The Influence of Aquaculture on Foraminifera and Sediment Properties in the Setiu Estuary and Lagoon of Terengganu, Malaysia

Abstract

In order to address how aquaculture has influenced the Setiu estuary and lagoon of northeast peninsular Malaysia, foraminifera, sediment grain-size, and carbon and nitrogen isotope ratios and abundances were analyzed in surface samples collected from beneath and around three floating fish cage complexes. Two currently active floating fish cage complexes, SET11-S43 and SET11-S40, in the Setiu lagoon, within four km of an inlet (salinity in the 20s), have mixed agglutinated and calcareous foraminiferal assemblages, generally dominated by Ammonia aff. A. aoteana and Ammobaculites exiguus. The majority of live foraminifera at these sites are agglutinated species; percent of live specimens is greater around the SET11-S43 fish cage complex, likely related to the presence of aquaculture-related organic rich mud. Percent agglutinated specimens decreases towards the inlet as density and diversity increase as a function of salinity. At an abandoned fish cage complex, SET11-S9A, located in a low salinity (<5) estuarine setting, Miliammina fusca and Ammobaculites exiguus dominate entirely agglutinated assemblages; there is no evidence of fish farm influence in surficial sediments. Side scan sonar data as well as grain-size analysis of surface sediment samples indicate that a muddy substrate extends up to tens of meters to the north of the lagoonal fish cage complexes with a surrounding sandier substrate, typical of most of the Setiu estuary and lagoon system. The percent carbon and nitrogen in sediment exhibit distributional patterns that strongly correlate with the distribution of fish cage mud. Greater concentrations of mud, carbon, and nitrogen in sediment are found to the north of the active fish cage complexes, SET11-S43 and SET11-S40, than to the south. The [delta]¹³C and [delta]¹⁵N signatures of the sediment are attributed to organic matter input from the surrounding mangrove forest while their distribution is a result of tidal currents, water depth, and the presence of the fish farm complexes. Since the abandonment of the SET11-S9A fish cage complex, sediment distribution and foraminiferal assemblages surrounding the complex are indistinguishable from the surrounding estuary. The influence of the active fish cages at SET11-S40 is minimal as a result of tidal currents and mixing although environmental effects are evident further north at the SET11-S43 fish cage complex which receives less marine influence.