Land Crab Cardisoma Guanhumi Research Articles

Is the threatened land crab Cardisoma guanhumi conquering human-dominated systems?

Land use changes are heralded as a major driver of biodiversity loss. However, recent findings show that cities, perhaps the most radical habitat transformation, sustain increasing numbers of threatened species. This emerging trend has been mostly chronicled for vertebrates from landlocked cities, although loss of biodiversity and rates or urbanization are higher in coastal marine systems. To advance our understanding on how threatened species may conquer human-dominated systems, we studied the threatened edible crab Cardisoma guanhumi and assessed how it is proliferating in croplands and urban systems at different spatial scales and whether populations show consequences of long-term exploitation. We gathered the data on crab populations covering the whole distribution range, including three countries reporting this as a threatened species. The abundance, distribution, and size structure of crab populations among different land uses at local scales were compared and published data for populations thriving in different habitats throughout their distribution range were compiled. We found that at local scale this species is able to thrive in natural and human-disturbed habitats, where food sources are heavily altered. At larger scales, the species showed no differences in abundance and size structure among natural and anthropogenic habitats. In areas near the southern distribution edge, crab populations were more abundant and composed of larger animals in urban areas and croplands than those in natural habitats, suggesting that human-disturbed systems are stepping stones to extend the geographic range. However, we found a long-term reduction in maximum body size, exacerbated by land use changes, that likely reflects exploitation regimes consistently targeting larger crabs. Despite its status as a threatened species, the long history of human exploitation combined with livestock farming practices may explain the proliferation of this crab in human-dominated systems, which emphasize the need to consider conservation in human-dominated systems.

Management and conservation of the land crab Cardisoma guanhumi (Crustacea: Gecarcinidae) based on environmental and fishery factors: a case study in Brazil

Management and conservation of the land crab Cardisoma guanhumi (Crustacea: Gecarcinidae) based on environmental and fishery factors: a case study in Brazil

Size distribution and sex ratio between populations of the artisanal harvested land crab Cardisoma guanhumi (Decapoda: Gecarcinidae), with the estimation of relative growth and size at sexual maturity in Puerto Rico

Introduction: Knowledge of growth patterns, sex ratio, and sexual maturity are of importance to exploited populations. The land crab Cardisoma guanhumi is an artisanal and subsistence exploited species in Puerto Rico. However, the growth patterns and sexual maturity of the local populations are not known. Objectives: This study has a double objective: (1) to compare the size and sex structure between populations and (2) to model the relative growth of structures related to reproduction to estimate the average size of morphometric sexual maturity (MSM) for both males and females. Methods: A total of 2 849 specimens were captured from nine dispersed populations on the island between 2001 and 2020. Carapace width (CW) was measured as an estimator of the absolute size of all individuals, together with the propodus length (PL) in males and the abdomen width in females (AW). Differences in length structure between sexes and populations were tested by applying goodness-of-fit tests based on Kernel Density Estimators (KDE). The relative growth pattern was modeled adjusting a spline from which the maximum of its second derivative was calculated as an estimator of the MSM, and bootstrapping was used to generate confidence intervals. Results: Differences were found in size structures, between sexes, and between sites. Our estimates of morphometric sexual maturity resulted in a sexual maturity size for males between 57.9 and 79.0 mm CW, while in females, morphological maturity occurs between 43.8 to 51.5 mm CW. Conclusions: We found inter-population differences in body size that can be attributed to differences in the history of changes of land use and the exploitation biased towards larger individuals, though differences in recruitment should also be considered. Current regulations in Puerto Rico protect female crabs but not to larger male crabs. The regulation establishes that crabs smaller than 64 mm carapace width cannot be captured, leaving immature male crabs over 64 mm CW unprotected. We suggest considering different size limits depending on the sex of the crab. This will allow the full range of sizes where sexual maturity is reached to be protected, increasing the likelihood of the population’s size to increase.

