guished the forms that by day assume essentially 

 a benthonic existence on or in the bottom, from the 

 forms that by day aggregate close to, yet free of. 

 the substrate, or which migrate to deeper water. 

 To increase our understanding of these activities 

 and to acquire a firmer base upon which to assess 

 other studies, we trapped zooplankters that 

 emerged from various substrata in the lagoons of 

 Kure and Midway Atolls, Hawaii during August 

 1977, making special effort to exclude forms from 

 the surrounding water column. 



Mcthccis 



Midway and Kure Atolls are about 90 km apart 



at the northwestern end of the Hawaiian Ar- 

 chipelago. They are very similar, each having a 

 lagoon that is relatively small (diameter about 8 

 km) and shallow (maximum depth about 15 m). 

 All our study sites were in approximately 5 to 7 m 

 of water near the outer leeward reefs. 



We made seven paired collections, each pair at a 

 different location. One of each pair sampled the 

 organisms that rose from the substrate during the 

 day, and the other sampled the organisms that 

 rose from the same spot during the night. Of the 

 substrates sampled, three were sand (two at Mid- 

 way, one at Kure), two were a mixture of sand and 

 coral rubble (one at Midway, one at Kure), and two 

 were small heads of both living and dead coral 



COD END 



STYROFOAM 

 FLOAT 



)0 cm 

 D)AMETER 

 OPEN)NGS 



SOIL 

 ANCHOR 



ALUMINUM 

 FRAME 



VELCRO STRIP 

 OUTSIDE 





Figure l. — Drawings of the meroplankton 

 trap. A. configuration when set on bottom; B, 

 configuration when lifted by diver. 



276 



