Field Natural Abundance Study

Natural abundance analysis makes use of the natural relative abundances of the stable isotopes of essential nutrients (13C/12C, 15N/14N and 34S/32S) for characterising the potential food sources, and then using the indicator of relative abundance (δ13C, δ15N and δ34S, respectively) for tracking the flow of the food from the sources (primary producers such as mangrove trees and microalgae, and anthropogenic sources such as organic matter from sewage pollution) to consumers (e.g. crabs, fish) in the community.

In order to investigate how trophic relay may occur in connected habitats, we have selected 3 locations with a relatively uninterrupted series of soft-sediment habitats for sampling of the food sources and the consumers: Lai Chi Wo in Yan Chau Tong, Shui Hau in South Lantau Island, and Mai Po in Deep Bay. All locations support a progression of intertidal mangroves to extensive tidal flats that extend to the shallow subtidal area, and are subjected to different degrees of anthropogenic input and disturbance.

Collecting plankton from the plankton nets.

Samples of all potential food sources and key consumers at different trophic levels will be collected for analysis of their stable isotope values. This data will be used to construct the food web at each sampling location.

A comparison of their fundamental food web structure including the dominant food source (e.g. natural vs anthropogenic, macrophytic vs microalgal) as well as the complexity of the food web (e.g. length of food chains, connectivity, isotopic niche of key organisms) among the field sites may shed light on how human disturbance may influence the trophodynamics of soft-sediment ecosystems.

Searching for crabs and gastropods among the dwarf mangrove trees.

Setting up the fyke net to trap fishes.

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