Temperate bioerosion: ichnodiversity and biodiversity from intertidal to bathyal depths (Azores)

Abstract

In the temperate Azores carbonate factory, a substantial fraction of the calcareous skeletal components is recycled by a remarkable biodiversity of biota producing bioerosion traces (incipient trace fossils). To study this biodiversity, experimental carbonate substrates were exposed to colonisation by epilithic and endolithic organisms along a bathymetrical gradient from 0 to 500 m depth, during 1 and 2 years of exposure. The overall bioerosion ichnodiversity is very high and comprises 56 ichnotaxa and ichnoforms attributed to cyanobacteria, chlorophytes, fungi, other micro-chemotrophs, macroborers, grazers and epilithic attachment scars. In the intertidal, hydrodynamic force, partial emersion and strong temperature fluctuations lead to the lowest ichnospecies richness. This contrasts with the highest ichnodiversity found at 15 m under the most favourable environmental conditions. Towards aphotic depths, a gradual depletion in ichnodiversity is observed, most probably because of the restricted light availability and a slowdown in ichnocoenosis development. Analysis of similarity (ANOSIM), in combination with non-metrical multidimensional scaling (NMDS), was used to highlight variability in the relative abundance of traces among depths, substrate orientations and exposure times. Ichnodiversity and abundance of traces decrease significantly with depth and are higher on up-facing versus down-facing substrates, whereas differences between years were not as pronounced. This study demonstrates that statistical methods of biodiversity analysis are not per se restricted to biotaxa but may well be applied also to ichnotaxa. In the analysis of trace fossil assemblages, this approach supports the recognition of diversity patterns and their relation to environmental gradients.

Taming an ichnotaxonomical Pandora's box: revision of dendritic and rosetted microborings (ichnofamily: Dendrinidae)

“…In addition, own material from previous studies was revisited (e.g., Wisshak et al 2005aWisshak et al , 2005bWisshak et al , 2011Wisshak 2006) and new material was investigated to solve some of the pending ichnotaxonomical issues. In this context, a large collection of Upper Cretaceous belemnites, brachiopods, bivalves, fish teeth and other biogenic skeletal substrates was kindly provided by the ambitious private collector Peter Girod (Berlin, Germany).…”

“…Among the observed specimens from the Azores experiment (Wisshak et al 2011; therein addressed as 'Dendroid form 2'), 16 specimens were complete (including a wide range of ontogenetic stages) and were documented by SEM images in planar view, allowing for accurate morphometrical measurements. These traces ranged from 120 to 1020 µm in maximum length (mean = 401 ± 264 µm) and 71 to 1371 µm in maximum width (mean = 430 ± 370 µm).…”

Taphonomy of Backshore Versus Deep-Marine Collected Nautilus Macromphalus Conchs (New Caledonia)

“…5H) and the 'superthin form' (Fig. 5I) (sensu Wisshak et al 2011) both produced by unknown heterotrophs. Rare borings include i. Flagrichnus profundus (Fig.…”

Microboring in a Freshwater Fluvial Unionid Bivalve Substrate

“…Organisms that create euendolithic microborings are a noted component of present day marine ecosystems, where they exploit both live and dead biogenically derived carbonate substrates, in addition to their occurrence in lithic substrates of purely abiogenic origin (e.g., Mao Che et al, 1996;Sch€ onberg and Tapanila, 2006;Wisshak et al, 2011;Wisshak, 2012 and references therein). Potential selection pressures favoring the adoption of a boring habit are outlined and discussed in Cockell and Herrera (2008).…”