Abstract
In tropical regions, different species of fiddler crabs coexist on the mangrove floor, which sometimes makes it difficult to define species-specific habitat by visual inspection. The aim of this study is to find key environmental parameters which affect the distribution of fiddler crabs and to determine the habitats in which each species was most abundant. Crabs were collected from 19 sites within the mudflats of Sepang-Lukut mangrove forest. Temperature, porewater salinity, organic matter, water content, carbon and nitrogen content, porosity, chlorophyll content, pH, redox potential, sediment texture and heavy metals were determined in each 1 m2 quadrate. Pearson correlation indicated that all sediment properties except pH and redox potential were correlated with sediment grain size. Canonical correspondence analysis (CCA) indicated that Uca paradussumieri was negatively correlated with salinity and redox potential. Sand dwelling species, Uca perplexa and Uca annulipes, were highly dependent on the abundance of 250 μm and 150 μm grain size particles in the sediment. Canonical Discriminative Analysis (CDA) indicated that variation in sediment grain size best explained where each crab species was most abundant. Moreover, U. paradussumieri commonly occupies muddy substrates of low shore, while U. forcipata lives under the shade of mangrove trees. U. annulipes and U. perplexa with the high number of spoon tipped setae on their second maxiliped are specialized to feed on the sandy sediments. U. rosea and U. triangularis are more common on muddy sediment with high sediment density. In conclusion, sediment grain size that influences most sediment properties acts as a main factor responsible for sediment heterogeneity. In this paper, the correlation between fiddler crab species and environmental parameters, as well as the interaction between sediment characteristics, was explained in order to define the important environmental factors in fiddler crab distributions.
Highlights
Fiddler crabs are common benthic macrofauna in intertidal mudflats of mangrove forest of south-east Asia [1]
U. rosea and U. triangularis were positively correlated with high concentrations of nitrogen content and negatively correlated with very fine sand particles (63 μm)
Pearson correlation showed a negative correlation between crab density and chlorophyll content and correspondence analysis (CCA) results indicated that none of the fiddler crab species were correlated with chlorophyll content
Summary
Fiddler crabs are common benthic macrofauna in intertidal mudflats of mangrove forest of south-east Asia [1]. These crabs stay near their burrows into which they can escape from predators, as well as refuge from high temperatures and desiccation [2]. Fiddler crabs have high tolerance to low oxygen level, high temperatures and varying salinities [3]. From 97 identified species of fiddler crabs, eight species have been recorded from west Peninsular Malaysia [4,5]. Seven species of fiddler crabs including Uca Paradussumieri, Uca rosea, Uca trinagularis, Uca forcipata, Uca perplexa, Uca annulipes and Uca vocans were distributed unevenly among the intertidal mudflats. There were some degrees of overlap between species territories as their habitats were not visually discernible
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