Abstract
This study is based on the hypothesis that the burrowing habit of fiddler crabs in polluted environment will predispose them to heavy metal contamination. The study was carried out in Eagle Island, a mangrove community. Thirty fiddler crabs ( Uca tangeri ) were captured by hand and butchered into parts and oven dried at 70°C for 48 hours. They were sent to laboratory to determine total hydrocarbon content (THC), Cadmium (Cd), Zinc (Zn) and Lead (Pb) concentrations. The laboratory procedure involved measurement by spectrophotometric method using the HACH DR 890 colorimeter (wavelength 420 nm) for heavy metals and microwave accelerated reaction system (MARS Xpress, North Carolina) for THC. The result indicate that there was no significant difference in THC and heavy metal concentration between crab parts (F 6, 49 = 0.32, P=0.925). However, Zinc had the highest concentration in the crab parts followed by Lead and Cadmium. Zinc was the highest in body tissue (83.57±17.04) mg/L followed by intestine (70.59±1.54) mg/L and ventral shell (67.44±1.1) mg/L. Lead was highest in ventral shell (44.5±34.5) mg/L while Cadmium was highest in carapace (10.02±3.99) mg/L. The order of concentration in the body parts of U. tangeri is Zn>Pb>Cd>THC. THC and Lead were higher in males than in females while Zinc and Cadmium were higher in females. External parts have higher THC, Cd and Pb while internal parts have higher Zn. This result indicates that heavy metals bioaccumulated in fiddler crabs, which can get biomagnified in humans if consumed.
Highlights
Crabs play unique role in mangrove forest and other coastal systems because they are ecosystem engineers (Nobbs and Blamires, 2015)
2.1 total hydrocarbon content (THC) and heavy metal concentration in body parts of fiddler crabs (Uca tangeri) The result (Table 1; Figure 3) indicates that there is no significant difference in THC and heavy metal concentration between parts (F6, 49 = 0.32, P=0.925)
Another study indicated that claw tissue, gill and gut of Goniopsis pelii had high Zinc concentration (Numbere, 2019)
Summary
Crabs play unique role in mangrove forest and other coastal systems because they are ecosystem engineers (Nobbs and Blamires, 2015). Rhizophora seedlings have torpedo shape and a pointed tip which pierces the soil after detachment from the tree to enable speedy growth (Ismail et al, 2010). This situation does not always occur especially when seeds drop on hard soil or on water surface during high tide, the crabs comes to the rescue by burying the seeds. There are different crab species in the coastal areas of the Niger Delta, but the two most common ground-dwelling crab species are the West African Red mangrove crabs (Goniopsis pelii) and the Fiddler crab (Uca tangeri)
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