Beneath the moonlit waves of Karachi’s shores, a hidden menace may be present in the glow of artificial lights, threatening the delicate balance of the sea’s microbacteria, which play a crucial role in balancing the intricate food cycle.

Dr Sadia Khalil at Karachi’s Pakistan Marine and Environment Lab carried out some lab tests for The Citizenry in this regard.

We have already mentioned in our main story how Artificial Light at Night (ALAN) can hamper the diel vertical migration (DVL), due to which the food cycle in the sea could be impacted.

To further narrow it down, Khalil studied the impact of ALAN on marine microbacteria in her lab. She intended to understand how marine micro bacteria behave under the influence of different artificial lights.

We collected water and sand samples from four different shores in Karachi: Emaar, Seaview, Hawksbay, and Mubarak Village. (You can see the location of these beaches and the light radiance they have in the interactive map in the main story.)

There was no significant impact on microbacteria’s Colony Forming Unity (CFU) at all of the above-mentioned beaches regarding ALAN’s influence. One colony, she said, means one bacterium.

However, interesting findings emerged when these were exposed to green, blue, red, and yellow lights for three days in Khalil’s lab. Initially, she explained that they grew heterophilic aerobic bacteria on nutrient media “containing complex carbohydrates and essential minerals in the presence of oxygen.” This form of bacteria is the most abundant bacteria in the sea.

Until they were not exposed to ALAN, she said, these bacteria continued to grow on their nutrient media. However, “when exposed to ALAN, their count significantly reduced,” she said, adding that they kept exposing the bacteria for three days.

The bacteria’s count, she said, significantly decreased in the presence of blue and green lights. “A small decrease (in bacteria count) was observed in red and yellow lights,” she said. “It seems that they (artificial lights) are having a lethal impact on bacteria and around the sea these lights should be avoided.”

Heterophilic aerobic bacteria play a very important role in the biodegradation nutrient cycle and are natural decomposers in the sea. “They decompose dead fishes, dead plants and every dead material into a main basic nutrient like nitrogen, carbon, phosphorous,” she explained, adding that these nutrients become part of another life.

If we disturb these bacteria counts, she said, that would mean the decomposition of dead plants and animals would be disturbed. This would mean there would be no nutrients for the primary consumers and it would impact the overall life forms in the sea.

On the basis of these results, she strongly recommended that regulations and policies must be drafted to avoid installations of blue lights near shores and in the boats and vessels. In our main story, we have already discussed that the white LED lights installed across Karachi’s beaches have a blue glow and are lethal for marine ecology.

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Story produced with Internews’ Earth Journalism Network support.