Temperature effects on asexual reproduction in three Mediterranean scyphozoans

Abstract

In recent decades, many areas worldwide have experienced mass occurrences of jellyfish. Previous studies on Aurelia spp. have shown increased asexual production of buds and new medusae (ephyrae) in warm temperatures, suggesting that those species might increase with global warming. Polyps of three scyphozoan species from the NW Mediterranean Sea, Aurelia aurita, Rhizostoma pulmo, and Cotylorhiza tuberculata, cultured at 21 ºC in the laboratory, were kept individually at three temperatures (14, 21, 28 ºC) for 210 days to test temperature effects on survival, budding of new polyps, and strobilation of ephyrae. Maximum survival of R. pulmo and A. aurita was at 14 ºC (39 % and 56 %, respectively), but at 21 ºC in C. tuberculata (6 %). Most A. aurita polyps died at 28 ºC. Production of polyp buds increased with warmer temperature for R. pulmo and C. tuberculata (6 and 36 buds polyp-1, respectively), but, A. aurita produced the most buds at 21 ºC (62 buds polyp-1). Strobilation of A. aurita polyps was active at 14 ºC (16 of 18 polyps), but not at 21 ºC (1 of 18) or 28 ºC (0 or 18). Strobilation frequencies were low in the other species. Our results show appropriate patterns for the seasonality of each species in the NW Mediterranean. A. aurita occurs earliest (around April and May) in cool waters, followed by R. pulmo, which becomes conspicuous during May and June, and finally by C. tuberculata in midsummer and the warmest conditions