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

Abstract

Decomposition of salt marsh plants results from physical, chemical and biological processes including abiotic and biotic fragmentation, microbial decay and chemical transformation. According to literature data, only a few species have the ability to feed directly on living plant material, so fungi and 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. Moreover, this nutrient regeneration may be seen as an effective factor in maintaining and stimulating bacterial production. In fact, it is well known that many detritus feeding species have very low assimilation efficiencies. The objective of the present study was to compare the nutrient mass balance of carbon; nitrogen and phosphorus in Spartina maritima covered areas and bare 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, water and plant material. Faunal activity was measured as a function of remineralised carbon, nitrogen and phosphorus. The experimental set-up included sixteen sub-experiments, which varied with respect to type of fauna, plant biomass and oxic status. Each sub-experiment was performed in small glass containers (3 L) containing about 900 g wwt sediment and 2.5 L estuarine water. Plant material, cut from intact plants, sediment cores and estuarine water were brought from the southern arm of the Mondego estuary (Portugal). The results showed that although the bacterial activity was responsible for the Spartina maritima degradation, the presence of meiofauna and macrofauna significantly enhanced the process. Moreover, the presence of Spartina maritima positively affected the mineralisation of the sediment carbon and nitrogen, especially when the three faunal components were present, and denitrification rates were highest in the presence of the macrofauna and meiofauna. The present study suggests that macrofauna and meiofauna have an important role on the ecosystem nutrient flux and that fauna might function as a sink for excess nutrients, that otherwise could be exported to the coastal waters