Nitrous oxide production associated with coastal marine invertebrates

Several freshwater and terrestrial invertebrate species emit the greenhouse gas nitrous oxide (N2O). The N2O production associated with these animals was ascribed to incomplete denitrification by ingested sediment or soil bacteria. The present study shows that many marine invertebrates also emit N2O at substantial rates. A total of 19 invertebrate species collected in the German Wadden Sea and in Aarhus Bay, Denmark, and 1 aquacultured shrimp species were tested for N2O emission. Potential N2O emission rates ranged from 0 to 1.354 nmol ind.(-1) h(-1), with an average rate of 0.320 nmol ind.(-1) h(-1), excluding the aquacultured shrimp Litopenaeus vannamei, which showed the highest rate of N2O emission measured so far for any marine species (3.569 nmol ind.(-1) h(-1)), probably due to very high nitrate concentrations in the rearing tanks. The N2O emitted by L. vannamei was almost exclusively produced in its gut by incomplete denitrification. Statistical analysis revealed that body weight, habitat, and exoskeletal biofilms were important determinants of animal-associated N2O production. The snail Hinia reticulata emitted about 3.5 times more N2O with an intact exoskeletal biofilm on its shell than with an experimentally cleaned shell. Thus, the N2O production associated with marine invertebrates is apparently not due to gut denitrification in every species, but may also result from microbial activity on the external surfaces of animals. The high abundance and potential N2O emission rates of many marine invertebrate species suggest significant contributions to overall N2O emissions from coastal marine environments and aquaculture facilities.