Discovery of an enteropneust associated with a mound-burrows trace in the deep sea: ecological and geochemical implications

Abstract

An exceptional box core sample taken in the Bay of Biscay (2100 m depth) revealed an organism beneath a relatively undisturbed mound surrounded by burrows. This type of biogenic microrelief is well known in the deep sea, but, as with many other benthic faunal traces, the responsible organism has remained unidentified. The fragile fragmented animal recovered is an enteropneust and likely the builder of the sampled mound-burrows complex. We report here the dimensions of the mound and burrows and data revealing their high density in several basins of the North Atlantic, and the correlation of the abundance of biological traces on the sediment surface with isotopic evidence of bioturbation. The enteropneust may be a pioneer species, creating these structures which constitute microenvironments favourable to the successive colonization of other observed organisms. The geochemical consequences of this common microrelief are discussed in terms of its influence on material exchange processes in sediments and its role in entrapment of horizontally transported suspended organic matter.