The Roles of Macrobenthic Mollusks as Bioindicator in Response to Environmental Disturbance : Cumulative k-dominance curves and bubble plots ordination approaches

Abstract

Floating net cage is one of the aquaculture practice operated in Indonesian coastal areas that has been growing rapidly over the last two decades. This study is aimed to assess the roles of macrobenthic mollusks as bioindicator in response to environmental disturbance caused by fish farming activities, and compare the samples within the locations using graphical methods. The research was done at the floating net cage fish farming area in the Awerange Gulf, South Sulawesi, Indonesia at the coordinates between 79°0500′- 79°1500′ LS and 953°1500′- 953°2000′ BT, at the polyculture and reference areas, which was located 1 km away from farming area. Sampling period was conducted between October 2014 to June 2015. The sediment samples were taken from the two locations with two sampling time and three replicates using Van Veen Grab for biotic and abiotic assessment. Mollusks as biotic parameter were fixed using 4% formalin solution and were preserved using 70% ethanol solution after 1mm mesh size. The macrobenthic mollusks were found as many as 15 species consisting of 14 families and 2 classes (gastropods and bivalves). Based on cumulative k-dominance analysis projected on each station, the line of station K3T1 (reference area; first sampling time) and KJAB P3T2 (polyculture area; second sampling time) are located below others curves, indicating the highest evenness and diversity compared to the other stations, whereas station K2T1 (reference area; first sampling time) and K3T2 (polyculture area, second sampling time) are located on the top, indicate the lowest value of evenness and diversity. Based on the bubble plots NMDS ordination, the four dominant taxa/species did not clearly show involvement in driving/shifting the ordinate position of station on the graph, except T. agilis. However, the two species showed involvement in driving/shifting the ordinate position of two stations of the reference areas from the first sampling time by Rynoclavis sordidula, and three stations of the polyculture areas from the first sampling time by Gemulla sp. away from other stations, thus are considered as bioindicators of environmental disturbance. These results imply that cumulative k-dominance curves and bubble plots ordination may be effective method to assess the indication of disturbance of the area.