The effect of temperature on the benthic stages of Cyanea (Cnidaria: Scyphozoa), and their seasonal distribution in the Niantic River estuary, connecticut

Abstract

Abstract There are three benthic stages in the life history of Cyanea: the polyp stage and two kinds of cysts; one kind is produced by the polyp (podocysts), and the other by the planula larvae (planulocysts); both types of cysts develop into additional polyps. Physical and biological factors affecting these benthic stages and their processes influence the success of the ecologically important medusa stage which is produced by asexual budding (strobilation) by the polyp. Experimentally, a transfer from low to high temperature was most favorable for podocyst formation by polyps, and the transfer from high to low temperature led to both the excystment of podocysts and the strobilation of polyps. In the benthos of the Niantic River, planulocysts and podocysts appear during the warmest time of the year having formed during a period of increasing temperature throughout spring. Both types of cyst excyst when temperature decreases beginning in late summer and continuing into early winter. During this period of declining temperature, polyps strobilate forming ephyrae, the young medusae. The relationship between seasonal temperature change and processes of the benthic stages in the field agrees with laboratory results; thus, change in temperature is at least minimally sufficient to account for the regular annual appearance of the medusa. Such a life history requires a longevous ephyral stage resistant to low temperatures and this seems to be the case. Indirect evidence is presented showing that the encysted stages may serve as a defense against predators and competitors for space which are active during the summer.