HIROTA: NATURAL HISTORY OF PLEUROBRACHIA BACHEI IN LA JOLLA BIGHT 



Table 1. — Rate of digestion experiments at 20°C for individual adults of five prey species and 

 various sizes of Pleurobrachia bachei. Medians and ranges are given for the diameters of the 

 ctenophores used in the trials and for the elapsed time in minutes from the prey entanglement with 

 the tentacles until each score of digestion is achieved. The values in parentheses are the medians 

 for the elapsed time to achieve scores 2 and 1 divided by the bodily organic weight of each respective 

 prey. Refer to the Methods for details. 



Diameter 

 (mm) 



Prey 



Trials 



Labidocera 

 trispinosa 



Acartia 

 tonsa 



Paracalanus 

 parvus 



Corycaeus 



anglicus 



Penilia 

 avirostris 



12 



Table 2. — The mean and range of organic weight of six prey 

 species of Pleurobrachia bachei. F, M, A, CV, and J refer to 

 females, males, adults, fifth copepodids and juveniles, respec- 

 tively. 



The three main physical parameters considered 

 in the course of the field studies are current veloc- 

 ity, water temperature, and tidal stage. Current 

 velocities in La Jolla Bight were measured on five 

 , occasions between November 1969 and June 1970 

 by tracking surface floats attached to parachute 

 and "vane" drogues (vane drogues were made of 



Figure 4. — The study area: La Jolla Bight and ac^jacent waters. 

 Sampling stations 1-5 and 6 are located 1.6 and 10 km offshore, 

 respectively. The juncture of Scripps Canyon with La Jolla Can- 

 yon is near station 5. The depth contours are in fathoms. 



301 



