California’s coastal waters are home to a variety of fascinating marine life, but one creature that never fails to catch a diver’s eye is the vibrant purple hydra coral. Found primarily in the cool, rocky waters of the Pacific, this unique species adds a splash of color to underwater environments and often becomes the subject of fascination for scuba enthusiasts and marine biologists alike. But why is this coral such a striking shade of purple? Let’s dive into the science behind this vibrant hue.

What is Hydra Coral?

First things first: Hydra coral, also known by its scientific name Stylaster californicus, is not a true coral but rather part of the hydrozoan family, a group of invertebrates that are more closely related to jellyfish. Unlike stony corals that build the large reef structures seen in tropical waters, hydra corals create intricate, branching colonies that form over rocky substrates. Their delicate structure, along with their distinct color, makes them stand out in California’s underwater ecosystems.

The Role of Pigmentation

The purple color of hydra coral is primarily due to pigments present within its tissue. These pigments, known as carotenoids and proteins, absorb certain wavelengths of light and reflect others, creating the purple hue that divers see. This coloration plays a role in protecting the coral from environmental stresses.

One of the most likely reasons for this vibrant coloration is protection from UV radiation. Even in the relatively dim underwater world, UV rays can penetrate the ocean and cause damage to marine organisms. The purple pigments may help shield hydra coral from UV rays, acting as a kind of natural sunscreen.

Light Absorption and Depth

Another factor that influences the coral's color is the depth at which it lives. Hydra corals are typically found in deeper, cooler waters, from around 15 to 200 feet. Light behaves differently underwater, with certain wavelengths penetrating deeper than others. Reds, oranges, and yellows are absorbed quickly, leaving behind the cooler tones like blues and purples. The pigments in hydra coral interact with the available light, making purple an effective color in these lower light environments.

Camouflage and Survival

Interestingly, the purple hue may also serve as a form of camouflage. In the rocky, kelp-dominated environments where hydra coral thrives, the surrounding environment tends to feature shades of brown, green, and deep blue. The purple color of the coral helps it blend into this backdrop, making it less visible to predators such as nudibranchs and other coral-feeding organisms.

The Influence of Cold Water

California's waters, especially along the central and northern coasts, are known for their cold temperatures due to upwelling currents. These cold, nutrient-rich waters are ideal for hydra coral. Unlike tropical corals, which rely on symbiotic algae (zooxanthellae) for energy through photosynthesis, hydra corals do not. They depend on plankton and organic particles carried by the currents. Because they don’t rely on light for survival, the color purple in hydra coral isn't related to photosynthesis but rather their environment and biology.

Environmental Adaptation

The purple hydra coral is also an indicator species, meaning its health can reflect the condition of its environment. Pollution, climate change, and rising ocean temperatures can negatively affect this coral, causing its brilliant color to fade or the coral itself to decline. Its vibrant purple hue, therefore, also serves as a sign of a healthy, thriving underwater ecosystem.

The striking purple color of California’s hydra coral is a perfect example of how marine organisms adapt to their environments. From UV protection to camouflage, this color serves multiple purposes that help the coral thrive in the cold, nutrient-rich waters of the Pacific. For divers, encountering this beautiful coral is always a treat—it's a reminder of the delicate balance of marine ecosystems and the wonders of underwater life.

Next time you’re diving in California’s waters, keep an eye out for this vibrant, purple coral, and take a moment to appreciate the fascinating science behind its color!