Purple urchin burrows in bedrock, with and without occupants.

<p>(A) A large tidepool outside the impact zone (site 4), with a dense population of live <i>Strongylocentrotus purpuratus</i> in November 2011. (B) Empty urchin burrows in a tidepool (site 16) after the mass mortality event. (C) Close-up of occupied purple urchin burrows, showing one urchin per burrow and 100% occupancy; note urchins are covered with debris. (D) Close-up of clean, empty urchin burrows such as those used to estimate pre-event densities.