Abstract
The aim of this study was to determine the development time of embryos and to estimate the hatching rates of resting eggs of cladocerans found in the sediment of Guanabara Bay, Rio de Janeiro, Brazil, under experimental conditions. Eggs were sorted by species (Penilia avirostris--Sididae; Pleopis polyphemoides and Pseudevadne tergestina--Podonidae) and incubated at a temperature of 25 degrees C, salinity 35 and photoperiod 12 hours light/ 12 hours dark. Hatching rates were about 38% for Pseudevadne tergestina and 28% for Pleopis polyphemoides. Embryos of resting eggs of Penilia avirostris developed comparatively slowly (hatching after 86 days of incubation), with a hatching rate of only 5%. It was observed that development and hatching of resting eggs of marine cladocerans suggest that pulses of recruitment may exist, thus contributing to the rapid appearance and maintenance of planktonic populations of these crustaceans in Guanabara Bay.
Highlights
Marine cladocerans are seasonally abundant microcrustaceans, widely distributed in estuarine and continental shelf waters and the open sea, where they comprise a significant portion of the mesozooplankton community
The first signs of embryonic development in resting eggs of P. polyphemoides occurred after 11 days of incubation
Hatching synchronism may be a rule among marine cladocerans, as related by Madhupratap et al (1996), who reported the same behavior
Summary
Marine cladocerans are seasonally abundant microcrustaceans, widely distributed in estuarine and continental shelf waters and the open sea, where they comprise a significant portion of the mesozooplankton community. Some authors (e.g., Egloff et al, 1997; Onbé, 1999) have suggested that gamogenesis (or sexual reproduction) is initiated under unfavorable environmental conditions. Females produce eggs that give rise to male and female individuals. The female produces, in general, a single, larger egg, with a resistant outer membrane and full of vitellus, which is called a resting egg. After releasing, the egg sinks towards the sea bottom until environmental conditions become favorable again. A female individual is born to restart parthenogenic reproduction. A sharp decrease of the planktonic population is observed, as well as increased production of resting eggs (Onbé, 1978a, 1985; Egloff et al, 1997)
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