The role of temperature in survival of the polyp stage of the tropical rhizostome jellyfish Cassiopea xamachana

Abstract

The life cycle of the tropical jellyfish Cassiopea xamachana involves alternation between a polyp (=scyphistoma) and a medusa, the latter usually resting bell-down on a sand or mud substratum. The scyphistoma and newly strobilated medusa (=ephyra) are found only during the summer and early fall in South Florida and not during the winter, while the medusae are found year around. New medusae originate as ephyrae, strobilated by the polyp, in late summer and fall. Laboratory experiments showed that nematocyst function, and the ability of larvae to settle and metamorphose change little during exposure to temperatures between 15°C and up to 33°C. However, tentacle length decreased and ability to transfer captured food to the mouth was disrupted at temperatures ≤18°C. Unlike temperate-zone species of scyphozoans, which usually over-winter in the polyp or podocyst form when medusae disappear, this tropical species has cold-sensitive scyphistomae and more temperature-tolerant medusae.