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

Abstract

Conducted a survey over an intertidal flat colonized by Spartina alterniflora in the euhaline, high-energy sector of Paranagua Bay. Some 98 taxa were found, with the nine most abundant species comprising >80% of total macrofauna. A two-factor principal component model, which explained 65.7% of the total variation within the data set, revealed a strong interaction among plant biomass vlaues, faunal parameters and time of year, as well as an inverse relationship between aerial and below-ground plant components, reflecting storage and growth events. Variation in total numbers of species and densities of the epifaunal Parhyalella whelpleyi(Amphipoda) and Bittium 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. Total infaunal numbers, and densities of the infaunal dominants, Isolda pulchella and Nereis 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 material is primarily 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. Infaunal abundance is apparently strongly affected by below ground Spartina biomass. Unexpectedly, higher aerial plant biomass 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 structuring the macrofauna of local salt marshes. -from Authors