Does coral need light at night?

Answered by Tom Adger

Coral reefs are incredibly diverse and complex ecosystems that rely on the symbiotic relationship between corals and photosynthetic algae called zooxanthellae. These algae live within the coral tissues and provide energy through photosynthesis, which is crucial for the growth and survival of the coral. As a result, light is vital for coral health and plays a crucial role in their daily biological processes.

During the day, corals actively absorb light for photosynthesis, converting sunlight into energy. This light is essential for the zooxanthellae to produce organic compounds, such as glucose, which are then shared with the coral host. The energy derived from photosynthesis fuels various metabolic activities, including growth, reproduction, and calcification.

However, the process of photosynthesis also generates excess energy within the coral tissues, which needs to be released. This excess energy can be harmful if not properly managed, potentially leading to oxidative stress and damage to the coral cells. Therefore, corals require a period of darkness, just as much as they need light.

During the night, corals undergo a series of physiological changes to release the excess energy accumulated during the day. This process, known as dark respiration, allows corals to maintain a balance between energy production and consumption. Dark respiration involves the breakdown of stored organic compounds, such as glucose, to release energy through cellular respiration.

The duration of the daily photoperiod, which refers to the period of light and darkness, is crucial for coral health. It is important to provide corals with an appropriate amount of light during the day to support their photosynthetic activity. However, excessive or prolonged exposure to light can be detrimental to corals, leading to photoinhibition and bleaching.

Photoinhibition occurs when corals are exposed to high light intensities that surpass their photosynthetic capacity, causing damage to the photosynthetic apparatus. This can result in a reduction or cessation of photosynthesis, compromising the energy supply to the corals. Bleaching, on the other hand, is a stress response where corals expel their zooxanthellae due to environmental stressors, such as high water temperatures or prolonged light exposure.

In natural reef environments, the daily photoperiod varies depending on the latitude, season, and depth of the reef. Corals have adapted to these variations and exhibit diurnal patterns of activity, where they maximize photosynthesis during daylight hours and minimize it during the night. This diurnal rhythm helps corals regulate their energy balance and avoid excessive light exposure.

When it comes to artificial lighting in aquariums or coral aquaculture systems, recreating a suitable photoperiod is essential for coral health and growth. It is recommended to mimic the natural light conditions of the coral’s native habitat. This involves providing a period of darkness at night to allow for dark respiration and prevent excessive light exposure.

Corals do require light for their survival, as it is vital for the photosynthetic activity of their symbiotic algae. However, they also need a period of darkness to release excess energy accumulated during the day. Balancing the duration and intensity of light exposure is crucial to prevent photoinhibition and bleaching, ensuring the overall health and well-being of coral reefs.