Feeding ethology and surface sediment reworking by the ampharetid polychaete Melinna palmata Grube, 1870: Effects on sediment characteristics and aerobic bacterial community composition

Abstract The present study was aiming at describing the feeding ethologyand assessing surface sediment reworkingtogether with associated effects on sedimentcharacteristics and aerobic bacterial community composition by the ampharetid polychaeteMelinna palmata , which exhibits very dense populations in the Arcachon Bay (French Atlantic coast). There was a plasticity in the main aspects (i.e., positioning of the tube at the sediment-water interface, stretching of the worms outside their tubes while feeding, location and mechanism of faeces production) constitutive of the current knowledge regarding feeding ethologyin ampharetids. On average, worms dedicated 84.6% of their time to the prospection of surface sedimentsand produced faeces exclusively at the water sedimentinterface, which resulted in surface sediment reworkingand induced the zonation of surface sedimentin three distinct areas, namely: undisturbed sediment, prospected and faecal mound areas. Average individual surface prospected area and surface sediment reworkingrate were 28 cm 2 and 6.8 mm 3 .h −1 , respectively. Surface sedimentswere coarser and their bulk organic contents were lower in prospected areas, intermediate in faecal mound areas and higher in undisturbed sediments. Oxygen penetrated deeper in the sedimentcolumn in faecal mound areas. Aerobic bacterial community composition associated with surface oxygenated sedimentswithin these three areas also significantly differed, which suggests that sediment reworkingper se (i.e., irrespective of changes in redox conditions) do have an effect on those compositions. These results are discussed in terms of potential food limitation in the very dense populations of M. palmata present in the Arcachon Bay. It is suggested that the high densities of these populations result from both hydrosedimentary fluxes due to tidal currents and from the enhancement of particle sedimentationin Zosteranoltei meadows.