FISHERY BULLETIN: VOL. 72. NO. 2 



nation causes great difficulty for the movement of 

 this prey into the proximal half of the gut where 

 digestion occurs. For example, the median time for 

 score 3 of Acartia is significantly shorter than the 

 corresponding median ofCorycaeus as determined 

 by a [/-test rP<0.05). Similarly, the rigid bifur- 

 cate rostrum, caudal spines, and denticulate 

 carapace oiPenilia are often hooked into the gut 

 wall of the ctenophore and delay passage of the 

 prey to the site of digestion. Contrary to this delay 

 in the passage ofCorycaeus and Penilia, the rela- 

 tively smooth-bodied calanoids are translocated 

 quite easily by peristalsis of the gut. More detailed 

 studies might indicate differences in the integu- 

 ment to penetration by the digestive enzymes or 

 perhaps differences in the specificity of the en- 

 zymes for protein or lipid components of the sub- 

 strate. 



FIELD ECOLOGY OF P. BACHEI 



Study Area and Previous Plankton Work 



The study location is La Jolla Bight (long. 

 117'20'W, lat. 33'N), including the coastal waters 

 (hereafter coastal waters refers to that area 

 bounded by the shoreline and a line parallel to it 

 out to a distance of about 8 km) south to Point 

 Loma and north to Oceanside (Figure 4). The 

 major physiographic features of the area are: 1) 

 Point La Jolla, which extends about 2 km west of 

 the shoreline at Scripps Institution and forms the 

 southern boundary of La Jolla Bight; 2) two sub- 

 marine canyons (La Jolla and Scripps Canyons) in 

 La Jolla Bight which bring water over 100 m deep 

 within 2 km of shore; 3) numerous kelp beds lo- 

 cated both north and south of Point La Jolla gen- 

 erally in 10- to 20-m depth and extending out to 1 

 km from shore. The area is not strongly influenced 

 by precipitation and runoff, so that seasonal and 

 annual variations in salinity are within 32-34 Vco 

 (Fager, 1968). The range of sea-surface tempera- 

 ture is 14-2 IX annually and approximates the 

 temperature difference between the surface and 

 50 m in July (Mullin and Brooks, 1967). The tides 

 are of a mixed semidiurnal type with a diurnal 

 inequality and total daily range that change twice 

 each month. Within a given month the maximum 

 daily tidal range is about 2 m and the minimum 

 about 1 m. Wind velocities are highly variable; 

 storms with wind speeds greater than about 7 m/s 

 generally come from the southwest to the north- 

 west quadrant. Santa Ana winds blow occasion- 



en 



£ 



X 



< 



tr 

 o 



V 0.01 - 



Q 

 O 

 CD 



0.0001 



0.001 - 



10 



20 30 40 50 60 70 

 DAYS AFTER HATCHING 



80 



90 100 



Figure 3. — Growth in bodily organic weight of Pleurobrachia 

 bachei at 15°C during the second laboratory generation, expres- 

 sed as a function of age in days. The values for bodily organic 

 weight at different ages were calculated from the observed 

 growth in diameter and a regression of organic weight on diame- 

 ter. The horizontal and vertical bars indicate the ranges for age 

 at weight and weight at age, and the numbers in parentheses are 

 the number of specimens observed in the data. 



ally from the northeast in fall, and diel variations 

 in wind velocities predominate in the east-west 

 directions. 



Previous plankton work in the study area in- 

 clude the extensive phytoplankton work of Allen 

 (1928, 1941), the California Cooperative Oceanic 

 Fisheries Investigations programs, and the plank- 

 ton study off La Jolla by the Food Chain Research 

 Group (Strickland, 1970). In general these previ- 

 ous studies provide basic information on species 

 lists and levels of abundance and variability of 

 phytoplankton, microzooplankton, and macrozoo- 

 plankton. In these coastal waters, however, very 

 little information is available on the patterns of 

 water circulation, variations in abundance of or- 

 ganisms in relation to variations in the physical 

 parameters (e.g., tidal motion, wind velocities 

 etc.), or the organization and interaction of the 

 species which inhabit this coastal region. 



300 



