Data from: Parasite infection alters nitrogen cycling at the ecosystem scale

Despite growing evidence that parasites often alter nutrient flows through
their hosts and can comprise a substantial amount of biomass in many
systems, whether endemic parasites influence ecosystem nutrient cycling,
and which nutrient pathways may be important, remains conjectural. A
framework to evaluate how endemic parasites alter nutrient cycling across
varied ecosystems requires an understanding of: (1) parasite effects on
host nutrient excretion, (2) ecosystem nutrient limitation, (3) effects of
parasite abundance, host density, host functional role, and host excretion
rate on nutrient flows, and (4) how this infection-induced nutrient flux
compares to other pools and fluxes. Pathogens that significantly increase
the availability of a limiting nutrient within an ecosystem should produce
a measurable ecosystem-scale response. Here, we combined field-derived
estimates of trematode parasite infections in aquatic snails with
measurements of snail excretion and tissue stoichiometry to show that
parasites are capable of altering nutrient excretion in their intermediate
host snails (dominant grazers). We integrated laboratory measurements of
host nitrogen excretion with field-based estimates of infection in an
ecosystem model and compared these fluxes to other pools and fluxes of
nitrogen as measured in the field. Eighteen nitrogen limited ponds were
examined to determine if infection had a measurable effect on
ecosystem-scale nitrogen cycling. Because of their low nitrogen content
and high demand for host carbon, parasites accelerated the rate at which
infected hosts excreted nitrogen to the water column in a dose-response
manner, thereby shifting nutrient stoichiometry and availability at the
ecosystem scale. Infection-enhanced fluxes of dissolved inorganic nitrogen
were similar to other commonly important environmental sources of
bioavailable nitrogen to the system. Additional field measurements within
nitrogen-limited ponds indicated that nitrogen flux rates from the
periphyton to the water column in high snail density/high infection ponds
were up to 50% higher than low infection ponds. By altering host nutrient
assimilation/excretion flexibility, parasites could play a widespread, but
currently unrecognized, role in ecosystem nutrient cycling, especially
when parasite and host abundances are high and hosts play a central role
in ecosystem nutrient cycling.