Table 11. Depth of occurrence and feeding characteristics of molluscs found 

 in Mugu Lagoon and Mission Bay marshes and tidal creeks (from Macdonald 1969, 



Table 5). [e=epifauna, i = infauna. followed by depth of burial] , 



Rasp Ciliary 

 Depth Algae & suspen- Deposit 



of detritus sion feeder 

 occur- from feeder (organic Pred- Scav- 

 Mollusc species rence substrate (plankton) detritus) ator enger 



Assiminea californica e x 



Cerithidea californica e 



Nassarius tegula i<5cm 



Acteocina sp. i<5cm 



Melampus olivaceus e 



Modiolus senhousei i<5cm 



Chione fluctifraga i<5cm 



Macoma nasuta i<5-20cm 



Protothaca staminea i<5cm 



Tagelus californianus i>20cm 



The smallest of the marsh crabs are 

 the fiddler crabs ( Uca crenulata ) . They 

 are best known for their elaborate mating 

 behavior in which the male waves his one 

 large cheliped or "fiddle." The genus Uca 

 is restricted to warm seas, and U^. 

 crenulata is not found north of Bolsa 

 Chica. Fiddler crabs usually coexist with 

 two grapsid crabs, Hemigrapsus oregonensis 

 and Pachygrapsus crassipes , in southern 

 California marshes. 



Willason (1980) compared ecological 

 preferences and examined interactions 

 between the shore crabs, Hemigrapsus 

 oregonensis and Pachygrapsus crassipes , at 

 Goleta Slough in order to understand their 

 distributions in the tidal creeks. Both 

 species are nocturnal, but he made 

 nighttime observation and excavated 

 burrows to collect crabs for field and 

 laboratory experiments. Densities of 



Hemigrapsus averaged about 75/m , while 

 Pachygrapsus averaged about 20/m . On 

 the average, Hemigrapsus individuals were 

 smaller (mean carapace width 15 mm) than 

 Pachygrapsus (mean = 26 mm), which may 

 relate to their different densities. Both 

 species were reproductively active during 

 spring and summer. Hemigrapsus had high 

 recruitment of young along the mudbanks, 

 while young of Pachygrapsus were most 

 numerous near the mouths of both Goleta 

 Slough and Carpinteria Marsh (Willason 

 1980). More solid substrates may be 

 necessary to estimate larval settling of 

 Pachygrapsus , or larval mortality may be 

 high in the muddier creeks. Within 

 different tidal creeks, there appeared to 

 be a negative correlation of the two 

 species, with an indication that 

 Pachygrapsus inhibited Hemigrapsus from 

 occupying its preferred lower bank 

 habitat. Experiments were designed to 



63 



