44. Epifaunal invertebrate community variation along a salinity-acidity gradient in a tropical estuary

M. Belal Hossain* and David J. Marshall

Environmental and Life Sciences, Faculty of Science, Universiti Brunei Darussalam, Jalan Tunkgu Link Brunei Darussalam, BE1410. Email: mbhnstu@gmail.com

The invertebrate communities associated with hard substrata in estuaries are generally underexplored, despite the prevalence of such substrata. We studied the variation in species composition, abundance and community structure of intertidal epifaunal invertebrates associated with a ‘rocky’ (barnacle-dominated) community along a salinity and pH gradient in a tropical South East Asian estuary (Brunei Darussalam, Borneo). Species richness, species diversity and abundance were concomitantly greatest at the most seaward station (relatively high pH and salinity), lowest at the middle stations and relatively high again at the most landward (low pH and salinity) of the Sungai Brunei estuary. A total of 34 species (taxa) occurred in 72 samples collected from four stations, and sample abundances for all species together ranged between 94.5 to 335.67 individuals per 100cm2. An abundance analysis at a coarse taxonomic level (class/order) suggested the existence of three distinct communities along the physicochemical gradient; the community varied from a tanaid-polychaete dominated one to a mussel-dipteran one, and then a mussel-amphipod-dipteran one, from the landward to the seaward stations. However, the community structure at the most seaward station was influenced by the abundance there being more than twofold that of the other stations. The pattern of three distinct communities was somewhat confirmed by a multivariate analysis (Bray-Curtis similarity and nMDS). The shift from amphipod dominance to polychaete dominance with increasing acidification is consistent with observations of other studies for non-estuarine coastal systems. In addition to presenting the first known description of community structure variation for hard substratum invertebrates along an acidification gradient in an old world tropical estuary, the present study also hints at the potential for using estuarine systems to understand community-level effects of marine acidification in general.