Carbon flux in Aquatic food webs

Carbon flux in Aquatic food webs: Investigating the influence of Basal carbon on the daily growth of larval fish and their dietary nutrition in the southern Murray-Darling Basin

As the dominant building block of life carbon is incorporated by organisms as biomass across trophic levels of freshwater food webs. From origins at primary production through to predatory vertebrate biomass and being recycled by microbial food webs carbon accumulates at different trophic levels in the form of biomass. Moving through multiple pathways, carbon and it’s stable isotopes present an appropriate measure for determining origins of carbon and which processes (e.g. terrestrial/aquatic primary production or microbial incorporation) are important for specific taxa and their growth (biomass accumulation). Fish larvae are some of the fastest growing organisms within the freshwater systems of the Murray-Darling basin. They are also characterised by high mortality (>99%, Chambers and Trippel 1997). Understanding the prey being consumed by larvae and carbon signatures of larval fish and their diet, will determine the importance of primary production sources as basal carbon for riverine food webs.
Though autotrophs in both riparian and aquatic habitats are thought to dominate carbon supply to food webs, labile dissolved carbon (<0.45µm), in the form of dissolved organic matter (DOM) is also incorporated to the food web through heterotrophic bacteria. With aged terrestrial carbon being shown recently to be extremely labile for microbial communities (Fellman et.al. 2014) this flux may have been under estimated in past years modelling food webs of freshwater systems. My research aims to determine the importance of carbon uptake by heterotrophic bacteria through fluorescence of aromatic DOM (fDOM) and stable isotope analysis of both dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC). This will be compared with stable isotopic signatures of riparian and aquatic vegetation and incorporated in isotopic bi-plots of the entire food web for all trophic levels below fish larvae. Fish larvae will be measured for total length, dissected for sagittal otoliths to determine daily growth and also dried for organism dry mass and preparation for isotope analysis. Understanding the flux of carbon in freshwater systems is of upmost importance as anthropogenic river regulation disrupts carbon flow along rivers and may impact organism growth having implications for the conservation and management of riverine taxa from riparian vegetation to aquatic vertebrates.

Luke McPhan PhD Candiate: Luke.McPhan@unsw.edu.au

Supervisor/s
Professor Andy Baker (UNSW)
Dr Kim Jenkins (UNSW/CSU)
Dr Paul Humphries (CSU)
Dr Lee Baumgartner (MDFRC)

Research Program: 
Wetland Ecology and Stable Isotopes
Research Themes: 
Rivers and Wetlands
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