Density dependent effects control reproductive strategy and population growth of Aurelia sp8 scyphistomae

SCHIARITI, A.; MELICA, V.; KOGOVEK, T.; MALEJ, A.

Cádiz

Workshop; PERSEUS International Workshop ?Coming to grips with the jellyfish phenomenon in the Southern European and other Seas: research to the rescue of coastal managers.?; 2015

Despiteof most studies about Aurelia scyphistomaeconsidered asexual reproduction simply as ?budding? and encystment, recentobservations suggest the reproductive strategy Aurelia can display is more complex than previously though. Ingeneral, Aurelia reproduction rates (numberof reproductive particles developed per scyphistoma; Rr) and furtherrecruitment to the substrate are increased by warmer temperatures and higherfood supply. Under these conditions, these scyphistomae propagate almostexclusively through non-motile buds and stolons (pooled as non-motile particles,NMP) colonizing bare substrate very rapidly. Yet, as density increase and baresubstrate become a limiting factor, density dependent effects appear loweringpopulation growth through a decrease in Rr. However, in addition to the NMP andpodocysts, Aurelia can develop motilebud-like tissue particles (MP). In contrast to the NMP, where new polyps remainattached close to the mother polyp, MP are ciliated particles that can swim ordrift before reaching a settlement place some distance away. In this context, weinvestigated the effects of scyphistoma density on Rr and reproduction strategyof the molecular species Aurelia sp8.The hypotheses were that polyp density affect Aurelia sp8 reproductive strategy and Rr. Specifically, wehypothesized that MP development is triggered under space-limiting conditions. Ourresults confirmed that density dependent factors control population growth of Aurelia sp8 scyphistomae by threedifferent ways: i) decreasing Rr; ii) triggering MP production; iii) inducingthe detachment of developed scyphistomae. Whereas the decrease of Rr reduce thenumber of new recruits, the MP production and the detachment of scyphistomaecontribute to minimize density dependent effects by allowing reproductiveproducts and scyphistomae to be drifted away. This way, not only the negativeeffects of intraspecific competition for space and food are diminished but alsothe potential colonization of new substrates and further increase inscyphistoma density is favoured at larger spatial scales.