Soldier Crab Research Articles

Burrow Morphological Characteristics of Soldier Crab (Dotilla myctiroides) on the Libong Island, Koh Libong Subdistrict, Kantang District, Trang Province, Thailand

Dotilla myctiroides, the soldier crab, digs burrows in sand flats and extracts nutrients from sediment. The present study investigated the burrow morphology of this soldier crab, at Laem Juhoi Beach, Libong Island, Koh Libong Subdistrict, Kantang District, Trang Province, Thailand. Randomly selected burrows were examined by injecting molten paraffin into them. The crab found inside a burrow was collected and measured for its carapace length. The shapes of the complete burrow casts were identified, and various morphological characteristics of the burrow casts were recorded. A total of 84 burrows were identified, all of them were the I-shaped or single-tube burrows. The burrows were categorized into two groups based on the burrow opening diameter: the <12 mm group and the ≥12 mm group. The burrow opening diameter ranged from 7.50 to 20.10 mm while the end diameter at the burrow bottom ranged from 8.40 to 21.00 mm, and the total length of the burrows ranged from 27 to 206 mm. The carapace length showed a significant correlation (p<0.05) with the burrow opening diameter in both groups. Additionally, the burrow opening with a diameter <12 mm group had significantly greater hole distances than the burrow opening with a diameter ≥12 mm group (p<0.05). The observed variations in hole distances suggest potential differences in ecological and behavioral factors that influence the burrow morphology of D. myctiroides in distinct size categories.

Influence of salinity on the horizontal distribution of soldier crab Mictyris guinotae in a subtropical river in Japan

ABSTRACT The horizontal distribution of Mictyris guinotae was studied in relation to gradients of salinity and sediment characteristics in sandy flats between 0 and 8.2 km from the mouth of a subtropical river. Lower salinity tolerance was also tested at seven salinity levels (0, 2, 4, 8, 12, 24 and 32) by a survival experiment for 14 days. Environmental clines were found in salinity but not in sediment characteristics. The upper limit of the occurrence of crab was 5.07 km upstream where seawater could reach during the spring flood tide. The densities of age-0 crabs tended to be higher at lower stations (0–0.65 km upstream), suggesting more recruits settle near the river mouth. Carapace length was significantly larger in the upper section (2.50–5.07 km upstream) in which salinity fluctuated or remained low (<10) for longer periods. It is unlikely that low salinity has a negative effect on post-larval growth. In contrast, body size was smaller in the lower section, possibly due to the effect of density. Some individuals died at the end of the experiment at salinity ≤12. The upper limit of appearance was explained by the salinity of riverine water and low salinity tolerance of the crab.

Burrowing-site selection by the soldier crab Mictyris guinotae Davie, Shih &amp; Chan, 2010 (Decapoda: Brachyura: Mictyridae)

AbstractThe soldier crab Mictyris guinotae Davie, Shih &amp; Chan, 2010 inhabiting sandy tidal flats in the Ryukyu Is., Japan, are deposit feeders in two regions: its upper habitat where it burrows and the shoreline. The crabs usually migrate between these two regions during the period of emergence at the daytime and night-time low tide. The aim of this study was to determine which kind of sediments are chosen by the crabs when burrowing. Experiments designed to investigate burrowing-site selection revealed that the crabs preferably burrowed in sediment that had been conditioned through feeding by conspecific crabs, but not in sediment that had been conditioned by conspecific crabs walking on its surface. Moreover, the crabs never showed any preference for burrowing in sediment that had been conditioned through feeding by the competitor fiddler crab Austruca perplexa (H. Milne Edwards, 1852); both soldier (prey) and fiddler (predator) crabs sympatrically inhabit the tidal flat, but segregate their habitats with a transition area. These results suggest that chemical cues in sediment conditioned through feeding by conspecific soldier crabs affect where crabs burrow.

