Gradients in Traits Composition and Their Relation to Environmental Complex-Gradients and Structuring Processes: a Study of Marine Sediment Species Communities

The biological reason for a species' presence under given environmental conditions is that the species possesses traits that make establishment and survival, usually also reproduction, possible under these conditions. Biological traits analysis (BTA), when coupled with environmental variables, can provide information regarding which traits are to be expected for a given environmental state. As such, BTA provides complementary information to multivariate analysis of community data based on species composition. In this study, BTA was conducted on a data set of sediment macrofauna collected from a temperate fjord system and related to a wide range of environmental variables. The biological traits were analysed in a multiple parallel ordination framework, which can enhance the reliability of the extracted gradient structure and evaluate the importance of weight given to abundance. Two traitclines, gradients in functional attributes of the species, were found in the study area. The first traitcline was related to bottom currents and sediment constituents while the second traitcline was related to current strength and particle deposition on the bottom. Together with a companion study of gradients in species composition (coenoclines), this study of functional features (traitclines) illustrates that the species composition may consist of taxonomically different, but functionally similar species, giving rise to strong gradients in species composition but weak gradients in trait category composition when subjected to ordination analyses.