Effects of bioturbation of fiddler crabs in relation to the growth of mangrove saplings (Rhizophora apiculata) in a mangrove reforested area

Bioturbation is an important process in the soft-bottom ecosystem to return nutrients in the environment. This study aimed to evaluate the effects of bioturbation activities on the growth of mangrove saplings (Rhizophora apiculata). A caging experiment using a total of 16 plots each measuring 1 × 1 m containing two mangrove saplings in each plot (N=32 saplings) with eight caged and eight uncaged plots were placed randomly in Guang-guang, Davao Oriental, Philippines. The set-up was monitored for five months. The length of internode, number of nodes, leaves and length of branches of the saplings were measured and counted. In addition, the number of mounds, holes and fiddler crabs were also counted in the uncaged, marked plots to determine their activities. Result of the comparison of the number of holes, mounds, and fiddler crabs showed high significant differences with the number of holes in the sediment being greater in the uncaged set-ups (holes > mounds = fiddler crab; P<0.001). Further, the result based on t-test showed high significant differences in terms of internode length (uncaged=35.68 cm vs caged=33.19 cm; t-value=-5.15; P<0.001), number of nodes (uncaged=8.70 vs caged=6.75; t-value=-8.55; P<0.001), and branch length (uncaged=6.0 cm vs caged=5.24 cm; t-value= -2.73, P=0.008) as well as for the number of leaves (uncaged=7.12 vs caged=6.0 leaves; t-value=-4.83, P<0.001). The study concludes that bioturbation by fiddler crabs can affect the growth of saplings.