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The anthropogenic construction activities on the coasts, such as pile-driving, generate vibrations that propagate through the substrate. Such substrate-borne vibrations could potentially affect marine organisms inhabiting the benthic environments. However, there is a lack of documented studies on the effects of vibrations on benthic animals. To investigate whether anthropogenic substrate-borne vibrations such as pile-driving operation influence the fiddler crab, Austruca lactea , we measured their locomotion response under vibrations of 35, 120, 250, 500, and 750 Hz generated by a vibrator. We compared the locomotion of crabs between control and vibration-treatment groups using videography. The duration of movements was significantly lower under 120 Hz vibrations compared to the control. Moreover, crab velocity was significantly higher under vibrations of 120 Hz and 250 Hz compared to the control group. Our result suggests that A. lactea can detect low-frequency substrate-borne vibrations and experience stress, leading to increased energy consumption. [Display omitted] • Fiddler crabs can detect low-frequency (120–250 Hz) substrate-borne vibrations. • Austruca lactea reduced movement duration or increased velocity to such vibrations. • The locomotion of them suggests that such vibrations could pose a stressor. • Vibrational disturbances should be considered for coastal construction. [ABSTRACT FROM AUTHOR]

Abstract Autotomy is a predator escape mechanism in many taxa, including crustaceans. Male fiddler crabs autotomize the major claw, despite its importance in mating, territoriality, and thermoregulation. This claw can be regenerated through molting. We investigated major claw autotomy in the fiddler crab Leptuca pugilator , testing hypotheses that (1) autotomy of the major claw accelerates the molting process, reflecting the importance of this appendage, (2) autotomy of the major claw results in increased feeding to accumulate energy reserves needed for regeneration, (3) this change in feeding is hormonally driven. Autotomy of the major claw accelerated molting. Yet contrary to expectations, autotomy of the claw initially inhibited feeding, with evidence for release of feeding inhibitory factor. These effects are specific to the major claw, and were not seen following autotomy of a walking leg. Acceleration of molting following autotomy of the major claw appears to be an adaptive response reflecting the costs of being without this multi-function structure. Highlights • We investigated major claw autotomy in the fiddler crab Leptuca pugilator. • Autotomy of the major claw accelerated molting. • Autotomy of the major claw reduced feeding behavior for at least 96 h. • Autotomy of a walking leg had no effect on molting or feeding. • Results represent an adaptive response reflecting the costs of losing the major claw. [ABSTRACT FROM AUTHOR]

Geographical variation is often the earliest stage leading to divergence and speciation. Osmoregulatory ability was assessed in 64 populations of 10 species of semi-terrestrial fiddler crabs along the Atlantic coast of Brazil between Amapá and Santa Catarina. In the laboratory, crabs were exposed for 5 days to media ranging in osmolality from 15 to 3550 mOsm/kg H 2 O. Hemolymph osmolality was measured in 10-μL aliquots using a Wescor 5520 osmometer. Survivorship, lower- (LLC 50 ) and upper (ULC 50 ) lethal osmolalities, and isosmotic concentrations [ISO] were estimated in populations for which habitat osmolality was also measured. All fiddler crab species were excellent hypo-/hyper-osmoregulators. Mean [ISO] was < 600 mOsm/kg H 2 O in the lone oligosaline species, between 650 and 770 mOsm/kg H 2 O in the seven mesosaline species, and > 800 mOsm/kg H 2 O in the two eusaline species. Intraspecific variation in [ISO] was significant only in Minuca rapax , emphasizing the importance of this parameter as a physiological set-point. Although ULC 50 varied intraspecifically in six species, habitat osmolality varied significantly for M. rapax and M. victoriana alone. Thus, intraspecific variation in ULC 50 likely results from local osmotic acclimatization. Since genetic variation appears to be minor and unstructured across populations in most fiddler crab species, the consistency of [ISO] reflects its importance as a physiological property. In contrast, intraspecific differences in ULC 50 among populations indicate that this character is ecophenotypic. Unquestionably, physiological studies on fiddler crab populations distributed over a wide geographical range can provide insight into the biological basis of adaptation and the evolution of species in this semi-terrestrial genus. [ABSTRACT FROM AUTHOR]

Fiddler crab burrow morphologies in tidal flat ecosystems depend largely on physical characteristics of the soil. Herein, we aimed to examine the relationship between soil texture profiles and the burrow depths and morphologies of four fiddler crab species: Tubuca arcuata , Gelasimus borealis , Xeruca formosensis , and Austruca lactea . We found that the burrow depths of T. arcuata , G. borealis , and A. lactea (range = 8–50 cm) were strongly affected by surface soil composition; only the burrow depth of X. formosensis (which reached 100 cm in some cases) was influenced by the presence of deeper, clay-rich soils. Specifically, X. formosensis relied more heavily on fine soils, such as clay or silt, when they burrowed deeper into sand-covered mudflats. We hypothesize that deep burrowers, such as X. formosensis, may coat clay-rich soils on their burrow walls to impede flooding and to prevent burrow collapse, suggesting that surface soil composition does not necessarily determine the burrow depth and composition for all fiddler crab species. [ABSTRACT FROM AUTHOR]

Understanding where and why organisms are experiencing thermal and hydric stress is critical for predicting species' responses to climate change. Biophysical models that explicitly link organismal functional traits like morphology, physiology, and behavior to environmental conditions can provide valuable insight into determinants of thermal and hydric stress. Here we use a combination of direct measurements, 3D modeling, and computational fluid dynamics to develop a detailed biophysical model of the sand fiddler crab, Leptuca pugilator. We compare the detailed model's performance to a model using a simpler ellipsoidal approximation of a crab. The detailed model predicted crab body temperatures within 1 °C of observed in both laboratory and field settings; the ellipsoidal approximation model predicted body temperatures within 2 °C of observed body temperatures. Model predictions are meaningfully improved through efforts to incorporate species-specific morphological properties rather than relying on simple geometric approximations. Experimental evaporative water loss (EWL) measurements indicate that L. pugilator can modify its permeability to EWL as a function of vapor density gradients, providing novel insight into physiological thermoregulation in the species. Body temperature and EWL predictions made over the course of a year at a single site demonstrate how such biophysical models can be used to explore mechanistic drivers and spatiotemporal patterns of thermal and hydric stress, providing insight into current and future distributions in the face of climate change. • Fiddler crabs are subject to thermal and hydric stress when attracting mates. • Direct measurements and 3D software were used to create a biophysical model. • The model accurately predicts water loss and body temperatures in the lab and field. • Specific morphological inputs improve model performance over simple geometries. • Modeling aids understanding of current distribution and response to climate change. [ABSTRACT FROM AUTHOR]

