Rates of ascidian mediated nitrogen cycling

Large solitary ascidians, like Herdmania grandis (Heller), can dominate
the benthic substrates of subtropical and temperate reefs, however their
influence on nitrogen cycling, particularly nitrous oxide (N2O)
production, is unknown. Here we incubated individual H. grandis and
compared fluxes of dissolved inorganic and gaseous nitrogen species to
fluxes from reef sediments. Nitrous oxide production rates per individual
ascidian (21 ± 8 nmol ind h-1) are the highest reported for any marine
invertebrate. An individual ascidian produced more N2O than a m2 of
sediment (1.7 ± 1.7 nmol m-2 h-1). Ascidian mediated N2O production was
found to occur under nutrient depleted conditions. While the addition of
15N labelled organic material showed that H. grandis facilitates both
nitrification and denitrification, the contribution of these pathways to
N2O production could not be ascertained. As the ecology of temperate reefs
change, any range expansion of H. grandis will increase coastal N2O
production.