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Laterality affects coloration in Red Sea Ghost Crabs ( Ocypode saratan )
The ability to change colors or appearance to blend into the background habitat is essential to ensure an individual’s survival. This is especially challenging in a heterogeneous habitat such as the intertidal zone of a seashore, which is the primary habitat of crabs. The Red Sea Ghost Crab (RSGC) is endemic to the Red Sea, and in Israel, it is found only at one beach. We discovered that right-clawed crabs are lighter colored (i.e., yellow, sand) than left-clawed crabs (brown, purple), consistent with their daily activity. The closest to the water were the sand-colored, left-clawed crabs, while the farthest up the beach were the yellow-colored, right-clawed crabs. Moreover, we observed purple-colored, left-clawed crabs during low UV radiation, while during high UV radiation, we observed brown-colored, right-claws crabs. In explaining the observed segregation, we speculate that claw lateralization and body colors are common in the social signaling system. Symmetrically identical individuals can signal their condition to their competitors by colors. However, this part of the signaling is under the pressure of the intensity of sunlight.
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Discovering All Marine Species
Ghost Crabs: Characteristics, anatomy and habitat
The ghost crabs or sand crabs are semi-terrestrial decapod crustaceans belonging to the Ocypodinae subfamily. They are mainly white in color, although they can vary it to camouflage with their surroundings .
Table Of Content
- 1 Brief Overview of Ghost Crabs 🦀
- 2.1 Ghost Crabs’ Anatomy 🦀
- 2.2 Other distinctive features 🦀
- 3 The Ghost Crabs’ Common Habitats 🦀
- 4 How Ghost Crabs Reproduce? 🦀
Brief Overview of Ghost Crabs 🦀
First described in 1860, the ghostcrabs have remained on our planet virtually unchanged since the Quaternary era, after the disappearance of the dinosaurs, evolving along with the first humans. Their presence is considered an indicator of healthy beaches, since they are particularly sensitive to chemical pollutants such as oil derivatives.
However, the main danger they face in tourist places relies in the destruction of their habitats by urbanization and the continuous walk of people, which prevents them from eating and build their underground dens.
The Ghost Crabs’ Main Characteristics 🦀
Ghost crabs’ anatomy 🦀.
There is a wide variety of ghost crabs, so depending on the species may differ in their general characteristics. Their sizes range from a few millimeters, up to four meters wide when their legs are extended.
These decapods have a thick exoskeleton composed of highly mineralized chitin, four pairs of legs, a pair of claws and elongated and swollen peduncles that can swivel 360 degrees.
Their carapaces are usually deep and have a square shape. The types of ghost crabs can be identified more easily by means of the area where they are found.
We can mention the O. quadratus , which inhabits the western Atlantic coast from New Jersey to Brazil , the O. ceratophthalmus, found on the beaches of the Indian and Pacific oceans a nd the ghost crab O. saratan, belonging to the Red Sea .
Other distinctive features 🦀
Ghost crabs emit a unique bubbling sound when they strike with their claws on the ground and rub their legs. Their scientific name, Ocypode means «fast feet», since they often move at a speed of up to 10 miles per hour.
When ghost crabs breathe oxygen, they need to keep their gills wet, so it is common to see them ingesting seawater or absorbing moisture from wet sand. As for their diet, it consists mainly of sea turtle hatchlings, turtle eggs, clams, insects and other crabs .
Now…. let´s watch them
The Ghost Crabs’ Common Habitats 🦀
Ghost crabs live in small burrows in the sand , preferring a solitary life with only one crab per burrow.
Such places are commonly dug at a 45-degree angle a nd can be up to 1.5 meters deep . They create their burrows with angled entrances so that the breeze blows in them, allowing the ghost crabs to be ventilated.
How Ghost Crabs Reproduce? 🦀
Ghost crabs, (like most crabs), depend on the sea to perpetuate their species . During mating, the male ghost crab deposits its «genetic material» into the female, holding its claws tightly.
After a quick and unpleasant encounter with the male, the female is released and fled to her burrow, maturing her eggs in her body and depositing them shortly after in the sea, which will later return in the form of larvae and live buried in the sand until they reach their adulthood.
From time to time they must dispute their food among themselves, which makes them fight and use their powerful pincers.
There are rarely deadly duels, but it is very common for them to lose a leg or a pincer during the fight .
Fortunately, they can recover such limb when they molt their exoskeleton . Since this is an external structure it just can´t grow, so the ghost crabs ( as most crabs)periodically grow a new one underneath, discarding the old one and growing a little more while the new «exoskeleton» hardens.
Unfortunately for them, that exoskeleton is not hard enough to withstand the stomp of a scared or distracted tourist.
let´s have a final look of them
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Sand Scavengers: Ghost Crabs in the Intertidal Zone of Chennai’s Elliot’s Beach
Species | Sep 29, 2023
Text and photos by: Yuvan Aves
Living on the foggy cusp of land, sea, sand, and sky, ghost crabs are the beach clean-up crew, the vultures of sandy coastal ecosystems.
The tide is low. Thin brushstroke clouds are dissipating in the March sky. It is one of those days at Elliot’s beach in Chennai when adult horn-eyed ghost crabs ( Ocypode brevicornis ) gang up and stroll together on the surf, where the foam is formed by breaking waves. Here and there, a few slow down, stop to inspect debris or pick up a morsel from the sand. Silhouettes of Caspian terns send some sprinting sideways into the waves, only to tip-toe out later. There are about thirty of them in a loose group, all strolling at the same pace and in the same direction, and there are one or two more groups further ahead. My friend Vikas and I follow the patrol along the shore. He lugs a massive telephoto lens under the midday sun — pointing it every few minutes at some bird in the sky, like a ghost crab’s eye.
Down this beach, past the fishing hamlets of Urur Kuppam and Olcott Kuppam, and beyond the forest department’s turtle hatchery, is the Adyar river’s estuary. The crab troop begins to scatter as we approach the river, where egrets and sand plovers are standing in the swash zone (where waves break) foraging wedge clams.