The objective of this study is to compare ecologically relevant measures of performance over a broad range of latitude of a species subjected to climate change. Do populations change in relative function over a wide range of latitude? Are populations at the low latitude trailing edge in danger of extinction in the onset of thermal stress? Coastal marine species with planktonic larvae can range over an enormous span of latitude and thermal environments. The fiddler crab Leptuca pugilator extends from high-latitude (41.75°N) winter-frozen Massachusetts tidal flats in the north to subtropical low latitude flats in Florida (24.55°N), where they may be active at the surface over most of the year. We characterized the air environment for males at three sites (New York – latitude 40.0°N, Beaufort, North Carolina – latitude 34.7°N, Panacea Florida, latitude 30.0°N) over the geographic-thermal range, and found major differences in temperature, wind speed, humidity, and vapor pressure deficit. Florida L. pugilator males preferred warmer sand than North Carolina and New York crabs. Local adaptation to latitude-dependent thermal conditions might suggest tradeoffs in performance as a function of temperature. We examined measures of predator escape performance (running speed and righting speed) and overall condition reflecting endurance rivalry success (endurance on a treadmill and major claw closing force) over a wide range of test temperatures. Predator escape rates increase steadily with increasing temperature, but endurance rivalry measures show an intermediate temperature peak of performance. We tested the hypothesis of tradeoffs, with expected local superiority of performance according to regional thermal differences. But instead, the trailing edge Florida males were superior to the higher latitude populations, over a broad range of temperature, but especially at higher temperatures, for all four types of performance measures. The trailing edge population of L. pugilator , in thermal terms, is therefore likely not vulnerable to near future further effects of warming in terms of performance measures related to male reproductive and feeding activities and escape from predators. Fiddler crabs appear to display niche conservatism for stronger performance at tropical temperatures. Such a natural tropical superiority in performance might have to be accommodated in future conceptions of response of marine species to climate change with broad latitudinal distributions in the tropics. • We compared performance of fiddler crabs (Leptuca pugilator) from a range of latitudes to evaluate response to thermal stress with climate change. • Evaluation of weather showed strong latitudinal differences in seasonal temperature, humidity, wind speed, and vapor pressure deficit. • We tested the hypothesis that performance of predator escape and endurance rivalry traits reflected latitude climate features. • The lowest latitude leading edge population from Florida showed superior performance of predator escape and endurance rivalry success traits. • We conclude that trailing edge fiddler crabs are well adapted to a wide range of thermal habitats especially those of high temperatures. [ABSTRACT FROM AUTHOR]

Many tropical ectotherms will probably not survive climate warming without having access to thermal refugia. Temperature affects adult survival, but has just as strong an effect on larval stages, often due to its effect on reproductive timing and incubation duration. Intertidal animals usually have tight constraints on the timing of larval release since the planktonic larvae must be washed out to sea on the highest nocturnal spring tides. Can females behaviourally compensate for the effects of temperature over the naturally occurring temperature range by shifting the timing of mating and/or fertilisation or by adjusting the incubation duration? This experiment compares the timing of key reproductive events, as well as the size of eggs and larvae, in fiddler crabs that incubate over a 6 °C range of temperatures. There was no effect of temperature on the timing of reproductive events or the size of eggs or larvae produced. In other crab species, the effect of temperature on incubation duration is exponential, with smaller decreases in incubation duration at higher temperatures. Since the natural incubation temperatures are unusually high for this species, the effect of further increases in temperature may not have had as marked an effect as it does for species breeding in slightly cooler temperatures. Future climate warming may not have as strong an effect as may be expected for this species. [ABSTRACT FROM AUTHOR]

The contamination of estuaries by metals can impose additional stresses on estuarine species, which may exhibit a limited capability to adjust their regulatory processes and maintain physiological homeostasis. The mudflat fiddler crab Uca rapax is a typical estuarine crab, abundant in both pristine and contaminated areas along the Atlantic coast of Brazil. This study evaluates osmotic and ionic regulatory ability and gill Na + /K + -ATPase activity in different salinities (< 0.5, 25 and 60‰ S) and oxygen consumption rates at different temperatures (15, 25 and 35 °C) in U. rapax collected from localities along the coast of São Paulo State showing different histories of metal contamination (most contaminated Ilha Diana, Santos > Rio Itapanhaú, Bertioga > Picinguaba, Ubatuba [pristine reference site]). Our findings show that the contamination of U. rapax by metals in situ leads to bioaccumulation and induces biochemical and physiological changes compared to crabs from the pristine locality. U. rapax from the contaminated sites exhibit stronger hyper- and hypo-osmotic regulatory abilities and show greater gill Na + /K + -ATPase activities than crabs from the pristine site, revealing that the underlying biochemical machinery can maintain systemic physiological processes functioning well. However, oxygen consumption, particularly at elevated temperatures, decreases in crabs showing high bioaccumulation titers but increases in crabs with low/moderate bioaccumulation levels. These data show that U. rapax chronically contaminated in situ exhibits compensatory biochemical and physiological adjustments, and reveal the importance of studies on organisms exposed to metals in situ , particularly estuarine invertebrates subject to frequent changes in natural environmental parameters like salinity and temperature. [ABSTRACT FROM AUTHOR]

The fiddler crab Uca annulipes (Milne Edwards, 1837) is thought to be widely distributed in the Indo-West Pacific. Previous studies showed consistent morphological differences between East African populations and those from the eastern Indian Ocean and Western Pacific. Here we provide detailed comparisons of the morphology and DNA sequences corresponding to the mitochondrial 16S rRNA gene fragment. As consequence, we refer to the populations from the western Indian Ocean as a new species, Uca occidentalis n. sp., whereas Uca annulipes has wide-ranging populations in the eastern Indian Ocean and West Pacific. The new species can be distinguished from U . annulipes by consistent morphological characters, including male first gonopods and male minor cheliped, which is supported by molecular evidence. [ABSTRACT FROM AUTHOR]

