by stocking one crab and one mudskipper in a test arena was repeated five times for each species–sex combination. The animal behaviour was video recorded for 24 h, and crabs were confirmed to be alive or dead after 72 h. A. perplexa females were most vulnerable to predation from mudskippers. The attack intensity from mudskippers was stronger during the nighttime than daytime against P. crassipes females and males and A. perplexa males, suggesting that mudskippers may avoid them by visually detecting the body colouration in P. crassipes and the body structure in males of both species (i.e. a large weaponry claw) during the daytime. Mudskippers eventually preyed on and consumed some individuals in both species–sexes. Mudskippers are known to shift their main food components from small crustaceans through polychaete worms to crabs, such as fiddler crabs, and unpalatable polychaete worms tend to be brightly coloured. We suggest that the red colouration of P. crassipes may be incidental mimicry of the unpalatable red/orange-coloured polychaete worms that mudskippers might have learned to avoid.

Fecundity and reproductive patterns of the fiddler crab Uca maracoani Latreille 1802-1803 in an Amazonian estuary in northern Brazil

ABSTRACT In this study, aspects of the reproductive biology of a Uca maracoani population from northern Brazil were examined. Ovigerous females monthly captured from December 2013 to November 2015 were measured and dissected to count, collect morphometric data, and classify the eggs. Ovigerous females were encountered throughout the two-year period but were absent during the months with the highest rainfall and lowest salinity, which indicates a seasonal–continuous reproductive pattern. The fecundity varied from of 12,233 to 85,000 eggs per female, and mean was 36,840 ± 3,361 eggs. The egg size increased progressively and significantly over the course of embryonic development. We found a direct relationship between the size of the females and their fecundity, and a clear trend was seen in which the larger females produced more eggs with larger sizes, which increased less in size during embryonic development. The presence of early- and late-stage eggs together in the same ovigerous mass in a considerable number of the ovigerous females suggests multiple spawning. The fecundity of U. maracoani is greater than that of other Atlantic fiddler crab species, and its reproductive strategy ensures its survival in the estuaries of the Amazon coast, which are subject to considerable fluctuations in salinity.

Temperature Extremes and Sex-Related Physiology, Not Environmental Variability, Are Key in Explaining Thermal Sensitivity of Bimodal-Breathing Intertidal Crabs

Global temperature increases are predicted to have pronounced negative effects on the metabolic performance of both terrestrial and aquatic organisms. These metabolic effects may be even more pronounced in intertidal organisms that are subject to multiple, abruptly changing abiotic stressors in the land-sea transition zone. Of the available studies targeting the intertidal environment, emphasis has largely been on water-breathing model organisms and this selective focus resulted in limited reliable forecasts on the impact of global warming on primarily air-breathing intertidal species. We investigated the thermal sensitivity of six phylogenetically related fiddler crab species that occupy different microhabitats on intertidal shores from south America and east Asia to test how bimodal-breathing intertidal ectotherms cope with thermal stress. We examined the metabolic physiology and thermal limits of the crabs by measuring their cardiac function and oxygen consumption along a thermal gradient. Their specific thermal microhabitat was also appraised. We found that subtropical fiddler crab species inhabiting vegetated microhabitats have lower upper lethal temperatures and therefore greater thermal sensitivity in comparison to their tropical counterparts. Additionally, females exhibited higher oxygen consumption and lower lethal temperatures in comparison to males. Our results contradict previous predictions that species from higher latitudes that experience greater temperature variability have broader latitudinal distributions, greater phenotypic plasticity and lower thermal sensitivity. Furthermore, the higher thermal sensitivity demonstrated by female fiddler crabs with respect to males strongly suggests a role of both gametogenesis and physiological dimorphism on the thermal performance of tropical and subtropical intertidal organisms. These observations ultimately, advocates for further studies on sex-biased and development-biased thermal sensitivity before drawing any generalizations based on a single sex or life stage.

