Habitat change in estuaries: Predicting broad-scale responses of intertidal macrofauna to sediment mud content

Abstract

There is a growing threat of habitat change in estuarine and coastal regions, yet there are few models that enable ecologists and resource managers to forecast the response of macrofaunal species to long-term changes in sediment type. This study details a novel strategy that enabled us to rapidly collect data on macrofaunal densities and sediment characteristics by sampling mud-to-sand transition zones in 19 estuaries. Species-specific models that predict probability of occurrence relative to sediment mud content were developed for 13 common macrofaunal species. However, the roles played by many macrofaunal species are influenced by density, not just occurrence. Over broad spatial scales, the constraint an environmental variable places on density can be represented by the upper (or lower) limit on density. Thus, the distribution of maximum density along the gradient from mud to sand was modelled as another indicator of a species' preference. Both the maximum and minimum values for number of taxa, number of individuals, Shannon-Wiener diversity and taxonomic distinctness were also modelled. For most variables, good models (r2 > 0.6) were developed. The models developed for the different species exhibited a wide variety of functional forms, highlighting the potential variation in response to habitat change even for closely related species with similar natural history characteristics. Probability-of-occurrence models and maximum-density models for a specific species also varied in functional form, emphasising that changes in both occurrence and density need to be considered when predicting likely responses to changes in habitat.