Thermal regimes regulate distinct components of the strobilation window in three scyphozoan species

Abstract

Strobilation links the benthic polyp stage of scyphozoans with the pelagic medusa phase and determines when juvenile medusae are released into the water column. Temperature is widely recognized as a major environmental cue for this transition, but comparisons among species remain difficult because both “temperature” and “strobilation” are often treated as single variables. Here, we tested whether separating different components of the thermal regime and of the strobilation process helps clarify species-specific responses. Polyps of Stomolophus sp. 2, Cephea cephea, and Aurelia coerulea were exposed to a standardized experimental framework including warming, cooling, constant temperature, and treatments combining warming and cooling, using species-specific absolute temperature ranges. Temperature regulated strobilation in all three species, but not through a single general pattern. Strobilation onset was associated mainly with warming in Stomolophus sp. 2 and C. cephea, whereas cooling was the clearest thermal condition associated with the onset in A. coerulea. After initiation, thermal effects were expressed through different response variables: strobilation duration and ephyra diameter in Stomolophus sp. 2, strobilation duration in A. coerulea, and repeated strobilation events and total ephyrae production in C. cephea. In Stomolophus sp. 2 and C. cephea, cooling after warming was also associated with interruption of ongoing strobilation. Our results support interpreting strobilation as a sequence of partially separable components, including opening, expression, and closure of a medusa-production window, rather than as a single integrated response. This framework helps reconcile apparent contradictions in the literature and provides a basis for more comparable studies on the environmental regulation of life-cycle transitions in Scyphozoa. Because strobilation connects benthic asexual persistence with pelagic medusa recruitment, identifying both inductive and inhibitory environmental cues may be essential to understand how selection shapes the timing and duration of medusa production.