Soldier crab (Mictyris brevidactylus), a resource of nutritional food material

ABSTRACT The chemical composition and nutritional quality in the meat of soldier crab (Mictyris brevidactylus) were analysed and evaluated. Soldier crab was rich in phosphorus, calcium and magnesium, and also was a good mineral source of copper, iron and zinc. The major fatty acids were docosahexaenoic acid (22:6n-3), eicosapentaenoic acid (20:5n-3) and palmitic acid (16:0). Crab meat was an n-3 polyunsaturated fatty acids (PUFAs)-rich food, as the ratio of n-3/n-6 PUFAs was 3.10. Glutamic acid (204 mg/g of protein) was the dominant amino acid in soldier crab protein, followed by glycine (162 mg/g), aspartic acid (100 mg/g), lysine (87 mg/g), leucine (84 mg/g) and alanine (82 mg/g), and the contents of methionine, histidine, serine and cysteine were low. Tryptophan and methionine were the first and second limiting amino acid, respectively, in soldier crab. The ratio of essential to non-essential amino acids was 0.58. The results indicated that soldier crab could be an ideal resource of nutritional food material with a desirable chemical composition.

Concept Design of the Underwater Manned Seabed Walking Robot

In this paper, a novel concept designed of a multi-legged underwater manned seabed walking robot is presented. The robot will be used in both shallow water current (1–2 m/sec) and deep water up to 500 m. It is powered by an external electric power source through tether cable. It walks on the seabed with six legs, which makes it distinct from conventional screw-propelled underwater robots. It can walk calmly without making the water turbid. Two anterior arms act as manipulators. All leg joints and manipulators are controlled by Brushless Direct Current Motors. Motivation for this concept comes from soldier crab that walk mostly forward and has an egg-shaped body. It is operated by a pilot sitting in a pressurized cabin, and promptly control operations of the robot and manipulator. Preliminary design of the pressurized cabin, using an empirical formula, “ASME PVHO-1 2007” standard, and validation was carried out through ANSYS Workbench. Hydrodynamic forces acting on the robot body and legs are utilized to withstand the water current and external forces to adjust legs and body posture for stability. Buoyancy rules are employed to control its rising and diving motion. All key technologies employed in the development of the robot and their approaching methods are explained. It will provide a safe operation space for humans in underwater operations.

Cellulose digestion abilities determine the food utilization of mangrove estuarine crabs

Food utilization and cellulose digestion abilities of six crab species were examined to clarify the mechanisms driving trophic and spatial segregation among species within a mangrove estuary on the Urauchi River, Iriomote Island, southern Japan. Dual stable isotope signatures (δ13C and δ15N) of dominant crab species inhabiting three microhabitats (bare sandy flat, bare muddy flat and mangrove forest) showed that most crab species, such as the soldier crab Mictyris guinotae and fiddler crab Gelasimus jocelynae, primarily assimilated microphytobenthos (MPB), while the sesarmid crab Parasesarma bidens inside the mangrove forest substantially utilized cellulose-rich mangrove detritus and leaf litter. Analyses of the chemical properties of sediment organic matter indicated that it comprised mainly mangrove detritus, which was more abundant on the muddy flat and in the forest compared to the sandy flat. In contrast, the standing stocks of MPB were at consistently low levels in each microhabitat, particularly inside the mangrove forest than on the bare flats. The enzyme assay revealed that P. bidens exhibited much higher cellulase activity, enabling the species to utilize refractory mangrove materials, whereas the other crab species with lower cellulase activity were highly dependent upon nutritious and easily degradable MPB, although the amount of the latter was largely limited in the mangrove estuary. These findings suggested that the assimilation efficiency of cellulose-rich plant materials as a carbon source, dependent upon the level of cellulase activity, essentially controls trophic and spatial segregation among crab species in the mangrove estuary. Given the greater biomass of plant detritus, it is likely that P. bidens plays an integral part in establishing the detritus food chain in the mangrove ecosystem through the effective digestion/assimilation of cellulose materials.

