Functional classification of bioturbating macrofauna in marine sediments using time-resolved imaging of particle displacement and multivariate analysis

Abstract. Activities by macrofauna may drastically alter rates and pathways of reactions in surface sediments during early diagenesis and numerous experiments have been designed to quantify the importance of bioturbation by individual species and faunal communities for element cycling in these environments. It is increasingly recognized that functional traits of fauna are critical for element transformations. An example of such functional trait is the capacity for particle transport across horizontal and vertical gradients in environmental characteristics. The present contribution describes a general procedure for functional classification of fauna using multivariate analysis based on a suite of experimentally derived variables for particle reworking.

The relocation of fluorescently labeled particles (luminophores) added to surface sediments was quantified by side-view imaging during a two-week experiment incubating several common bioturbating species of marine benthic macrofauna: Glycera alba, Nephtys incisa, Lipobranchius jeffreysii, Scalibregma inflatum (Annelida), Brissopsis lyrifera (Echinodermata), Abra nitida, Nuculana pernula, and Thyasira sarsii (Mollusca) in thin glass aquaria.

Multivariate analysis revealed groups of species with similar mode of reworking based on reworking variables associated with quantity and time (bulk), as well as vertical distance (depth) of particle transport. Most pronounced effects on bulk transport were found in the N. pernula, A. nitida and L. jeffreysii treatments, while only a limited quantitative capacity to relocate particles was observed in the T. sarsii and N. incisa treatments. Although stochastic patterns were observed for some species, a prominent capacity for vertical transport of surface deposited particles was demonstrated for the annelids and T. sarsii.

From these results, three main groups of fauna with common reworking behavior were identified. B. lyrifera, A. nitida and N. pernula were species with only a limited effect on the vertical transport of particles. In contrast, while N. incisa and T. sarsii were able to relocate particles vertically, they shared a restricted capacity for bulk sediment transport. Despite high intraspecific variation, G. alba, L. jeffreysii and S. inflatum had the capacity for bulk and vertical transport of particles.

Despite the challenge to generalize species functionality and reworking capacity of benthic macrofauna, our results demonstrated that time-resolved high-resolution imaging of particle displacement, in combination with multivariate analysis, provides a general experimental tool for functional classification of benthic macrofauna.