Abundance of Zooplankton 



The average volume of 5.3 ml of zooplankton per 1 m? reef substratum at 15 m 

 depth on the East Fore Reef indicates that only 3-4% of the reef energy needs, 

 as determined by Johannes, et al . (1970) for an area of high coral cover, could 

 be met by the capture of all of the demersal zooplankton (table 2). While the 

 6 m site yielded more zooplankton, it was rarely more than 12% of the amount 

 necessary to sustain the corals. Gut analyses of various reef plankti vores, 

 such as corals (Porter, 1974) and crinoids (Liddell, 1980, 1982), and observations 

 of feeding by corals (Johannes and Tepley, 1974) confirm that inadequate numbers 

 of zooplankton are caught to meet the estimated energy needs of these reef 

 inhabitants. 



A comparison of results from this study with those of Alldredge and King 

 (1977); Porter and Porter (1977); Porter, et aK (1977); McWilliam, et al. 

 (1981); and Walter, et al . (1982) is presented in table 3. Volume and numbers 

 of zooplankton collected over Jamaican reefs were larger than those of the 

 other studies. This difference may reflect either real differences in the 

 biology of the reefs studied or merely differences in the amount of swarming 

 copepods captured because of imperfect fit of the traps to the substrata. 

 Nonetheless, these studies together indicate the range of values for the amount 

 of demersal zooplankton to be found over coral reefs. Further study using 

 identical collection methods, including sealing efficiency and plankton mesh 

 size, is necessary to determine the differences betwen the Caribbean reef 

 studied in this work and the Pacific reefs studied by others. 



Variability in Abundance of Zooplankton 



The high degree of spatial and temporal heterogeneity in zooplankton volume 

 (figs. 2, 4) is probably attributable to the swarming behavior of the dominant 

 copepod, Oithona colcarva . Although swarms of this species were not observed 

 by the author at Jamaica, other members of this genus are known to swarm in 

 large numbers (Emery, 1968; Hamner and Carleton, 1979). 



One result of this variability was that patterns of differences in 

 zooplankton volume between sites varied from night to night, although certain 

 statistically significant trends were discernible when data from all nights 

 were pooled. This illustrates how sampling frequency might influence conclusions 

 about the presence or absence of differences between collection sites; depending 

 on which nights were sampled, contrary conclusions could be drawn. McWilliam, 

 et al . (1981) also reported on the variability of zooplankton abundance from 

 consecutive nights. 



Factors Affecting Abundance of Zooplankton 



This study indicates that zooplankton volumes for fore reef sites are 

 negatively correlated with depth within the range of 6-24 m. This is, therefore, 

 a very important consideration when extrapolating from studies done over shallow 

 reefs (all of the previous work) to those which may be deeper. 



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