Dark chocolate-brown mudflat stretches form the cheeks of the river’s mouth where different ghost crabs show up — red ghost crabs ( Ocypode macrocera ). The young ones are drab brown, but the adults are red as cherries. They are not beachcombers like their sibling species, but sand-sifters. They live away from the wave action, forage organic matter from the mud and leave a trail of near-polygonal chunks of processed soil outside their burrows. Reds are shy and seldom venture more than a metre from their lairs. At the estuary, the river flows into the sea carrying the shadows of the city. Waves foam at its mouth, and the water is sometimes greenish, smelling of algal broth and effluents. A broken bridge juts over it. A bunch of college youth stand at its precipice and take selfies. The bridge stands in three disjunct pieces as a testimony to the temperament of this river-sea junction. In the 1970s, a flood shattered most of the bridge and sent its fragments into the Bay of Bengal. Yet, the Greater Chennai Corporation is considering another road over the estuary that will evict the fishing hamlets that have been here for centuries. Under the bridge’s southern fragment, fields of fiddler crabs appear as the tide falls. Ring-legged fiddlers ( Austruca annulipes ) and fluorescent blue variegated fiddlers ( Austruca variegate ) wave the larger of their claws vehemently over their heads. If you keep silent, you can hear the air murmur with pincer sounds. The Students’ Sea Turtle Conservation Network has recorded over two hundred olive ridley sea turtles nesting on this beach in winter.
The horn-eyed ghost crabs are now loosely dispersed; many have begun their return stroll away from the river towards the beach again. Two have found a beached eel carcass and are cleaning its spine out disc by disc. Another one crouches among the waves, feigning dead for a while — eye-stalks drooping, legs collapsed — but then jumps to life and zips off into the sea when we approach too closely.
A fisherman and his young boy cross us with a bag of ghost crabs they have just dug out from the intertidal zone. They tell us that stew made of them is an important food for breastfeeding mothers in their hamlet. Paa nandu , karuvaali nandu , kuzhi nandu are some local Tamil names for ghost crabs. Their meat is used as fish bait; it is also strewn on the shore at low tide to lure lugworms to the surface.
Fisherfolk say that these creatures are good weather-forecasters. If a crab chucks sand at a distance from its burrow as it digs, then the weather will be calm. If it throws sand cautiously close or stays inside its burrow all day, then strong winds, rain or tidal surges can be expected.
To me, the life and physiology of ghost crabs (subfamily Ocypodinae) is sheer science fiction or the stuff of mythology. They are everyday company, yet their utter “otherworldliness” fascinates me immensely. Ghost crabs are coastal chimeras, edge-of-the-world denizens, living on the foggy cusp of land, sea, sand, and sky. They have lungs and gills to breathe in both air and water. They can hear and drink with the setae (hair) on their feet, speak in pincer signs, stridulations, and gut rumbles. They have panoramic 360-degree vision, and the cylindrical retinas atop their eerie, ghostly periscope eyes can see you coming from 50 metres away. For a ghost crab, the horizon is not a mere line in the sky but a full circle. They can be forward-strolling on the shore and instantly change direction and skedaddle sideways when they want to, dashing off at 15 kmph — faster than any land crustacean. They move and live and breed to lunar rhythms — feeling the moon’s tug in their blood thickening and thinning, moulting and growing during full and new moon phases. Watch them throughout the day, and their mooniness becomes more apparent. They change the colour of their carapaces according to background brightness — paler during the day and near full moons, distinctly darker at night and near new moons. They are compulsory company to all of Chennai’s beachgoers. They may cross your path, scurry into your slippers, scour the leftovers from food shacks and picnics. But their indispensability to a sandy beach ecosystem remains entirely unsung among the general public.
Beach sand has very little microbial life in it. A washed-up eel or a stargazer can lie rotting there for weeks if ignored. If not for ghost crabs — the principal beach clean-up squads and public health officers of sandy shores – beaches would be less livable and hygienic places for numerous life forms, including us. They are crucial scavengers here, the vultures of sandy coastal ecosystems. A 2014 study in the journal of Oceanography and Marine Biology by biologists Serena Lucrezi and Thomas Sclacher shows that ghost crabs facilitate the major transfer of energy from marine ecosystems into sandy and dune habitat food webs, making them a keystone species.
I also like to call them land pirates in the most crabbish, voguish sense. They snatch hatching baby sea turtles crawling to the ocean, steal shorebird eggs and chicks, and if times are hard, they may even eat each other. Their burrowing bio-turbates the sand — mixes up and distributes minerals and nutrients — making the subsoil more livable for wedge clams, olive sea snails, lugworms, mole crabs, purse crabs, ribbon bullia, and many other creatures of Chennai’s intertidal zone. Rivers bring sediment. Wind and waves make the beach over millennia. These ten-legged beach-keepers have been the beach’s indispensable maintenance crew.
Out of the estuary, a mullet torpedos three feet above the water, catches the sun’s glint, and splashes back in. A hermit crab examines a discarded pill bottle. A fisherman drags out his hand-cast net, which has caught shivering silver bellies and mackerel. A small cloud of little stints come into view over the ocean, “shshing” softly overhead as they swerve down into the creek. Down on Earth, tower snails have screwed themselves upside down into the tidal flats, their black opercula (lid) facing the sky as they wait for the tide to rise. Numerous discarded face masks wash up at the river mouth, some ear-loops entangled on razor clams, murex shells, and dismembered pincers. Four beached sand stars lie in a square, mysteriously outside a ghost crab burrow. The creature must have been dragging them towards its lair before the sand thudded with giant bipedal footsteps, making it abandon them for the time being and vanish into the ground.
About the contributor
is a Chennai-based naturalist, writer and activist. He enjoys introducing the natural world to children and is the author of A Naturalist's Journal - a collection of essays on countryside wilderness.
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Does Size Matter? The Case of the Courtship Pyramids in Red Sea Ghost Crabs ( Ocypode saratan )
1 Eilat Campus, Ben Gurion University of the Negev, Eilat 88000, Israel
2 Rabin High School, 51 Yotam Street, Eilat 88104, Israel; moc.liamg@5051sokroklahcim
Jakub Z. Kosicki
3 Department of Avian Biology and Ecology, Adam Mickiewicz University, Poznań, Uniwersytetu Poznańskiego Str. 6, 61-614 Poznań, Poland; lp.ude.uma@okabuk
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Male ghost crabs ( Ocypode spp.) are known to build sand structures near the entrance to their burrows. It has always been assumed that the structure played a role in sexual selection and mate attraction. We hypothesized that the larger males would make relatively larger pyramids in order to enhance fitness. We studied Red Sea ghost crabs at Eilat, Israel, and found that the larger crabs actually did not put much effort into building pyramids, and it was the medium-sized crabs that invested the most in building the pyramids.
