Macrofauna - plant-biomass interactions in a euhaline salt marsh in Paranagua Bay (SE Brazil)

To assess if benthic macrofaunal parameters correlate with above-and below-ground plant biomass, we conducted a 14 mo survey over a n intertidal flat colonized by Spartina alterniflora in the euhaline, high-energy sector of Paranagua Bay (Southeastern Brazil).Variations in species richness, overall abundance of epifauna and infauna, and densities of numerically dominant species in relation to Spartina biomass values were analyzed using principal components analysis and stepwise multiple regression.Ninety-eight taxa were found, with the 9 most abundant species comprising more than 80 % of total macrofauna.A 2-factor principal component model, which explained 65.7 % of the total variation within the data set, revealed a strong interaction among plant biomass values, faunal parameters and time of year, as well as an inverse relationship between aerial and below-ground plant components, reflecting storage and growth events.Vanation in total numbers of species and densities of the epifaunal Parhyalella whelpleyi (Amphipoda) and Bittjum varium (Gastropoda), and the infaunal Lucina pectinata (Bivalvia) was not significantly related to the various plant biomass measures, suggesting that other processes may be involved in the regulation of local species richness.On the other hand, total infaunal numbers, and the densities of the infaunal dominants, Isolda pulchella and Nerejs oligohalina (Polychaeta), were significantly predicted by live below-ground biomass expressed as dry weight, but not as ash-free dry weight.This indicates that plant matenal is pnmarily used as a refuge or physical support to tubes, rather than as a food source.Total epifaunal and Littorina flava (Gastropoda) numbers were negatively correlated to live above-ground plant biomass.We advance some hypotheses to explain such a n unexpected pattern, taking into account feeding strategies and predation pressure as influenced by plant characteristics We infer that infaunal abundance is in fact strongly affected by below ground Spartlna biomass.Unexpectedly, higher aerial plant b ~o m a s s did not bear higher epifaunal or infaunal numbers; such relationships would be better expressed by negative linear interactions or nonlinear models Plant architecture is a major force, together with seasonal oscillations in detrital input and predation pressure, in structunng the macrofauna of local salt marshes.