Vidussi F, Mostajir B, Fouilland E, Floch LE, Nouguier J, Roques C, Got P, Thibault-Botha D, Bouvier T, Troussellier M
Ultraviolet radiation, UVB, Food web, temperature, light manipulation, mesocosm, MEDIMEER, Montpellier, France, 1.8 m3
The responses of the plankton food web to increases in temperature and ultraviolet B radiation (UVBR, 280–320 nm) were experimentally investigated at a coastal Mediterranean site during spring. Eight moored mesocosmswere used to compare natural plankton food web responses (control mesocosms) with three treatments simulatingexpected future local temperature and UVBR increases, as follows: (1) 3uC increase in water temperature, (2) 20%increase in incident UVBR, and (3) simultaneous 3uC increase in water temperature and 20% increase in incidentUVBR. The plankton food web was resistant to elevated UVBR, having only moderate effects on planktonabundances and structure. In contrast, warming induced significant shifts in the plankton food web structure andfunction. Specifically, the abundance of protozooplankton (ciliates and flagellates) increased and the developmenttime of copepods from nauplii to adults decreased. In the warm mesocosms, the emergence of copepod adultstages midway through the experiment resulted in a decrease in ciliates and consequently in an increase inheterotrophic flagellates. One unexpected result was that warming reduced the abundance of heterotrophicbacteria midway through the experiment. These results indicate a trophic-cascade effect under warming. Theincrease in adult copepods diminishes ciliates and in turn favors heterotrophic flagellates that consume bacteria.Warming also induced an increase in net oxygen production, indicating an increase in net primary production