todropscience:

BADASS SEA URCHINS DRILL HOLES IN SOLID ROCK

In temperate rocky reefs, sea urchins are abundants, and often occur in cavities within the rock, and fit so tightly, it is natural to assume they sculpted these “pits. For a long time, scientists have wondered if they did really mold them by themselves, but until now there was no data to support this idea. A new study has allowed to see how these animals create these pits of the rocks thanks to an experiment carried out with purple sea urchins (Strongylocentrotus purpuratus). The results, published in the journal PLoS ONE, reveal that they are the sculptors of these holes.

Scientists recreated environmental conditions where sea urchins lives, with fine and medium-grained sandstone rocks, lulita and granite from three California reefs where these echinoids tend to inhabit, and where researchers also did field measurements. After observing them, researchers proved that sea urchins actually excavate rocks,

with just their teeth,

removing material from all the rocky surfaces. In the lab, rates of excavation varied greatly according to the type of rock. While each sea urchin excavated about 32 grams of medium-grained sandstone for a year, which would allow them to excavate a medium hole in less than five years, the excavation in granite was 37 times slower, a task so hard that it would take more than a century to make a hole.

In medium-grained sandstone reefs, sea urchins can produce almost 200 tons of sediment per hectare in just one year. When compared with the field observations, the scientists were able to confirm this difference: granite holes were shallower than the sandstone holes, and sea urchins living in granite were flatter.

• Photograph:

  Michael Russell 

• Reference: 

  Russell et al. 2018. Bioerosion by pit-forming, temperate-reef sea urchins: History, rates and broader implications. PLoS ONE.