Like all algae, red algae depend on photosynthesis to produce food. Most varieties of algae live near the surface of the water in order to get enough sunlight to live. Since they can absorb blue light, red algae can live in much deeper water where light of long wavelengths -- like red -- can't reach.

**Explanation:**

**Pigments in Red Algae:**

Red algae, also known as Rhodophyta, are a group of algae that are capable of surviving in deep sea environments. They get their characteristic red color from the presence of specific pigments, namely phycoerythrin and phycocyanin.

**Deep Sea Environment:**

The deep sea is characterized by extremely low light levels, as sunlight cannot penetrate the depths of the ocean. This lack of light poses a challenge for photosynthetic organisms to carry out photosynthesis, which is the process by which they convert light energy into chemical energy for survival.

**Phycoerythrin:**

Phycoerythrin is a red pigment found in red algae. It absorbs light in the blue and green wavelengths and transfers the absorbed energy to chlorophyll for photosynthesis. The pigment allows red algae to utilize the limited light available in deep sea environments more efficiently.

**Advantages of Phycoerythrin:**

Phycoerythrin offers several advantages to red algae in deep sea environments:

1. **Absorption of Blue and Green Light:** Phycoerythrin absorbs light in the blue and green wavelengths, which are more abundant at deeper depths than red light. This allows red algae to capture and utilize a broader spectrum of light for photosynthesis.

2. **Efficient Energy Transfer:** Phycoerythrin efficiently transfers the absorbed energy to chlorophyll, which is the primary pigment responsible for photosynthesis. This enables red algae to maximize their photosynthetic efficiency even in low light conditions.

3. **Protection against Photodamage:** Phycoerythrin acts as a protective shield against potentially damaging high-energy blue and green light. It prevents the formation of harmful reactive oxygen species, which can cause damage to cellular components.

4. **Increased Light Harvesting:** The presence of phycoerythrin increases the overall light-harvesting capacity of red algae. It allows them to capture and utilize more light energy, compensating for the limited availability of light in deep sea environments.

**Conclusion:**

In conclusion, red algae are capable of surviving in deep sea environments due to the presence of phycoerythrin pigment. This pigment enables them to efficiently capture and utilize the limited light available for photosynthesis, providing them with a competitive advantage in these challenging conditions.

Red algae (Rhodophyceae) contain Chl a and d and main pigment is Phycoerythrin . Red algae are red due to Phycoerythrin.it helps in photosynthesis in great depth in ocean and also on surface of water.