TEMPORAL PATTERNS OF ZOOPLANKTON MIGRATION 



Sharon L. Ohlhorst 

 Department of Fisheries and Wildlife 

 and 

 W. David Liddell 

 Department of Geology 

 Utah State University 

 Logan, Utah 84322 



ABSTRACT 



The NOAA/NULS-1 underwater habitat facility at St. Croix was utilized 

 during July 1982 for a study of the temporal patterns of migration into the 

 water column by reef zooplankton. Samples were collected for 6 days at 9 

 daily time intervals using mesh emergence traps, diver pushed plankton nets, 

 and surface plankton net tows. This is the first study to sample such finely 

 spaced time intervals. Preliminary analysis from 2 days indicated that there 

 was migration throughout the night, with increased activity found prior to 

 sunrise as well as following sunset. This is the first time a predawn rise of 

 zooplankton has been documented. 



The cyclopoid copepod, Oithona colcarva , dominated most time intervals, 

 although it was not nearly as abundant as in an earlier Caribbean reef zooplankton 

 study. Most zooplankton taxa followed the same general pattern of activity, and 

 the relative abundance of the common taxa generally remained the same throughout 

 the 24 hours. The time intervals around sunset were an exception, however. 

 For example, during the hour following sunset, calanoids, harpacticoids, 

 polychaetes, and pagurid larvae were relatively more abundant than during the 

 hour prior to sunset, while copepod nauplii and amphipods were less abundant 

 during this postsunset time interval. Significantly more taxa were captured 

 during the first hour of darkness than during any other time interval. 



The effects of different trap designs and types of reef substrata on 

 zooplankton samples also were examined. There was no significant difference in 

 the number of individuals collected between treatments using sealed and unsealed 

 traps or between those using unsealed traps over coral and sand substrata. 

 This is in contrast to other studies; two possible explanations for these 

 discrepancies relate to the types of substrata over which sealed and unsealed 

 traps are compared and to differences in trap sealing efficiency when different 

 substrata types are being compared. 



INTRODUCTION 



The zooplankton that reside within or near coral reef ecosystems have only 

 recently begun to receive the attention of researchers. Zooplankton have been 

 studied from various * icific reef communities primarily by using various 

 modifications of emergence traps (Alldredge and King, 1977, 1980; Porter and 

 Porter, 1977; Porter, et al . , 1977; Hobson and Chess, 1979; Birkeland and 



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