Anthropogenic water conditions amplify predatory impact of the non-native Oriental river prawn Macrobrachium nipponense

Abstract

Investigating non-native species’ impacts on recipient communities in the context of local habitat conditions is vital to understanding their potential invasiveness. This study used comparative functional response experiments to assess the potential predatory impacts of the non-native Oriental river prawn Macrobrachium nipponense compared to the native Malayan river prawn Macrobrachium malayanum in Singapore. Functional responses of these species were compared under different water temperature and pH conditions, representing Singapore’s warmer, near-neutral artificial/modified fresh waters, and cooler, more acidic natural forest streams, where the two species are respectively abundant. Four water condition treatments of different temperature-pH permutations were tested: A (26 °C, pH 5.5), B (26 °C, pH 6.5), C (29 °C, pH 5.5) and D (29 °C, pH 6.5). Results found both species to exhibit Type II functional response across all treatments, but M. nipponense responses were significantly higher than those of M. malayanum in all of them. Overall, its functional response was also significantly amplified when water conditions resembled that of the artificial habitat, with higher attack rate, lower handling time, and higher maximum feeding rate. Results imply that M. nipponense can inflict ecological impact in Singapore in terms of predation on the invertebrate prey community. The predatory impact of M. nipponense can also be exacerbated by changes in water parameters (i.e. increasing temperature and/or pH) associated with anthropogenic change, highlighting the importance for conservation of natural freshwater habitats in Singapore.