Mangrove forest ecological function is influenced by the environmental settings and the benthic fauna composition

Abstract

Benthic communities perform many important roles within mangrove ecosystems and are responsible for facilitating many of the functions attributed to mangrove forests. For instance, they are instrumental in mediating mangrove system productivity, and provide crucial food for juvenile nekton. Despite their importance, very few studies have investigated the benthic community of mangrove forests, and among those the results are inconsistent. This variability manifests in strong location effects, with low organism density and species richness in Indo-Pacific mangroves, compared to West Atlantic sites. These regional difference are confounded by differences in within-region environmental settings (e.g. rainfall, tidal range, spatial location along the coastal mosaic), and this complicates the development of a clear understanding of underlying consistencies. To assess the influence of contrasting environmental influences on the benthic community of mangrove forests we studied the benthic community of Rhizophora stylosa forests at two coastal estuaries and along the shores of two islands within a 75 km radius. The results showed that the community composition differed among settings, with several taxa only occurring at one of the two forests type. Furthermore, Peracarida, a common prey found in the gut of juvenile fish, was only found through the island forests, but never observed within the estuarine forests. This indicates that environmental setting can play a key role in determining the nature of mangrove benthic assemblages and their potential ecological roles. Consequently, caution is required when attributing the ecological roles of mangrove forests without accounting for changes in settings. Additionally, we only investigated a single mangrove species within the same climatic region, meaning that even greater variability is likely when the full range of mangrove types, conditions and areas are assessed. Understanding this variation is important because it implies that mangrove forest restoration projects are unlikely to achieve their desired outcomes unless setting-specific conditions are understood and taken into account.