Excretion of organic matter and nutrients from invasive quagga mussels and potential impact on carbon dynamics in Lake Michigan

The Laurentian Great Lakes have been infested with invasive quagga mussels resulting in unprecedented changes in foodweb structure and ecological function, especially over the past decade. Nevertheless, impacts of quagga mussels on the dynamics of carbon and nutrients in the Great Lakes remain poorly quantified. Here, we report yields, composition and size-spectra of dissolved organic matter (DOM) and nutrients excreted from quagga mussels and their potential impact on carbon dynamics in Lake Michigan. Clearance rates of different sized microparticles indicate that quagga mussel ctenidial fibers can efficiently retain particles as small as 0.5-μm. Smaller-sized mussels have higher DOM excretion rates (0.076 ± 0.004 μmol-C/mg-DW/d) compared to larger mussels (0.012 ± 0.0002 μmol-C/mg-DW/d). Nitrogen excretion rate was up to 0.24 ± 0.01 μmol-N/mg-DW/d, 3 times higher than dissolved organic carbon (DOC), while inorganic phosphorus excretion was only 0.0076 ± 0.0030 μmol-P/mg-DW/d. Excreted DOM was mostly chromophoric and high-molecular-weight in nature with a colloidal size spectrum centered at 1-5 kDa, had a low C/N but higher N/P ratio, and was comprised of up to 78% carbohydrates with high propotion of structural polysaccharides. Fluorescence EEMs and PARAFAC analysis identified two major fluorescent DOM components: a tryptophan-like and a UVC humic-like, suggesting that excreted DOM could be potentially labile. Compared with field measurements, only ~ 12% of organic matter consumed by quagga mussels is excreted/egested, and the vast majority is likely respired as CO2, potentially contributing to an increase in CO2 concentration in the water column and changes in carbon dynamics in Lake Michigan after the colonization of invasive quagga mussel.