## 3 Results
### Using Iss to Monitor Mangrove Removal  
Three crab species, namely, _U. arcuata_, _U. borealis_, and _M. banzai_, were observed at the sampling sites within the mangrove region before mangrove removal (Figure 2). After mangrove removal, _U. arcuata_, _U. borealis_, and _U. lacetal_ were also observed. This indicates \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Species** & \(H^{\prime}_{c.k.m.}\) (**S\({}_{l}\)**)** & **Rank** & \(D_{c.k.m.}\) (**S\({}_{l}\)**)** & **Rank** \\ \hline _Helicama doerjesi_ & \(1.2\times 10^{-1}\) & 8 & \(1.4\times 10^{-3}\) & 9 \\ _Helicic fomosensis_ & \(1.2\times 10^{-1}\) & 6 & \(1.1\times 10^{-3}\) & 6 \\ _Mictyris brevidactylus_ & \(4.5\times 10^{-1}\) & 1 & \(1.8\times 10^{-1}\) & 1 \\ _Macrophthalmus banzai_ & \(3.8\times 10^{-1}\) & 2 & \(5.5\times 10^{-2}\) & 3 \\ _Macrophthalmusb reviatus_ & \(1.5\times 10^{-1}\) & 11 & \(2.7\times 10^{-3}\) & 11 \\ _Ocypode ceratophthalmus_ & \(1.5\times 10^{-1}\) & 8 & \(2.8\times 10^{-3}\) & 8 \\ _Ocypode stimpsoni_ & \(1.1\times 10^{-1}\) & 7 & \(4.6\times 10^{-4}\) & 7 \\ _Ocypode sinensis_ & \(1.3\times 10^{-2}\) & 14 & \(2.5\times 10^{-6}\) & 14 \\ _Uica acreatata_ & \(3.5\times 10^{-1}\) & 3 & \(4.1\times 10^{-2}\) & 2 \\ _Uica formosensis_ & \(1.1\times 10^{-1}\) & 10 & \(6.2\times 10^{-4}\) & 9 \\ _Uica laceta_ & \(2.9\times 10^{-1}\) & 4 & \(2.4\times 10^{-2}\) & 4 \\ _Uica perplexa_ & \(1.0\times 10^{-2}\) & 18 & \(1.0\times 10^{-6}\) & 18 \\ _Uica borealis_ & \(1.7\times 10^{-1}\) & 5 & \(3.7\times 10^{-3}\) & 5 \\ _Scopimen longiadactyla_ & \(6.7\times 10^{-3}\) & 20 & \(3.1\times 10^{-7}\) & 20 \\ _Scopimen globosa_ & \(5.4\times 10^{-3}\) & 15 & \(1.5\times 10^{-7}\) & 15 \\ _Scopimen bitympana_ & \(5.7\times 10^{-2}\) & 13 & \(2.7\times 10^{-4}\) & 13 \\ _Seylla serrata_ & \(6.9\times 10^{-3}\) & 15 & \(3.3\times 10^{-7}\) & 15 \\ _Pagurus dubius_ & \(6.5\times 10^{-3}\) & 20 & \(3.2\times 10^{-7}\) & 20 \\ _Digogenes penicillinus_ & \(5.3\times 10^{-3}\) & 18 & \(1.4\times 10^{-7}\) & 18 \\ _Parapagurus digesenes_ & \(1.2\times 10^{-2}\) & 17 & \(1.0\times 10^{-6}\) & 17 \\ _Parapagurus obtusifrons_ & \(2.2\times 10^{-2}\) & 12 & \(4.4\times 10^{-5}\) & 12 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Probabilities of contribution to biodiversity (\(H^{\prime}_{c.k.m. }\) and \(D_{c.k.m. }\)) and each rank by crab species (\(S_{i}\)). that _U. lacetal_ returned to this area after mangrove removal. _U. arcuate_, _U. lacetal_, and _U. borealis_ were generally found in mangroves, salt marshes, and sandy or muddy areas in the Siangshan Wetland. The densities of five ISs and untargeted species in the two regions ( mangrove: A1, A5; non-mangrove: B1, B5) were compared (Figure 3). The density of crab species varied from month to month, but the densities measured in the mangrove region were significantly lower than those in the non-mangrove region. Comparing ISs with untargeted species, the density change of ISs can be seen more clearly from Figure 3. These results indicate that these benthic organisms were forced to migrate from their original habitat to nearby areas because of the spread of mangroves. After mangrove removal, the density of these species gradually recovered to the original level. Specifically, three crab species, namely, _U. arcuate_, _U. lacetal_, and _U. borealis_, returned to the original habitat shortly after mangrove removal. Because fiddler crabs are omnivorous scavengers and eat items such as fish flakes, pellets, dried bloodworms, and brine shrimp in captivity, their feeding habits also played a vital role in the preservation of wetland environments. By sifting through sands, they aerate the substrate and control anaerobic conditions from occurring ([PERSON] et al., 1995) ([PERSON] et al., 1995). Regarding habitat, fiddler crabs prefer a wet environment. This means they are more likely to live along waterways and tidal pools in the wetlands after the tide's ebb. The expansion of mangroves often blocked the waterways, resulting in sediment gradually drying on land.