Bioturbation functional roles associated with mangrove development in French Guiana, South America

Abstract

This study aims to qualify, quantify, and compare the sediment reworking rates induced by the meso- (0.25–1 mm) and macro-infauna ([1 mm) along a mangrove growth gradient in the sedimentary dynamics of the French Guiana coast. The characterization of the role of small-infauna bioturbation in mangroves is new despite their known numerical dominance in tropical environments. Bare sediment, pioneer mangroves, and young mangroves were investigated during the dry season and spring tide to characterize their environment, infaunal functional community structure and sediment reworking rates. The biodiffusion differed significantly between mangrove stages, co-varying mainly with density and functional richness. On the contrary, the non-local transport remained similar, despite the mangrove-agespecificity of infauna functional compositions, which responded to modifications in the nature and content of organic matter. The first mangrove infaunal functional sequence is described: organisms that first colonize deposited mud generate the maximum biodiffusive mixing and induce a total downward particle flux (BDF) as high as in the young mangroves; in the pioneer mangroves, the infauna variables and BDF are stressed to minimum values. Our study sheds light on the functional contribution of the small infauna in a mangrove coastal area and quantifies its role in particle transport during mangrove development.