Dragonflies and Damselflies are well-studied group of invertebrates (Cordoba, 2008) with their increasing recognition in conservation worldwide (Samways, 2008). In a regional context, this fact is reflected in dragonflies and damselflies as being the only insect group that are currently being globally assessed by the World Conservation Union (IUCN, 2009).
Dragonflies have excellent potential as indicators of habitat integrity (Samways, 2008). For this study, the aim is to use bio- and chemical indicators were believed to have potential in assessments of freshwater habitat quality and health. These indicators are low-cost, easy-to-use and are already used for measuring habitat heath and recovery (Samways, 2008). They have great potential for environmental assessment, when used complementarily with other indicators. This study adopts a theory-based perspective as against a taxonomy-based approach, where enquiry is the prevailing thread for reasoning as opposed to creating a list of odonates. In this research, the merits of odonates as a subject for ecological assessment will be weighed in light of their possible limitations.
The motivation for using the Odonata order as indicators of Ecological health of freshwater sources stems from an observation made by Murphy (1997) regarding the distribution of three species of Prodasineura within Singapore’s Central Catchment Area. From his observations, each of the three species had totally different habitats, demonstrating that odonates can be used as a bio-indicator for eco-monitoring. It has been found that each type of water body has a characteristic odonate species assemblage (McPeek, 2008). McPeek (2008) further elaborated that oxygen availability and fish predators have limited some species to smaller streams while large, active dragonflies are relegated to ponds and lakes, where fish cannot colonize. Although this is a recognized fact, there are no detailed studies on each individual species in light of these observations, in particular in Singapore context. In a study by Silva et al. (2010) at Turvo Sujo River in Southeastern Brazil, they tested the use of adult odonate individual species and community assemblage measures to evaluate the effect of riparian vegetation cut-off and sewerage discharges. They found that physiochemical parameters of water as well as odonate abundance and assemblages are affected by possible water pollution due to municipal sewerage discharges.
Hence, these three studies demonstrated the possibility of using the odonates as an indicator for the ecological health of freshwater resources. The following diagram shows the possible relationship between the adult odonates as an indicator of the water physiochemical parameters. If this hypothesis holds true, then we will have a convenient method of conducting an initial assessment of the water quality before other complimentary and more accurate methods are used.
Fig 1: Conceptual relationship between odonates and water quality upon which this study was based
However, in order to verify my hypothesis, I had to carry out a verification exercise to show the relationships between the odonates and the water parameters of their respective habitats. If the correlation can be established, the odonates could then be confirmed as a useful bio-indicator for Singapore’s freshwater habitats.