Temperature-driven asexual reproduction and strobilation in three scyphozoan jellyfish polyps

Abstract

Increased atmospheric carbon dioxide (CO2) and subsequent climate warming is a critical threat to our oceans. Increased ocean temperatures are speculated to be a driving factor in controlling jellyfish populations worldwide; warmer temperatures increase asexual budding of benthic polyps, and many species strobilate in the spring as water temperatures begin to warm following cold winters. As ocean temperatures rise, it is important to determine thermal triggers in reproduction in jellyfish populations. This study investigated the effects of temperature on 1) asexual (budding) reproductive rates, 2) timing of strobilation, and 3) strobilation success (number of polyps strobilating and number of ephyrae per polyp), for Aurelia aurita, Chrysaora quinquecirrha, and Chrysaora fuscescens polyps exposed to constant temperatures of 5 °C, 10 °C, 15 °C, and 20 °C. Asexual reproduction rates were similar for all species and increased with increasing temperature. Strobilation occurred at 10 °C for all species and all three species began strobilation at the same time (21–23 days). Aurelia aurita and C. fuscescens also strobilated at 15 °C, but strobilated later, had less polyps strobilating, and produced less ephyrae per polyp than the same species at 10 °C. If temperature contributes to instigation of strobilation, ocean temperatures and the timing of warming will be a primary control of the size and distribution of adult populations. Slight warming may benefit temperate species such as A. aurita that can strobilate successfully at increased temperatures, but other species may be restricted by warming waters. Further, if warming is such that proper overwintering temperatures do not occur, polyps may not be exposed to conditions enabling strobilation. While it has been speculated that jellyfish will be favored under warmer ocean conditions, future climate change may prohibit species that require specific conditions to strobilate.