Summer occurrence of marine cladocerans in Uragami inlet, central Honshu, Japan
2019
Onbé, T. | Kumai, H.
Occurrence of marine cladocerans was studied in Uragami Inlet, central Japan, by collecting zooplankton every other day from July to September 1976. Four species belonging to three genera appeared in the following order of abundance: Penilia avirostris, Pseudevadne tergestina, Pleopis polyphemoides and Pleopis schmackeri. The pattern of population abundance in relation to surface temperature differed with species, exhibiting a species-specific characteristic feature of temperature preferences. Comparison of this relationship with other localities revealed that each species of cladocerans is adapted to its own local temperature regime. The two congeneric species of Pleopis showed a clear separation in time without the period of coexistence, whereby avoiding possible interspecific competition. Gamogenesis was detected only in Penilia avirostris in August. The abundance of gamogenetic females responsible for resting egg production was highest at the innermost station, and gradually decreased towards the two outer stations. The trend corresponds well with the abundance of benthic resting eggs recovered from the sea-bed sediments of the same stations in December of the same year. Lastly, ecological implications of the gamogenesis and feeding habits of marine cladocerans are also discussed.
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