Seasonal alternation of the ontogenetic development of the moon jellyfish Aurelia coerulea in Maizuru Bay, Japan

Abstract

Outbreaks of moon jellyfish Aurelia spp. are frequently reported from many parts of the world’s coastal areas. Aurelia spp. canonically show a metagenetic life cycle in which planulae transform into sessile polyps, which can drastically increase in number through asexual reproduction. Therefore, their asexual reproduction has been recognized as one of the major causes of the outbreaks. Aurelia spp. also show direct development that lacks asexual reproduction during the polyp stage, which prevents us from understanding the mechanisms of its outbreaks. To clarify the seasonality of the metagenetic and direct-development life cycles of Aurelia sp. in Maizuru Bay, Japan, we conducted field observations and laboratory experiments throughout the year. Additionally, the two life cycle types were genetically analyzed to confirm that they belong to the single species Aurelia coerulea, which dominates in coastal waters in Japan. From July until October, Aurelia coerulea produced smaller eggs and planulae all of which developed into polyps. However, from December until May, larger eggs and planulae were produced and 90% of the planulae developed into planktonic ephyrae bypassing the sessile polyp stage. Our results demonstrated that a single species, A. coerulea, seasonally shifts between their two life cycle types at a water temperature threshold of 20°C in Maizuru Bay. The higher energy storage of larger planulae was suggested to enable the planulae to develop into ephyrae without external energy input through feeding during the polyp stage. The adaptive significances of the two life cycle types were also discussed.

Temperature Increase Drives Critical Slowing Down of Fish Ecosystems

“…Precipitation is rather high from summer to winter that is the rainy season in this area. Sea-surface temperature ranged from 5.2 to 31.8°C, sea bottom temperature from 8.5 to 29.6°C, which were measured near the surface and at the depth of 10 m underwater during the diving, respectively [86].…”

Life Cycle of Edible Jellyfish Acromitus hardenbergi Stiasny, 1934 (Scyphozoa: Rhizostomeae) Inhabiting a Brackish-Water Environment

“…The size of fully-developed A. hardenbergi polyps was about 0.4 mm, which is smaller compared to other scyphistomae. Therefore, A. hardenbergi polyps made ephyrae as large as possible by mono-disc strobilation and tiny residuum tissue remained, like the direct development of planula (planula strobilation) in Aurelia coerulea [47][48][49][50]. However, the residuum could not develop into the polyp, and it disappeared.…”

Morphological characteristics of ephyrae of Aurelia coerulea derived from planula strobilation

“…However, it was reported that A. aurita in Germany, and A. aurita [later changed to A. coerulea (Scorrano et al 2016)] in Japan (Fig. 1) have shown another variation in their life cycle, where the planula ostensibly metamorphoses directly into an ephyra, omitting the polyp stage after settling on substrate (Haeckel 1881;Hirai 1958;Kakinuma 1975;Miyake et al 2019;Suzuki et al 2019;Yasuda 1975Yasuda , 1979Lucas 2001). This was called 'Ephyra pedunculata ' by Haeckel (1881) and Hirai (1958) and is currently referred to these days as 'direct development' (Berrill 1949;Hirai 1958;Kakinuma 1975;Yasuda 1975Yasuda , 1979Arai 1997;Lucas 2001).…”

“…2. The mature oocytes of medusae in the areas where the planula-strobilation type is distributed are large (Kon and Honma 1972;Yasuda 1988;Suzuki et al 2019). 3.…”

“…3. Medusae inhabiting the area where the planula-strobilation type is distributed produce large planulae from winter to spring and small planulae from summer to autumn (Yasuda 1988;Suzuki et al 2019). 4.…”