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Fishery Bulletin 101(3) 



sum of the esophageal and labial growth. Urchin jaws do 

 not wear or erode as teeth do. Calculating test growth from 

 changes in jaw size may yield a conservative estimate for 

 sublegal red sea urchins (Kalvass et al., 1998). 



In the PIT-tagged urchins, growth was measured as the 

 change in test diameter after one year. Juvenile urchins 

 less than 30 mm are too small to survive PIT tag implan- 

 tation. Large adults (>100 mm) may grow too little in one 

 year to allow growth in test diameter to be measured. 

 Standard errors in measures of test diameter with calipers 

 range from 1-2 mm which may be greater than the growth 

 increment in adults. 



Jaw size versus test size 



The relationship between jaw length and test diameter was 

 determined from a large sample {n=384) of red sea urchins 

 (sample independent of this study) ranging in size from 

 newly settled individuals to large adults. From this sample 

 we obtained an allometric equation relating jaw and test 

 size. Using this equation we converted all the measures 

 of growth (from fluorescent and PIT tagged urchins) into 

 initial and final jaw size (one year later). 



Jaw size is a plastic trait that can vary spatially (Ebert, 

 1980b; Rogers-Bennett et al., 1995). Food availability has 

 been correlated with the size of Aristotle's lantern (com- 

 posed of ten jaws and five teeth) such that lanterns are large 

 when food is scarce. Therefore, we examined the relationship 

 between jaw size and test size, segregating the data from 

 the shallow and deep Salt Point sites. To do this we used 

 an ANCOVA (Table 1) with the natural log of test diameter 

 as the covariate. Measurements of the jaw size at tagging 

 from the fluorescent marks allowed for estimates of the test 

 size at tagging using the allometric relationship (Eq. 1). As 

 a control to test for bias in the conversion of jaw size to test 

 diameter with Equation 1, we compared the measured test 

 size at the time of recapture to the predicted test size at the 

 time of recapture using the allometric relationship (Eq. 1). 

 Results indicated that, although there was error in the pre- 

 dicted test size from jaw size, there was no bias. 



Results 



Red urchin growth 



We present growth data from a total of 211 red sea urchins 

 that were tagged internally and recaptured after one year 

 in northern California. Recaptured urchins ranged in test 

 diameter from 7 to 131 mm at the time of tagging. We recov- 

 ered 161 out of 609 (26.4%) tetracycline-tagged wild urchins 

 from the two sites at Salt Point. In addition, 38 of the 240 

 (15.8%) stocked juvenile urchins tagged with calcien were 

 also recovered. It is unknown whether untagged urchins 

 included tagged adults which were not growing and therefore 

 not taking up the tetracycline stain. In the Caspar Reserve 

 12 of 53 (22.6%) PIT-tagged wild urchins were recovered. 



We examined spatial variation in growth and found that 

 the change in size (AJ) was not significantly different for 

 urchins in the shallow, as compared to the deep Salt Point 

 sites (ANCOVA F=0.246, n = 199, P=0.62) with initial jaw 

 size (J,) as the covariate (independent variable). Similarly, 

 growth rates were not significantly different between 

 juveniles recovered in shallow and deep sites (ANCOVA 

 F=0.387, 11=38, P=0.54). Richards function parameter esti- 

 mates (J^, K, n ) generated from the shallow site were sta- 

 tistically identical to those for the deep site. Size-frequency 

 distributions of urchins recovered from the shallow site 

 were not significantly different than those at the deep site 

 (K-S mean difference=0.162, P=0.67). Therefore, growth 

 data from the shallow and deep sites were pooled. 



Urchin density at the shallow site (4.2 urchins/m'-^) was 

 greater than at the deep site (0.75 urchins/m^). In addition, 

 drift algae abundance was twice as great in the shallow 

 (2.7 g/m^) as in the deep site (1.4 g/m'-) at the time of urchin 

 harvest ( 18 September 1993 ). This resulted in less algae per 

 urchin in the shallow site compared with the deep site (0.63 

 g/urchin and 1.85 g/urchin respectively) for that sampling 

 date. Guts of urchins from the deep habitats contained 

 more optimal food (fleshy red and brown algae) than guts 

 of urchins in the shallow sites «=2.79, df=19, P=0.012). Gut 

 fullness was generally uniform, roughly 50 mL/urchin. 



