Variability in Volume of Zooplankton Within Reef Sites 



Volumes of zooplankton from the 15 m site ranged from 0.4-50.8 ml/m 2 (X = 

 5.3 ml/m 2 ) (figs. 2, 4) and, on any one night, differed among sites by 0.4-49.2 

 ml/m 2 (X difference in volume/night = 8.0 ml/m 2 ). The variability occurring 

 between consecutive nights was as great as that between randomly paired nights 

 (Mann Whitney U Test, p > 0.05). This wide range in volumes was found for all 

 three sites, with samples from 24 m showing the least variation (fig. 4). 



Differences in Abundance of Zooplankton Between Reef Sites 



The results of the zooplankton sampling from all three sites are presented 

 in figure 4. Volume of zooplankton is inversely correlated with depth (Spearman 

 Rank Correlation, p < 0.01). The shallow (6 m) site yielded the greatest volume 

 (X = 10.2 ml/m 2 ), while the 24 m site yielded the least (X = 3.2 ml/m 2 ). 

 Pairwise comparison of volumes from all nights shows that volumes from 6 m vs. 

 24 m and 15 m vs. 24 m are significantly different (Mann-Whitney U Test, p < 

 0.01), but not 6 m vs. 15 m. However, these relationships do not hold for every 

 night considered separately. When the sites are paired night by night, the 

 volume at 6 m is greater than at 24 m only 45% of the nights (N = 11), and the 

 volume at 15 m is greater than at 24 m only 57% of the nights (N = 14). While 

 overall the volumes from 6 m and 15 m do not differ significantly, volumes from 

 6 m are greater than those from 15 m on 45% of the nights. 



When the total numbers of individuals captured at each site (table 1) are 

 compared, similar patterns are observed as for volume. More individuals occurred 

 at 6 m than at 24 m (Mann Whitney U Test, p < 0.0006) and more at 15 m than at 

 24 m (Mann Whitney U Test, p < 0.002), but there was no difference between 6 m 

 and 15 m. However, the pattern changes when the dominant copepod is removed 

 from calculations. With Oithona colcarva Bowman removed, the site at 6 m does 

 not have significantly more individuals than 15 m or 24 m (Mann Whitney U Test, 

 p > 0.05), and, curiously, the 24 m site has significantly more than the 15 m 

 site (Mann Whitney U Test, p < 0.002). 



The Effect of Lunar Phase on Abundance of Zooplankton 



The phase of the moon appears to influence volumes of zooplankton, although 

 the results from different depths are conflicting. The 6 m site yielded a 

 significantly greater volume on nights of the new moon than full moon, while 

 the 15 m site yielded a greater volume on nights of the full moon than new moon 

 (Mann Whitney U Tests, p < 0.01). 



The lunar effect on numbers of zooplankton was significant only at the 6 m 

 site, where significantly greater numbers (Mann Whitney U Test, p < 0.03) were 

 captured on nights of the new moon than full moon, both for total plankton and 

 for plankton without 0. colcarva . However, with only 7 nights (2 full moon, 5 

 new moon) sampled, this deserves further investigation. 



When numbers of zooplankton captured in different phases of the moon are 

 compared among sites, collections at 6 m did not differ from those at 15 m or 



105 



