Diel reproduction and vertical distributions of the marine cladocerans, Evadne tergestina and Penilia avirostris, in contrasting coastal environments

Evadne tergestina and Penilia avirostris were sampled during several diel cycles in the well-mixed, turbid Inland Sea of Japan and the more stratified, less turbid Gulf of Mexico shelf. Parthenogenetic female Evadne contained embryos with pigmented eyes only at night, and apparently released neonates near dawn or in the morning. There was no significant diel vertical migration in the Gulf of Mexico, and a ‘reverse’ migration in the Inland Sea. Female Penilia could contain mature embryos at any time, but were most likely to do so at night. Penilia did not migrate dielly, and in the Gulf of Mexico was concentrated in a nepheloid layer near the bottom.