What Makes Hydra Coral Special?

Hydra coral (Stylaster californicus) is part of the hydrozoan family, closely related to jellyfish rather than the stony corals we often associate with coral reefs. Instead of building massive reef structures, hydra coral forms delicate, branching colonies that cling to rocky underwater landscapes. This coral’s intricate shape and bold color make it a standout feature of California’s underwater ecosystems.

Why is Hydra Coral Purple?

The purple hue of hydra coral is due to pigments in its tissue, mainly carotenoids and proteins. These pigments work by absorbing certain wavelengths of light and reflecting others, producing the vibrant purple that’s visible to divers. This coloration is more than just beautiful—it plays an important role in protecting the coral from environmental stressors.

One theory suggests that the purple pigments help protect the coral from UV radiation. Even though the underwater world may seem dim, UV rays can still penetrate and cause harm. The coral’s purple color acts like a natural sunscreen, shielding it from potential UV damage.

Depth and Light Interaction

The color of hydra coral is also influenced by the depth at which it lives. Found at depths ranging from 15 to 200 feet, the coral inhabits waters where light behaves differently. As you descend, reds, oranges, and yellows are filtered out, leaving behind cooler colors like blue and purple. Hydra coral’s pigments interact with the available light, making the purple shade particularly effective in these lower light conditions.

Camouflage in a Kelp Forest

Interestingly, the purple color might also serve as a form of camouflage. In the kelp forests and rocky habitats where hydra coral thrives, the environment is a blend of deep blues, greens, and browns. The purple hue helps the coral blend into its surroundings, making it less noticeable to predators like coral-feeding nudibranchs. This camouflage strategy may contribute to the coral’s survival in these vibrant ecosystems.

Surviving in Cold Water

California’s coastal waters are known for their cool temperatures, thanks to upwelling currents that bring cold, nutrient-rich water from the deep. These conditions are perfect for hydra coral, which doesn’t rely on sunlight for energy as tropical corals do. Instead, hydra coral feeds on plankton and organic particles swept along by the currents. Since it doesn’t depend on photosynthesis, its purple color has nothing to do with light absorption for energy but is instead tied to its natural environment.

Environmental Significance

The purple hydra coral is considered an indicator species, meaning its health can reflect the overall condition of its environment. Pollution, climate change, and rising ocean temperatures can impact the coral, sometimes leading to the loss of its brilliant color. As such, the vibrant purple of healthy hydra coral is not just a beautiful sight, but also a sign of a thriving underwater ecosystem.

Final Thoughts

The stunning purple hue of California’s hydra coral is a testament to the fascinating adaptations marine organisms develop in their environments. Whether it's shielding from UV rays, blending in with the rocky seascape, or thriving in cold, nutrient-rich waters, this coral’s coloration serves many purposes. For divers, spotting this vibrant coral is always a highlight—a reminder of the intricate and delicate balance that sustains life beneath the waves.

Next time you explore California’s waters, take a moment to appreciate the beauty and biology behind this purple marvel. The hydra coral’s story is one of survival, adaptation, and, of course, the natural beauty of the ocean’s depths.