Abstract
The lithobiont community encrusting an early Pleistocene palaeocliff cropping out north of Augusta (SE Sicily, Italy) was investigated based on field observations and laboratory inspection of two rocky samples. Bryozoans, serpulids, brachiopods and bivalves encrusted part of the exposed surfaces that were bored mostly by clionaid sponges. Bryozoans, with at least 25 species detected on the rocky samples, are the most diversified skeletonized lithobionts also accounting for the highest number of colonies/specimens and highest coverage. Brachiopods, with the only species Novocrania anomala and a few but large cemented valves, cover wide surfaces. Serpulids, with two species identified on the sampled rocks and further two on the outcrop, were intermediate. A multiphase colonization is present, including a final epilithobiont community locally formed on eroded surfaces exposing a network of pervasive borings. The co-occurrence of very sciaphilic species having circalittoral to bathyal distributions suggests that the studied community thrived on a rocky substratum located near or at the shelf break, probably belonging to the shelf break (or RL) biocoenosis, also in agreement with observations on the fossil content of neighboring marly sediments. The observed relationships among colonizers largely represent mere superimpositions, and real interactions are not enough to state species competitiveness.
Highlights
In overviews on palaeoecology and the evolution of hard substrata marine communities, references [1,2] remarked how hard substrates offer a unique opportunity for examination of spatial distribution, overgrowth competitive interactions and community succession, because organisms cemented to or boring in them can be preserved in their own life position
The present paper aims at: i. describing the lithobiont community discovered on early Pleistocene hard bottoms cropping out near Augusta (SE Sicily); ii. assessing residual palaeobiodiversity; iii. reconstructing the palaeohabitat; iv. investigating the nature of interactions documented by preserved encrusters
Bryozoan colonies were very abundant, but the identification of species was difficult on the outcrop owing to colony preservation and visibility of diagnostic characters
Summary
In overviews on palaeoecology and the evolution of hard substrata marine communities, references [1,2] remarked how hard substrates offer a unique opportunity for examination of spatial distribution, overgrowth competitive interactions and community succession, because organisms cemented to or boring in them can be preserved in their own life position. Shells, bones and small sized lithic clasts dispersed on soft bottoms can be ephemeral and subject to displacement during taphonomic processes; whereas boulders, blocks, hardgrounds, bioconstructions and rocky outcrops offer the advantage of remaining stable for a long time being usually preserved essentially in their primary position because less prone to physical transport. This has a twofold advantage for palaeoecologists, enabling examination of organism interactions and certainty about the original spatial location of their substrata, providing impressive information for reconstructing the extension and morphology of depositional basins at any time and their evolution. The only existing data relate to Plio-Pleistocene cliffs in Mediterranean localities where strong tectonic activity produced exposed sindepositional fault palaeoscarps with blocks detached from them and collapsed into the basins, providing hard surfaces suitable for organism colonization at a relevant depth [8,12,13,14]
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