of the zooplankton. There was no measurable change in salinity at any site 

 during rain periods (Ohlhorst, 1980). 



Interpretation is further complicated because no correlation between volume 

 of zooplankton and lunar phase or rainfall was found at the 24 m site, and the 

 6 m site yielded results opposite to those at 15 m, with more zooplankton 

 captured on new moon (= "nonrain" in this study) than full moon nights. At the 

 6 m site, there is an obvious advantage for zooplankton that do not enter the 

 water column on full moon evenings, as visual predators should be more active 

 on these nights. It is, therefore, surprising that yields of zooplankton at 

 15 m were the reverse (highest on full moon evenings), since the reefs at 15 m 

 were well illuminated on these nights also. 



Although Glynn's (1973) collections of plankton from the surface water in 

 Puerto Rico sampled a different component of the reef zooplankton, his collections 

 over a shallow reef (< 5 m) through one lunar cycle yielded a pattern consistent 

 with that found for the shallow (6 m) site in this study; more zooplankton were 

 collected on the new moon nights than on the full moon nights. In the study by 

 Alldredge and King (1980) in the Pacific, abundance of zooplankton was not 

 correlated with lunar phase. 



There was no seasonality observed in zooplankton volumes in this study, 

 although some periods of the year were less intensively sampled (fig. 2). 

 Periods of high zooplankton yields reflected the occurrence of rain within 48 hr 

 of sampling; however, collections of very low volumes were interspersed with 

 these high volumes, casting doubt on any real causative effect (such variation 

 also is found in other reports of seasonality; Glynn, 1973). It appears, there- 

 fore, that zooplankton volumes are indicative of previous rainfall, but rainfall 

 is not necessarily predictive of high zooplankton yields. Moore (1967) and 

 Grahame (1976) found no patterns of seasonality in their collections of surface 

 zooplankton from the south coast of Jamaica. In contrast, McWilliam, et al . (1981) 

 did find seasonality on a Pacific reef, with more zooplankton in the summer. 



With the exception of the trend for greater abundance of zooplankton on 

 "rain" nights at the 15 m site and for lower yields on full moon ("rain") nights 

 at the 6 m site, there was no indication that certain of the nights were more 

 conducive than others for zooplankton migration. Neither the pairing of 

 collections on the same night from the 15 m and 24 m sites nor the pairing of 

 collections on the same night from the eight 15 m trap locations produced a 

 significant correlation (Spearman Rank Correlation, p > 0.05). It appears, 

 therefore, that abundance of zooplankton cannot be predicted on the basis of 

 any environmental parameter which would be experienced throughout the reef. 



Composition of Zooplankton 



As reported earlier for Jamaican reefs (Ohlhorst, 1980, 1982), copepods are 

 the dominant organism collected in demersal emergence traps placed over the 

 reef. Because of the great variance, the sites rarely differed significantly 

 and the ranks of abundances for copepod taxa were correlated between sites. 



Due to the absence from the 6 m site of a number of categories of organisms 

 and the presence of Lucifer sp. which was rare elsewhere, the rankings of 



112 



