Nematode production in artificial ponds: a long-term perspective

Nematodes are the most abundant multicellular animals on Earth and play an important role as intermediaries in energy fluxes. However, estimations of nematode biomass turnover and secondary production have been poorly defined for decades and it is difficult to reach a consensus about the importance of nematodes for ecosystem functioning. Here we monitored monthly the nematode species composition, abundance and biomass over 3-10 years in a set of artificial urban ponds, and we used different allometric models to estimate biomass turnover and secondary production. During the first 3 years of colonisation of the pond bottom, the nematode community was rather species-poor and mostly composed of small bacterivorous species (Monhysterids); however, the community quickly reached impressive numbers (up to 21 million individuals m−2) achieving a maximum annual production of 3.8-11.6 gC m−2 year−1 depending on the allometric model used for estimation. However, over the long-term (3-10 years), abundance and community structure eventually became dramatically altered by anoxic events occurring in one pond, dampening nematode production to low levels (0.3-0.6 gC m−2 year−1) without clear resilience. The comparison of models helped us to formulate general recommendations in order to popularise the use of nematode secondary production as a useful ecosystem diagnostic tool. Overall, results indicated that under good conditions of oxygenation nematodes are a highly productive component of the zoobenthos of ponds. We also discussed the consequences of this finding for sustainable pond aquaculture, as nematodes constitute an important local and nutritive resource for juveniles of economically important fish, such as carp and tilapia.