Diluted Seawater and Ammonia-N Tolerance of Two Mangrove Crab Species. New Insights to Understand the Vulnerability of Pristine Islands Ecosystems Organisms

Mangrove ecosystems are the primary receptors of anthropogenic pollution in tropical areas. Assessing the vulnerability of these ecosystems can be expressed, among other indicators, by studying the health of ‘ecosystem engineers’. In this study, mangrove forests facing opposing anthropogenic pressures were studied (i) in the uninhabited island of Europa (Mozambique Channel), considered as a pristine ecosystem, and, (ii) on the island of Mayotte, facing regular domestic wastewater discharges. Using an ecophysiological approach, the effects of diluted seawater (DSW) and increased ammonia-N were studied for two fiddler crab species: Gelasimus tetragonon (GT) on the island of Europa and Paraleptuca chlorophthalmus (PC) on the island of Mayotte. Osmoregulation curves and osmoregulatory capacity were determined along with O2 consumption rates after a 96 h exposure period. Histological analyses were also carried out on two important metabolic organs: the hepatopancreas and the posterior gills. Results indicate that both crab species are good hyper-hypo-osmoregulators but only PC can maintain its osmoregulatory capacity when exposed to ammonia-N. Oxygen consumption is increased in GT after 96 h of exposure to ammonia-N but this does not occur in PC. Finally, a thickening of the gill osmoregulatory epithelium was observed after 96 h in PC when exposed to ammonium but not in GT. Therefore, the two species do not have the same tolerance to DSW and increased ammonia-N. PC shows physiological acclimation capacities in order to better manage nitrogenous enrichments. GT did not show the same physiological plasticity when exposed to ammonia-N and could be more at risk by this kind of stress. These results along with those from other studies regarding the effects of domestic effluents on mangrove crabs are discussed. Therefore, the greater vulnerability of organisms occupying pristine ecosystems could induce major changes in mangrove functioning if crabs, that are engineer species of the ecosystem, are about to reduce their bioturbation activity or, even, disappear from the mangrove forests.

Diversity and Distribution of Fiddler Crabs (Crustacea: Brachyura: Ocypodidae) around the Arabian Sea.

Nine species of fiddler crabs (Crustacea: Ocypodidae: Gelasiminae) are known from the Arabian Sea and adjacent waters (Red Sea, Gulf of Aden, Gulf of Oman and Arabian/Persian Gulf): five species of Austruca, one Cranuca, two Gelasimus and one Tubuca. COI sequence data match morphological species boundaries and shows high connectivity within each. The fauna is highly endemic, with three species of Austruca (A. albimana, A. iranica and A. sindensis) confined to this region, and four others restricted to the Indian Ocean. restricted to the Indian Ocean. Austruca albimana and A. iranica speciated locally and now have narrowly overlapping ranges in Oman. Our results confirm the westernmost distributions of Austruca annulipes and Tubuca alcocki are Pakistan and the Red Sea, respectively. A key for the nine species is also provided to help identification.

Larder Hoarding Versus Immediate in situ Food Consumption in Two Fiddler Crab Species: Is it an Evolutionarily Stable Strategy?

Larder hoarding behavior in central place foragers has been widely studied in vertebrates, albeit, not as extensively as scatter hoarding. However, scant information is available for the invertebrate taxa, especially aquatic species. We investigated this phenomenon via an in situ food supplementation experiment in a community of two sympatric fiddler crabs, Austruca annulipes (n = 80; 40 males and 40 females) and Gelasimus vocans (n = 60; 30 males and 30 females), in a Singapore mangrove patch with an intermediate resource level. As the semiterrestrial intertidal crabs can only forage after emergence from their burrows during exposure period, the duration of time available for feeding is finite and constitutes an important constraint in the optimization of food intake. The activity budget (in terms of time spent on feeding activities, all above-ground non-feeding activities, and burrow-sequestration) as well as the occurrence (if any) of larder hoarding behavior in these two species after they first emerged were recorded by hourly intervals (three hours of observation) to determine the effect of time left for foraging on larder hoarding. Regardless of species, A. annulipes and G. vocans spent most of the time feeding when the tide was out, despite overall significant behavioral heterogeneity (multivariate analyses using ANOSIM) indicating that both species prioritized hunger satiation over other activities. Our results also showed that although the two sympatric crabs live in the same mangrove area with similar food resource levels, only A. annulipes larder hoarded. The propensity to larder hoard did not differ significantly between the sexes, nor among the three time periods of the feeding duration. Gelasimus vocans, one of the species of crabs known to form feeding droves, did not larder hoard at all. We propose that A. annulipes is a species that can deploy larder hoarding as a foraging strategy when it encounters valuable food resources, and such a strategy is highly advantageous for the species as it generally inhabits sandy habitats that are poor in nutrient levels. Hence, larder hoarding can be considered a mixed evolutionarily stable strategy (ESS) adopted by A. annulipes. In contrast, G. vocans that commonly inhabits muddy sediments-with a high level of food resources-did not larder hoard, even when provided with supplemented food, suggesting perhaps that its mixed ESS is droving behavior.

