The Yongala's "Halo of Holes" - systematic bioturbation close to a shipwreck

Abstract

Large-scale systematic bioturbation is documented in 30 m of water depth around the Yongala shipwreck in the Great Barrier Reef. The "Halo of Holes" contains over 1,200 individual depressions with diameters of up to 10 m, tightly packed in a concentric, three-quarter ring around the wreck. Two distinct zones in this halo consist of either only shallow or only deep holes. Deep holes (up to 1.5 m depth) show signs of ongoing bioturbation. Shallow holes support diverse sessile faunal assemblages of sponges, soft corals, and hard corals in an otherwise flat seafloor dominated by marine plants. The holes are most likely of biogenic origin, but the animal(s) responsible for these earthworks are unknown to date. The bioturbators are ecosystem engineers, creating a habitat for assemblages that are absent elsewhere on the adjacent seafloor. The previously undocumented halo of holes and its biota indicate that the "ecosystem wreck" extends further beyond the spatial confines of the hull of a wreck than previously considered.