Impact of Human Disturbance on Fiddler Crab (<i>Uca tangeri</i>) Burrow Morphology, Distribution and Chemistry at Eagle Island, Niger Delta, Nigeria

Fiddler crabs are described as ecosystem engineers because of their burrow constructing ability. It was hypothesized that human activity will impact crab burrows. The study area was delineated into lowly, medium and highly impacted plots. Crab holes were randomly counted and their width, length and surface area estimated. Burrow soils were collected and analyzed for Cadmium (Cd), Lead (Pb) and Zinc (Zn) using spectrophotometric method (HACH DR 890 colorimeter). The result indicates that burrow width was significantly different between impacted plots (P < 0.05). Lowly impacted plot had the largest width while highly impacted plot had the smallest width. In contrast, there was no significant difference in burrow length (P > 0.05), but highly impacted plot has the longest length while lowly impacted plot has the shortest length. Again, the surface area of crab burrow varies significantly (P < 0.05), and lowly impacted plot had the largest area (507.95 ± 61.84 cm2) followed by medium (390.30 ± 57.65 cm2) and high (265.16 ± 30.85 cm2) impacted plots. Similarly, lowly impacted area has more number of burrows (n = 55) followed by medium (n = 30) and highly (n = 23) impacted plots. Highly impacted plot had the highest Cd and Pb concentration whereas lowly impacted plot had the highest Zn concentration. This implies that burrow morphology and chemistry exemplify the level of anthropogenic impact.

Burrow morphology of Uca uruguayensis and Uca leptodactylus(Decapoda:Ocypodidae)from a subtropical mangrove forest in the western Atlantic

The continuous excavation of burrows by fiddler crabs generates bioturbation in the sediment,which can be estimated from burrow morphology.The aim of the present study was to describe the burrow morphology of Uca uruguayensis and U.leptodactylus and its relationship with demography of resident individuals and to estimate the level of bioturbation in the sediment generated by each species.For all individuals from each of the 2 species,sex was determined and the carapace width(CW;mm)measured.Burrows were characterized according to burrow diameter(BD;mm),maximum burrow depth(MBD;mm)and burrow volume(BV;cm^(3)).The density of each species in the study area was also evaluated.In both species,the males were larger and occupied burrows with higher BV compared to females.Differences between sexes in relation to the burrow characteristics might reflect sexual dimorphism within the group and are probably related to the fact that males use the burrows for mating.BD and BV showed significant positive relationships with the size of resident crabs.The amount of sediment removed per burrow was estimated from mean BV:10.78 cm^(3)of sediment/burrow for U.uruguayensis and 12.38 cm^(3)of sediment/burrow for U.leptodactylus.Despite the density and depth differences between the 2 species,the similarity in burrow volume suggests that U.uruguayensis and U.leptodactylus present the same importance in terms of the bioturbation process.Burrow morphology is highly associated with characteristics of the occupant,although extrinsic factors should also be considered,and its description can provide estimates on the bioturbation generated by Uca species in mangrove forests.