Light Pollution Shown to Negatively Some Static Marine Organisms
A new study reveals the harmful influence of artificial light at night on the immobile species, the snakelocks anemone.
The study, "The disruption of a symbiotic sea anemone by light pollution: Non-linear effects on zooxanthellae and molecular indicators," was published in Science of the Total Environment and is a collaborative effort between the University of Prince Edward Island, Plymouth Marine Laboratory and the University of Exeter.
The issue of artificial light at night (ALAN) is rapidly growing in prominence. However, there are still significant research gaps before there is a good understanding of how a range of marine organisms are impacted by ALAN, especially when combined with other stressors.
It is important to understand these impacts not only in light of the multiple pressures faced by marine organisms, such as warming, acidification and pollution, but also as ALAN sources are expanding globally. In fact, ALAN is becoming pervasive with biologically-relevant light pollution affecting nearly 76% of the seafloor near well-lit cities, which is predicted to increase further in the future.
The research demonstrated a significant negative effect of high ALAN levels on the symbiotic algae (zooxanthellae) that live on the anemones, and on the enzyme (superoxide dismutase) that helps both the anemone and algae cope with oxidative stress.
By integrating PML’s novel Marine Artificial Light at Night Research (MARLAN) Facility with its innovative tidal experiment system, natural light and tidal conditions for the urchins were mimicked. This allowed the anemones to acclimatize before experimental ALAN levels were introduced.
In comparison to natural conditions, anemones exposed to ALAN showed significantly higher zooxanthellae under mild ALAN (10 lx), whereas, counts were significantly lower under strong ALAN (50 lx) conditions.
10 lx is roughly the equivalent to the light levels at sunset, whereas, 50 lx is equivalent to an overcast day. In comparison, a well-lit office space requires approximately 300-500 lx.
Previous research has shown an increase in zooxanthellae following exposure to various light spectra, which reversed at a higher ALAN intensity (50 lx), resulting in a drastically lower number of symbionts, even below control levels. Another study showed that zooxanthellae growth rate increased with light intensity up to a threshold and then declined.
These studies suggest that after a threshold is reached, photoinhibition and damage to the photosynthetic apparatus were causally associated with the loss of symbionts. Photosynthesis rates were not measured in this latest study but the evident loss of zooxanthellae at the stronger ALAN levels suggests a similar mechanism is at play.
Anemones exposed to a low ALAN levels showed a decline in SOD concentration compared to controls, but the more severe ALAN levels caused a sharp 350% increase in SOD concentrations. Since the anemones were showing signs of bleaching, the study team interpret this as a physiological response involving a decline in the number of zooxanthellae well below control levels, and in parallel, the rise in SODs to cope with stress.