Seasonal variation in biometric parameters in a population of the endangered blue land crab (Cardisoma guanhumi): Indicators for assessment and management

Cardisoma guanhumi is a land decapod crustacean distributed along the eastern Atlantic. Currently, this species is included in the Brazilian list of aquatic species overexploited or threatened with overexploitation. This study performed biometric analysis and assessed reproductive dynamics of the blue land crab Cardisoma guanhumi in Acaú-Goiana Extractive Reserve, a coastal marine protected area in northeast Brazil. From January 2019 to December 2020, biometric data were evaluated from 539 captured individuals by an artisanal trap. In addition, male gonads and hepatopancreas were removed and fixed in formalin solution to analyse morphological reproductive indicators by gonadal (GSI) and hepatosomatic (HSI) index calculation. In summary, the population of blue land crab showed 322 males and 217 females. We observed a difference in variation of mean seasonal carapace width (54.73–56.67 mm). The condition factor ranged from 0.97 to 1.07, showing significant differences between the years and the seasons with high values observed in the dry season in 2019 and 2020. The weight–length relationships showed negative allometric growth for males (b=2.586, a=0.010) and females (b=2.229, a=0.291). The monthly distribution of the hepatosomatic (HSI) index did not show a clear annual pattern, but GSI differed between the months, indicating two seasonal groupings of Jan–Feb and May–August–Nov. The reproductive indicators of C. guanhumi evaluated here may indicate that the environmental influence and fishing pressure are the main factors that drive its reproductive seasons. Thus, it is noteworthy to indicate conservation efforts from January to April, when should be considered the breeding season for the species. In addition, long-term monitoring in the Extractive Reserve Acaú-Goiana must be considered for studies of population structure and gene flow of Cardisoma guanhumi, prioritizing the preservation of their habitats.

Genetic diversity of the blue land crab Cardisoma guanhumi (Latreille 1825) in the Alvarado Lagoon System in Veracruz, gulf coast of Mexico

In the Alvarado Lagoon System (ALS) in south-central Veracruz on Mexico's gulf coast, the blue land crab, Cardisoma guanhumi, a semi-terrestrial crustacean species, represents an important fishery resource, but one that is subject to overexploitation and habitat destruction. Identifying genetic diversity and the genetic unit are required to establish efficient conservation strategies. The present study's goal was to assess the genetic structure and degree of genetic diversity of C. guanhumi populations along the ALS. A fragment of the D-loop region of the mtDNA (750 bp) and a partial sequence of the COI gene (580 pb) was sequenced for 120 specimens collected at four sites in the ALS. Genetic diversity indices were estimated for each marker. The study sites' gene flow was estimated, as was the effective population size and the mutational rate for each locality. A haplotype network was built to estimate the gene genealogies of the populations. A Tajima's neutrality test, Fu tests, and mismatch analysis were performed to detect demographic expansion. Results show that this C. guanhumi population has high genetic diversity with a large gene flow among the localities studied and expanded during the recent evolutionary past. All haplotypes from both markers are novel for the species, according to the NCBI GenBank. The high genetic diversity and genetic connectivity among sites suggests that the size of blue crab populations in the ALS has not been drastically affected by past exploitation. Finally, management strategies are proposed to protect the species.

Long-term monitoring of crab Cardisoma guanhumi (Decapoda: Gecarcinidae) captures in Jobos Bay Estuary, Puerto Rico

