Empirical food webs of 12 tropical reservoirs in Singapore

Abstract

Food webs summarise trophic interactions of the biotic components within an ecosystem, which can influence nutrient dynamics and energy flows, ultimately affecting ecosystem functions and services. Food webs represent the hypothesised trophic links between predators and prey and can be presented as empirical food webs, in which the relative strength/importance of the respective links are quantified. Some common methods used in food web research include gut content analysis (GCA) and stable isotope analysis (SIA). We combine both methods to construct empirical food web models as a basis for monitoring and studying ecosystem-level outcomes of natural (e.g. species turnover in fish assemblage) and intentional environmental change (e.g. biomanipulation). We present 12 food webs from tropical reservoir communities in Singapore and summarise the topology of each with widely-used network indices (e.g. connectance, link density). Each reservoir was surveyed over 4–6 sampling occasions, during which, representative animal groups (i.e. fish species and taxonomic/functional groups of zooplankton and benthic macroinvertebrates) and all likely sources of primary production (i.e. macrophytes, periphyton, phytoplankton and riparian terrestrial plants) were collected. We analysed gut content in fishes and bulk isotope (d13C and d15N) profiles of all animals (i.e. fishes and invertebrates) and plants collected. Both sets of information were used to estimate the relative strength of trophic relationships using Bayesian mixing models. We document our protocol here, alongside a script in the R programming language for executing data management/analyses/visualisation procedures used in our study. These data can be used to glean insights into trends in inter- and intra-specific or guild interactions in analogous freshwater lake habitats.

Toward eDNA‐based bioassessment of freshwater reservoirs with small volumes of water: Robust molecular protocols

“…The metazoan assemblages of the two reservoirs are known to differ (Clews et al, 2014; Liew et al, 2018; Wilkinson et al, 2022), but we here confirm the differences also for a different set of metazoan taxa detected with a COI primer. Previously, a macroinvertebrate survey using colonizer‐type samplers left in the reservoirs for four weeks captured nine families of macroinvertebrates in Bedok Reservoir and Pandan Reservoir, but only three families were detected in both waterbodies (33.3%) (Clews et al, 2014).…”

“…A minimum criterion is that the eDNA signatures should be distinct for reservoirs that are known to differ significantly with regard to water quality based on physicochemical properties and/or macroinvertebrate communities. This is the case for the two reservoirs that were sampled in our study (Bedok and Pandan Reservoir (Clews et al, 2014; Liew et al, 2018; Lim et al, 2016; Wilkinson et al, 2022)). At the same time, the methods should yield similar eDNA signatures for water samples from several sites within the same reservoir as long as it is known to have good water mixing (“biological replicates”: Zhan et al, 2014; Zhou et al, 2011).…”

“…A minimum criterion is that the eDNA signatures should be distinct for reservoirs that are known to differ significantly with regard to water quality based on physicochemical properties and/or macroinvertebrate communities. This is the case for the two reservoirs that were sampled in our study (Bedok and Pandan Reservoir (Clews et al, 2014;Liew et al, 2018;Lim et al, 2016;Wilkinson et al, 2022)).…”

“…Previously, a macroinvertebrate survey using colonizer-type samplers left in the reservoirs for four weeks captured nine families of macroinvertebrates in Bedok Reservoir and Pandan Reservoir, but only three families were detected in both waterbodies (33.3%) (Clews et al, 2014). Similarly, fish surveys using cast netting, trapping, and electrofishing found that only 5 of 19 species of fishes were shared between reservoirs (26.3%) (Liew et al, 2018;Wilkinson et al, 2022). Our metabarcoding study using a universal metazoan COI primer applied to water eDNA mostly found mOTUs that belonged to the zooplankton community or could not be identified with standard bioinformatic techniques.…”

“…Here, we test how the amount of DNA template and number of PCR cycles affect the detected metazoan communities based on eDNA from small water samples. We sampled two tropical reservoirs that are 20 km apart but are known to have very different water quality and biodiversity (Bedok Reservoir and Pandan Reservoir: Clews et al, 2014; Liew et al, 2018; Lim et al, 2016; Wilkinson et al, 2022). For both reservoirs, three sites were sampled (“biological replicates”).…”