Life history and population dynamics of the potentially edible jellyfish Lychnorhiza lucerna (Rhizostomeae)

SCHIARITI, A.; MORANDINI, A.; GAITAN, E.; GIBERTO, D.A.; DA SILVEIRA, F.L.; MIANZAN, H.

Mar del Plata

Congreso; Third International Jellyfish Blooms Symposium; 2010

Asociación Argentina de Ciencias del Mar e Instituto Nacional de Investigación y Desarrollo Pesquero

The life history and population dynamics of Lychnorhiza lucerna were studied on populations from Argentina (34-38ºS) and Brazil (25ºS). L. lucerna presents a metagenetic life cycle. The gonochoristic medusae lack brooding structures but exhibit sexual dimorphism in gonad coloration. Fertilization seems to be external. The life span of the medusae is chiefly determined by environmental conditions. While the appearance of L. lucerna in Argentina is highly seasonal (January-May) and almost no medusae survive winter, in Brazil it is present throughout the year, probably due to the higher temperatures. Neither polyps nor sexually undifferentiated medusae were found in Argentina. Moreover, nearly all medusae present in this region (5-33 cm) are ripe. Therefore, medusae present in Argentina would not constitute a local population but comes from polyp beds located northwards. In Brazil, although ripe medusae are present all over the year, the presence of higher abundances and smaller undifferentiated specimens (1.5-5 cm) suggests a near-continuous recruitment during spring and summer. Occurrence decreases in coincidence with lower temperatures of autumn and winter when largest specimens appear (up to 50 cm). In the laboratory, the potential perennial scyphistomae preferentially colonize hard substrates. Therefore, although L. lucerna presents repeated spawning events during its occurrence, suitable (hard) substrate could be limited for settlement and survival of planulae in Argentinean coasts dominated by soft bottoms. Conversely, abundance of mangroves could serve as suitable substrate for polyps in Brazil.