Macrobenthic fauna community and optimum sampling protocol for the lower part of inner Songkhla lake, southern Thailand

Aims of the investigation were to determine the species diversity and abundance, and the optimum sampling protocol for macrobenthic fauna at the lower part of the Inner Songkhla Lake. The study was conducted from February 1999. A total of seven phyla and 59 species (excluding polychaete larvae) were identified: Annelida (58 species), Crustacea (56 species), Mollusca (23 species), Platyhelmintnes (1 species), Cnidaria (4 species), hexapoda (7 species) and Chordata (10 species). The most dominant species were polychaetes (Ceratoneris burmensis, Namalycastis indica, Minuspio sp. 1, Pseudopolydora kempi and Prionospio cirrifera), a gastropod (Maginella sp.), a pelecypod (Macoma sp.) an amphipod (Photis longicaudata), and a tanaid (Ctenapseudes sp.). A dendrogram of 9 stations, using group averages clustering from Bray-Curtis similarities on 4th root-transformed abundances showed four groups of stations with 60-63 percent similarity while a dendrogram of 6 months showed three groups of months. The results of linking biotic and 13 environmental variables (rho w) showed the best 3-variable combination of percent sand, total nitrogen and dissolved oxygen (rho w=0.82) in temporal analysis and the best 8-variable combination of percent clay, percent silt, organic carbon, soil pH, depth, dissolved oxygen, total suspended solid and temperature (rho w=0.84) in time analysis. For determination of the optimum sampling protocol, significant differences were found among the macrobenthic communities of different replications at a significant level of 98.9 percent. Results showed at 95 percent Bray-Curtis similarity that 7 grabs are necessary for a representative sample, but that 26 rare species were lost. The differences in the number of replicates are related to the habitat and the season. The number of replicates that are suitable for assessing the macrobenthic fauna in the phyla Annelida, Crustacea, Mollusca and all other phyla were 3, 7, 7 and 11 replicates, respectively. A comparison of macrobenthic fauna community structure between samples collected by the 2 mesh sizes was determined using Bray-Curtis similarity and analysis of similarity (ANOSIM). No significant differences were found among mesh samples at a significance level of 95 percent. But using the GT=0.5 mesh size, 170 species (including polychaete larvae) and 90194 individuals were found. No significant differences were found but using only the 1.0 mesh size resulted in the loss of 12 rare species and 38264 individuals. Thus any assessment of diversity and abundance of marobenthic fauna based on such a sample will probably be low.