Male sand fiddler crabs, Uca pugilator (Ocypodidae), possess a single enlarged claw that is used in ritualized contests over breeding burrows. Ability to close the claw forcefully, which increases with claw size and stoutness, may promote success in contests. As the density of males at breeding burrows changes across the lunar cycle, the frequency of contests may also change and affect the advantage associated with a powerful claw. At an Atlantic coast salt water marsh in northern Florida, we investigated claw size, claw stoutness, and pinching force with daily samples of foraging and courting males made across three lunar cycles. Foraging and courting males constituted the vast majority of surface-active males. Foraging males occurred in dense aggregations, droves, on moist, low-elevation sediments. Courting males, recognized by claw-waving displays, were at burrows in dry, high-elevation sediments where they fed relatively little. On average, courting males had greater claw-closing force than droving males but claw length and stoutness did not vary by activity. Claw-closing force, claw length, and claw stoutness of courting males were greatest on and near the days of new or full moons, when the densities of courting males peaked. No temporal patterns were observed for droving males. Mark/recapture of males revealed that claw power declined during courtship and increased while droving. Moreover, males switched from droving to courting as claw power increased and switched from courting to droving as claw power decreased. In the laboratory, the claw-closing force of unfed males decreased over time but rebounded quickly after males were given food. We suggest that males cycle between activities in response to strength and condition. However, it appears that males with larger, stouter claws are more likely to court at new and full moons, when the number of mating-receptive females peaks. [ABSTRACT FROM AUTHOR]

Temperature is one of the primary environmental variables limiting organismal performance, fitness, and species distributions. Yet, understanding temperature effects requires thorough exploration of thermal constraints and organismal responses that can translate to fitness and non-lethal long-term consequences under both constant and changing thermal regimes. We examined the thermal ecology of the fiddler crab Uca panacea , including critical thermal limits, thermal sensitivity of locomotion, operative environmental temperatures, preferred body temperatures, and acclimation ability. Operative environmental temperatures frequently reached the critical thermal maximum (41.8±0.8 °C, mean ± s.e.m.), especially in unvegetated microhabitats, indicating the need for behavioral thermoregulation to maintain diurnal activity patterns. Preferred body temperatures (21.1–28.6 °C) were substantially below the thermal optimum (30–40 °C), although further research is needed to determine the driver of this mismatch. Critical thermal limits shifted 2–4 °C in response to exposure to low (20 °C) or high (35 °C) temperatures, with full acclimation occurring in approximately 9 d. This capacity for rapid acclimation, combined with the capacity for behavioral thermoregulation, is a strong candidate mechanism that explains the broad habitat use and could help explain the successful pantropical distribution of fiddler crabs. [ABSTRACT FROM AUTHOR]

[Display omitted] • How fiddle crab burrows affected the soil GHGs effluxes was assessed. • Crab burrow volume in the vegetated salt marsh was smaller than in the mudflat. • Crab activities could enhance coastal wetland CO 2 efflux. • With crab disturbances, soil CH 4 efflux increased significantly. • Fiddler crabs play an important role in coastal blue carbon sequestration. Saltmarshes are important global carbon (C) sinks, but the considerable uncertainty in the C budget and the underlying mechanisms limit the estimation of greenhouse gas emissions (GHG, e.g., CO 2 and CH 4) in the context of global climate change. To ascertain the mechanistic understanding, we assessed how crab burrows morphology and greenhouse gas effluxes changed in response to interactions of fiddler crab burrow density, soil organic matter content (high vs low), and presence/absence of Spartina alterniflora (vegetated saltmarsh vs nearby unvegetated mudflat) on the coast of New England (USA). The crab burrow volume in the vegetated saltmarsh was smaller than that in the mudflat, and crab burrow volume greatly correlated with soil CO 2 efflux, indicating that crab activities could enhance coastal wetland CO 2 efflux. Soil CO 2 and CH 4 effluxes rates were significantly positively correlated with crab burrow density, organic matter content, and vegetation types. Specifically, the higher soil organic matter content and crab burrow density greatly increased soil heterotrophic respiration in the saltmarsh. Overall, with crab disturbances, soil CO 2 and CH 4 efflux increased by 32.1% and 47.9%, respectively. This study highlights that fiddler crab burrowing activity plays an important role in the C sequestration of coastal blue C ecosystems (BCEs). [ABSTRACT FROM AUTHOR]

This study endeavored to probe the impact of environmental heterogeneities on heavy metals allocation in fiddler crab (Austruca iranica) in the marine environment of Pakistan. All studied metals showed spatial variations in fiddler crabs, except Pb, and average accumulation pattern seen as Fe > Zn > Cu > Pb > Ni > Co > Cr > Cd. Trace element pollution index (TEPI) presented high metal trails in subpopulations of the fiddler crab. According to the sediment-biota accumulation factor (AF), they are viable accumulators of Cu, Co, Cd, Zn, and Pb. A new site-specific proxy, i.e., the accumulation index (AI) proposed here, is based on the sum of all AFs of studied metals from each site to evaluate the metal trails in subpopulations of crab. Both genders are beneficial for environmental monitoring, as crabs did not perceive gender variations in any metal concentration. Among the extrinsic factors, hydrographic attributes (salinity and pH) and sedimentological traits (moisture and mud) significantly interacted with metal levels in crabs. Fiddler crabs also showed their usefulness in the Pb and Cd surveillance as they constantly imperiled with these metals through sediments. This investigation urged that fiddler crabs are severely tainted with metals, and this toxicity can further amplify through the food chain. Beyond the fate and provenance of pollutants, multiple environmental factors exist that synergistically affect the heavy metal influx in fiddler crabs. • High metals imprints investigated in marine sediments from five coastal habitats. • Austruca iranica reflects the environmental levels of Pb and Cd hence prove themselves as a potential indicator. • Accumulation Index presented low metals concentrations at the highest contaminated site. • Extrinsic factors have strong impressions on metal levels in fiddler crabs. [ABSTRACT FROM AUTHOR]