Display, wherein males attempt to maximize fitness by attracting sexually mature females to mate, is known to drive speciation by Sexual Selection. We researched the Red Sea Ghost Crab ( Ocypode saratan ; RSGC), in which males build display pyramids to attract females. The study was conducted at the beach in Eilat, Israel. At each session, we measured the height (in cm) of all pyramids and the dimensions (height, breadth; in cm) of the burrow entrance. We assumed that the size of the entrance represented the relative size of the carapace width of the occupant. The mean (± SE) entrance volume was 230.8 ± 11.7 cm, and the height of the pyramid was 11.8 ± 0.49 cm ( n = 54). The results of our study did not support our hypothesis because we had expected to find a linear correlation between body size and pyramid height, i.e., the larger the male, the larger the pyramid. However, our results show that the largest males in the population either built small pyramids or not at all, and the cut-off of the larger crab’s body size appears to be around 350 cm 3 . We discovered a step-wise function in the data in that crabs with the smallest body size of ca. 250 cm 3 constructed the highest pyramids, with a declining tendency between 250–350 cm 3 and extremely low pyramids beyond 350 cm 3 . However, our findings need to be further studied with a stress on the ambiance and elucidate whether the habitats differ in temperature, humidity, prey-base, etc., before concluding as to why the larger males desist from building pyramids. This study underwrites the importance of studying the mating systems of the macro-fauna of the beaches that are fast disappearing owing to anthropogenic development.
Since the theory of speciation and natural selection were co-proposed [ 1 , 2 ], the subject is still debated, and many subsequent models either support or refute their theory [ 3 , 4 ]. One of the major hypotheses in natural selection theory is that of speciation by Sexual Selection (SSS) [ 5 ], wherein it is argued that female preferences drive male traits, especially display, resulting in reproductive isolation [ 6 ].
Display, wherein males attempt to maximize fitness by attracting reproductive females to mate, is known to drive SSS [ 6 ]. The subject of display has been found to occur in a wide range of empirical studies such as quantity and quality of prey [ 7 , 8 ], color and ornamentation [ 9 ], vocalizations [ 10 ], ritual dance [ 11 ], chemical [ 12 ], and several other qualities that Zahavi collated under the “Handicap Principle” [ 13 , 14 ].
Trying to impress females to choose themselves in a lek mating system requires males to outdo their competition by being either more vocal or colorful, executing a more elaborate dance and/or having exemplary ornamentation [ 15 ]. Although this has not been clarified for any of the Ocypode species studied to date globally, from our observations in the field, we are convinced that the ghost crabs have a lek mating system, wherein the males display and build their pyramids in proximity to each other, and attract females from the surrounding areas of the beach [ 16 ]. Our speculations are supported indirectly by biased sex ratios in other ghost crabs and in New World fiddler crabs [ 17 , 18 , 19 ].
According to this, we researched a little-studied species of the genus Ocypode , Red Sea Ghost Crab ( O. saratan ; RSGC), in which males build display pyramids to attract females [ 20 , 21 ]. In spite of the two detailed studies of the RSGC, neither classified the mating system nor did they study whether body size of the adult male influenced pyramid size. Hence, we initiated a study on a sandy beach in Eilat, Israel, where the species is readily observed. We hypothesized that size would influence the final product and that the larger the male, the larger the height of the pyramid would be, in accordance with the Handicap Principle [ 13 ]. We reasoned that in order to maximize fitness, males would try to attract females from greater distances and broadcast their size in relation to their competitive neighbors by maximizing the size of their pyramids and taking advantage of their larger body size to build higher and more prominent pyramids.
2. Material and Methods
Ghost crabs (Genera Ocypode and Holpocypode spp.) are considered to be reliable bioindicators of beach and environmental quality [ 22 , 23 , 24 ]. Ghost crabs are facultative scavengers, foraging on any form of organic material, but also predate other macro-invertebrates; and since they have no terrestrial competitors on the beaches and are able to endure long periods of starvation, are top predators in the simple food web of the sandy beaches [ 25 ]. Some of the display behaviors in the Ocypode species include air-borne sounds and substrate vibrations by either rapping or stridulating; visual courtship cues were male waving or chela-forward display; or petrified display-signals that males make from sand excavated from their burrows [ 18 ].
The RSGC is endemic to the Red Sea, and the only studies published to date on the species are from more than half a century ago [ 20 , 21 ]. Recently, RY and his high school students have initiated a study of the species [ 26 ]. They found that the RSGC is the most conspicuous member of the sandy beach communities in the Red Sea and that male burrow complexes consisted of a sand-pyramid ( Figure 1 ), a pathway leading to it and around it, a vestibule at the entrance and a spiral burrow, which are only constructed by sexually mature adults. Physiological differences were noted in relation to body size by studying their branchial morphology, gill area and branchial volume in different-sized crabs [ 21 ]. RSGC was found to have fewer gills and less gill area than aquatic crabs, and the smallest crabs had the highest heart rates; blood characteristics indicated adaptation to semiterrestrial habitats and high ambient temperatures.
A typical Red Sea Ghost Crab ( Ocypode saratan ) burrow entrance with the sand pyramid on the outside. (Photo RY).
It was found that the pyramids are on average 16.5 (±2 cm, n = 100) high and the base circumference averaged 28 cm (±5, n = 100) wide [ 20 ]. For the construction of a new pyramid, a crab required an average of 1850 cm 3 (±550, n = 45) of sand excavated from within the burrow and required about 80 min (±15, n = 25) to construct. He also suggested that the pyramids appear to be the sign-stimulus for attracting females, intruding males are fought off by the owner, and the nearest-neighbor-distance was 134 cm. In another study, it was reported that a male will guard his pyramid for 4–8 days, during which it does not feed [ 21 ]. Only when the female is in the vicinity of the pyramid do the males initiate vibration signals to convince the female to enter the burrow [ 21 , 27 ]. It was also reported that sexual selection by females is influenced by the fact that they choose to enter the burrows of like-handed males, i.e., the larger cheliped is on the same side in both individuals [ 20 , 26 ].