Abstract: The densities of the land crab Cardisoma guanhumi has been dropping for the past decades, as a result numerous management strategies, laws and regulations throughout the tropics have been developed to reduce population declines. The reasons for declines include: overfishing, habitat degradation and loss, and continued capture in Natural Protected Areas (NPA). In Puerto Rico, an admistrative order of 1999, regulates a closed season, prohibits the captures of crabs through the year from NPA and has a legal size for capture (64 mm). The goal of this research was to monitor spatial-temporal dynamics of captures for C. guanhumi after the implementation of the admistrative order. Crabs captured from thirty-one hunters in six communities surrounding the Jobos Bay Estuary (JBE) in south east Puerto Rico was studied over a period of 15 years, 2004 through 2018. The size (carapace width and length), sex and color were documented for 1531 crabs. There was significant difference in crab size through time and space. The smallest crabs with captured in the west of JBE and in the year 2004, while the largest crabs were captured in the west and in 2013. As expected smaller hunting areas had smaller crabs due to higher hunting pressure. Further, there was significant difference in crab color by size, smaller crabs were orange, intermediate size was brown and larger crabs were blue. Color of crab can therefore be used to determine legal limit. From 2009 to 2018 three percent of hunters captured crabs smaller than the legal-size limit. Although there was no significant relationship between climate (temperature, rainfall) and crab size, smaller crabs were captured in 2013-2016 during years of lower rainfall. Also, crab size increase from 2004 until 2013 coincided with mangrove recovery in the JBE. The laws and management strategies in Puerto Rico for the protection of crabs by size and prohibition in NPA, is not enough. Therefore, the impact of climate variability, sea level rise and anthropogenic pressures on crab habitat, therefore, warrants further investigation.

Parámetros de crecimiento de Cardisoma guanhumi en el departamento del Magdalena, Colombia

In Colombia, the blue land crab Cardisoma guanhumi faces two main threats: extraction and habitat loss. This project aims to show an approximation of the growth parameters of C. guanhumi in protected areas within the Magdalena department. Individuals were captured monthly from May to October 2016 in five localities in the Tayrona National Natural Park (PNNT) and the Salamanca Island Road Park (VIPIS). A total of 816 crabs were collected, each of which was measured, weighed, sexed and released. Both sexes showed a negative allometric length-to-weight ratio. Using the FiSAT II program's ELEFAN I routine, the size frequencies obtained were analyzed in order to determine the growth parameters for 1) the department, considering gender, and 2) the PNNT, where the data from VIPIS wasexcluded. The asymptotic carapace width was higher for males (109.16 mm) than for females (96.74 mm), but the growth coefficient (K) was higher for females (0.19 year-1) than for males (0.15 year-1). Growth performance indexes were similar: 3.252 for males and 3.250 for females. The FISAT II length converted catch curve routine was used to calculate the total (Z), natural (M), and fishing (F) mortalityrates, as 0.41, 0.36, and 0.05 year-1 respectively. The grow coefficient K was higher for the PNNT (0.29 year-1) than for the Magdalena department (0.15 year-1), thus, longevity was lower for the PNNT (tmax= 10.42 years) compared to the department (tmax= 20.06 years). Ingeneral terms, the C. guanhumi population in the study area is longevous, slow growing, with low extraction morality. The data obtained in this work are important in the management of this species, as its slow growth makes it vulnerable to overfishing.

The ecosystem engineering role of the Neotropical crab Cardisoma guanhumi on mangrove soil properties

The land crab Cardisoma guanhumi is one of the most common species in mangroves of the American Atlantic coast and Caribbean islands however, studies of its effects on the physical and chemical soil properties are scarce. This study compares specific physicochemical properties of soil between C. guanhumi burrows (B) and adjacent zones (AZ), and provides the first insights on their role as an ecosystem engineer in mangroves. The study was conducted in an estuarine system dominated by Rhizophora mangle, located at the Rio Chico estuary, Miranda state of Venezuela. Random soil samples were taken digging each burrow until reaching the bottom and at the same depth for AZ. Data analysis was carried out using Bayesian inference. Credible mean differences between B and AZ, were found for sand (B = 26.53 ± 10.76, AZ = 17.25 ± 5.7%), silt (B = 73.16 ± 10.77, AZ = 82.42 ± 5.69%), pH (B = 8.71 ± 0.36, AZ = 9.12 ± 0.30), soil organic matter (SOM, B = 0.43 ± 0.21, AZ = 0.17 ± 0.06%), total N (TN, B = 786 ± 232, AZ = 529 ± 107 µg g−1), Mg (B = 4.42 ± 0.60, AZ = 3.48 ± 0.71 cmolc kg−1) and K (B = 0.12 ± 0.05 AZ = 0.06 ± 0.02 cmolc kg−1). Chemical variables as SOM, K, Mg and TN showed the highest values of effect size (> 1.4). With the exception of the pH, all chemicals variables—which were different between B and AZ—showed strong and decisive evidences of correlations with SOM. When SOM variable was controlled, the relationships between pH–TN, TN–K and Mg–K decreased, even though the correlation evidence between each pair remained. Differences in chemical contents found in B respect to AZ suggest that the activities of C. guanhumi (feeding, moulting, excretion and defecation) within their burrows promote the spatial heterogeneity of mangrove soils.

