Influence of environmental and biological drivers on the population dynamics of the ctenophore Bolinopsis vitrea in the Rio San Pedro (Bay of Cadiz, SW Spain)

Large accumulations of gelatinous zooplankton (GZ) occur in many coastal and estuarine regions worldwide. The ability of this species to rapidly reproduce and adapt to new habitats ensure them to inhabit different ecosystems with wide environmental and economic impacts on these areas and on the human activities occurring near the shore. The present study is a comprehensive analysis of the population dynamics of Bolinopsis vitrea, a native ctenophore of oligotrophic waters. The overall aims are to explore the connection of this species with the environmental variables to which it is exposed in the Rio San Pedro (RSP), an estuarine ecosystem in the Bay of Cadiz, and to investigate the influence of this species on the biogeochemical cycles in the ecosystem. Samplings were conducted every month from 2014 until 2017, to study the temporal variability at different scales, with a particular attention on the blooms that occur during spring and earlier summer. The environmental variables analyzed represented important stressors affecting the internal dynamics of the population, with direct and indirect effects on abundances and biovolume of ctenophores and mesozooplankton. Our results highlighted a coupling between the meteorological conditions in the area and the development of B. vitrea population, regulating the dimensions of the population and explaining the interannual differences in the phenology of its blooms occurring in the RSP. An eight yearlong dataset (2010-2017) has confirmed the high variability that can occur due to these conditions. Moreover, the excretion and respiration rates of this organism influence the biogeochemical cycles with a trend in increasing correlated with its size. Furthermore the excretion of TEP (transparent exopolymeric particles), that increases with the ctenophore’s size, may represent a link between the dynamic of B. vitrea and the bacterioplanktonic communities inhabiting its mucus and the water column surrounding the ctenophores.