engleski

Microbial response to the presence of invasive ctenophore Mnemiopsis leidyi in the coastal waters of the northern Adriatic

Seasonal invasions of ctenophore Mnemiopsis leidyi in the Adriatic are recorded since 2016, affecting zooplankton and fish stocks. M. leidyi is known to release significant quantities of their total excreta as labile dissolved organic carbon which support and control microbial production. Pico- and nanoplankton at the fundaments of the marine food web can alter their activity and community structure by utilising labile organic substrates. Besides, their rapid response to environmental disturbances can indicate ecosystem perturbations. The influence of invasive blooms on the microbial community was investigated at five locations in the coastal waters of Rovinj (Croatia), in 2019. The abundance of M. leidyi was determined by visual census at the sea surface. Heterotrophic prokaryotes (HP), cyanobacteria (CB) and heterotrophic nanoflagellates (HNF), were enumerated by epifluorescence microscopy. Dissolved (DOC) and particulate organic carbon (POC) were measured by standard HTCO method. Ctenophore displayed a patchy distribution ranging from 0.05-100 M. leidyi/m3. The microbial community mirrored a similar spatial pattern, indicating coupling between them. Indeed, HP, CB and HNF were significantly more abundant at ctenophore concentrations ≥ 1 M. leidyi/m3, increasing in numbers where M. leidyi was more abundant. In the absence of ctenophore, values ranged: 0.08- 0.9∙10^6 HP/mL, 2.6-6.5∙10^4 CB/mL and 2.6- 9.8∙10^3 HNF/mL, while maximums of about 1.7∙10^6 HP/mL, 10^6 CB/mL, and 3.3∙10^4 HNF/mL, were found in swarms. Carbon content (DOC, POC) was also found to be higher in swarms. It appears that HP utilises DOC resulting in increased concentration of nutrients due to enhanced remineralisation. Consequentially, released nutrients might stimulate CB growth. Greater abundances of HP and CB are consumed by HNF and sustain their rise in abundance. We conclude that intensive blooms of M. leidyi influence major components of pico- and nanoplankton, releasing dissolved surface-active organic matter that stimulates and fuels the microbial loop.

Mnemiopsis leidyi ; heterotrophic prokaryotes ; cyanobacteria ; heterotrophic nanoflagellates ; organic matter ; microbial loop

nije evidentirano