Diversity and Distribution of Fiddler Crabs (Crustacea: Brachyura: Ocypodidae) in Vietnam.

Based on recently collected material and records in the literature, 14 species of fiddler crabs (Crustacea: Ocypodidae: Gelasiminae) are reported from Vietnam. DNA barcoding analyses using the mitochondrial gene COI (cytochrome c oxidase subunit I) was performed to identify examined materials and their precise distributional range. Thirteen species-level taxa are identified and, with the exception of Galsimus borealis and G. vocans, have minimum interspcific divergences of at least 7.27%. The identified species include seven species of Tubuca Bott, 1973, three of Austruca Bott, 1973 and three of Gelasimus Latreille, 1817, and one Paraleptuca Bott, 1973. Two new records of Vietnam are herein reported: Tubuca rhizophorae and T. dussumieri. The southernmost distribution limits of East Asian G. borealis, T. acuta and T. arcuata are in northern Vietnam, A. lactea in central Vietnam, whereas northernmost limit of Southeast Asian T. rhizophorae and T. forcipata in southern Vietnam. A dichotomous key to identify the 14 Vietnamese species is provided.

Length of a sexually selected ornament-armament in fiddler crabs (Decapoda: Brachyura: Ocypodidae): One way, over deep time and space

Abstract Using three data sources, we measured claw lengths of the extremely large major claws of 70 species of fiddler crabs, spread over four major biogeographic regions and all 11 genera, as a function of carapace length. Despite a diversity of biogeography, body size, type of sexual signaling and mating behavior, and details of claw morphology, all species groupings follow the same linear relationship. No subgroupings could be determined, by region, among diverse genera, by ancestral-derived status, or by data source. Major claw size is known to be implicated in female selection of mates, which might be expected to diversify claw lengths among species and genera, as might differences in combat might be expected to diversify claw length, as it does in other claw traits. The constancy suggests a possible functional constraint on major claw length across the fiddler crabs, which is to be determined. Efficient folding of the claw as the male rapidly retreats into a burrow, or a protection of the carapace from frontal attack by predators or combatants in an initial aggressive encounter might select for this pervasive relationship. Tests are suggested. The sexually selected major claw is more variable than the naturally selected minor claw, but this difference in variability could be attributed partially to regeneration of the major cheliped and even variation in shape. A surprising similar trend of closing force index for the major claw exists for a large number of species spread throughout the genera and major regions occupied by fiddler crabs, but a considerable variation exists in a variety of functional traits. Thus, the constancy of length relationship stands out distinctly from a considerable background variation in form. As a sexually selected trait, the claw length constancy begs for an explanation.

Attraction waves of male fiddler crabs: A visual display designed for efficacy

Animal signals can be very complex, particularly those used in mate attraction. They can contain multiple elements that have different functions- some based on signal efficacy and some on signal content. In this study, we show that the fiddler crab, Austruca lactea, produces a complex mating signal with three sequential wave types, each given in a different context. We suggest that the first two wave types are alerting signals that are designed for signal efficacy. They function to draw female attention before the male switches to the content-carrying signal that is used for female mate choice. We show that males produce ‘broadcast waves’ when no female is visible to them. These waves are given steadily, but at a slow rate, throughout the diurnal low tide mating period. They are effective at drawing the attention of the rare and unpredictable mate-searching females. Once a distant female becomes visible to the male, he switches to producing ‘directed waves’; they are given at a faster rate and their temporal distribution matches the abundance of mate-searching females. Both broadcast and directed waves appear to be designed for signal efficacy rather than signal content. They are alerting signals that draw female attention to the presence and location of the male. The third wave type is the courtship wave; it is given when the female is close to the male and is equivalent to the typical information-carrying mate choice wave found in other fiddler crab species.