Caracterização Topográfica do Habitat do Cardisoma guanhumi Latreille, 1828 (Decapoda, Gecarcinidae) na Apa Costa dos Corais (Pernambuco e Alagoas, Brasil)

In the period from July to September 2012, a survey was made of the number of burrows of blue land crab ( Cardisoma guanhumi ), both in twelve profiles distributed in areas of mangrove, positioned perpendicularly to the wetlands of the Una's River (Pernambuco) and Camaragibe's River (Alagoas), aiming to acquire information on the distribution of holes in different types of topographies. The depth of burrows and the salinity and temperature of the water at the bottom of the burrows was registered. In Pernambuco and Alagoas, the profiles covered steep areas (with a gradient of 4.5°) and shallow areas (with a gradient of 0.02°). The maximum distance between existing burrows in the profiles, ranged from 58m and 359.5m, compared to a benchmark level (RN). The burrows depths ranged from 0.45m to 1.90m, with an depth average of 0.99m (DP = 0,29). The maximum depth of the burrows can be justified by the fact that there is less availability of water in northeastern soils.It is recommended, studied the mangroves, the establishment of an exclusion zone to preserve the habitat of Cardisoma guanhumi , a distance of at least 200m above the high tide mark. Keywords: blue land crab; mangrove; burrows.

Mitochondrial DNA Variation Reveals a Sharp Genetic Break within the Distribution of the Blue Land Crab Cardisoma guanhumi in the Western Central Atlantic.

The blue land crab Cardisoma guanhumi is widely distributed throughout tropical and subtropical estuarine regions in the Western Central Atlantic (WCA). Patterns of population genetic structure and historical demographics of the species were assessed by mtDNA control region sequence analysis to examine the connectivity among five populations (n = 97) within the region for future conservation strategies and decision-making of fishery management. A total of 234 polymorphic nucleotides were revealed within the sequence region, which have defined 93 distinct haplotypes. No dominant mtDNA haplotypes were found but instead a distribution of a few low-frequency recurrent haplotypes with a large number of singletons. A NJ-tree and a median-joining haplotype network revealed two distinct clusters, corresponding to individuals from estuaries located along the Caribbean Sea and Brazilian waters, respectively. AMOVA and FST statistics supported the hypothesis that two main geographic regions exists. Phylogeographical discontinuity was further demonstrated by the Bayesian assignment analysis and a significant pattern of isolation-by-distance. Additionally, tests of neutral evolution and analysis of mismatch distribution indicate a complex demographic history in the WCA, which corresponds to bottleneck and subsequent population growth. Overall, a sharp genetic break between Caribbean and Brazilian populations raised concerns over the conservation status of the blue land crab.

