Ecological responses to fluctuating and extreme marine acidification: lessons from a tropical estuary (the Brunei Estuarine System)

  • David Marshall
  • Sorya Proum
  • M. Belal Hossain
  • Aimimuliani Adam
  • Lee Hoon Lim
  • Jose H. Santos


The impact of acidification on marine ecosystems has become a topic of priority research, following realization of unabated ocean acidification (OA), derived from globally-rising atmospheric CO2. Many coastal and estuarine ecosystems have historically been acidified through various processes, and it is possible that we can learn and make predictions about OA impacts from the ways estuarine species and communities adapt and respond to acidified water. Studying estuarine acidification, nonetheless, aids understanding of the processes that affect ecological structure and functioning, important for coastal conservation and management. A broad-based research programme was implemented at UBD between 2011 and 2015, to investigate how variation in acidity and salinity affected assemblages and species in the Brunei Estuarine System (BES), an ecologically and economically important natural system in the region. This review summarizes studies that investigated for the BES, (i) the physical habitats and water physicochemistry, (ii) responses of planktonic and benthic microbial and faunal assemblages to exposure to variable and potentially highly acidic water, (iii) effects of acidification on ecological processes, such as barnacle dispersal and recruitment, (iv) behavioural and physiological mechanisms of organisms to cope with highly fluctuating and extreme pH water, with special reference to the gastropod, Indothais gradata, and (v) contaminant uptake by Indothais gradata under acidified conditions. The significance of the findings to the ecology of the BES, gaps that need addressing, and how estuarine acidification may contribute to predicting responses to OA are evaluated and discussed.