Abstract: Salinity may play an important role in the larval Biology and Ecology of many brachyuran decapod crustaceans. Usually, ontogenetic changes in salinity tolerance represent a good indicator of larval dispersal in marine coastal ecosystems. In an experimental laboratory study, we investigated the effects of eight different salinities (Sal. 0–35) on zoeal development of the neotropical fiddler crab Uca rapax from a northern Brazilian estuary. In the study area the species reproduces year-round, including the wet season when low salinities (≤5) are frequent, resulting from heavy tropical rainfalls and input of freshwater mostly from the Amazon River. Larval survival and development duration from hatching to megalopa of U. rapax were significantly affected by salinity. All larvae died in Sal. 0–20, while they successfully developed through five zoeal stages to megalopa in higher salinities (Sal. 25–35). However, in Sal. 25 the survival rate was still significantly lower (33.8±4.8%) and the zoeal development duration was longer (13.7±0.5days) than in salinities 30 and 35, where >90% of the larvae successfully survived after an average of 11.8–12.4days of development, respectively. Our results strongly suggest that the early life-history stages of U. rapax perform ontogenetic migrations towards adjacent coastal or fully marine waters to develop in favourable high salinities. Comparison with two other sympatric crab species, e.g. Ucides cordatus and Uca vocator, suggests that the larval ‘export’ strategy is a convergent adaptation exhibited by decapod species in the Amazon region to avoid mass mortality within parental mangroves that are frequently subjected to strong salinity fluctuations caused by the specific meteorological and hydrological conditions. [Copyright &y& Elsevier]

Abstract: The Deepwater Horizon accident in the Gulf of Mexico resulted in a sustained release of crude oil, and weathered oil was reported to have washed onto shorelines and marshes along the Gulf coast. One strategy to minimize effects of tarballs, slicks, and oil sheen, and subsequent risk to nearshore ecosystem resources was to use oil dispersants (primarily Corexit® 9500) at offshore surface and deepwater locations. Data have been generated reporting how Corexit® 9500 and other dispersants may alter the acute toxicity of crude oil (Louisiana sweet crude) to marine organisms. However, it remains unknown how oil dispersants may influence bioaccumulation of petroleum hydrocarbons in nearshore crustaceans. We compare bioaccumulation of petroleum hydrocarbons in fiddler crabs (Uca minax) from exposures to the water accommodated fraction (WAF) of weathered Mississippi Canyon 252 oil (~30 d post spill) and chemically-enhanced WAF when mixed with Corexit® EC9500A. Whole body total petroleum hydrocarbon (TPH) concentrations were greater than background for both treatments after 6h of exposure and reached steady state at 96h. The modeled TPH uptake rate was greater for crabs in the oil only treatment (k u =2.51mL/g/h vs. 0.76mL/g/h). Furthermore, during the uptake phase TPH patterns in tissues varied between oil only and oil+dispersant treatments. Steady state bioaccumulation factors (BAFs) were 19.0mL/g and 14.1mL/g for the oil only and oil+Corexit treatments, respectively. These results suggest that the toxicokinetic mechanisms of oil may be dependent on oil dispersion (e.g., smaller droplet sizes). The results also indicate that multiple processes and functional roles of species should be considered for understanding how dispersants influence bioavailability of petroleum hydrocarbons. [Copyright &y& Elsevier]

Abstract: Animals can change color either rapidly in response to changes in their immediate environment or slowly as the seasons change. Such plasticity can permit local adaptation but it can also be constrained by physiological and behavioral mechanisms. Here, we explore how different temperature regimes along a latitudinal gradient spanning the natural range of a species of fiddler crab may affect the ability of crabs to change color rapidly in response to acute changes of temperature. Uca pugilator populations from New York (NY), North Carolina (NC) and Florida (FL) were exposed in air to 5°C and 35°C and carapace shade intensity (from dark to light color) and contrast was recorded. In general, individuals darkened when exposed to cold conditions, and lightened when exposed to warm conditions. Males from different populations differed in the magnitude of response to temperature, but had similar directional changes in shade (dark under cold conditions and light under warm conditions) suggesting differences among populations in the ability to change color. Females showed similar directional changes but there were no differences among populations. Differential responses of crabs to temperature suggest that crabs have local physiological adaptations and can acclimate quickly to withstand fluctuating or extreme temperatures. [Copyright &y& Elsevier]

Abstract: Color change can serve a number of functions, and can be a singular aperiodic event or a rhythmic process driven by responses to environmental cues or endogenous rhythms. Endogenous pigmentation rhythms have been identified in a number of taxa, with fiddler crabs being the subject of much of this research. Despite a long history of experimental studies of chromatophore-level rhythmicity in fiddler crabs, few studies have considered the entrainment cues for these rhythms or extended findings to whole-organism coloration, information important for understanding the biological properties of circadian systems and understanding the functional significance of these rhythms. This study examined the circadian pigmentation rhythm in the subtropical fiddler crab Uca panacea at both the cellular (melanophore) and organismal levels, including expression in artificial light/dark cycles and constant darkness, entrainment by light/dark and temperature cycles, and relationships between melanophore rhythms and the spectral reflectance of the carapace. On the melanophore level, crabs exhibited a circadian rhythm in pigment dispersion, with maximum dispersion occurring during the day and maximum concentration occurring during the night. This rhythm persisted under ambient or reversed light/dark cycles, with maximum pigment dispersion occurring during the light phase, or under constant darkness. Both light/dark and temperature cycles entrained the rhythm, although light/dark cycles resulted in greater phase shift. The circadian rhythm in melanin dispersion within melanophores is associated with a circadian rhythm in organismal coloration, with carapace reflectance low during the day and high at night. Because of the high absorption of UV radiation by melanin, the functional significance of this rhythm may be as a mechanism of UV‐protection during the day when crabs are exposed to high levels of UV radiation while foraging on open sand flats of the intertidal zone. [Copyright &y& Elsevier]

