Piercing the Mystery: Predator Identification Using the Perforated Tests of the Sea Urchin Brissus unicolor (Leske, 1778)

Drilling predation on echinoids (sea urchins) has been known to occur in marine ecosystems since the Jurassic Period; however, it has rarely been studied in existing species. Tests of the irregular sea urchin Brissus unicolor (Leske, 1778), which frequently occurs in shallow substrates of the Canary Islands, mostly show very evident perforations through their skeletons. The aim of this study was to describe the characteristics of these perforations in order to determine their possible origins as well as document their size, site selectivity, and frequency of occurrence among different sample sites. Of the 104 tests of B. unicolor that were collected from 15 locations off the island of Tenerife (Canary Islands, Spain), 94% showed a least one perforation. These boreholes exhibit a circular morphology, penetrating the sea urchin tests perpendicularly and entirely. Notably, they display a unique acid signature, diverging from those documented in the fossil record and other relevant studies. Our analysis showed size and site selectivity by the predator as the perforations were mainly located on the oral side of the test. The perforations are attributed to drilling predation. The characteristics of these boreholes on B. unicolor match published records of predation marks suggesting that they are produced by the predatory gastropod family Cassidae, with Semicassis undulata (Gmelin, 1791) considered to be the most probable predator.