Fiddler crab

Males of many species defend resources to attract females. Surprisingly, defense of multiple female breeding sites (e.g., nests or burrows) appears to be rare, primarily reported in fish and birds. In fiddler crabs, burrows are a vital resource for reproduction and survival. Both sexes defend individual territories centered on a single burrow. We examined burrow acquisition and defense in Uca capricornis to test whether males defend multiple burrows as a novel strategy to acquire additional mates. When crabs were experimentally forced to acquire a new burrow, females often settled into an empty burrow near resident males. We documented more empty burrows around males than expected by chance and, in addition, larger males had a greater proportion of empty burrows in their immediate vicinity. We experimentally introduced crabs into empty burrows next to focal males: newly introduced males were soon evicted, whereas females were courted and stayed. These results suggest that male U. ca...

Fiddler crabs are abundant, semi-terrestrial crustaceans inhabiting tropical, subtropical and warm temperate coasts worldwide. Some species build above-ground sedimentary structures at or near the opening to their burrows. The functions and shapes of these constructions vary interspecifically and according to the sex of the builder. Here, we compile the dispersed reports on these structures, suggest uniform naming for different shapes, review explanations for their functions and explore associations between the attributes of builders and their structures. We found that 47 fiddler crab species build at least one type (or subtype) of structure, including chimneys, hoods, pillars, semidomes, mudballs, and rims. Sedimentary structures show a strong association with sediment type as well as builder front type, genus and sex, but not with fiddler crab clade. Experimental studies have revealed distinct, sometimes multiple functions for some of these structures (e.g., female attraction, red...

Quantification of mangrove crabs is notoriously difficult. Several techniques have been applied in the past, but have rarely been tested. This paper looks at the use of burrow counts (BUR), binocular counts (BIN) and excavation (EX) for quantifying the fiddler crab Uca annulipes (H. Milne Edwards). Fieldwork took place at Maruhubi mangrove (Zanzibar, Tanzania). Twelve 1 m2 quadrats were assessed on one spring cycle and one neap cycle. The results showed a strong correlation between carapace width (CW) and burrow diameter (BD), namely CW (mm) = 1.37BD (mm) -0.64 (r2=0.98; p-2 (EX), 43.3 m-2 (BIN) and 104.8 m-2 (BUR). Of these, 37% (EX), 19% (BIN) and 42% (BUR) were juveniles (U. annulipes. Whilst binocular census may be most appropriately carried out on spring tides, burrow quantification may be better on neap tides. A major reason for BIN underestimates and BUR overestimates were discrepancies in juvenile counts. Thus, 28% (spring) to 39% (neap) of adults, but 72% of excavated juven...

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

Density and distribution patterns of two species of fiddler crabs, Uca annulipes (H. Milne Edwards, 1837) and U. vocans (Linnaeus, 1758) were studied on Pulau (=Island) Hantu Besar, Singapore. Twenty-five and 26 1m 2 quadrats were sampled at the upper and lower shore levels of the lagoonal beach. Sediment samples from each quadrat were analysed for %sand, %mud and %organic content. A two-way analysis of variance (ANOVA) of crab density against species and shore level position showed the interaction term, 'Species × Shore level' to be significant (p 0.05). After this interaction term was removed from the model, only the main factor, 'Species', was significant (p<0.05). Subsequent ANOVAs showed U. annulipes was significantly (p<0.05) associated with sediments containing higher sand content regardless of shore level, and U. vocans was significantly (p<0.05) associated with sediments that had higher mud content. These results provide quantitative data to support...

Spatial and temporal trends in pore water geochemistry and sediment microbial community structure are compared at three intertidal sites of a saltmarsh on Sapelo Island, GA. The sites include a heavily bioturbated, unvegetated creek bank, a levee with dense growth of Spartina ...

Mating signals are often directed at numerous senses and provide information about species identity, gender, receptiveness, individual identity and mate quality. Given the diversity of colourful body patterns in invertebrates, surprisingly few studies have examined the role of these visual signals in mate recognition. Here, we demonstrate the use of claw coloration as a species recognition signal in a fiddler crab (Uca mjoebergi). Furthermore, we show that distinct carapace colour patterns inUca capricornisenable males to discriminate between their female neighbours and unfamiliar females. This is the first empirical evidence of the social importance of colour markings in fiddler crabs and the first example of visually mediated species and neighbour recognition in invertebrates other than insects.