Abstract: Melatonin has both neuritogenic and neuroprotective effects in mammalian cell lines such as neuroblastoma cells. The mechanisms of action include receptor-coupled processes, direct binding and modulation of calmodulin and protein kinase C, and direct scavenging of free radicals. While melatonin is produced in invertebrates and has influences on their physiology and behavior, little is known about its mechanisms of action. We studied the influence of melatonin on neuritogenesis in well-differentiated, extensively-arborized crustacean x-organ neurosecretory neurons. Melatonin significantly increased neurite area in the first 24h of culture. The more physiological concentrations, 1nM and 1pM, increased area at 48h also, whereas the pharmacological 1μM concentration appeared to have desensitizing effects by this time. Luzindole, a vertebrate melatonin receptor antagonist, had surprising and significant agonist-like effects in these invertebrate cells. Melatonin receptors have not yet been studied in invertebrates. However, the presence of membrane-bound receptors in this population of crustacean neurons is indicated by this study. Melatonin also has significant neuroprotective effects, reversing the inhibition of neuritogenesis by 200 and 500μM hydrogen peroxide. Because this is at least in part a direct action not requiring a receptor, melatonin''s protection from oxidative stress is not surprisingly phylogenetically-conserved. [Copyright &y& Elsevier]

Abstract: The study aimed at investigating the effects of sewage loadings on the behaviour of two fiddler crabs species maintained in a system of experimental mesocosms, built in a mangrove area in Tanzania and inundated with different seawater/sewage mixtures. Our results show that sewage loads led to a modification of the overall activity budget of the crab community as a result of increased hypertrophic conditions (high COD, increased chlorophyll-a concentrations). During their activity period, crabs inside contaminated mesocosms seemed to satisfy their feeding demand faster than those of the control cells, spending a significant longer time in other activities like courtship and territorial defence. Apart from being a good biological indication of ecosystem eutrophication, such a reduced foraging activity by fiddler crabs also depresses their sediment bioturbation activity, important factor for the health of mangrove systems, suggesting practical implications regarding the efficiency of mangrove-based wetlands for treatment of domestic sewage. [Copyright &y& Elsevier]

Abstract: Following hatching, larvae of the fiddler crab Uca minax (La Conte) are exported from the adult habitat in estuaries to coastal and shelf waters where they undergo development prior to re-entering estuaries as postlarvae (megalopae). Studies of the spatial distribution of both newly hatched zoeae (Stage I) and megalopae indicate they undergo rhythmic vertical migrations associated with the tides for dispersal and unidirectional transport (selective tidal-stream transport) both within estuaries and between estuaries and the nearshore coastal ocean. We tested the hypothesis that U. minax zoeae possess a circatidal rhythm in vertical migration that facilitates offshore transport in ebb tidal flows, while postlarvae (megalopae) return to estuaries using a similar flood-phased endogenous rhythm. We also determined if the expression of the rhythm was influenced by the salinity conditions zoeae and megalopae experience as they transition between low-salinity regions of estuaries and high-salinity coastal waters. Stage I zoeae were collected by holding ovigerous female crabs in the lab until hatching. Megalopae were collected from the plankton and identified to species using molecular techniques (PCR-RFLP). Under constant laboratory conditions, both zoeae and megalopae exhibited endogenous circatidal rhythms in swimming that matched the principal harmonic constituent of the local tides (12.39±0.07 h; X̅±SE). Upward swimming in Stage I zoeae occurred 2.5-4 h after high tide near the time of expected maximum ebb currents in the field. Rhythmic swimming of megalopae occurred slightly earlier in the tide (2.5±0.09 h after high tide; X̅±SE) but was not entirely synchronized with flood currents, as expected. Salinity conditions had no apparent effect on the expression or pattern of the rhythms. Results indicate that this circatidal rhythm forms the behavioral basis of selective tidal-stream transport (STST) in early stage U. minax zoeae, but does not undergo a sufficient phase shift to account for vertical distribution patterns exhibited by megalopae in the field. [Copyright &y& Elsevier]

Abstract: The benthic fauna in mangrove forests is usually dominated by burrowing sesarmid (Grapsidae) and fiddler crabs (Ocypodidae). They are herbivores that retain, bury, macerate and ingest litter and microalgal mats. Most species within these two groups actively dig and maintain burrows in the sediment as a refuge from predation and environmental extremes. Based on the current knowledge on the biology and ecology of these crabs, it seems obvious that their activities have considerable impact on ecosystem functioning. However, no convincing conceptual framework has yet been defined into which the role of these crabs can be identified and characterized. The attributes by which these abundant animals affect the microbial and biogeochemical functional diversity fit well into the concept of ecosystem engineering. The conceptualization of mangrove benthic communities within this framework is distinguished and documented by examples provided from the most recent literature on mangrove ecosystem functioning. It appears that the features and processes driving the engineering effects on distribution and activity of associated organisms operate differently for sesarmid and fiddler crabs. The most obvious and well-documented difference between engineering effects of the two types of crab seems to be associated with foraging. More attention must be devoted in the future to elucidate engineering aspects related to crab burrows in mangrove environments. Particularly comparative work on the burrow-dwelling life styles of the two types of crab is needed. [Copyright &y& Elsevier]

Abstract: Male sand fiddler crabs, Uca pugilator, wave a claw to attract females to a breeding burrow. The effect of claw size on the likelihood of attracting mate-seeking females is little studied although in some other species females preferentially approach larger males. We used paired mirrors to reflect different sized images of the same male in a South Carolina (USA) back-beach habitat. Use of mirrors controlled for waving rate (but not velocity), waving motion, claw color, and claw shape. Female choice was attributed to instances in which a female contacted one of two mirrors. Paired mirrors were inclined toward one another in an arena defined by blinds and containing a single male. Two reflections of the male were visible to females moving approximately 50 cm toward the mirrors. The male was behind a small internal blind and not directly visible. In one-half of the trials, a non-magnifying mirror was placed at the bottom of mirrors so that only the elevated claw was magnified. Thus, body and burrow size and apparent distance were controlled. Receptive females preferred the larger reflection whether or not the body of the male was magnified, suggesting the importance of claw size. Non-receptive females did not exercise a choice. Control arenas, without a male, rarely attracted females. The results suggest that females choose on the basis of claw size. Selection on females may favor response to larger-clawed males because use of the claw in contests between males over burrows maintains the honesty of claw size as a signal of burrow quality. [Copyright &y& Elsevier]