Intertidal zone preferences of fiddler crabs in tropical mangroves reflect species specific selection across multiple spatial and temporal scales

In mangroves, species specific spatial habitat zonation preference of fiddler crabs could influence the functioning of mangrove ecosystems. Spatial zonation of fiddler crabs in tropical Malaysian mangroves across different temporal scales has not been studied extensively. In this study, the abundance and species richness of several fiddler crab species across a mangrove intertidal zone were examined in relation to environmental variables. Fiddler crab abundance was sampled with salinity, pH, temperature, and sediment grain size in three mangrove sites in Penang Island, Malaysia. The sampling design involved collecting crabs and environmental habitat variables in six 2 m × 2 m quadrats within three mangrove study sites from March 2017 to February 2018. Data were analysed using multivariate (PERMANOVA, SIMPER, and BEST in PRIMER v7.0) and univariate analyses (ANOVA and Pearson’s r in STATISTICA v 13.30). Univariate and multivariate analysis revealed multiple spatial and temporal scales influenced each fiddler crab species differently (ANOVA p < 0.05). Fiddler crab abundance varied across and within sites, intertidal zones, and sampling months (PERMANOVA, p < 0.001). Austruca annulipes, Gelasimus vocans and Tubuca paradussumieri were found mostly at the lower intertidal zone, which was characterized by a higher sand faction. Tubuca rosea, Tubuca forcipata, and Austruca bengali occupied and coexisted in the middle and higher zones of the intertidal, although this pattern varied across the different sites in this study. BEST analysis indicated that porewater salinity and sediment particle size were important factors in structuring patterns of fiddler crab assemblages. Based on univariate correlation analyses, the total abundance of fiddler crab increased with increased temperature (temperature ranged from 26.9 °C to 31.7 °C), and increased porewater salinity (salinity ranged from 10‰ to 35‰).

Distinguishing ten sympatric species of fiddler crab (Decapoda: Ocypodidae) using a suite of phenotypic characteristics.

Ten species of fiddler crab are reported inhabiting the intertidal zone of a shore on Kaledupa Island, Indonesia. This is one of the highest recorded numbers of fiddler crab species living in sympatry, equating to over two-thirds of those known from the Wallacea biogeographic region and more than half of all those recorded from Indonesia. The descriptions to identify and distinguish these ten species are provided using a suite of characters e.g., carapace, major cheliped, male gonopods, gastric mills, life colouration in males and females, and notes on their ecology and distribution. Specimens were observed and collected in the Wakatobi National Park, near the village of Ambeua on Kaledupa island, Sulawesi Tenggara, Indonesia. Gastric mills are described for the first time for Gelasimus jocelynae, Paraleptuca crassipes, Tubuca coarctata, T. demani and T. dussumieri. A tabulation of anatomical features and colouration for all species in this study is provided as a support for field studies. It identifies features that support the recently proposed taxonomic revision of fiddler crabs by Shih et al. (2016).

Cold water temperatures define the poleward range limits of south American fiddler crabs

Temperature increase due to climate change has caused shifts in the range distribution of several organisms globally. In coastal intertidal environments most organisms have an amphibious life cycle and their poleward range limits may be delimited by their thermal tolerance during the pelagic larval stages. Fiddler crabs are key species in intertidal environments and their early larval stages occur in coastal waters. We evaluated the mean and monthly minimum sea surface temperature (SST) gradient over the South American coast and compared it to the minimum and maximum critical thermal limits (CTmin and CTmax) of the first larval stage of eight fiddler crab species to assess whether temperature delimits their distributional ranges. We found a clinal decrease in mean SST of 0.28 °C per latitudinal degree along the distribution of fiddler crabs in South America. Cold tolerance differed among the larvae of fiddler crab species, which corresponds to the latitudinal temperature gradient observed in their poleward range limits. Thus, our results suggest that cold water temperature can define the poleward range limits of South American fiddler crabs. The CTmax cannot explain the northern poleward range limits of the fiddler crabs. Fiddler crabs larvae showed a similar tolerance to high temperatures (mean 40.5 °C) regardless of species (except Leptuca uruguayensis) and these are higher than environmental temperatures observed in South America. We also observed an increase in mean SST of 0.9 °C in the last 37 years. This increase in water temperature may explain the recent poleward range expansion of one South American fiddler crab species, Leptuca cumulanta. Therefore, we showed that differential thermal responses at the early larval stage have consequences on the geographic range limits of the fiddler crab species. Our findings allow us to hypothesize that fiddler crabs’ poleward range limits may expand to higher latitudes in the future due to global warming.