Abstract
Ecological profiling of non-native species is essential to predict their dispersal and invasiveness potential across different areas of the world. Cassiopea is a monophyletic taxonomic group of scyphozoan mixotrophic jellyfish including C. andromeda, a recent colonizer of sheltered, shallow-water habitats of the Mediterranean Sea, such as harbors and other light-limited, eutrophic coastal habitats. To assess the ecophysiological plasticity of Cassiopea jellyfish and their potential to spread across the Mare Nostrum by secondary introductions, we investigated rapid photosynthetic responses of jellyfish to irradiance transitions—from reduced to increased irradiance conditions (as paradigm of transition from harbors to coastal, meso/oligotrophic habitats). Laboratory incubation experiments were carried out to compare oxygen fluxes and photobiological variables in Cassiopea sp. immature specimens pre-acclimated to low irradiance (PAR = 200 μmol photons m−2 s−1) and specimens rapidly exposed to higher irradiance levels (PAR = 500 μmol photons m−2 s−1). Comparable photosynthetic potential and high photosynthetic rates were measured at both irradiance values, as also shown by the rapid light curves. No significant differences were observed in terms of symbiont abundance between control and treated specimens. However, jellyfish kept at the low irradiance showed a higher content in chlorophyll a and c (0.76±0.51SD vs 0.46±0.13SD mg g-1 AFDW) and a higher Ci (amount of chlorophyll per cell) compared to jellyfish exposed to higher irradiance levels. The ratio between gross photosynthesis and respiration (P:R) was >1, indicating a significant input from the autotrophic metabolism. Cassiopea sp. specimens showed high photosynthetic performances, at both low and high irradiance, demonstrating high potential to adapt to sudden changes in light exposure. Such photosynthetic plasticity, combined with Cassiopea eurythermal tolerance and mixotrophic behavior, jointly suggest the upside-down jellyfish as a potentially successful invader in the scenario of a warming Mediterranean Sea.
Highlights
Jellyfish are among the most versatile marine invertebrates
In the present work we investigated the short time reaction in the mixotrophic strategy of Cassiopea switching from a simulated eutrophic to meso/oligotrophic conditions in order to explore its rapid acclimation potential
The ELP condition was associated with a lower Chl content = 0.46±0.13 (SD) mg g-1 ash free dry weight (AFDW), compared to the RLP condition (Chl content = 0.76±0.51 (SD) mg g-1 AFDW) (Fig 1B)
Summary
Jellyfish are among the most versatile marine invertebrates. They can form large aggregations, thanks to a variety of reproductive and trophic strategies that allows a rapid increase in their abundance [1,2,3]. Out of over two hundred and twenty taxa of scyphozoan jellyfish are recognized so far [17], nearly 20–25% of them (mostly belonging to the rhizostomid Kolphophorae sub-order) having symbiotic associations (obligatory or facultative mutualism) with Symbiodium spp. and other Symbiodiniaceae dinoflagellates These include several rhizostome species, such as the Mediterranean Cotylorhiza tuberculata [18], 10 different species of upside-down jellyfish (Cassiopea spp.) [19, 20], the spotted jellyfish Phyllorhiza punctata [21], and the golden jellyfish Mastigias papua, where up to 10% of its protein biomass is produced by their endosymbiotic dinoflagellates [22]. Knowledge of the ecophysiology and trophic strategies of jellyfish may contribute to understanding the mechanisms driving the structure and organization of marine communities in a warming ocean scenario [33]
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