Soldier crab paleo-ichnology and its preservation in beach rock along the Pilbara Coast, Western Australia: its geoheritage significance

Ichnofossils, although small-scale geological features, can be of geoheritage significance. The Western Australian soldier crab (Mictyris occidentalis Unno 2008) presents an unusual and unique association between the crab and its ichnology because, as the species progresses through life, its behaviour becomes more complex and its traces commensurably more varied. The links between crab ichnology, life stage, behaviour, and environment are so direct that where traces are preserved they can be used to interpret fossil crab sizes, population structures, behaviour and paleo-environment. In this context the ichnofossils comprise important paleo-ecological and paleo-environmental indicators. Middle Holocene soldier crab ichnofossils occur in 5000 year-old beach rock at Port Hedland, Western Australia. The ichnofossils include rosettes, pustules, pellet-roofed tunnels, back-filled burrows and swirl lamination, air cavities and tidal-current-degraded discard pellets. They provide information on soldier crab population sizes and behaviour, and the nature of the environment along middle Holocene shores. The ichnofossils are of geoheritage significance in their own right for the paleontological and paleo-environmental information they present, however, given the rarity of their preservation, and the location of well-developed beach rock largely restricted to the arid Pilbara Coast, these ichnofossils are an uncommon and significant geological tool for use in paleo-environmental, paleo-ecological and paleoclimate reconstructions. They are of geoheritage significance because of their diagnostic signatures and rarity of occurrence. The limitations of current classifications of traces and ichnofossils, owing to restricted definition of terms, are highlighted by these ichnofossils as several ichnological products in the complex range of soldier crab traces are not possible to classify.

Occurrence of unusual swarm of soldier crab, Dotilla myctiroides (H. Milne Edwards, 1852) in Gulf of Mannar, Southeast Coast of India

Occurrence of unusual swarm of soldier crab, Dotilla myctiroides (H. Milne Edwards, 1852) in Gulf of Mannar, Southeast Coast of India

CDNA sequences of GHF9 endo-β-1,4-glucanases in terrestrial Crustacea

This study aimed to sequence and identify a glycosyl hydrolase family 9 (GHF9) endo-β-1,4-glucanase expressed in the midgut gland of the herbivorous gecarcinid land crab, Gecarcoidea natalis. Hence this would explain the gene responsible for the production of previously purified and characterised endo-β-1,4-glucanases. Three different transcripts, two complete and one partial were sequenced from cDNA and an open reading frame of 1383bp was produced. Translated, this would produce a putative protein of 460 amino acid residues, including a 16 amino acid residue signal peptide. The mature protein (without signal peptide) is predicted to have a molecular mass of 47.6–47.7kDa; this closely matches the molecular mass (47.4kDa) of one of the three endo-β-1,4-glucanase/lichenase enzymes purified previously from G. natalis. It is therefore proposed that the gene described here encodes one of the previously characterised enzymes. The presence of multiple transcripts suggests gene duplication. To confirm that the gene is widely expressed within the Crustacea, cDNA encoding a GHF9 endo-β-1,4-glucanase was also sequenced in diverse crustaceans, the deposit feeding soldier crab, Mictyris platycheles and the terrestrial hermit crabs, Coenobita purlatus and C. brevimanus. An open reading frame of 1356bp was sequence from M. platycheles, while an incomplete open reading frames of 1384 and 1523bp were respectively sequenced from Coenobita brevimanus and C. perlatus. The midgut gland of M. platycheles contained activity (0.704±0.218μmol reducing sugars produced. min−1·mg−1 tissue wet weight) of a 26.3±0.3(5) endo-β-1,4-glucanase isozyme (determined from activity staining). These species, particularly M. platycheles does not consume and digest significant amounts of plant cellulose. This implies that the ancestral enzyme is not a cellulase, but rather it may be involved in hydrolysing cellulose like polysaccharides within other organisms such as algae.

Microhabitat differences in crab assemblage structures in a subtropical mangrove estuary on Iriomote Island, southern Japan

Crab assemblage structures in sandy flat, muddy flat and mangrove forest microhabitats in a mangrove estuary of the Urauchi River, Iriomote Island, southern Japan, differed clearly among the three microhabitats, species and individual numbers being greater inside the mangrove forest than on the flats. A similarity index showed distinct differences in species composition among the microhabitat assemblages, primarily due to the differential distributions of dominant species, such as the soldier crab Mictyris guinotae, sentinel crab Macrophthalmus convexus and sesarmid crab Perisesarma bidens. A canonical correspondence analysis indicated that the differences likely arose from among-microhabitat differences in the physical environment, the mangrove forest being characterized mainly by structurally complex mangrove roots, lower soil porewater temperatures and higher relative substrate elevation, the sandy flat by lower organic content of the sediment and higher porewater oxygen amount, and the muddy flat by higher levels of sediment water and organic material. The findings suggested that microhabitat-related physical differences are important factors determining crab distribution patterns in mangrove estuaries.

