Assessment of Marine Meiobenthic Assemblages in Transplanted Mangrove Forests along the Inner Gulf of Thailand

Abstract

Two transplanted mangrove forests in the Inner Gulf of Thailand were selected for this study. One was on the mud flat in Samut Songkhram Province and another was on sand flat in Phetchaburi Province. There were differences in species and ages of mangroves transplanted in the study sites. Sediment samples were collected randomly for analyses of meiobenthic communities and granulometric properties. Samples were collected from under 7-year old & 4 - year old Avicennia alba and 4 - year old Sonneratia caseolaris stands in Samut Songkhram site and from 7 - years & 1- year old Rhizophora apiculata and 7 - year old Avicennia alba stands. Average meiobenthic densities (ind.10 cm-2) varied, ranging from 452.62 ± 23.24 - 654 ± 59.42 in Samut Songkhram and 382.96 ± 45.38 - 627.30 ± 56.89 in Phetchaburi sites. There were significant differences in their densities among samples. Higher densities occurred in samples under older transplanted tree stands in both sites. Also, within stands of the same age of transplanted trees, meiofaunal average densities were different between mangrove species. In Samut Songkhram site, average density in Avicennia alba samples (540 ± 42) was higher than that in Sonneratia caseolaris samples (453 ± 23). Also, this value in Avicennia alba samples (627 ± 57) was higher than that in Rhizophora apiculata samples (587 ± 44) in Phetchaburi site. For meiobenthic composition, there were a total of eight taxa recorded, namely nematodes, copepods, polychaetes, oligochaetes, halacarids, tardigrads, kinorynchs and tanaids. According to an average percentage of their total abundances in Samut Songkhram and Phetchaburi mangrove forests, nematodes were the most dominant with values of 92.74 ± 1.0 and 93.21 ± 0.76%, while harpacticoid copepods were second with values of 6.51 ± 0.47 and 6.42 ± 0.69 in each sites, respectively. Analysis of meiobenthic assemblages using non-parametric multi dimensional scaling showed differences between sampling sites and transplanted mangrove species. Minor meiobenthic taxa, such as oligochaetes, halacarids, tardigrads, kinorynchs and tanaids, also showed significant differences which could be related to habitats, tree species and age of mangrove stand. Results of the present study reveal that meiobenthic assemblages can be used to detect subtle environmental effects and are, therefore, ideal organisms to use to monitor the mangrove recovery.