HOBSON and CHESS: TROPHIC INTERACTIONS 



Table 3.-Ostracods collected in the water column, day and night. 



present including Candacia spp., Clausocalanus 

 sp., Ctenocalanus sp., Euchaeta sp., Labidocera 

 spp., Lucicutia sp., Metridia pacificus, Pa- 

 racalaniis sp., and Rhincalanus na^utu^. The 

 major cyclopoid was Coryceus sp. (Figure 5E), but 

 others, including Oithona sp., were present. 



Harpacticoid Copepods 



Our daytime collections took relatively few 

 harpacticoids, all near the bottom. They were more 

 numerous in the night collections, however, when 

 they appeared in both middepth and near-bottom 

 samples. One form predominated, a species of 

 Porcellidium, probably undescribed, designated 

 Porcellidium species A (Figure 5G). Our night 

 middepth collections {n = 6) took x = 21.6 

 specimens of this species, whereas the near-bot- 

 tom collections {n = 6) took x = 37.3. During the 

 day Porcellidium species A was absent in all 

 middepth collections {n = 6), but the near-bottom 

 collections {n = 6) took x = 16. Only one other 

 harpacticoid was collected in daylight, a form here 

 designated as harpacticoid species A. Our daytime 

 middepth collections (n = 6) took x = 1.8 

 specimens of this species, but it was absent in all 

 daytime near-bottom collections, and all collec- 

 tions made at night. Three other forms— a second 

 species of Porcellidium, and two species of Eupel- 

 ta (all probably undescribed)-were taken only at 

 night: a combined mean of 0.7 in the middepth 

 collections, and a combined mean of 3.2 in near- 

 bottom collections. 



Other Copepods 

 No other copepods were seen in the water 



column, and very few were taken in the plankton 

 net. An occasional caligoid or monstrilloid ap- 

 peared in the collections, but were too few to 

 suggest a pattern. 



Cirripedian Larvae 



Most of the tiny cypris larvae of the barnacles 

 (Figure 5D) are smaller than 1 mm. Their occur- 

 rence in the collections (Tables 1, 2) was irregular, 

 and without consistent differences between day 

 and night, or between middepth and near-bottom 

 samples. 



Nebaliaceans 



At night we occasionally observed and collected 

 one species, probably Nebalia pugettensis (Figure 

 5J; see Smith and Carlton 1975). However, they 

 were neither seen nor taken during the day. 



Mysids 



Siriella pacifica (Figure 5M) was the most 

 widespread mysid over the study area. It remained 

 sheltered on the sea floor and close to kelp during 

 the day, but during late twilight moved into open 

 water, where it spent the night (Table 4). On five 

 evenings we noted when S. pacifica had first risen 

 as much as 1 m above the bottom, and found this 

 level attained 29 to 42 (x = 37.6) min after sunset. 

 On six mornings, the last individual 1 m above the 

 bottom was seen 32 to 50 {x = 38.7) min before 

 sunrise. The stomach contents of 30 S. pacifica 

 collected during day and night were examined: 

 DAYTIME-of 10 (8.5-10.5 mm, x = 9.6) collected 

 amid giant kelp during midafternoon (5 from the 



573 