Abstract: Adult-associated chemical cues can stimulate settlement and metamorphosis of invertebrate larvae into habitats with an enhanced likelihood of juvenile and adult survival. For example, sediments from adult fiddler crab habitat stimulate fiddler crab megalopae to metamorphose (molt) sooner than sediments without adult cues. A similar stimulation of molting occurs after exposure to waterborne chemical cues from adult habitats and to exudates and extracts of adult crabs. We tested whether sediments from habitats without adult Uca pugnax (Smith), which do not stimulate molting of their megalopae, could become stimulatory through brief exposure to adult crabs. Sediments were collected from tidal flats at several distances (∼1 m, ∼50 m, and ∼5.4 km) from adult habitats, and incubated for 24 h with or without adult crabs. Molting rates of laboratory-reared megalopae exposed for 48 h to adult-conditioned sediments were compared to those for untreated controls. Sediments collected in or within 1 m of adult habitat elicited the highest molting rates, and natural sediments from 50 m and 5.4 km had little or no effect on molting. However, incubating sediments collected away from adult habitat with adult crabs produced a higher molting response, and the magnitude of the enhancement increased with distance from adult habitat. Results suggest that the chemical cues that adult crabs release are retained by sediments and consequently stimulate molting of megalopae, regardless of the nature of the sediments themselves. Lack of chemical cues may retard colonization of newly created or heavily disturbed habitats that are otherwise suitable settlement and adult habitat. [Copyright &y& Elsevier]

Abstract: In the reproductive season, mature females of the fiddler crab Uca perplexa leave their burrows and wander about their habitat for mating. To clarify whether the fiddler crabs respond to colour or luminosity, I examined the behavioural responses of the males to the wandering females before and after the females were painted white, red, black or blue. The behaviours of the males were categorized into three types: lateral–circular wave and lateral–straight wave for courting, and repelling. Before painting, almost all of the males courted the females. After painting, significantly fewer males courted the red-, black- and blue-painted females than courted the white-painted females. These results mean that the fiddler crabs can discriminate colours or luminosity. The role of body colour as a visual signal in crab society is discussed. [Copyright &y& Elsevier]

Abstract: An explanation for animal groups is the selfish herd, characterized by aggregation as each member tries to shield itself from a predator by moving into a tight gap between other members. We test the hypotheses that: (1) droves, the large feeding groups of fiddler crabs, are selfish herds; (2) the miniherds that form when droves fragment on approach of a large predator are selfish herds; (3) selfish herds form when refugia are unlikely to be reached before an approaching predator arrives; and (4) the composition of selfish miniherds is biased toward individuals most vulnerable to predation. The study was conducted in South Carolina (USA) by videotaping the movements of sand fiddler crabs Uca pugilator when approached by a human predator. In both droves and miniherds, interindividual distance decreases with predator approach, consistent with behavior in a selfish herd. However, two other expectations for selfish herds—herd cohesion and sacrificing distance from the predator in order to get closer to other herders—are only met in miniherds. Crabs farther from refugia are more likely to form and remain in miniherds, indicating that selfish herding is only favored when refugia cannot be quickly reached. The composition of the smallest miniherds, consisting of 2–18 crabs, is biased toward females and small males. These individuals may be more vulnerable to predation because they lack the enlarged claw of large males that deters some predators. The small miniherds are relatively homogeneous with respect to the size and sex of their members, which may enhance cohesion and effectiveness as selfish herds. Miniherds will be effective selfish groups when predator attack has a significant vertical component and when the strike distance is large relative to both the size of the prey and the distance between group members. Droves are not selfish herds but permit crabs to flee feeding grounds as members of selfish miniherds. [Copyright &y& Elsevier]

Abstract: [1.] Male Uca pugilator whose major cheliped was immersed in 3°C water bath experienced a significant drop in Tb. Thus, the enlarged claw of male Uca pugilator may have an unexplored function: thermoregulation. [2.] Crabs prefer warmer substrates (19–24 and 28–30°C) over cooler (15–17°C). [3.] Mean selected temperature (MST) may not be an accurate reflection of Tb. Crabs in a thermal chamber preferred temperatures between 25 and 30°C but their average Tb was 23.2°C. [Copyright &y& Elsevier]

Abstract: Intertidal sandflats inhabited by fiddler crabs are ideal systems in which to study the effects of physical and biological processes. This study addressed two questions: (1) Do fiddler crab feeding and tidal inundation have measurable effects on the sandflat over one tidal cycle? (2) Does the sandflat change over the course of a year? In field exclusion/inclusion experiments, fiddler crabs reduced sediment organic content by 40%, Chlorophyll a levels by 20% and meiofaunal density by 60% in one tidal cycle. Effects were most pronounced in the spring when organic content and meiofaunal densities were maximal. Effects of foraging were not erased by the tide and accumulated over time. The sandflat had highest levels of all variables in spring and minimal levels during summer and fall. Crabs graze the sandflat to minimum levels in the spring. Due to crab foraging, the flat is barren during the summer and fall, and recovers during the winter when crabs are minimally active. [Copyright &y& Elsevier]

The fiddler crab Uca panamensis (Stimpson, 1959) inhabits rocky shores. We examined its preference for feeding substratum—sand or rock—and its manner of feeding. The crab made its burrow in the sand among rocks but preferred to feed on rocks. The feeding time decreased as the distance between the burrow and the rock increased. We consider this to be a result of exclusive interaction among the crabs because they defended their feeding area on the rocks against others.The crab wetted a small area of rock with water held in the branchial chambers before and during feeding. It pinched up the wetted surface in the minor chelipeds, which have bundles of setae on the posterior tips of the dactyl and pollex, and put the material into its buccal cavity. It never expelled sand pellets while feeding on rock, which indicates that it swallowed the food particles directly, without sorting. The bundles of setae retained water by capillary attraction, which suggests that they capture the suspended fine food particles scraped from the rock. The wetting action may prevent the fine materials from dispersing. We consider that morphological alteration of the minor chelipeds, the application of water from the branchial chambers, and direct swallowing permit the fiddler crab to feed on fine materials attached to rocks. [Copyright &y& Elsevier]

