Reconstruction of the salinity history associated with movements of mangrove fishes using otolith oxygen isotopic analysis

Abstract

Recent degradation and loss of tropical estuaries due to human impact have made necessary the protection of essential habitats for estuarine fishes. A better understanding of estuarine use patterns contributes greatly to identifying essential habitat conditions. This study presents quantitative reconstruction data of the salinity history experienced by individual estuarine fishes using an otolith oxygen isotope. 18 O otolith was determined from the kuhliid Kuhlia rupestris and pomacentrid Chrysiptera cyanea for use as freshwater and marine end-member references, respectively. The salinity histories of 3 species of estuarine mangrove fishes, often dominant in tropical East Asian estuaries, viz. the apogonid Fibramia amboinensis, the pomacentrid Neopomacentrus taeniurus and the terapontid Terapon jarbua, were examined. The 18 O otolith ranges of -5.4 to -2.3 for F. amboinensis and -3.7 to -2.3 for N. taeniurus corresponded to 6 to 30 psu and 19 to 30 psu, respectively, when compared to the 2 extreme salinity values of the reference fishes. Terapon jarbua, in contrast, exhibited a 18 O otolith range of -3.0 to -1.8 , corresponding to 25 to 34 psu. Field observations in other studies have indicated that F. amboinensis and N. taeniurus may be resident species, hovering near mangrove roots and tolerating a variable salinity environment, whereas T. jarbua may be a vagile species that can move to areas of preferred higher salinity conditions. Such behavioral ecologies are largely consistent with the salinity histories reconstructed from 18 O otolith data. These results suggest that F. amboinensis and N. taeniurus may be estuarine resident fishes, whereas T. jarbua may be a marine migrant.