Destruction of conspecific bioturbation structures by Amphiura filiformis (Ophiuroida): evidence from luminophore tracers and in situ time-lapse sediment-profile imagery

Abstract

Bioturbation processes of a dense ophiuroid assemblage were studied by in situ time-lapse sediment-profile imagery (t-SPI) and laboratory tracer-experiments. The burrows of 4 Amphiura fili- formis (Ophiuroida) individuals were visible throughout the t-SPI deployment. Mean burrow excavation was 2.9 cm 2 h -1 . Mounding ranged from 0 to 7.12 cm 2 h -1 . Loss of sediment from the sediment-water interface ranged from 0 to 7.0 cm 2 h -1 . Bioturbation at the station was dominated by A. filiformis, whose presence appeared to mask the activity of conspecifics. Species interactions were investigated in terms of particle reworking by laboratory luminophore-tracer experiments of monocultures and species mix- tures using A. filiformis, Leptopentacta elongata (Holothuroida) and Nephtys hombergii (Polychaeta). Bioturbation by these large species fit a symmetric non-local model well. Species interactions led to underyielding with respect to predicted additive species-effects. Treatments containing A. filiformis were significantly different from treatments without A. filiformis, and not significantly different from each other. When the data was processed on a per capita basis, multiculture treatments containing N. hombergii underyielded due to the high biomass of N. hombergii and its relatively low bioturbation activity. Ordination of a distance matrix derived from tracer profiles showed that tracer profiles produced by multispecies treatments were most similar to the strongest bioturbator, due to destruction of con- specific structures by the strongest bioturbator. Species interactions are not additive in terms of particle bioturbation, and may be difficult to predict without knowing in situ densities.