FIGURE 1. — Four diseased Strongylocentrotus franciscanus col- 

 lected on 31 July 1976 from 3-5 m depth off Ano Nuevo Island, 

 Calif. Each animal is about 10 cm in diameter. Note the large 

 portion of test denuded of spines in each animal. 



and a nearly normal white inner layer (the "cal- 

 lus" layer, see Pearse and Pearse (1975) for de- 

 scription of the layers of the test plates and 

 methods for examining them). Portions of the 

 inner layer of the affected area were discolored 

 reddish brown, however, often with a rather 

 blotchy appearance. Clorox 1 cleaned and thin- 

 ground preparations of the plates showed that 

 middle layer of the diseased plates had lost much 

 of its trabecular structure and there were large 

 spaces between the middle layer and the inner 

 layer. In the most diseased plates, the inner layer 

 could be separated easily from the middle layer of 

 the plates. The ambulacral system with the water 

 vascular canals, ampullae, and radial nerve were 

 all discolored reddish brown under the diseased 

 portions of the test and much of these tissues were 

 speckled with dark reddish-brown flakes, prob- 

 ably clumped coelomocytes. The internal organs 

 in other portions of the diseased animals appeared 

 normal. 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



The symptoms noted in the diseased animals at 

 Aho Nuevo Island in 1976 seemed identical to 

 those described for diseased animals found at 

 Point Loma in 1970 by Johnson ( 1971 ). Such simi- 

 larity suggests that the same disease organism 

 may be involved in these mass mortalities. Alter- 

 natively, the symptoms could reflect a general re- 

 sponse to localized infections or disruptions of the 

 test from a variety of physical, chemical, or biolog- 

 ical agents. As Johnson (1971) cautioned, careful 

 microbiological work needs to be done before the 

 causative agent( s) of these mass mortalities can be 

 identified. 



The Aho Nuevo Island site of the mass mortality 

 was revisited on 24 September 1976. Sea urchins 

 were scarce compared with the earlier visit and 

 most were nestled in crevices. Only one animal 

 was found with symptoms of the disease; it had a 

 narrow strip down one interambulacrum which 

 was denuded of spines. However, when this ani- 

 mal was examined in the laboratory, it was found 

 that a large portion of the diseased interambu- 

 lacrum and adjacent ambulacrum was covered 

 with short regenerating spines, and the ambulac- 

 rum was concave and grossly deformed. Six other 

 normal-appearing animals were brought into the 

 laboratory and two of these had small areas on the 

 test with regenerating spines. From these obser- 

 vations, it appeared that the mass mortality had 

 ceased and some of the animals survived and re- 

 generated their lost spines. 



The second mass mortality of S. franciscanus we 

 found in 1976 occurred at 4-6 m depth off the east 

 side of Point Santa Cruz (lat. 36°57'05"N, long. 

 122°01'30"W); this area was described by Matti- 

 sonetal. ( 1977). Animals looking "sick" and losing 

 spines were seen in the area in early June (A. L. 

 Shanks, J. D. Trent pers. commun.). We did quan- 

 titative studies at fixed stations off Point Santa 

 Cruz on 28-30 June 1976 and again on 10-11 

 September 1976. Although we found no animals 

 with denuded tests at our study stations, there was 

 a notable decrease in the number of animals pres- 

 ent compared with the counts made in the previ- 

 ous two summers (Figure 2). The number of ani- 

 mals at the seaward edge of the kelp forest main- 

 tained densities of about 55-65/10 m 2 during the 

 summers of 1974 and 1975. Fifty and one hundred 

 meters seaward of the kelp forest, lower densities 

 of 20-30 animals/ 10 m 2 occurred on the barren- 

 appearing rocks. In the summer of 1976, we found 

 only about 20 animals/10 m 2 at the edge of the 

 kelp forest and about 1-2/10 m 2 50 and 100 m 



646 