The study was conducted on the northeast beach in Eilat, Israel (29°32′34″ N, 34°58′39″ E to 29°32′33″ N, 34°58′41″ E). Eilat is situated in the northwestern corner of the eastern arm of the Red Sea. Owing to shore-development projects by the local municipality wherein gravel was used to layer the sandy shores for the sake of beach tourism, a short section of ca. 400 m still remains in its original, sandy substrate. This stretch is further divided into two sections—ca. 100 m of sandy beach for unregulated tourism and a further 300 m that extends eastwards into a military fortification and the international border with Aqaba, Jordan.
We conducted our study on the tourist section of the beach. At each session, we located all sand pyramids that were visible on the beach and measured their height (in cm), and the dimensions (height, breadth; in cm) of the burrow entrance. We assumed that the size of the entrance represented the relative size of the individual living in it, i.e., the carapace width [ 20 , 28 , 29 , 30 , 31 ]. Observations were made mostly in the morning hours, before the arrival of the tourists. Only those pyramids that were not disturbed by humans were measured. All observations were conducted during the months of March, April and May 2020. We conducted a total of 95 hrs of observation during which we successfully measured 54 pyramids.
We analyzed relationships between entrance volume (as relative size of the individual) and the heights of the pyramids as linear and/or quadratic tendency. In the first step, both variables were standardized, and the mean value was used as a reference point:
x—not standardized variable;
µ—mean value calculated from population.
Thus, the standardized variable means how much of the entrance volume/height of pyramids deviates from the average of the whole population. We then described the relationship of both variables using the equation of a linear and a quadratic function, where the standardized height of the pyramid was used as the dependent variable. Next, we performed Mandell’s test to check which model better described our relationship. We also calculated an extreme of quadratic functions according to the equation:
which indicates to what volume of the entrance the height of the pyramid increases and vice versa from what volume of the entrance the height of the pyramid decreased. All calculations were performed in R 4.0.3 [ 32 ].
The mean (± SE) entrance volume and height of the pyramid were respectively 230.8 ± 11.7 cm and 11.8 ± 0.49 cm, resp., n = 54. We found a negative significant correlation between these variables for both raw and standardized variables: r = −0.60, p < 0.001, n = 54; r = −0.60, p < 0.001, n = 54. The beta-coefficient (± SE) for linear relationships was −2.64 ± 4.82 and was different from 0 (t = −5.33, p < 0.001), and R 2 for this relationship was 0.36. For quadratic function, the beta-coefficient (± SE) was −1.65 ± 6.06 and also was different from 0 (t = −2.72, p = 0.008), but in this case, R 2 was higher than for linear regression and was 0.42. Mandel’s test to check which model is better suited to the data was significant (F = 7.39, p = 0.008), which suggested that the quadratic function better describes our relationship than the linear model. The extreme of the entrance volume was 169.01 mm, and after crossing this point of burrow entrance volume, the height of the pyramid decreased ( Figure 2 ).
The linear (Red line) and quadratic (green line) model which shows how height of pyramid is related to the volume of the entrance to the burrow of the Red Sea Ghost Crab ( Ocypode saratan ).
The results of our study did not support our hypothesis. We had assumed that size would matter in that we expected to find a linear correlation between body size and pyramid height. We had predicted that the larger the male, the larger would be the pyramid. However, our results show the opposite in that the largest males in the population either built small pyramids or not at all; and the cut-off of the larger crab’s body size appears to be around 350 cm 3 . We discovered a step-wise function in the data in those crabs with the smallest body size of ca. 250 cm 3 constructed the highest pyramids, with a declining tendency between 250–350 cm 3 , and extremely low pyramids beyond 350 cm 3 ( Figure 1 ).
We suspect the differences in the height of the pyramid between our research and those from more than half a century ago [ 20 ] result from the range of body size of RSGC in different geographical zones or that there is a seasonal or annual effect that has not been described to date. Further, the subject of anthropogenic disturbance could contribute to the subject of the height of the pyramids. We assume that frequent disturbance by beach tourism could influence the time and energy invested by a male ghost crab in the upkeep of his sand pyramid. Another point that needs to be addressed is the nearest-neighbor-distance and the parameters that influence burrow placement on the beach. In O. ceratopthalmus, on Seychelles, males only constructed copulation burrows around the full moon and only below the high tide mark [ 33 ]. This was not the case in our study, wherein all burrows and related pyramids are found throughout the moon’s cycle and also are above the high tide mark.
The results are in contrast to the SSS and the Handicap Principle, wherein it is always assumed that the larger, greater or more excessive the demonstration by the male, the better attraction of females and increased fitness. For example, female Southern Grey Shrikes ( Lanius meridionalis ) are attracted to males with larger larders, and in extreme conditions, even choose to be polygynous over monogamy, which is the norm in the species, as the mating system for the season [ 7 , 34 ].
In the past, the extreme dimorphism between the sexes and elaborate and diverse decorations of males even lead to mistakenly identifying them as separate species [ 35 ]. As previously mentioned, many of these extravagant displays were supposedly explained by the Handicap Principle [ 13 ] and supported by many a study [ 36 ]. The principle states that for signals/traits specialized for communication to be effective, they must be reliable, and in order to be reliable, they must be costly, and cost makes false signals unprofitable [ 37 ]. However, not only are there a wide range of different assumptions and theories that have evolved from the initial idea [ 38 ], there are also those who have found that the conclusions of the Handicap theory are incorrect and found no evidence for altruism or handicap [ 37 , 39 , 40 ]. Similarly, in our study, we find that the behavior of the male RSGC is actually contrary to what was expected if they were to conform to the principles of the Handicap theory. In our case, the largest were the smallest and with an inverse correlation with the smaller males building the larger pyramids. Although we have not evaluated the relative fitness of the different sizes of the RSGC, other studies of crustaceans substantiate the idea that female preferences are biased towards the larger individuals of the population [ 20 , 21 ]. Hence, our study does not substantiate the Handicap Principle and substantiates the findings of those who did not find evidence in its support.
The mating system in Uca spp. was classified as resource-defense polygyny in some species and as resource-free and promiscuous in others [ 19 ]. In our case, we assume that the proximity of the male pyramids to each other suggests a lek system and that the only resources the males seek are safe burrows for attracting females, i.e., resource-defense and promiscuous [ 15 ].