Population dynamics of the soldier crab Mictyris guinotae (Brachyura: Mictyridae) in Amparu Tidal Lagoon on Ishigaki Island, Japan

The life history of the soldier crab Mictyris guinotae in Amparu Tidal Lagoon on Ishigaki Island, Japan was investigated through population measurements with detailed size classifications. Surveys and measurements were carried out at 15 sampling points every 2 weeks during the 4-month incubation season starting in December 2005, and twice in April and in June 2006 when juveniles started and finished settlement, respectively, in the lagoon. Supplementary measurements were conducted every month from December 2006 to May 2007 to corroborate the results of the first experiment and to examine the growth rate of the juvenile population.The results showed that (a) the peak of incubation was from mid-January to mid-February, and the season of juvenile settlement was April to early June, which means that the duration of larval life in the ocean was about 2 months; (b) juveniles were distributed widely in the lagoon, and adults clustered to the west and south of the lagoon where the bed sediment was relatively fine with high ignition loss; (c) the survival rates of adults and juveniles in 1 year were 0.73 and 0.17, respectively, and the mean longevity of adults was about 3.7 years; (d) reproduction efficiency from eggs to juveniles was about 0.0040, which is much smaller than the survival rate of juveniles as well as adults, which means that the propagation of M. guinotae is mainly controlled by the condition that the larvae experience in the ocean.

Circatidal activity rhythms in the soldier crab Mictyris guinotae

Mictyris guinotae is endemic to the Ryukyu Islands, Japan. During low tide, the crabs emerge onto the tidal flat to feed, and then burrow into the sand before the incoming tide. They feed in droves during daytime, but separately at night. Under constant conditions without sand sediment, crabs exhibited a bimodal daily activity pattern, with a free-running period of ~12.8 h, comprising an active phase of ~11 h alternating with a resting phase of ~1 h, and a lag of ~3 h between the activity peak and low tide. Crabs were more active during the notional night-time than during the notional daytime. In crabs placed in an arena with sand sediment, a free-running period of ~12.8 h comprised a surface-active phase of ~3 h and a subsurface resting phase of ~9 h, with a lag of 1.5 h. In contrast to the non-sand condition, more crabs were active during daytime than during night-time. Thus, M. guinotae possesses circatidal and circadian locomotor rhythms that are modified by the sediment.

Visual image of neighbors to elicit wandering behavior in the soldier crab

The soldier crab appears in great numbers and feeds while wandering during daytime low tide. When they see an approaching object, they screw themselves into the sand. The mechanism of formation of mass wandering has not been clarified. In this study, to investigate if the soldier crabs use visual images of neighbors as a stimulus for wandering, dummy crabs were presented to crabs. In the experiments, one, two, four, or eight dummies were placed in a circle on a sand arena. Each crab was placed in the center of the arena and observed whether it burrowed into the sand or wandered. The proportions of wandering individuals in each experimental treatment were compared with the expected value. Significantly more crabs were wanderers when only two and four dummies were present. This result suggests that soldier crabs chose burrowing or wandering depending on visual image of the distribution of the neighbors.

Collective behavior of soldier crab swarm in both ring- and round-shaped arenas

In study of collective behavior, though collective foraging behavior against surroundings is one of the most vivid examples about how animal group responses to external environment, relative experiment is rare. In this paper, we show an experiment with respect to collective foraging using a swarm of soldier crabs Mictyris guinotae, which live in the tideland and can form large swarms. We recorded the behaviors of soldier crab swarms with 10, 20, 30, 40 individuals in experimental arenas. Thanks to markers attached to crabs' shells and image-processing software, we obtained time series of individuals' position during 30 min. As a consequence, we found the soldier crabs form densely swarm to some extent in the ring-shaped experimental arena. Moreover, when we calculated the time between direction changes of the swarm, we found that it followed power-law distribution, containing very long moves. Such movement pattern is frequently found in foraging behavior of single animals. Our results, therefore, suggest that collective swarms show a type of foraging behavior as a single group.

