Abstract
Sanderia malayensis is a scyphozoan species present in the Indian and Pacific Oceans, ranging from the Suez Canal to Japan. Although this jellyfish is commonly kept in aquariums around the world, there is a knowledge gap regarding its biology and ecology, especially at the polyp stage. In this study, we tested the asexual reproductive activity of S. malayensis at three different temperatures: 10, 15 and 20 °C. Results showed significant increases of polyps at 15 and 20 °C, and a minimum at 10 °C, corresponding with daily budding rates of 6.61% ± 0.92%, 5.85% ± 2.36% and 0.66% ± 0.24%, respectively. Moreover, a second experiment was carried out to report about the ability of S. malayensis to prey on Aurelia solida at the ephyra stage. Unidirectional predation of S. malayensis ephyrae on A. solida and an absence of inverse predation was observed. These results could give new insights on the potential fitness and survival of this species if it will ever invade the Mediterranean Sea.
Highlights
In the last decades, jellyfish blooms have increased in various regions of the world [1,2,3,4], including the Mediterranean Sea [4,5,6,7,8]
Sanderia malayensis polyps used in this study were kindly provided by staff of the Wien Zoo (Schönbrunner Tiergarten, Wien, Austria) in December 2017, and Aurelia solida polyps were provided by the researchers of the NIB (National Institute of Biology, Slovenia), and both were cultured at the laboratory of OGS (National Institute of Oceanography and Applied Geophysics of Trieste, Italy)
We observed the following budding types: Type 1–2, ‘Sanderia-type’ lateral budding (Figure 1A,B), Type 4, reproduction from parts of stolons/stalks, Type 6b, motile bud-like tissue particles (Figure 1C), Type 6c, planuloids originating from tentacles tips/tentacle pieces (Figure 1D), Type 7, regenerations from the gastric cavity (Figure 1E), Type 8, longitudinal fission, either intra-tentacular and from the bottom
Summary
Jellyfish blooms have increased in various regions of the world [1,2,3,4], including the Mediterranean Sea [4,5,6,7,8]. One of the main issues related to the knowledge of scyphozoan jellyfish is the unbalance between the well-studied medusa stage and the poorly studied polyp stage [11,12,13], even if the polyp stage probably represents the key factor for the fitness of many scyphomedusae. The majority of the blooming scyphozoans have a benthic polyp stage that reproduces asexually and in turn produces and releases ephyrae (a process called “strobilation”), which will develop in medusae. Temperature and food availability have been proposed as the most important environmental factors directly influencing the reproduction rate of the majority of scyphozoan species [14], their reproductive patterns usually still have to be unveiled
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