Ultrastructure of the spermatophores and spermatozoa from the gecarcinid land crab, Cardisoma guanhumi Latreille, 1828, (Crustacea, Brachyura, Gecarcinidae) from the western Atlantic

The ultrastructure of the sperm of the gecarcinid land crab Cardisoma guanhumi is described by scanning and transmission electron microscopy. Ultrastructural sperm morphology lends support for the monophyletic origin of the Thoracotremata, and for the placement of C. guanhumi in that clade. Additionally, it further attests the low level of variability within the thoracotreme clade. With regard to ultrastructural morphology, small differences concerning the apical button, the hyaline periopercular rim, the inner acrosome zone, and the outer two lamellations in the outer acrosome zone have been found between the spermatozoa of C. guanhumi and Cardisoma carnifex, the only other species in this genus studied for spermatozoal morphology.

Population estimation and site fidelity of the land crab Cardisoma guanhumi (Decapoda: Brachyura: Gecarcinidae) on Vieques Island, Puerto Rico

Overharvesting of the land crab Cardisoma guanhumi (Latreille, 1828) has occurred in some locations including Puerto Rico. We placed passive integrated transponder (PIT) tags in this crab, C. guanhumi, to estimate a population on the southern coast of Vieques island, Puerto Rico. We were able to recapture marked animals approximately 1 year after tagging. We estimated the population of C. guanhumi on the southern central coast Vieques to be approximately 29 000 individuals. The recapture locations of individuals averaged 136 m (SE ± 55.1) from their point of initial capture. This is remarkable because these crabs are reported to move annually inland up to several kilometers for mating. Either some C. guanhumi do not move during mating season, or they return to the same location they left. The carapace size of captured C. guanhumi suggests hunting was not greatly pressuring populations at the time of this study. These findings may help natural resource managers implement a conservation plan that will allow sustainable harvest of this population.

Development of male reproductive system of the blue land crab Cardisoma guanhumi Latreille, 1828 (Decapoda: Gecarcinidae)

AbstractShinozaki‐Mendes, R.A., Silva, J.R.F. and Hazin, F.H.V. 2011. Development of male reproductive system of the blue land crab Cardisoma guanhumi Latreille, 1828 (Decapoda: Gecarcinidae). —Acta Zoologica (Stockholm) 93: 390–399.In this study, the reproductive tract of the Cardisoma guanhumi was described both macroscopically and microscopically. The maturation stages of the reproductive system were defined, and the development of germ cells was described. The reproductive tract is made up of a pair of testis, a pair of vas deferentia, and a pair of ejaculatory ducts. The germ cells were classified in the order of development as spermatogonia (diameter: 10.5 ± 0.11 μm), spermatocytes (9.7 ± 0.07 μm), spermatids (initial phase: 5.5 ± 0.06 μm; final phase: 4.3 ± 0.05), and spermatozoa (SPZ) (4.0 ± 0.03 μm). The testis is made up of a germ zone, a maturation zone and collector ducts, which lead to the anterior vas deferens (AVD), containing solely SPZ. The spermatophores (SPH) start to be formed in the AVD, through the secretion of spermatophoric and protein matrices. In the median vas deferens, the SPH, already fully formed, are stored, while in the posterior vas deferens, a large production of a glycoprotein matrix is observed. Based on macroscopic and microscopic description of the male reproductive tract, three maturation stages are proposed: immature, maturing, and mature.

Effect of harvesting, vegetation structure and composition on the abundance and demography of the land crab Cardisoma guanhumi in Puerto Rico