Early researchers concluded that in field conditions, the negative effects of burdening offspring with handicap genes outweighed the advantages of mating with a fitter male and, thus, disproved the Handicap Principle [ 41 , 42 ]. In our study, it appears that body size suffices to ensure fitness. We assume that the larger males are so prominent in the colony or are able to broadcast their size differently (auditory [ 27 ]) that they do not need to invest energy in building prominent pyramids or to patrol them against intruders [ 20 , 21 ] and care for their constant upkeep. One must also take into account that larger body size entails a greater investment in locomotion as compared to smaller congeners and may explain some of the discrepancies found in our study. Our study concurs with the study wherein the larger individuals derived higher benefits with lower investment as compared to smaller males [ 43 ]. It was also found that the sand structures are constructed only by males that are able to fend off intruders and that other conspecifics regarded the structures as indicators of the owner’s fighting potential [ 44 ].
In conclusion, we present the results of our study on display in Red Sea Ghost Crabs wherein the degree of investment in display-related sand pyramids is related to body size, but against the intuitive assumption that larger males build larger pyramids, we found that the smaller the male is the larger the pyramid it needs to build to try and obtain the attention of the vying females. However, our findings need to be further studied with a stress on the ambience and to elucidate whether the habitats differ in temperature, humidity, prey-base, etc., before concluding as to why the larger males desist from building pyramids. This study underwrites the importance of studying the mating systems of the macro-fauna of the beaches that are disappearing due to anthropogenic recreational activities and development.
We thank the editors and two anonymous reviewers for improving an earlier draft of this manuscript.
R.Y.—Conceptualization; Data curation; Investigation; Methodology; Project administration; Resources; Supervision; Validation; Writing—original draft; M.K.—Conceptualization; Data curation; Investigation; Writing—original draft; J.Z.K.—Data curation; Formal analysis; Software; Visualization; Writing—original draft. All authors have read and agreed to the published version of the manuscript.
This research received no external funding.
Institutional Review Board Statement
Not applicable. Observational only.
Informed Consent Statement
Data Availability Statement
Conflicts of interest.
The authors declare no conflict of interest.
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Ghost Crab (Sand Crab)
What is a ghost crab.
Table of Contents
Table of content.
This animal is also known as “Sand Crab” or “White Crab”. These are also known as “Mole Crabs”.
This animal has a pale body color that is similar to the color of sand. This makes it nearly invisible when it crawls about over sand. It is because of this apparent invisibility that the crab has got its unique name. The name is also suggestive of the fact that the activities of this creature are mainly restricted to night.
This animal has five pairs of legs. The first pair is called Chelipeds and is shaped like claws. The legs, when jointly used, can make crabs move in any direction – forward, backward or sideways. In male crabs of this species, one claw is slightly larger than the other.
It has large black eyes that are supported on stalks. Its eyes help it see in any direction. There are horns attached to the end of the eyes of male crabs. It is by these horns that the gender of a crab is recognized. The eyes of these creatures are sensitive to changes in light.
The large eyes of these crabs give them a wide field of vision. The eyesight of these creatures is very good. This helps them spot predators very quickly and find out any other threats.
It is about 2-3 inches in size.
It has a water-tight exoskeleton (external skeletal structure) which prevents the creature from becoming dry. The body covering also lends support to its muscles and organs.
With increasing maturity, the crab begins to lose its external skeleton. It comes off at a point, only to be replaced by a new, slightly larger shell. The new shell takes some time to harden and until that happens, the crab remains vulnerable.
This creature is found in sandy beaches of tropical as well as subtropical coasts. It can be found anywhere from the American Atlantic Sea, the Mediterranean Sea and the Red Sea to coasts along the American Pacific and the Indo-Pacific.
These crabs are usually found in sandy beaches and backshores where they live in burrows. Crabs usually burrow a deep hole to keep themselves cool during the daytime. They remain in burrows during daytime and when winter is at its coldest.
It is omnivorous, meaning it feeds on both animals and plants. It can also devour other crabs and detritus. The creature feeds on snails, clams, turtle hatchlings, lizards and small crabs. Ghost Crab foods also include organic matter.
Source – umces
This is an exceptional creature that possesses the unique ability to store oxygen in airbags located close to its gills. When the creature buries itself in the sand during winter hibernation, it survives on this stored oxygen.
The crab can move on the sand at about 10 miles per hour and is able to change is direction suddenly.
It burrows into the sand at a 45-degree angle for a depth of up to 4 feet. It creates holes of 1-2 inch width. Adult crabs of this family occasionally dig a burrow with two entrance shafts.
The digging activities of these crabs have been reportedly heard even 2 meters (6.5 ft) away.
Ghost crabs generally look for food at night. This is also the time when they dig and repair their burrows. They search beaches for any animal or plant that has been washed ashore. It is rare to see these crabs during daytime as they are mainly active during the night.
Mature male ghost crabs neatly pile the burrowed sand next to their entrance. Young and female crabs do not make a neat pile and the sand they dig out is scattered in all directions beside their entrance. Female crabs can identify a male residence by the neat sand pile and get a mate for themselves.
Younger crabs burrow and make homes in the area of shore that is closer to water. Older crabs are seen to burrow away from water.
These crabs can make three types of sounds, by stroking their right claw on the substratum of their leg, by rubbing their legs together and through their gill chamber.
The animal breathes in through its gills. They periodically make their gills moist with seawater. The gill chamber produces bubbling sounds that can be heard by people who go for tanning at the beach.
The creature retreats to the ocean while laying eggs. The eggs of this creature turn into marine larvae.
This crustacean communicates through sounds with other members of its family. The creature has a unique mechanism on its right claw known as a Stridulating organ. When it strokes this against the bottom of its leg, a squeaky noise is produced. A crab produces this noise to warn other crabs not to enter its burrow. Male crabs also use this sound to attract female mates.
Ghost Crabs can make very good pets if properly looked after. If you are planning to breed these crabs in your home, here are some steps that you have to follow.
- Get a tank of about 20 gallon size. If you want to keep over four crabs in only one tank, it is advisable that you buy one of larger size.
- Fill half of the Ghost Crab tank with thick sand.
