Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, University of Salento, Lecce, Italy.
Centre Scientifique de Monaco, Ecophysiology Team, Monaco, France.
PLoS One. 2021 Mar 19;16(3):e0248814. doi: 10.1371/journal.pone.0248814. eCollection 2021.
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.
对非本地物种进行生态特征分析对于预测它们在世界不同地区的扩散和入侵潜力至关重要。Cassiopea 是一个伞形动物门混合营养水母的单系分类群，包括最近在地中海受保护的浅水区栖息地（如港口和其他光照有限、富营养化的沿海栖息地）中殖民的 C. andromeda。为了评估 Cassiopea 水母的生理可塑性及其通过二次引入在马雷诺斯特鲁姆（Mare Nostrum，地中海的旧称）扩散的潜力，我们研究了水母对光照过渡的快速光合作用反应——从低光照条件到高光照条件的过渡（作为从港口到沿海、中/寡营养栖息地的过渡范例）。进行了实验室孵育实验，以比较在低光照（PAR = 200 μmol 光子 m-2 s-1）下预适应和快速暴露于更高光照水平（PAR = 500 μmol 光子 m-2 s-1）的 Cassiopea sp. 未成熟标本的氧气通量和光生物变量。在这两种光照条件下，快速光曲线均表明，Cassiopea sp. 具有相当的光合作用潜力和高光合作用率。在对照和处理标本之间，共生体丰度没有观察到显著差异。然而，与暴露在高光照水平下的水母相比，在低光照下饲养的水母的叶绿素 a 和 c 含量较高（0.76±0.51SD 与 0.46±0.13SD mg g-1 AFDW），Ci（每细胞叶绿素量）较高。总光合作用与呼吸作用的比值（P:R）>1，表明自养代谢有显著的输入。Cassiopea sp. 标本在低光照和高光照下均表现出高光合作用性能，表明其具有适应光照暴露突然变化的高潜力。这种光合可塑性，加上 Cassiopea 广温耐受性和混合营养行为，共同表明这种颠倒的水母可能是地中海变暖情景下成功入侵的潜在物种。
