In the laboratory it has been shown (Fisher 

 1976) that increased phosphate and nitrate levels 

 in the seawater did, in fact, increase the number of 

 epibiotic filaments and concurrently the number 

 of egg mortalities. Conversely, chemotherapeutic 

 and antibiotic treatment reduced filamentous 

 growth and egg mortalities. It was also shown that 

 both the number of filaments and the number of 

 egg mortalities decreased exponentially with 

 increasing depth into the egg masses (to a depth of 

 9 mm). 



This study is similar to the original field study 

 (Fisher and Wickham 1976) with modifications 

 based on the information gained in the laboratory. 

 All samples were collected from the same position 

 on the egg masses to discount probable errors due 

 to mortality variations within each egg mass. 

 Only samples with eyespot development and no 

 signs of hatching were used, restricting the var- 

 iation in developmental states to approximately 2 

 wk. Mortality estimates were made from both the 

 peripheral eggs of a sample and the total sample to 

 determine the in situ significance of the peripheral 

 mortalities reported for the laboratory conditions 

 (Fisher 1976). 



Procedures 



The crab eggs were sampled between 26 De- 

 cember 1975 and 27 January 1976 from four 

 regions: Pacifica, Drakes Bay, Russian River, and 

 Eureka. Relative to the mouth of San Francisco 

 Bay, Pacifica is slightly south, Drakes Bay 

 slightly north, Russian River 80 km north, and 

 Eureka 400 km north. Samplers in each area were 

 supplied with curved forceps, vials partially filled 

 with 10% Formalin 2 in seawater, and a data sheet 

 for recording date, depth, and Loran reading for 

 each sample collected. As ovigerous females were 

 captured, small clusters of eggs were removed 

 about 1-2 cm from the posterior tip of the abdomen 

 along the midventral line with the curved forceps 

 and placed in the vials of preservative. 



After arrival at Bodega Marine Laboratory, the 

 samples were examined under a dissecting 

 microscope for the presence of eyespots. The 

 samples were discarded if eyespots were lacking or 

 if embryos were beginning to hatch. Laboratory 

 observations have shown the time from eyespot 

 appearance to the time of hatch to be about 2 wk 



while the entire external incubation period is 

 about 2 mo. 



Ten setae were randomly selected from the 

 remaining samples (Pacifica, 27; Drakes Bay, 17; 

 Russian River, 21; Eureka, 23). The first 25 eggs 

 on the distal ends of these setae were examined 

 under the dissecting microscope for mortalities. 

 This provided a peripheral mortality estimate. 

 Percentage peripheral mortalities were calculated 

 from the average mortalities for each region. 



The 10 setae from each sample were returned to 

 the sample vials and transferred to a second in- 

 vestigator. Ten to fifteen setae were then ran- 

 domly selected and an overall mortality estimate 

 was obtained by counting all the live and dead 

 eggs in this subsample (approximately 1,500 

 eggs). Percentage overall mortalities were cal- 

 culated for each sample and then averaged for 

 each region. 



Results 



Drakes Bay samples had the highest mor- 

 talities, while those from the Russian River and 

 Eureka had the lowest. The peripheral and overall 

 mortality estimates were consistent for all regions 

 except for Drakes Bay where peripheral mor- 

 talities averaged 39.4% and overall mortalities 

 averaged 27.6% (Table 1). A Student's t statistic 

 for the means of two samples showed all regions 

 except Eureka and the Russian River to be sig- 

 nificantly different (P<0.05) from all other reg- 

 ions using both peripheral and overall mortalities. 

 By the same analysis, the peripheral and overall 

 mortalities within each region were statistically 

 similar (P>0.1). 



TABLE 1. — Average Dungeness crab egg mortalities for each re- 

 gion sampled. The first 25 eggs on the distal end of 10 setae from 

 each sample were examined. 



2 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Discussion 



These results agree with the original study 

 completed during the 1974-75 season. High 

 numbers of egg mortalities were found in the 

 Drakes Bay region and low numbers in samples 

 from the Eureka and the Russian River regions. 



236 



