The effect of macrofauna, meiofauna add microfauna on the degradation of Spartina maritima detritus from a salt marsh area

Decomposition of salt marsh plants results from physical, chemical and biol ogical processes including abiotic and biotic fragmentation, microbial deca y and chemical transformation. According to literature data, only a few spe cies have the ability to feed directly on living plant material, so fungi a nd bacteria seem to be the principal competitors for the organic substrates . Nevertheless, by consuming bacteria, protists and fungi associated to the detritus, macrofauna and meiofauna recycle the incorporated nutrients. Mor eover, this nutrient regeneration may be seen as an effective factor in mai ntaining and stimulating bacterial production. In fact, it is well known th at many detritus feeding species have very low assimilation efficiencies. T he objective of the present study was to compare the nutrient mass balance of carbon: nitrogen and phosphorus in Spartina maritima covered areas and b are bottom sediment, with and without contribution of macrofauna, meiofauna and microbial populations. Nutrients mass balance was studied taking into account the initial and final nutrient concentrations in the sediment, wate r and plant material. Faunal activity was measured as a function of reminer alised carbon, nitrogen and phosphorus. The experimental set-up included si xteen sub-experiments, which varied with respect to type of fauna, plant bi omass and oxic status. Each sub-experiment was performed in small glass con tainers (3 L) containing about 900 g wwt sediment and 2.5 L estuarine water . Plant material, cut from intact plants, sediment cores and estuariae wate r were brought from the southern arm of the Mondego estuary (Portugal). The results showed that although the bacterial activity was responsible for th e Spartina maritima degradation, the presence of meiofauna and macrofauna s ignificantly enhanced the process. Moreover, the presence of Spartina marit ima positively affected the mineralisation of the sediment carbon and nitro gen, especially when the three faunal components were present, and denitrif ication rates were highest in the presence of the macrofauna and meiofaunal The present study suggests that macrofauna and meiofauna have an important role on the ecosystem nutrient flux and that fauna might function as a sin k for excess nutrients, that otherwise could be exported to the coastal wat ers. (C) 1999 Editions scientifiques et medicales Elsevier SAS.