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. Bulletin - Southern California Academy of Sciences. Science. PURPLE SEA URCHIN MASS MORTALITY 27. Fig. 3. Sea urchins, primarily Strongylocentrotus purpuratus, which were killed in a mass mortality event and stranded on the tideline at Malibu Lagoon State Beach. A) Freshly dead animals deposited by the falling tide on October 9, 2010 at 1519 h. B) Close view of the dead sea urchins in A, which are fully spined and have intact peristomial membrane and Aristotle's lantern. C) Five days after the breach on October 12, 2010, the assemblage of dead animals extends towards Malibu Pier. D) Dead urc

. Bulletin - Southern California Academy of Sciences. Science. PURPLE SEA URCHIN MASS MORTALITY 27. Fig. 3. Sea urchins, primarily Strongylocentrotus purpuratus, which were killed in a mass mortality event and stranded on the tideline at Malibu Lagoon State Beach. A) Freshly dead animals deposited by the falling tide on October 9, 2010 at 1519 h. B) Close view of the dead sea urchins in A, which are fully spined and have intact peristomial membrane and Aristotle's lantern. C) Five days after the breach on October 12, 2010, the assemblage of dead animals extends towards Malibu Pier. D) Dead urc Stock Photo
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. Bulletin - Southern California Academy of Sciences. Science. PURPLE SEA URCHIN MASS MORTALITY 27. Fig. 3. Sea urchins, primarily Strongylocentrotus purpuratus, which were killed in a mass mortality event and stranded on the tideline at Malibu Lagoon State Beach. A) Freshly dead animals deposited by the falling tide on October 9, 2010 at 1519 h. B) Close view of the dead sea urchins in A, which are fully spined and have intact peristomial membrane and Aristotle's lantern. C) Five days after the breach on October 12, 2010, the assemblage of dead animals extends towards Malibu Pier. D) Dead urchins in beach wrack are still largely intact, although spines are missing on some abraded tests on October 14, 2010. (Photos A, B courtesy M. Ralston/AFP; C courtesy D. Murray, Heal the Bay). October 12 (Krug, pers. comm.). On October 13, six days after the breach, I counted 2,000 dead S. purpuratus on the high tide mark between the eastern boundary of Malibu Lagoon and Malibu Pier. Among them were a small number of S. franciscanus, a Pugettia sp., a Panulirus sp. carapace, and a dead cormorant. The mean test diameter of dead S. purpuratus in a sample (n = 103) haphazardly collected from beach wrack that day, was 49.8 ± 6.0 mm (X ± SD). The peristomial membrane and Aristotle's lantern were intact in all but three specimens, and only 24 specimens were partially denuded of spines. Evidently, the relatively undamaged specimens were victims of the mass mortality event. However, one animal was entirely denuded of spines, and the ventral side of the test of two others was broken open. The latter, broken individuals had probably been attacked by sea gulls (Figure 4), as evidenced by the type of damage that they exhibited. Indeed, western gulls were observed scavenging dead urchins on the beach before, during and after the +0.9 cm low tide at 1652 h on that same day. On October 15, before and after a +18 cm low tide at 1811 h, I watched airborne western gulls repeatedly release S. pu