[Display omitted] • An endangered fiddler crab was exposed to human trampling for 46 days. • Surface activities of the crab decreased during trampling. • Feeding and courtship rhythms collapsed under cumulative trampling events. • To recover surface activity, a longer time than the trampling period was needed. • Intensive trampling events may negatively affect fiddler crab fitness. Human recreational visits to tidal flats increase trampling pressure, which has a significant impact on the coastal benthic ecosystem. The fiddler crab Austruca lactea , which inhabits the upper intertidal region, is endangered in temperate regions such as Japan and South Korea. The vulnerability of their habitat to human activities along with their limited summer reproduction period may have contributed to the decrease in fiddler crab populations in these regions. We conducted experiments to elucidate the effects of trampling on the surface activities and courtship behaviors of A. lactea , which represent ecological indicators for tidal flat ecosystems. During the 46-day trampling period, we observed the number of active crabs on the surface of the tidal flat under three different trampling intensities (heavy trampling = 60 steps/m2; moderate trampling = 20 steps/m2; and no trampling). The density of individuals of both sexes active on the surface and that of courting males significantly decreased under both heavy and moderate trampling intensities. In addition, the feeding and courtship rhythms of male A. lactea collapsed under continuous trampling events. We monitored the site once per week, and surface activity did not recover fully until the sixth week after the trampling period. Our results demonstrated that trampling on the tidal flat disrupted the intensity and timing of crab surface behavior and male reproductive surface behavior, and thus may, ultimately, have an impact on the population dynamics of A. lactea. [ABSTRACT FROM AUTHOR]

In mid-Atlantic estuaries, three fiddler crab species, Uca pugilator, Uca pugnax and Uca minax, co-occur, with their adults occupying different habitat types distinguished by salinity and sediment size. Some evidence exists that selective settlement is responsible for this separation but the mechanism is largely unknown. We tested the hypothesis that field-caught megalopae would be stimulated to molt in the presence of adult species-specific environmental acoustic cues and conspecific chemical cues. We placed megalopae in seawater with and without adult chemical cues, exposed them to one of three sound treatments for 8 days, and recorded the time each megalopa took to metamorphose. Time to molt was unaffected by sound treatment either alone or in combination with chemical cues. In the absence of adult chemical cues, very few megalopae molted regardless of the sound treatment. Molting in the presence of habitat sound and chemical cues varied by species. Many U. pugilator molted in all sound and odor combinations, including the no odor and no sound treatment, and molted sooner in conspecific and congeneric odors. U. pugnax was stimulated to molt by chemical cues from either U. pugilator or U. pugnax , but molting was similar across sound treatments. Lastly, due to the small number of U. minax in the experiment , no statistical analyses or conclusions could be made. Our results do not support the hypothesis that sound stimulates molting of fiddler crab megalopae, but provide additional evidence that chemical odors from adults act as molting cues. • Habitat-related sound alone did not stimulate metamorphosis in these three Uca spp. • Sound combined with adult Uca chemical cues did not affect metamorphosis either. • Adult chemical cues affected metamorphosis more than sound in these Uca species. [ABSTRACT FROM AUTHOR]

• Sediments in are not polluted with PTEs based on the geo-accumulation index (I geo). • Uca rapax and Avicennia germinans have bioaccumulated PTEs. • Arsenic is biomagnified in Uca rapax based on trophic transfer. In southern Puerto Rico along the coastline bordering the Jobos Bay National Estuarine Research Reserve, environmental encroachment has exposed mangrove forest to different sources of pollution. Potentially toxic element concentrations from the F1 Tess (exchangeable), F4 Tess (oxidizable), mangrove leaf litter (MLL), and fiddler crab whole body soft tissue were analyzed to assess the fate and transport of pollutants from the environment and its transition into flora-fauna via trophic transfer. Geo-accumulation factor values suggest the bay has experienced limited to no pollution when combining the concentrations of potentially toxic elements extracted from the F1 Tess and F4 Tess sediment fractions. These geochemical sedimentary compartments are considered "bioavailable" to flora-fauna as evidenced by the bioaccumulated Cd-Ba-V-Cu-Zn-As-Se in the leaf litter of the black mangrove Avicennia germinans and in the fiddler crab Uca rapax. The biota-sediment accumulation factor (F1 Tess + F4 Tess) demonstrated that Uca rapax behave like a de-concentrator for most pollutants and as a macro-concentrator for Cu-As, while the bioconcentration factors identified only Cu-As-Se as being actively bioaccumulated in the fiddler crabs. Of all the potentially toxic elements studied, As is the only one to be biomagnified via sediment- Avicennia germinans leaf litter- Uca rapax food chain. An unexpected find of this study was that the excavated sediment "pellets" by Uca rapax contained up to 4x the concentrations of Cd-Ba-V-Cr-Co-Ni-Cu-Zn-As-Se when compared to the F1 Tess sediment fraction from the surface, thus suggesting a variable redox boundary within the fiddler crab's burrow. [ABSTRACT FROM AUTHOR]

Fiddler crabs (Uca) are ecosystem engineers in coastal ecosystems. Many anthropogenic and natural factors can affect the time allocated to various behaviours in Uca. However, the behaviour of U. arcuata , a widely distributed fiddler crab in Asia, has not been studied in mainland China. Here, we used binoculars to record the time budget of ten behaviours of U. arcuata to investigate the potential effects of sex, tides, and pollution on these behaviours. We found that the crabs spent 42.3%, 27.0%, and 10.6% of their time on feeding, feeding while walking, and stationary respectively. The crabs spent <1.5% of their time on copulation and grooming. The total foraging time (feeding + feeding while walking) did not differ among the three polluted sites. However, crabs spent more time on feeding but less time on feeding while walking. The feeding rate and probability of burrowing and grooming decreased while the possibility of locomotion and stay in burrow increased with increasing nutrient concentration. Females spent 13.9% more time on feeding and fed 54.9% faster than males. Males had a higher tendency to grooming and combat while they were less likely to walk than females. Regarding to the influence of tide, fiddler crabs fed 11.2% faster at ebb tides than at flood tides, and they were more likely to walk and stay in burrows at flood tides than at ebb tides. Our results indicated that nutrient pollution had stronger impacts on the behaviours of crabs than sex and tide. In polluted mangroves, increasing nutrient concentration reduced the quantity of sediment processed by fiddler crabs due to their smaller feeding area, slower feeding rate, and reduced frequency of burrowing activities. These results imply that mitigating nutrient pollution in mangroves may benefit the restoration and management of coastal ecosystems through the enhanced engineering functions of fiddler crabs. Unlabelled Image • Uca act as ecosystem engineers in mangroves by foraging and burrowing activities. • Ten behaviours of Uca arcuata were observed in the Futian Nature Reserve, China. • Fiddler crabs spent the most time on feeding and feeding while walking. • Nutrient pollution and sex are factors that influence crab behaviour. • Foraging and burrowing activities decreased with increasing nutrients. [ABSTRACT FROM AUTHOR]