Cardisoma guanhumi is the focus of an important artisanal fishery in Puerto Rico. Data on land crab landings point towards a dramatic decline in their abundance. This is cause for concern given the intrinsic value of the fishery and the important role these crabs play in coastal ecosystems. In this paper we examine the effect of harvesting and habitat quality on the abundance, survival, and size structure of C. guanhumi. To accomplish this we conducted a capture-mark-recapture study for a period of 18 months at three localities with minimal or no harvesting, and three with intense harvesting. Habitat quality at the six study sites was assessed by measuring vegetation composition-structure and litter biomass. We also conducted a leaf consumption experiment to evaluate leaf litter selectivity and limitation. Mean crab abundance differed significantly among sites, and this variation was significantly explained by differences in crab survival among sites. Sites with less harvesting tended to have higher survivorship and more crabs than sites where harvesting took place. Crabs mean size differed among study sites and was inversely related to abundance. Vegetation composition and structure, leaf litter standing stock and leaf-litter consumption differed among study sites. However, only some of these habitat characteristics are directly related to crab abundance or demography. There is a tendency for sites with a high leaf litter standing stock and large basal area to have the largest crabs but in low abundance. This study shows that C. guanhumi populations are very sensitive to increases in mortality that result from harvesting, and that the historical decline in abundance of this crab in Puerto Rico can be explained, in part, by an increase in trapping effort. Our results also indicate that C. guanhumi is a very plastic species, capable of occupying diverse types of coastal forests and a leaf litter generalist.

Regulation of Blood Pressure in the Land CrabCardisoma guanhumi

We examined the cardiovascular responses to acute and chronic changes in blood volume (BV) in the land crab Cardisoma guanhumi. Acute reduction in BV caused an increase in activity in the dorsoventral muscles (DVMs) and to a lesser extent in the epimeral attractor muscles (EAMs). Contraction of the DVMs and EAMs will decrease the volume of the dorsal sinus and the thorax as a whole, respectively. BV reduction also caused bradycardia with frequent periods of cardiac arrest. There was a small drop in hemolymph pressure. BV expansion had the reciprocal effect on DVM and EAM activity but had no effect on heart rate (fH). After the cardioregulatory nerves were cut, acute hypovolemia had no effect on fH but still caused a moderate increase in DVM activity. After dehydration-induced BV reduction, DVM activity increased, whereas hemolymph pressure, fH, and EAM activity were maintained close to control levels.

Roles of eyes, leg proprioceptors and statocysts in the compensatory eye movements of freely walking land crabs (Cardisoma guanhumi)

The compound eyes, the canal organs of the statocysts and proprioceptors in the legs all generate compensatory eye movements in the horizontal plane in the land crab Cardisoma guanhumi. Frequency analyses of the compensatory eye reflexes elicited by each of these inputs show that visual (V) and proprioceptive (P) reflexes respond best below 0.1 Hz, while statocyst (S) reflexes only achieve a high gain above this frequency. They thus increase the range of frequencies over which compensation can occur. Eye and body movements were recorded in an arena under all possible combinations of crabs seeing or blind (V+ or V-), with or without statocysts (S+ or S-) and freely walking or passively transported on a trolley (P+ or P-). Intact crabs (V+S+P+) show good stabilisation of the eyes in space, the only movements with respect to external coordinates being saccadic resetting movements (fast phases of nystagmus). The eyes thus compensate well for body turns, but are unaffected by translatory movements of the body and turns that are not accompanied by a change in the orientation of the long axis of the body in space. In the absence of any one sense, compensation for rotation is significantly impaired, whether measured by the increase in the width of the histograms of changes in the angular positions of the eyes in space ( capdelta &phgr; E), by the mean angular velocity of the eyes (slope of regression line, mE) with respect to the angular velocity of the body (mB) or by response gain plotted against angular acceleration of body turn (a). The absence of two senses reduces the crab's ability to compensate still further, with the statocyst-only condition (V-S+P-) being little better than the condition when all three senses are absent (V-S-P-).Such multisensory control of eye compensation for body rotation is discussed both in terms of making use of every available cue for reducing retinal slip and in making available the information content of the optic flow field.