- Keep little shells, rocks and small plants in the tank. This will recreate an atmosphere similar to a sea shore and keep your crabs entertained!
- Sift the sand with a small branch or sifter to keep the contents of the tank clean. Do this once every week to rotate fresh sand. The more the crabs you have in the tank, the more frequently you should rotate the sand.
- Use clams and oysters or even old vegetables and fish to your crab. Repetition in diet can tire your crabs and make their survival difficult. Try to find out which foods your crab like. Feed that often to your crab and also balance it with other foods.
Female crabs of this species have a rounded abdominal flap. Thousands of eggs are incubated inside the flap. These are freed into the sea after being matured. The eggs mature into larvae at sea after over two months and then return back to the shore.
Studies have shown the density of Ghost Crab harvesting to be around 3000-5000 every km every year.
Know some of the most interesting facts associated with these creatures.
- These crabs can hold oxygen in their air sacs for about six weeks.
- It wets it gills for two purposes, reproduction and respiration. Occasionally, the crab draws up water from moist sand to moisten its gills.
- The strong hairy legs of this animal make it run very fast and achieve speeds of about 10 miles per hour. This makes this crab the fastest among all crustaceans.
- The crab has club-shaped eyestalks and it boasts of a 360° vision. This helps it see and catch insects that are even in mid-air.
- It has the exceptional capability to shrink back its eyes into grooves located on the frontal area of its shell.
- Contrary to what many think, these creatures cannot swim in water. However, female crabs can keep themselves afloat by turning upside down in water. This is done to let the egg mass under their abdomen respire freely.
- Occasionally, the crabs go out into the sea to protect themselves from predators such as raccoons and birds .
- They devour baby turtles while they hatching out in the sand. The crabs drag the baby turtles into their burrows and eat them up.
- Crabs of this species usually engage in a combat that is non-contact. The combat style is more ritualistic in style and ends in contact in very rare cases.
Want to know how these crabs look like? Here are some useful Ghost Crab Pics. Check out these Ghost Crab photos to get an idea about the appearance of these creatures.
Source – webs
Source – examiner
This crab changes its pace as its speed increases. It can walk for an indefinite period of time on four pairs of legs. At very high speed, it raises its fourth pair off the ground. At highest speed, it uses only the first two pairs of walking legs to keep running.
19 responses to “Ghost Crab (Sand Crab)”
I have some very good examples of ghost crabs that are thousands of years old. They are calcified and only found in the area I live, in Florida. If you are intereted I can send pics. I also have a paper on the subject from a local university.
I’m writing a field report on ghost crabs right now (Ocypode quadrata). I’d be very interested in reading the paper you’ve got =).
this helped me with my science project on ghost crabs thanks
I am a park ranger in Florida. I will be doing a ranger program on ghost crabs soon. A couple of pics of the ghost crab fossils would be great to add to the program! Thank you! Hope you see this comment.
[…] Animal Spot: Ghost Crab […]
I’m interested in seeing more photos of the sand crabs 🙂 would you mind sending me some?
yes, we study bird nest productivity on our Florida State park beaches and ghost crabs have been documented in eating snowy plover eggs,chicks and make attempts at eating adult plovers. They also eat least tern eggs and harass least tern adults on nests. We have some footage on youtube looking at defense mechanisms feigning broken wing to lure ghost crabs away from snowy plover nests.
Question about sand crabs – we have been watching them all week at a NC beach. However, last night there were none to be found. It is close to a full moon – does this have any impact on them? All other nights have been cloudy. If not, any idea why they would be out one night and not another?
My husband and I found one on the coast of Galveston over labor day weekend. It was a pregnant female. She had her thousands of larvae last night. Would love some advice on how to care for all the larvae. We have an established 100 gallon saltwater tank and would hate to put all the larvae in there with all the fish.
These things are cool! Is it possible to spot a Ghost Crab in Maine? I’ve never heard of these types of crabs. Would a ghost crab pinch like an ordinary crab? Thanks.
It’s interesting to hear that this crab is nocturnal. My husband and I have been frequenting the Playalinda Beach near Titusville Florida, and this last month we have been watching many many ghost crabs during the day. We are absolutely fascinated by them! They display all of the characteristics and activities that you mention. We have seen one baby that is almost minuscule and is already displaying the exact behavior of burrowing out its hole. From our chairs we can sometimes see six or seven of them at a time within our vision. They are very very cautious and can move like lightning. We took a video with our phone that shows a crab flinging its load of sand away from its hole. Very entertaining creatures. Thank you for this interesting information.
It was pretty weird to hear they were nocturnal.
Do they have a type of exercise or health for the ghost crab just asking because if they do that is a cool thing!
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I’m originally from Rhode Island but currently living in Central Florida. I was sitting on the Beach in Cocoa and all of sudden I felt a tickle on my toe. I sit up to find a white and yellow crab at my feet. I was so shocked to see this crab so close to me and not to mention how this crab touched my toe. Very interesting and beautiful crab. Came on here to find more info.
How do they flick the sand out of their burrow?
We live near a protected barrier island, and enjoy taking our small whaler out to spend part of a beautiful day, to walk the sandy beach that extends about 20 undeveloped beautiful miles, sit and watch waves without people except for the usual few surfers, locals, and visitors. I saw this crab, who appeared to be alive, with so much color and very large, yet was not moving. I took a photo of it and sent it to the island’s preserve group who studies and protects the island’s wildlife. It is apparently a ghost or sand crab. I could not believe they shed their exoskeletons! It looked larger than one of the normal N. C. sized crabs, but now I know why it looked alive yet was not, nor was it inside it’s body at all, not dead, just the shell left behind. I can attach a photo if you are interested. Thanks for the information on your site that they actually recommended to me, from the Masonboro Island Reserve.
Thank you Debbie! It would be helpful if you’d attach a photo or two of the exoskeleton that you saw.
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Galapagos ghost crab
The ghost crab is a small sand-coloured crab with a box-like body and long eyestalks, found commonly across the beaches of the Galapagos Islands.
Galapagos ghost crab / Painted ghost crab / Cart driver crab
2 – 3 years
Ghost crabs are commonly found on tropical and subtropical sandy shores across the world. There are over 20 species of Ocypode around the world, two of which are in the Eastern Pacific ( Ocypode occidentalis and Ocypode gaudichaudii ). Ocypode gaudichaudii are found all along the eastern Pacific coast of Central and South America.
