Aurelia solida dynamics

A. solida were present in the water column from winter until early summer (Fig. 3A). The net hauls showed that A. solida ephyrae occurred from December to January, whereas medusae were observed 1–2 months after the start of ephyra strobilation (February 2013 and January 2014). Maximum abundances of ephyrae were found in December (1.2 ind m- 3 in 2012; 3.9 ind m- 3 in 2013). All individuals sampled in February 2013 (6.5 ind m-3) and January 2014 (0.07 ind m-3) were juveniles, while the maximum abundance of adults was observed in March 2013 and April 2014 (2 ind m-3 and 1.8 ind m-3, respectively). No significant difference (t -test; p = 0.39) in population abundance was observed between 2013 and 2014 (1.2 ± 2 ind m- 3 in 2013; 0.6 ± 1.3 ind m- 3 in 2014). The occurrence period of A. solida seemed to be related to the SST. Ephyrae only appeared after the SST fell below 15°C (13.8°C in December 2012; 14.7°C in December 2013), whereas the last observation for adults (in both Bizerte Lagoon and Channel, pers. obs.) coincided with 24.5°C SST (early July 2013 and mid-June 2014). While ephyra abundance was higher during the second year (3.9 ind m-3), abundance of the adult stage was not significantly different between the two years (U- test, p = 0.5; 2013 = 0.5 ± 0.9 ind. m-3; 2014 = 0.3 ± 0.9 ind. m-3)

A. solida mean (x ± SD) bell diameter increased gradually to reach a maximum of 14.6 ± 3.3 cm (n = 35) in June 2013 and 16.4 ± 2.4 cm (n = 36) in mid-April 2014. The largest sampled medusae reached 23.4 (April 2013) and 22.3 cm (April 2014) (Fig. 3B). Bell diameter shrinkages were observed since June 2013 and April 2014, occurring one to two months after the first appearance of brooding females (April 2013 – March 2014). The first occurred in May 2013, while the two others occurred gradually since June 2013 and April 2014 after the spawning event. Overall, no significant difference in bell diameter was observed between the two years (t -test, p = 0.89).