Corals on the Move: Following the Light

Corals (scientifically Cnidarians) are beautiful lifeforms in the deep sea. While we have always seen them attached to a substrate (at least most), scientists have discovered an intriguing exception- the walking coral! This group of corals has been free to move around and explore the ocean. However, we are still unaware of their lifestyle, including how they walk and navigate. Let’s dive deep and find out what makes this coral unique.

Cnidarians come in two forms.

They may be stationary or sessile, attached to a substrate, or mobile or free-living. Some mushrooms exhibit both these forms in their lifecycle. Most of these corals travel deep into the ocean for survival and reproduction, where competition and temperature variations are less. In fact, these two factors result in mass bleaching.

How they move- 2 hypothesis

Many believe in two modes of locomotion that mushrooms employ. They are

1. Passive- they are carried by water currents
2. Active- through phototaxis or automobility
   

Factors that make them move

3 factors contributed to their movement. They are-

1. Tissue inflation- this helps provide the lift and friction for peripheral tissues. This is an inherent part of both active and passive movement.
2. Ventral foot pads- which increased the surface area
3. Contraction and twisting of peripheral tissues- to drag the coral forward
   

However, it is important to note that this type of movement was not towards the light and was therefore not phototactic.

In a recent study led by Brett M Lewis, they studied locomotion in free-living corals using a model organism- Cycloseris cyclolites.

How did they conduct the study? Methodology

They used specialized aquariums with controlled lighting and advanced microscopes to capture the locomotion of the study organism.

It was covered by a black screen to avoid interference from other light sources.

The model organism was introduced to the special aquarium 6 hours before experimenting so the coral could acclimatize to the new conditions.

Time-lapse videos were used to record and measure the distances traveled by the coral.

Some interesting results

Scientists studied how the Cycloseris cyclolites, a free-living coral exhibits photo-lactic behaviour towards blue and white light. The results were interesting. These mobile- corals were attracted/moved towards blue light (86%) compared to white light (20%). They even covered more distances when flashed with blue light compared to white.

Blue-light sensitivity of corals

In marine reefs, the light fades quickly within the top 10 meters and the red light disappears first. Below this depth, blue light, at around 480 nm travels the farthest, making it essential for navigation. Many Corals are highly sensitive to blue-green light (around 460 nm) due to their advanced sensory systems.

While we have always seen corals as static organisms, the ability of Cycloseris cyclolites to move in response to light challenges our traditional view. This phototactic behavior not only enhances their survival but also deepens our understanding of reef ecology. While we continue to research the secrets of walking corals, we can remind ourselves that the ocean is full of surprises—some of which are slowly moving right before our eyes!