Saowapa Angsupanich, Amnat Siripech, and Mongkhongrat Charoenpornthip

pp. 365 - 390

Abstract

A bimonthly investigation of macrobenthic fauna at the area from Ban Pak Khat to Ban Leam Chong
Thanon in the Inner Songkhla Lake from February 1998 to February 1999 was undertaken to determine the
species richness and abundance. A total of 7 phyla and 161 species were identified. Annelida (58 species),
Arthropoda (64 species) and Mollusca (23 species) were the major phyla while Nemertea (1 species),
Platyhelminthes (1 species), Cnidaria (4 species) and Chordata (10 species) were the minor. Fifty-seven species
of Polychaete annelids were found. The highest species richness (14 species) was in the Nereididae Family, of
which Ceratonereis burmensis and Namalycastis indica were predominant. Nephtys sp. and Heteromastus sp.
were not so highly abundant but appeared at almost all stations through every sampling month, while Prionospio cirrifera and Pseudopolydora kempi were found in higher densities but with narrower distribution.
Ficopomatus sp. and unidentified Terebellidae were not commonly found, but occasionally reached a high
density. Amphipods gave the highest species richness (22 species), with Photis longicaudata distributed widely
and in all months. Five species of Tanaidaceans were found with Apseudes sapensis the second most dominant
(max. 5044 individuals m^-2 in February) in the overall fauna. Isopoda were not as densely found as
tanaidaceans but there were many species (18 species). Cyathura sp.1 was the most dominant isopod.
Brachidontes arcuatulus was the most dominant bivalve (max. 29449 individuals m^-2 in April), especially at
stations with a sand-gravel substrate. The mean density of total macrobenthic fauna among stations ranged
from 920 to 10620 ind. m^-2 while the monthly densities ranged from 1520 to 6160 ind.m^-2. The mean density of
macrobenthic fauna was highest in the dry season (April). The species richness among stations ranged from
65 to 105 species while varying from 81 to 112 species during the different months. The highest species richness was in the SW monsoon season (light rain, June-August). Polychaetes and molluscs tended to decrease
in the NE monsoon season with heavy rain from December-February, while crustaceans increased during
this time. The best fitting of the environmental variables to explain the macrobenthic fauna community
pattern of the Inner Songkhla Lake was an 8-variable combination of %clay, %silt, %organic carbon, soil
pH, depth, dissolved oxygen, total suspended solid and temperature (harmonic rank correlation coefficient,
ρ_w = 0.84).