This article originally appeared in Hakai Magazine.
Deep within a marine lab in southwest France, serene rooms house numerous Pacific oysters enclosed in glass tanks, tranquilly living their oyster lives. Every morning, the room’s lights gradually brighten, expertly simulating the emergence of the sun. However, at night, the test groups experience a perpetual dim glow, replicating the light pollution that plagues numerous marine species even in their natural habitats.
The recently published results of this experiment, according to Hakai Magazine, demonstrate that artificial light at night can disrupt the behavior of oysters and impact crucial genes responsible for maintaining their internal clocks.
Marine scientist Damien Tran, one of the authors of the study from the French National Centre for Scientific Research in Paris, expressed surprise that even the lowest level of nighttime light tested disrupted the oysters’ circadian rhythm. The intensity of the light was lower than that of a full moon, highlighting the sensitivity of these creatures to light pollution.
The mechanism through which oysters “see” remains somewhat of a mystery. While other bivalves possess eye-like organs, oysters likely rely on specialized light-detecting cells on their skin. The exact nature and function of these cells have yet to be definitively identified by scientists.
For the experiment, the researchers divided the oysters into four tanks placed in separate rooms, subjecting each tank to a different intensity of artificial light at night. They then compared the behavior of these oysters with those in a control tank that experienced complete darkness at night.
Laura Payton, another marine scientist involved in the study, explained that the opening and closing of the oysters’ shells were the observable behaviors used in the experiment. Electrodes were attached to half of the oysters in each tank to determine when they opened their shells for activities such as feeding, breathing, and mating. In the control tank, oysters were most active during the middle of the day and started closing their shells when the lights went out.
However, exposure to artificial light at night caused the oysters in the other four tanks to remain open at inappropriate times, with their highest activity occurring in the early evening. Furthermore, the difference in gene expression between day and night was virtually eliminated by exposure to nighttime light. For example, a gene in oysters equivalent to one in mammals responsible for melatonin production, which is typically more active at night, became highly active during the day, disrupting the natural circadian rhythm.
This disruption in oysters’ behavior and gene expression, akin to insomnia in humans, could have negative implications for their long-term health. Although the specific consequences have yet to be thoroughly studied, the potential impact on oyster populations could greatly affect the ecology and economy of many regions worldwide. Oysters have vital roles in filtering water, protecting shorelines, and serving as a food source and employment opportunity in communities.
Marine ecologist Emily Fobert from the University of Melbourne, who was not involved in the research, finds the results compelling. However, she raised concerns about the study’s methodology, as only one tank of oysters was exposed to each intensity of artificial light. Fobert suggests that multiple tanks per light level would have strengthened the study’s findings, as it would have ruled out other factors within the tank potentially influencing the results.
Nonetheless, the growing issue of artificial light at night poses a significant threat to numerous marine species. Payton emphasizes the need to assist oysters, as they cannot simply escape when their environment is disrupted. Technologically, we possess the power to improve conditions for these affected marine species. Payton believes there are vast opportunities to make a positive difference.
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