SPATIAL COMPARISONS OF DRILLING PREDATION IN THE SERRIPES ZONE, TJӦRNES, ICELAND, AND THE RED CRAG FORMATION, EAST ANGLIA, ENGLAND, ACROSS THE TRANS-ARCTIC INVASION

Ecosystem conservation efforts can use the fossil record to give a deep-time perspective on how organisms in paleo-ecosystems reacted to ecosystem change, such as the introduction of invasive species, before anthropogenic impacts. Drill holes from invasive naticid gastropod predators on bivalve prey can be quantified to provide evidence of the impact of these invasive predators on ecosystems.

The trans-Arctic invasion (TAI) occurred ~3.5 Ma, because of the opening of the Bering Strait, which allowed for an asymmetrical faunal interchange between the Pacific and Atlantic oceans. The Serripes zone (3.6-2.6 Ma) of the Tjörnes peninsula, Iceland, well characterizes the TAI. It can be correlated to the Red Crag Formation (2.54 Ma) of East Anglia, England, because both of these localities are of similar age and contain similar taxa. Predator-prey interactions can be analyzed in these post-invasion deposits to make spatial comparisons of the extent and effect of the TAI across the North Atlantic.

Specimens from the Serripes zone were analyzed in collections housed at the Icelandic Institute of Natural History. Red Crag Formation specimens were analyzed at the Academy of Natural Sciences at Drexel University in Philadelphia, PA. Height and length of bivalve specimens were measured. The occurrence of complete and incomplete (unsuccessful) drill holes and drill hole diameter were recorded for all whole bivalves. Drilling frequency (DF = % mortality) and prey effectiveness (PE = % of attempted drill holes that were incomplete) were calculated.

The Serripes zone included 37 bivalve species (1295 specimens), whereas 78 bivalve species (531 specimens) were found in the Red Crag Formation. Rarefaction curves were created for the two localities to compare species richness. The curve for the Serripes zone is flatter than that of the Red Crag Formation, which indicates that more complete sampling occurred in the Serripes zone. DF was higher in the Red Crag Formation (0.082) than the Serripes zone (0.058). PE was lower in the Serripes zone (0.167) than in the Red Crag Formation (0.333). Comparison of size of the prey bivalve Astarte to drill hole size portrays that invasive naticids selected smaller-sized prey in the Serripes zone than in the Red Crag Formation.