Autotomy is a predator defence mechanism by which individuals voluntarily release an appendage to escape a predator or escape a fouled moult. The decision to autotomize is driven by the costs of autotomy (i.e., the loss of the appendage) vs. the risk of predation. In many cases, autotomized appendages have few alternative functions, yet male fiddler crabs autotomize the sexually selected large claw that is critical for mate attraction. We conducted an experiment with Austruca mjoebergi to understand the role of claw autotomy by males during the mating season. Males more readily autotomized a leg relative to the enlarged claw, reflecting the much greater cost of being without the major claw. Larger crabs had a lower probability of claw autotomy than did small crabs, reflecting the greater fitness cost of claw autotomy experienced by larger crabs. The sexually selected fiddler crab claw is a multifunction structure with benefits that may outweigh the survival probability resulting from autotomy when individuals are threatened by predation. • We investigated major claw and walking leg autotomy in male fiddler crabs Austruca mjoebergi. • Males were more willing to autotomize a walking leg than the major claw. • Smaller males were more willing to autotomize the major claw than were larger males. • Results reflect the high costs of losing the major claw, which change over the life of a male crab. [ABSTRACT FROM AUTHOR]

Performance in poikilotherms is known to be sensitive to temperature, often with a low-sloping increase with temperature to a peak, and a steep decline with increasing temperature past the peak. We complemented past measures of performance by measuring heartbeat rates of the fiddler crab Leptuca pugilator in water and in air as a function of a range of temperatures previously shown to affect other measures of performance. In water over a range of 20–50 °C, heartbeat increased steadily to a peak at 40 °C and then steeply declined to near zero at 50 °C. In air, heartbeat also increased, but to a peak at 35 °C and then with a gentler decline than was found in water. Part of this different response may be due to evaporative water loss, which reduced body temperature in air, and therefore thermal stress, relative to body temperature when crabs were immersed in water. Increased availability of oxygen from air, according to the oxygen and capacity-limited thermal tolerance hypothesis, likely increased aerobic scope past the thermal peak, relative to within water, where oxygen delivery at higher temperatures may have been curtailed. We compared the heart rate performance relations to two previous measures of performance – endurance on a treadmill and sprint speed, both done in air. The peak performance temperature increased in the order: treadmill endurance time, sprint speed, heart rate in air, and heart rate in water, which demonstrates that different performance measures give different perspectives on the relation of thermal tolerance and fitness to temperature. Endurance may therefore be the limiting upper thermal stress factor in male fiddler crabs, when on hot sand flats. Temperature preference, found to be for temperatures <30 °C in air, could be a bet-hedging evolutionary strategy to avoid aerobic scope affecting endurance. • We measured heart rate of the fiddler crab Uca pugilator as a function of temperature. • In water, heartbeat increased from 20C to a peak at 40C with decline to zero at 50C, and in air the peak was 35C with a near plateau to 45C. • Evaporative cooling and increased aerobic scope from higher O 2 availability from air may have contributed to a lowered peak thermal effect. • Endurance on a treadmill had the minimum thermal peak, but the peak also corresponded to the plateau of heartrate in air. • Temperature preference might be a bet-hedging strategy to avoid endurance stress. [ABSTRACT FROM AUTHOR]

Fiddler crabs are deposit feeders that play critical roles as ecological engineers in tidal flats. Recently, anthropogenic disturbances have led to fiddler crab habitat loss and/or degradation; therefore, we developed a mathematically derived habitat suitability index (HSI) model to aid in habitat assessments of fiddler crabs. Based on what is known about the life histories of fiddler crabs, the variables of an HSI model included submersion time, interstitial salinity, and soil 1) grain size, 2) organic matter content, and 3) heat capacity. We acquired density data from four fiddler crab species— Xeruca formosensis , Tubuca arcuata , Austruca lactea , and Gelasimus borealis— at five sites on the western coast of Taiwan to develop the HSI models. Significant positive correlations existed between the HSI output and fiddler crab density for all target species except for those X. formosensis inhabiting the topsoil layer (0–20 cm). For the deep burrowers X. formosensis , however, a positive linear relationship was documented when only those data from the 40–60 cm layers were considered and if the habitat was a sand-covered mudflat. Mapping for each species was conducted using the HSI models with the highest reliability, and four classification levels were established for the habitat suitability of each species at one of the study sites. Based on this field test of a fiddler crab HSI model, we have developed a platform for the proactive conservation of fiddler crabs inhabiting subtropical tidal flats. • Habitat suitability indices and mapping for Taiwanese fiddler crabs were conducted. • Soil heat capacity was first introduced for crabs' habitat evaluation. • For deep burrowers, vertical soil texture is a requirement for a sand-covered mudflat. • The HSI models and maps of fiddler crabs are useful for conservation planning. [ABSTRACT FROM AUTHOR]

Territory quality is often critical for reproductive success, survival and ultimately fitness. Holding a good quality territory can make a male more attractive to females but can also have several other advantages. It can decrease the effects of environmental stressors, for example, by reducing the need for behavioural thermoregulation or decreasing the risk of predation. We found that, in the fiddler crab Austruca mjoebergi , male territories differed in the shaded mangrove and unshaded open areas of the habitat. The lower temperatures and wetter sediments of the mangrove areas resulted in lower desiccation rates allowing males to spend longer periods of time on the surface than they did in the sun-exposed open areas. Males lived at higher densities in the mangrove areas, and preferentially selected shaded territories when given a choice. Male fights to attain/retain territories in the mangrove areas were longer than those in the open areas. Because females do not preferentially mate with males with territories in shaded mangrove habitats, the advantages to males in maintaining these territories is likely a reduction in thermal and/or desiccation stress. • Territory quality is critical for reproductive success, survival and, ultimately, fitness. • We examined territory preferences in the fiddler crab Austruca mjoebergi. • A. mjoebergi habitat includes open un-shaded areas of mudflat interspersed with areas shaded by mangroves. • Males showed a strong preference for territories located under the mangrove canopy. • Territory preferences in this species are driven by physiological needs. [ABSTRACT FROM AUTHOR]