They are small, red-orange crabs with sandy dots across the back of the carapace (hard upper shell). They have a box-like body, thick elongated eyestalks, and one claw is larger than the other in both males and females for feeding and digging their burrows. Their eyestalks allow them to see 360ᵒ to detect potential predators and prey. Their vision is so precise it allows them to grab insects out of the air. The only blind spot they have is directly overhead. The eyestalks are tipped with horn-like projections called styles.
Their large eyestalks and long slender legs are useful adaptations for terrestrial life. They spend most of their lives in the intertidal zone and are unable to swim. However, females carry their eggs beneath their bodies and frequently enter the water to ventilate the eggs by turning them upside down and then return once ready to release them in the water.
Ghost crabs are the fastest runners of all crustaceans reaching 3.4 metres/second and move more than 300 metres a day when feeding. This has earned them the nickname ‘el carretero’ or the ‘cart driver’ crab in Peru.
Ghost crabs are mainly detritivores but are also active predators and scavengers. They eat organic matter such as algae and animal detritus found among the sand, as well as dead fish, insects, and marine organisms. They leave large numbers of little sand balls across the beach which they have searched through for food. Ghost crabs in the Mediterranean have been known to predate on eggs in sea turtle nests.
Galapagos ghost crabs in Galapagos
Where and when to see them.
Where to see them: They can be seen on the beaches all around the Islands.
When to see them: Ghost crabs can be seen during all hours of the day, but are most active at night when they emerge from their burrows to maintain them or forage.
Shorebirds and gulls are native predators but they are also preyed on by introduced rats, cats and dogs. They could also be at risk from marine plastic pollution.
There are currently no projects specifically focused on the conservation of the Galapagos ghost crab. However, we are working with partners to assess the risks of marine plastic pollution to wildlife as part of our Plastic Pollution Free Galapagos programme .
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"45% of all plastic used along the Pacific coastline of South and Central America is inadequately managed, leaking 1 million tonnes of plastic each year."
We are working with partners across the Eastern Pacific to make Galapagos plastic pollution free once again, identifying the sources and impacts of plastic and supporting innovative solutions.
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Everything You Need To Know About Ghost Crabs: Unveiling The Mysterious Creatures!
Ghost crabs, such cool creatures with their stealthy movements and unique features, have long fascinated beach goers and marine enthusiasts alike.
These nocturnal creatures can be found scuttling across sandy shorelines and burrowing into the coastal terrain, capturing the curiosity of both the casual observer and the seasoned researcher.
We will dig into everything you need to know about these elusive crustaceans, examining their behaviors, biological traits, and distinctive characteristics. Believe it or not, there are actually 20 species of ghost crabs.
Known scientifically as Ocypode quadrata, ghost crabs derive their common name from their pale, translucent appearance and their evasive tendencies.
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They are true masters of camouflage, with their coloration helping them blend seamlessly into their beach environments upon which they reside.
Here is a picture of a crab, so you know what you are looking for. This is a male – notice the larger claw:
This incredible adaptation not only aids them in evading predators but also enhances their efficacy as hunters, whether it be foraging for the diverse array of food sources available to them or strategically capturing prey.
These funny, little guys exhibit remarkable versatility within their behavioral repertoire, engaging in a wide range of activities from digging intricate burrow systems to displaying fascinating social interactions within their colonies.
We can get a deeper understanding of the ecology and importance of these captivating crustaceans as we dig into their habit. As we journey into the world of ghost crabs, prepare to be amazed by the complexities and wonders of these enigmatic creatures.
What’s So Special About Them?
These little crabs are fascinating creatures that catch the eye of beach goers and marine enthusiasts alike. One of the most captivating features of these crabs is their ability to blend in with their sandy surroundings.
This incredible camouflage not only protects them from predators but also allows them to sneak up on their prey with ease. Unfortunately though, their prey is often baby sea turtles who already have an uphill battle for survival.
Another remarkable trait is their speed. These little guys are known for being incredibly fast runners, able to sprint at speeds up to 20 km/h!
They accomplish this through their unique sideways gait, which allows them to move quickly while still remaining low to the ground. This speed, combined with their amazing camouflage, makes them efficient and elusive hunters.
Ghost crabs are also equipped with an interesting set of eyes. Their two large, stalked eyes can rotate 360 degrees, giving them a panoramic view of their environment. This allows them to keep a watchful eye on potential threats while also surveying the landscape for prey.
In addition to their physical adaptations, ghost crabs are nocturnal creatures, venturing out after sundown to scavenge and hunt. They are often seen scurrying along the shoreline, leaving intricate tracks in the sand as evidence of their nighttime activity.
Finally, ghost crabs have an amazing ability to “breathe” both on land and underwater. They possess gills for breathing in water, and specialized structures called branchiostegal lungs, allowing them to extract oxygen from the air.
This remarkable adaptation enables these crabs to thrive in the ever-changing environment of the intertidal zone.
Scientific Name and Sand Crab Comparison
What is the scientific name for ghost crabs.
Ghost crabs often referred to as little white crabs belong to the genus Ocypode within the family Ocypodidae. There are around 20 ghost crab species found around the world, and one of the most common species is Ocypode quadrata , also known as the Atlantic ghost crab.
Are They Sand Crabs?
While ghost crabs are also referred to as sand-colored crabs, it’s essential to note that they are not the same as mole crabs.
Sand crab is a general term, including various crustaceans living in sandy habitats. Yes, ghost crabs can be considered a type of sand crab.
How Do They Compare To Mole Crabs?
In comparison to mole crabs ( Emerita ), these crabs display some differences. Mole crabs are small, rounded crabs with no visible legs, residing in the swash zone of sandy beaches.
On the other hand, ghost crabs are larger, agile, and possess visible legs, which allow them to quickly scuttle across the sand.
Mole Crabs :
- Small and rounded
- Live in the swash zone
- No visible legs
Ghost Crabs :
- Larger and agile
- Live in burrows
- Possess visible legs including four pairs of walking legs
Ghost crabs are not related to stone crabs. Stone crabs ( Menippe spp.) belong to a different family, Menippidae, and are known for their large, strong claws.
