movements. Low tide was at 1646 hours and 

 was -0.08 m. ; high tide occurred at 2256, and 

 was 4 m. A light fog sometimes hampered 

 vertical visibility but generally did not obscure 

 the sun. 



BEHAVIOR OF ZOOPLANKTON 



Cladocerans and copepods were the most 

 numerous zooplankton, accounting for more 

 than 90 percent of the plankters. Less abun- 

 dant groups included gastropods, brachyurans, 

 and decapod larvae, cirriped nauplii, and chae- 

 tognaths. Total volumes of zooplankton and 

 the distribution of seven species of copepods 

 were examined to determine any behavioral 

 changes during the eclipse. 



Though the light intensity on July 19 was 

 lower and more variable than on the day of the 

 eclipse, this difference did not totally negate 

 the comparison of zooplankton distribution on 

 the test and control days. Miller high-speed 

 samplers (without meters) were used at Bar 

 Harbor; and Clarke-Bumpus samplers (with 



JULY 19 



1800 1900 2000 2100 



TIME led! I 



Figure 4. — -Surface volumes of zooplankton from two 

 sampling locations compared with surface illumina- 

 tion at Boothbay Harbor. 



meters) at Boothbay Harbor. The zooplankton 

 volumes from surface tows in the two locations 

 are compared in figure 4, along with the 

 changes in light intensity during the 2 days. 

 Although this comparison does not account for 

 amounts of water strained for either gear, the 

 duration of tows in each locale were nearly the 

 same, and the changes in zooplankton abun- 

 dance which were recorded for the different 

 gears followed similar trends. On both days, 

 the surface volumes of zooplankton decreased 

 at or near sunset and then increased rapidly 

 during the following hour. On the day of the 

 eclipse, a similar decrease was noted at totality, 

 both at Bar Harbor and Boothbay Harbor. This 

 phenomenon was also evident in the quantita- 

 tive data from the Clarke-Bumpus samplers. 

 Volumes of collections made at the surface 

 were 130 cc./lOm.^ an hour before the eclipse, 

 67 cc./lOm.' at totality, and 105 cc./lOm.^ an 

 hour after totality. The decrease in volume also 

 was noted at 20 m. — 231 cc. lOm.^ an hour 

 before totality, 165 cc./lOm.^ at totality, and 

 222 cc./lOm.^ an hour later. At intermediate 

 depths, 3 to 10 m., there was no pronounced 

 change in volume at totality. 



The distribution of seven species of copepods 

 differed measurably on both the test and con- 

 trol days and during the period of the eclipse. 

 On July 19, Pseudocalanus minuhis and Acar- 

 tia longiremis occupied shallower strata of 

 water than on July 20, which was the brighter 

 day. These species also showed the most pro- 

 nounced response during the eclipse. The up- 

 ward movement of these two species and the 

 differences in vertical distribution between 

 days are shown in figure 5. The responses of 

 Centropages hamatus, Tortanns discaudatus, 

 Calanus finmarchicus, Temora longicornis, and 

 Eti-rytemora herdmani were not as well defined 

 as those of P. mimitus and A. longiremis, and 

 the responses of some species differed at the 

 two sampling locations. For example, the 

 numbers of C. finmarchicus and T. longicornis 

 from the surface to 10 m. increased during the 

 eclipse at Boothbay Harbor, but declined at Bar 

 Harbor. The abundance of E. herdmani was 

 so limited in Bar Harbor that its distribution 

 could not be plotted reliably; in Boothbay Har- 

 bor this species was one of the most abundant 



MARINE ORGANISMS DURING SOLAR ECLIPSE 



263 



