Polychaete is among the largest and most diverse benthic animal in many marine ecosystems. However, in Malaysia the study on community ecology of polychaete from soft bottom habitats, especially at the offshore areas of southern South China Sea has not been widely explored.  My master research focuses on determination of polychaete community structure (density, diversity and evenness) in soft bottom macrobenthos, the taxonomy and classification of polychaetes in the study area as well as the relationship between polychaetes community structure and sediment parameters.

The sampling was conducted in April and July 2011 at 43 sampling stations covered offshore areas of Pekan-Dungun (A1 to A19), Kuala Terengganu (B1 to B11) and Kudat-Balambangan Island (C1 to C13). At each sampling station, sediment samples for polychaetes (n=5), particle size analysis (PSA) (n=3) and total organic carbon (TOC) (n=3) were taken by Smith McIntyre grab (0.1 m2). Sediment for polychaetes was sieved through a set of wire mesh sieves (5.0, 3.0 and 0.5 mm) and polychaetes retained on the sieve were collected, fixed with 10% buffered formalin and were brought back to the laboratory together with the sediment for PSA and TOC for further analysis. In the laboratory, polychaete samples were rinsed, sorted, counted, identified and preserved in 70% ethanol.

Overall, a total of 12,477 individuals of polychaetes were recorded and classified into 47 families and 217 genera. Spionidae was found to be the most dominant family and Aonidella cirrobranchiata was the most abundant species. In terms of polychaete occurrence, the cumulative number of polychaete species was found to be parallel with the increasing number of sampling stations, in which the cumulative number of species relatively highest at the offshore area of Pekan-Dungun. However, the mean total density of polychaetes at Kudat-Balambangan Island and Pekan-Dungun was significantly higher compared to offshore Kuala Terengganu.

Despite the differences of cumulative number of species and the mean total densities of polychaetes, the mean value of diversity (3.88 to 5.65) differ significantly, however evenness index (0.72 to 0.92) did not differ significantly between all study areas. Besides, the density of polychaetes has a significant correlation with the percentage of silt and organic carbon in the sediment, whereas their diversity did not correlate significantly with any type of particle size characteristics and organic carbon content in the sediment. On the other hand, the evenness of polychaete community was weakly correlated with sediment characteristics (sand and silt).

The occurrence of the high number of identified species was relatively highest at the stations where the sediment type was dominated by silty-clay, silty-clay-loam and silt-loam. In addition, the mean total density of polychaetes relatively highest for the stations which are nearer to the shore and depths below 60 m. This indicated that the areas with those kinds of sediment types, depths and the locations of specific stations, which are closer to the shoreline might be the preferable habitats for polychaete. The data obtained from this study might contribute as additional information on the biodiversity of polychaetes community, their abundance and distribution at the offshore areas of southern South China Sea and eventually provide significant baseline information for sustainable management of South China Sea Large Marine Ecosystem (LME).

Fig. 1. Map of sampling areas off Pekan-Dungun, Kuala Terengganu and Kudat-Balambangan Island, surrounding countries within southern South China Sea area and the border of Malaysia Exclusive Economic Zone (EEZ).

Fig. 2. Sediment was removed from Smith McIntyre grab.

Fig. 3. Seabed sediment sample was washed and sieved through a series of wire mesh sieve to collect macrobenthos samples.

Fig. 4. Percentage abundance (%) of polychaete families at southern South China Sea (offshore Pekan-Dungun, Kuala Terengganu and Kudat-Balambangan Island).

Fig. 5. Polychaete species at offshore Pekan-Dungun, Kuala Terengganu and Kudat-Balambangan Island.

Fig. 6. Density of polychaetes at offshore Pekan-Dungun, Kuala Terengganu and Kudat-Balambangan Island (n=5, mean±SD).

Fig. 7. Diversity (H’) and evenness (J’) index of polychaetes at each station in southern South China Sea (offshore Pekan-Dungun, Kuala Terengganu and Kudat-Balambangan Island).

Table 1. Variation in polychaete abundance in sediment at offshore Pekan-Dungun, Kuala Terengganu and Kudat-Balambangan Island.