They inhabit rocky shores and estuaries, while ghost crabs prefer sandy habitats.
Appearance and Location
These fascinating creatures are known for their unique appearance and quirky behaviors. Let’s take a closer look at the physical attributes and the locations where they can be found.
What Color Are Ghost Crabs?
Ghost crabs display a wide range of colors, typically blending in with their surrounding environment. Their colors can range from a sandy or light brown to a pale yellow or gray.
They might even have hues of blue or green, depending on their specific environment and light. Young ghost crabs are much darker than adult ghost crabs.
How To Tell The Difference Between Male and Female Ghost Crabs
Male ghost crabs are larger than females and have one claw larger than the other. See pic above.
Where Can You Find Ghost Crabs?
Ghost crabs can be found up and down the Atlantic Coast and on many East Coast Beaches. During the summer months you will find them on the white sand beaches including those up north in Rhode Island to North Carolina’s Outer Banks down along both sides of the Sunshine State’s Coastline.
Younger ghost crabs burrow closer to the water’s edge while older ghost crabs burrow higher on the beach. Another interesting fact is the female deposit their fertilized eggs near the surf line.
This allows the winds and tides to help the little guys find something to latch onto as they grow.
Are There Ghost Crabs In Florida?
Absolutely! Ghost crabs can be found throughout the coastal regions of Florida and on both the Atlantic Ocean side of the state and the Gulf Side.
They are commonly found on sandy beaches and dunes, especially in those areas with a significant amount of vegetation. Often in a small hole you might overlook if you aren’t paying attention.
Where Can I Find Ghost Crabs In Florida?
Ghost crabs can be found on many beaches including:
- Panama City Beach: One of Florida’s Panhandle coastal beaches, Panama City Beach, is a go-to spot for observing ghost crabs scuttling along the shoreline.
- Henderson Beach State Park : Along with other local wildlife, located near Destin on Florida’s Gulf Coast, this state park is a great spot on the Panhandle to find ghost crabs.As you walk along the beach, watch for movement on the sand from the corner of your eye.
- St. Augustine Beach: With a rich history and a lengthy stretch of shoreline, St. Augustine Beach offers an ideal environment for ghost crabs to thrive.
- Siesta Key: In addition to its crystal-clear waters, Siesta Key’s pristine sand creates the perfect habitat and is a great place to search for ghost crabs.
Remember that these creatures are nocturnal, making nighttime the best time to spot them moving about with a flashlight.
One Ghost Crab Per Damp Sand Burrow
Ghost crabs are known to occupy damp sand burrows, which they create to escape the sun, predators, or seek shelter during high tide. Each burrow is unique, as it is built by a single crab using its powerful claws.
The burrows can be found scattered along the beach in areas where the sand is moist enough for them to dig. It’s not uncommon to come across these distinct holes that serve as a ghost crab’s humble home.
Interactions with Humans
Can ghost crabs hurt you.
Ghost crabs pose little to no threat towards humans as they are non-aggressive creatures. While their snapping claws might look intimidating, they usually use them for digging burrows and catching prey.
In a rare situation where a ghost crab might feel threatened, it could pinch a human, but the pain would only be mild and short-lived. But you should be careful and respect the crabs’ natural habitat by not intentionally provoking them or disrupting their burrows.
Are Ghost Crabs Good To Eat?
Although ghost crabs are not poisonous, they are generally not one of the top choices for a crab dinner. Compared to larger crabs, their meat is minimal and not as flavorful.
Ghost crabs have a primarily nocturnal lifestyle and feed on various small creatures like insects, smaller crabs, and even sea turtle eggs. Due to their diet and small size, they are not commonly found on plates.
Some cultures do enjoy consuming ghost crabs, especially in coastal regions where they are abundant. The crabs are usually boiled or steamed, similar to the cooking methods for other edible crab species.
For those who decide to give this seafood option a try, it is crucial to catch the crabs sustainably and responsibly to avoid causing harm to the local ecosystems that often include sea turtle nests.
Ghost Crab Hunting
Where can you go ghost crab hunting.
Ghost crab hunting is an exciting activity for the entire family, and it can be done on various beaches across the globe.
These little friends are nocturnal creatures are commonly found along the shores of the Atlantic, Pacific, and Indian Oceans.
Some popular locations for ghost crab hunting include the East Coast of the United States, the Gulf Coast, and Australia’s sandy shores.
What Do You Need To Take With You When Ghost Crab Hunting?
You want to be prepared and ready to enjoy your ghost crab hunting experience. That means the right equipment.
The best way to catch them is to be aware of their nocturnal habits, and hunt at the right time of day or should I say night.
Here are a few essential items to have with you:
- A large bucket or container : To gently hold the ghost crabs you capture.
- A small net or scoop : A tool that helps you catch the crabs without hurting them.
- Comfortable footwear : For walking along the beach and protecting your feet from sharp objects.
- Appropriate clothing : Light, breathable clothing that can get wet or sandy is a good choice.
- A sea turtle-safe flashlight : More on this in the next subsection.
Why You Should Use A Sea Turtle Safety Flashlight/Red Flashlight
When ghost crab hunting at night, it is crucial to protect the local sea turtles by using a sea turtle-safe flashlight , also known as a red flashlight. This type of light has two essential benefits:
- Protecting sea turtles : Sea turtle hatchlings rely on the natural light from the moon to navigate their way to the ocean. Bright, white flashlights can disorient them, leading them away from the sea and into danger. A red flashlight ensures the hatchlings can safely make their journey.
- Preserving night vision : Red light does not disrupt human night vision as much as bright, white light would. Using a red flashlight allows for better visibility of the surroundings without disturbing your night vision – making it easier to spot the elusive ghost crabs.
Ghost crab hunting can be a fun adventure that gives you a chance to observe these fascinating creatures in their natural habitat.
Grab your gear and head to the nearest beach. With a little bit of patience and luck, you may be able to catch these small crabs with fast feet for a fun experience the whole family will enjoy.
You might also enjoy:
Fun Facts About Horseshoe Crabs
Best Places To See Flamingos
Fun Outdoor Adventures Florida
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Denise Sanger lives a life split between her love for fitness and her passion for travel particularly to the BEACH. Denise also has a love of marketing and lives in beautiful Suwannee County, Florida. You can find out more about Denise here: About Denise
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