The disruption of a symbiotic sea anemone by light pollution: Non-linear effects on zooxanthellae and molecular indicators.

Artificial Light at Night (ALAN) is a pervasive stressor that may affect coastal organisms, particularly sessile forms associated with photosynthetic symbionts. We examined the effects of ALAN upon the symbiotic snakelocks anemone (Anemonia viridis)'s relationship with photosynthetic zooxanthellae, as well as molecular indicators of oxidative stress and metabolism. Anemones were exposed to natural daylight/night or either mild or strong ALAN intensities for four weeks, before quantifying zooxanthellae, superoxide dismutase (SOD) enzymes, and respiration rates. In comparison to natural conditions, anemones exposed to ALAN showed significantly higher and lower zooxanthellae counts, under mild and strong ALAN, respectively. In turn, SOD concentrations were lower and much higher when exposed to mild and strong ALAN, respectively, with no change in respiration rates. Concurrent bleaching suggests that ALAN is harmful to this, and possibly other species associated with symbiotic microalgae. And while we didn't measure heat stress, such bleaching may potentially act synergistically with other larger-scale forms of bleaching associated with rising ocean temperatures.