Smalley, 1981; McWi 1 1 i am , et aL, 1981; and Walter, et aK, 1982). Fewer 

 studies of reef zooplankton from the Caribbean have been conducted (Ohlhorst, 

 1980, 1982, 1985; Robichaux, et a_U , 1981; and Youngbluth, 1982). While the 

 diel migration patterns of these zooplankton have been shown to influence the 

 behavior of nocturnal plankti vorous fish (Hobson, 1974; Hobson and Chess, 1978; 

 Robertson and Howard, 1978) and might affect the behavior of other reef 

 planktivores (Porter, 1974; Sebens, 1977; Liddell, 1982), few studies have 

 investigated the diel migration patterns of reef zooplankton in detail (Alldredge 

 and King, 1980; Ohlhorst, 1982; Walter, et a_L, 1982). The only study of 

 migration by Caribbean reef zooplankton "[conducted at Jamaica by Ohlhorst, 

 1982) suggests that there is no single pulse of migratory activity; rather 

 zooplankton rise into the water column at variable rates throughout the night 

 with a peak of activity during the second hour after sunset. Also, different 

 taxa were shown to exhibit differing migratory patterns. While these observations 

 are consistent with those from the Pacific, it is important to determine whether 

 or not such patterns occur elsewhere in the Caribbean. Additionally, more 

 frequent sampling than previously conducted would be of value in refining the 

 patterns of zooplankton migration. 



One of the reasons for the paucity of detailed studies addressing this 

 question is the physiological limitation placed upon safely conducting the 

 repeated sampling dives which are necessary for such studies. Previous studies 

 which have addressed the question of migratory patterns of reef zooplankton 

 have been restricted to sampling widely spaced time intervals or sampling very 

 shallow (< 5m) sites. Data from Ohlhorst (1985) suggests that caution should 

 be used when extrapolating data from shallow sites to greater depths. The 

 present study examines the migratory patterns of reef zooplankton at an 

 intermediate (15 m) depth at St. Croix through repeated sampling of finely 

 spaced time intervals. This sampling was made possible by saturation diving 

 from the N0AA/NULS-1 Underwater Habitat, HYDROLAB. 



METHODS 



Sampling of reef zooplankton was conducted from the N0AA/NULS-1 HYDROLAB 

 located at 15 m depth in the Salt River submarine canyon on the north coast of 

 St. Croix, U.S. Virgin Islands (17°45' N, 64°45' W) during July 1982. Samples 

 were collected from both reef and sand areas located approximately 15 m east 

 of the Habitat. To eliminate biases caused by the proximity of the study sites 

 to the Habitat, all of the external lights of the HYDROLAB remained off for the 

 duration of the study. Saturation diving from the HYDROLAB enabled two teams 

 of divers to collect plankton samples at closely spaced intervals over a 6-day 

 period. 



Zooplankton were sampled by three methods: (1) Emergence traps, which 

 covered 0.5 m^, were placed over various types of reef substrata to capture 

 zooplankton moving from the reef site into the water column. Certain of these 

 traps were sealed over their substrata by a skirt (Robichaux, et al . , 1981), 

 while others were affixed more loosely over their substrata. J2) Diver pushed 



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