The Burrow Microhabitat of the Land Crab Cardisoma guanhumi: Respiratory/Ionic Conditions and Physiological Responses of Crabs to Hypercapnia

Cardisoma guanhumi in Puerto Rico spend much of the dry season in burrows that descend to groundwater Burrows are sometimes 3-4 m deep and may be capped with dried mud for over 3 mo. Samples of gas and water from burrows at three locations in Puerto Rico were analyzed for O₂, CO₂, and ions. Osmolality and ion composition varied widely with location, from about 10% to 130% of seawater. Both gas and water Po₂'s were generally 90-120 mmHg, although some water samples were extremely hypoxic (Po₂ < 20 mmHg). Most burrows were extremely hypercapnic, with gas and water Pco₂'s up to 60 and 90 mmHg, respectively. Whether the burrow was plugged or even occupied by a crab made little difference to ion or gas concentrations. Radiotelemetry of the vertical position of crabs in their burrows indicated that they did not avoid hypercapnia and hypoxia by staying close to the entrance. Cardisoma guanhumi are thus exposed to extreme changes in Pco₂ when they descend deep in their burrows after foraging at dawn and dusk. Imp...

Diet of the killifish Rivulus marmoratus collected from land crab burrows, with further ecological notes

One-hundred eleven specimens of the cyprinodont fish Rivulus marmoratus were trapped from burrows of the great land crab Cardisoma guanhumi in east central Florida and the entire alimentary tract removed for analysis of food items. Three categories of burrows (inactive, active and sealed) were sampled to examine possible relationships between burrow type and presence of R. marmoratus. Forty percent of the guts examined contained no food items, while the remaining 60% contained items of both terrestrial and aquatic origin. Capture rates among burrow categories did not vary significantly, and most collections consisted of 1 or 2 individuals per burrow. Mean standard length of fish within a burrow declined when more than 3 specimens were captured from a burrow. Supplemental observations on reproductive status and burrow water temperature are noted.

ACTIVITIES OF URICASE, XANTHINE OXIDASE, AND XANTHINE DEHYDROGENASE IN THE HEPATOPANCREAS OF AQUATIC AND TERRESTRIAL CRABS

ABSTRACT To examine the effect of habitat on urate metabolism in crabs, we measured the activities of xanthine oxidase (XOD), xanthine dehydrogenase (XDH), and uricase in the hepatopancreas of two species of aquatic crabs, the blue crab Callinectes sapidus and the stone crab Menippe mercenaria, and two species of land crabs, the blackback land crab Gecarcinus lateralis and the blue land crab Cardisoma guanhumi. Only aquatic crabs showed measurable activities of uricase: 11.5 ± 1.1 nmol urate oxidized per min and per g tissue for C. sapidus (N = 4) and 1.2 ± 0.7 nmol min-1 g-1 (N = 11) for M. mercenaria. These crabs also exhibit a higher XDH activity than XOD activity (approximately 4-5 fold). This is also the case for C. guanhumi but not for G. lateralis which has similar low activities of both enzymes. The possible physiological implications of these results are discussed regarding nitrogenous excretion, blood oxygen transport, and the adaptation of crabs to a terrestrial habitat.

Heart Rate and Hemolymph Pressure Responses to Hemolymph Volume Changes in the Land Crab Cardisoma guanhumi: Evidence for "Baroreflex" Regulation

Hemolymph volume in restrained land crabs (Cardisoma guanhumi) was altered in 5% increments by rapid infusion of filtered seawater into, or rapid withdrawal of hemolymph from, an infrabranchial sinus. Associated changes in intracardiac hemolymph pressure and in heart rate were measured. Elevation of hemolymph volume resulted in a brief (<20 s) rise in hemolymph pressure followed by a return toward control levels. Heart rate changed in a reciprocal fashion to hemolymph pressure, briefly decreasing during and immediately following infusion and then rising back toward control levels. The net effect after infusion or withdrawal was a readjustment in both hemolymph pressure and heart rate to stable new levels. A significant inverse correlation between heart rate and hemolymph pressure was evident, with heart rate decreasing approximately 2 beats · min⁻¹ · mmHg⁻¹ rise in hemolymph pressure. Collectively, these data indicate that changes in hemolymph pressure result in reflex adjustments in heart rate in a manner analogous to baroreceptor reflexes in vertebrates.