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 (SES): research to the rescue of coastal managers; 2015

CSIC

Despite of most studies about Aurelia scyphistomae considered asexual reproduction simply as ?budding? and encystment, recent observations suggest the reproductive strategy Aurelia can display is more complex than previously though. In general, Aurelia reproduction rates (number of reproductive particles developed per scyphistoma; Rr) and further recruitment to the substrate are increased by warmer temperatures and higher food supply. Under these conditions, these scyphistomae propagate almost exclusively through non-motile buds and stolons (pooled as non-motile particles, NMP) colonizing bare substrate very rapidly. Yet, as density increase and bare substrate become a limiting factor, density dependent effects appear lowering population growth through a decrease in Rr. However, in addition to the NMP and podocysts, Aurelia can develop motile bud-like tissue particles (MP). In contrast to the NMP, where new polyps remain attached close to the mother polyp, MP are ciliated particles that can swim or drift before reaching a settlement place some distance away. In this context, we investigated the effects of scyphistoma density on Rr and reproduction strategy of the molecular species Aurelia sp8. The hypotheses were that polyp density affect Aurelia sp8 reproductive strategy and Rr. Specifically, we hypothesized that MP development is triggered under space-limiting conditions. Our results confirmed that density dependent factors control population growth of Aurelia sp8 scyphistomae by three different ways: i) decreasing Rr; ii) triggering MP production; iii) inducing the detachment of developed scyphistomae. Whereas the decrease of Rr reduce the number of new recruits, the MP production and the detachment of scyphistomae contribute to minimize density dependent effects by allowing reproductive products and scyphistomae to be drifted away. This way, not only the negative effects of intraspecific competition for space and food are diminished but also the potential colonization of new substrates and further increase in scyphistoma density is favoured at larger spatial scales.