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The underwater world is a realm filled with natural light cues that guide it’s inhabitants behaviors and physiological processes. As human activity expands beneath and under the surface, artificial light sources have become increasingly prevalent. This fact raises important questions about how these lights affect the intricate ecosystem.

Natural light regulates crucial activities underwater. Processes such as photosynthesis, reproduction, predator-prey interactions, and circadian rhythms are cued by the presence or absence of light. However, the introduction of artificial light sources underwater disrupts these fundamental processes and can have both short and long term consequences for marine life.

There are two main sources of artificial light that can potentially threaten an ecosystem. In the first place, temporary exposure such as a vessel floating over a reef for a few days or the beam of underwater lights or cameras can potentially have an impact on the environment. Secondly, light sources such as coastal cities or man made infrastructure, like lighthouses, pose a permanent source of artificial light above the surface which translates as a constant glow underwater. These sources of light, although in most cases unavoidable, need to be responsibly managed to mitigate the perpetual threat to the organism’s habits and behaviors.

Artificial light is necessary

Artificial lights used in scuba diving illuminate the underwater environment, enabling divers to observe marine life with greater clarity and detail. This enhanced visibility can foster appreciation for the beauty and complexity of the underwater ecosystem, raising awareness about the need for conservation efforts. 

 

The use of artificial light can offer unique opportunities to explore and study the behavior of nocturnal species, revealing their natural activities that would otherwise remain hidden in darkness. Researchers can gain valuable insights into the feeding, mating, and hunting behaviors of these creatures, contributing to scientific knowledge and conservation efforts.

The negative impact of artificial light

Fish have evolved remarkable visual adaptations that allow them to thrive in their aquatic environments. Their eyes possess specialized structures, including lenses, retinas, and various photoreceptor cells, which enable them to perceive a wide range of light wavelengths. Different species exhibit varying degrees of sensitivity to different colors and intensities of light, allowing them to excel in their respective ecological niches and responsibilities. High-intensity or poorly shielded artificial lights such as dive lights, can cause glare or create intense contrasts underwater. This can lead to temporary or permanent visual impairment in fish, affecting their ability to navigate, locate food, and evade predators. 

Artificial light sources, can confuse nocturnal species, which rely on natural moonlight for navigation. Disoriented organisms may struggle to find food or return to their habitats, leading to diminished fitness and survival rates. Some sources of illumination can also attract plankton, small fish, and other prey species. Consequently, predatory species like sharks or barracudas, snappers or groupers may gather around these light sources, altering natural food chain dynamics, hunting and feeding habits.

 

Long or permanent exposure to artificial lights can also alter reproductive cycles. Many marine species rely on specific light cues to time these cycles. Artificial light can disrupt these cues, causing irregularities in breeding patterns, egg hatching, and larval development, ultimately affecting population dynamics and biodiversity.

Artificial light and coral bleaching

Artificial light can also impact coral bleaching. Excessive or prolonged exposure to intense artificial light, especially UV light, can increase the stress levels on corals. High intensity lights used in coastal developments, marinas, or aquariums can create localized hot spots of light, leading to elevated temperatures in the surrounding water. This, in turn, adds to the thermal stress that can trigger coral bleaching events.

 

Additionally, these types of lights directly affect coral's symbiotic relationship with zooxanthellae, the algae that lives within their bodies, and depends on the right balance of light and darkness to carry out photosynthesis. This disruption can weaken the coral's ability to obtain energy from their symbiotic algae, making them more susceptible to bleaching, and altering biological processes, including their growth, reproduction, and stress responses.

 

Moreover, some artificial lights, such as blue LED lights used in coastal areas or underwater structures, can enhance and promote the growth of harmful opportunistic algae species. These algae will compete with zooxanthellae and negatively impact the health of their hosts, also leading to coral bleaching.

Mitigating the impact of artificial light

To minimize the potential detrimental effects of artificial lights, education and awareness are crucial. For scuba divers, certain measures can be taken to improve responsible dive practices. Divers should adhere to responsible guidelines, such as avoiding shining lights directly on marine life, using low intensity or specialized dive lights, and turning off unnecessary lights when not in use.

Technological advancements, ongoing research and innovation should focus on utilizing and developing coastal lighting systems that minimize the negative effects on adjacent marine life. This includes exploring the use of motion activated lights, light filters, and directing light beams away from sensitive habitats particularly on permanent man made structures.

It is essential to recognize the potential impact of artificial lights on sea creatures. By understanding and mitigating the negative effects while leveraging the positive aspects, we can strike a balance that allows us to coexist, explore and appreciate the wonders of the underwater world while ensuring the long term health and preservation of marine ecosystems. Responsible practices, education, and technological advancements will be key in minimizing our impact and fostering a harmonious coexistence between humans and the fragile creatures of the deep.

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