NOTES 



MORTALITIES AND EPIBIOTIC 



FOULING OF EGGS FROM 



WILD POPULATIONS OF THE 



DUNGENESS CRAB, CANCER MAGISTER''' 



Cultured crustaceans have been found to be sus- 

 ceptible to fouling by a variety of epibionts. Nilson 

 et al. (1975) recently described mortalities attrib- 

 uted to epibiotic fouling in the eggs and larvae of 

 the American lobster, Homarus americanus, the 

 larvae of the prawn, Pandalus platyceros, and lar- 

 vae of the Dungeness crab, Cancer magister Dana. 

 This same type of fouling has also been found on 

 juveniles of Penaeid shrimp, where it causes death 

 in rearing ponds with low oxygen content by in- 

 habiting the gill filaments and suffocating the 

 animal (Johnson et al. 1974; Lightner et al. 1975). 

 The organisms most commonly encountered have 

 been filamentous bacteria and algae. 



Work on the larval cultivation of the Dungeness 

 crab at the Bodega Marine Laboratory, Bodega 

 Bay, Calif., revealed heavy fouling on the eggs of 

 oviposited female crabs held in rearing tanks. 

 Further investigation showed that the condition 

 also existed on eggs of crabs obtained from local 

 fishermen. Egg masses with extensive fouling also 

 showed a large number of empty egg cases, al- 

 though eyespot development on the remaining 

 embryos showed the time until hatching to be dis- 

 tant. Similar fouling of the eggs of wild caught 

 Atlantic blue crabs, Callinectes sapidus, has been 

 observed and well documented (Sandoz et al. 1944; 

 Rogers-Talbert 1948). With Callinectes, however, 

 the predominant fouling organism appears to be 

 the fungus Lagenidium callinecti. 



These observations of fouling and mortality in 

 the natural population suggest a possible explana- 

 tion for the decline in Dungeness crab catches 

 recorded in the San Francisco Bay region since 

 1960 (Biostatistical Section 1961, 1963, 1964, 1965; 

 Greenhood and Mackett 1965, 1967; Heimann and 

 Frey 1968a,b; Heimann and Carlisle 1970; Pinkas 

 1970; Bell 1971; Oliphant 1973). In order to inves- 

 tigate this possibility, a distributional study was 

 undertaken, comparing mortalities and epibiotic 



fouling of crab eggs from various locations along 

 the coast of northern California. 



Materials and Methods 



Egg samples of C. magister were obtained from 

 fishermen along the northern California coast 

 during the period from 27 November 1974 to 30 

 January 1975. A total of 105 samples of eggs from 

 individual crabs were obtained from six regions 

 which included the following localities (Figure 1): 

 region I — Pacifica (4 samples); region II — 

 Drake's Bay (18 samples); region III — Point Reyes 

 (39 samples); region IV — Bodega Bay, Russian 

 River, and Gualala (10 samples); region V — Fort 

 Bragg (20 samples); region VI — Eureka (14 sam- 

 ples). 



In the field, a portion of eggs were removed from 

 the Dungeness crab egg masses and placed in vials 



Froncisco Boy 



'This work was supported by California State Legislature 

 Aquaculture funds. 



^This work was done at the University of California, Bodega 

 Marine Laboratory at Bodega Bay, CA 94923. 



Figure l.— The coast of northern California showing the 

 Dungeness crab collection sites: I - Pacifica; II - Drake's Bay; III 

 - Point Reyes; IV - Bodega Bay, Russian River, and Gualala; V - 

 Fort Bragg; VI - Eureka. 



201 