The complete mitogenome of the soldier crab Mictyris longicarpus (Latreille, 1806) (Crustacea: Decapoda: Mictyridae)

The Mictyris longicarpus (soldier crab) complete mitochondrial genome sequence is reported making it the first for the family Mictyridae and the second for the superfamily Ocypodoidea. The mitogenome is 15,548 base pairs made up of 13 protein-coding genes, 2 ribosomal subunit genes, 22 transfer RNAs and a non-coding AT-rich region. The soldier crab mitogenome gene order is characteristic of brachyuran crabs with a base composition of 36.58% for T, 19.15% for C, 32.43% for A and 11.83% for G, with an AT bias of 69.01%.

Complex Ichnology of the Western Australian Soldier Crab Mictyris occidentalis Unno 2008—The Rosetta Stone to Interpreting Its Population Age Structure and Age-Related Behavior

The Western Australian soldier crab, Mictyris occidentalis Unno 2008, presents an unusual association between crab and ichnological features. As the crab progresses through life, its behavior becomes more complex and its ichnological products more varied: from small, sandy clots and pustules, progressing to various types of shallow, pellet-roofed feeding tunnels and then, when emergent and swarming, eruption structures (exit holes), discard feeding pellets, and re-entry rosettes. The size of tunnels, exit holes, pellets, and re-entry rosettes are commensurate with the size of the crabs. The link between crab ichnological product, life stage, and behavior is so direct that its ichnological features can be used as a surrogate to reconstruct population age structure and age-related behavior. In effect, as it progresses through life from being wholly infaunal to alternating infaunal and epifaunal with swarming behavior, autoecologically and palaeoecologically, the ichnology of the Western Australian soldier crab is a “Rosetta Stone” (used metaphorically, for a series of inscriptions on the tidal flat surface) that can be interpreted to determine species occurrence and population age structure, unravel age-related behavior, and, if preserved as ichnofossils, interpret fossil crab sizes, population structures, behavior and palaeoenvironment.

A new species of Mictyris Latreille, 1806 (Crustacea: Decapoda: Brachyura: Mictyridae) from the Andaman coast of Thailand, with notes on its ecology and behavior.

A new species of soldier crab (genus Mictyris Latreille, 1806) is described from the Andaman Sea coast of Thailand. Mictyris thailandensis sp. nov. differs morphologically from its described congeners by its pale plain colouring, the differently shaped apex of the male first gonopod, and by chela features. It also has significant genetic divergence (cytochrome oxidase I > or = 11.95%) from other described species.

Collision-based computing implemented by soldier crab swarms

Collision-based computing schemes are implemented using propagating and interacting localisations. When two or more travelling localisations collide, they may reflect or merge into a new localisation. Presence/absence of a localisation in a specified site of a physical space represents True/False values of Boolean variables. Incoming trajectories symbolise inputs and outgoing trajectories are outputs. Logical gates are implemented by collisions between the localisations. We demonstrate how primitives of the collision-based computing can be implemented using swarms of soldier crabs in laboratory experiments. Soldier crabs, Mictyris guinotae, exhibit coherent collective behaviour on an intertidal flat at a daytime low-tide period. The soldier crabs' swarm often moves as a single entity with definite yet dynamically changing boundary. We utilise swarms of soldier crabs to implement a Boolean logic gate. The gate has two inputs and three outputs. Values of the inputs and outputs are represented by crab swarm size or a proportion of crabs in the input and output channels. We demonstrate that the gate performs logical conjunction and negation.

1A1-B03 ゆらぎ指標に基づいた生物の群行動解析(バイオミメティクス・バイオメカトロニクス(1))

This paper analyses the group behavior of soldier crab. In particular, we adopt method of animal-robot interaction and analyses based on fluctuation index. In the experiment, the mobile object interacts with sixteen soldier crabs. From experiment analyses, it was found that collective behavior of crabs has scale free. And this behavior is not affected by the mobile object.

2P1-I08 動的ネットワークとしてのミナミコメツキガニの群れ(スワームロボティクス)

2P1-I08 動的ネットワークとしてのミナミコメツキガニの群れ(スワームロボティクス)