Predation by drilling gastropods and asteroids upon mussels in rocky shallow shores of southernmost South America: paleontological implications

GORDILLO, SANDRA; ARCHUBY, FERNANDO M

ACTA PALAEONTOLOGICA POLONICA

INST PALEOBIOLOGII PAN

Lugar: Warsaw; Año: 2012 vol. 57 p. 633 - 646

0567-7920

To achieve a better understanding of predation pattern recorded in the fossil record it is essential to study predator-prey interactions in the modern seas. It includes the data collected from the field observations as well as from the experiments in captivity. Such an approach allows recognition of the bioeroders, its description and also provides quantication of these interactions. This work offers a case study of the traces of predation resulting from the predator-prey interactions between three mussels: Mytilus chilensis, Brachidontes purpuratus, and Aulacomya atra; and their five natural enemies: the gastropods Trophon geversianus, Xymenopsis muriciformis, and Acanthina monodon, and the asteroids Cosmasterias lurida and Anasterias antarctica living along the intertidal and/or subtidal rocky shores in Tierra del Fuego.  The predatory damage to mussel shells varies according to the predator and prey species and techniques for attacking prey are highly specialized, and depend on prey species. A. monodon drills a hole on B. purpuratus, but this predator uses the outer lip of its shell as a wedge to open the valves of M. chilensis and A. atra. T. geversianus always makes holes, but while it drills the valve-walls of M. chilensis, it prefers to drill the valve edges of A. atra and B. purpuratus, with different characteristic patterns. Shells of most mussels killed by C. lurida have not suffered mechanical damage, but some mussels were crushed or fractured along the margins. Comparatively, time required to successfully attack a prey was lower in C. lurida (24 hours), followed by A. monodon (36 hours), and higher in T. geversianus (9 to 10 days). Traces of predation were not randomly distributed across size classes of mussel prey, reflecting selectivity for a particular size class. Also, drill holes were usually placed at specific places of the shell, indicating site selectivity. Some paleontological implications can be derived from this paper. For instance, different patterns of shell damage can be due to different predator species (e.g. wall vs. edge drillings), although the same predator species can leave different marks when consuming different prey (e.g. T. geversianus). Most disconcerting for paleontologists are predation cases that do not leave marks on the prey shell that can be detected in the fossil record (e.g. asteroids), or leave ambiguous marks (A. monodon when preying with the spine). In conclusion, besides the opportunity to identify some traces of predation by drilling gastropods in fossil mussels, this work gives criteria to address predation in some particular paleontological cases that would otherwise be dismissed by researchers.