Purple Hydrocoral

Purple Hydrocorals (Stylaster californicus) are a distinct species native to the California coast from San Francisco to Baja, along with the reef habitats and islands found along this range. Because they are endemic to their habitat, they are often called the California hydrocoral. This is one of the few species of coral found in California waters.

Hydrocorals are not considered true corals but are classified more as soft ones despite having a hard skeleton. They even contain stinging cells called nematocysts.

Appearance

The Purple Hydrocoral is aptly named for its brilliant shades of purple but can also be found in varying other colors from red to orange, to salmon, to shades of blue.  

They can form flat, encrusting sheets on rocks or corals, or they can grow into upright, branching structures resembling miniature trees.

Forming a calcium carbonate skeleton structure, much like stony corals, this species grows at a very slow rate, thought to be 1/4 inch per year. The growth patterns vary from lacy formations to a dense network of branches. This hydrocoral grows from 6 to 12 inches in height and has a base that can reach 24 inches across.

The surface can be relatively smooth in some species, while others have a bumpy or ridged texture due to the arrangement of polyps. Individual polyps, the tiny feeding units of the colony, are often visible as small, raised dots or bumps. When extended, polyps can create a fuzzy or feathery appearance.

The skeleton provides structural support and can be visible in areas where the living tissue is thin or absent.

Habitat

Their colonies are found predominantly off Catalina Island in the Farnsworth Bank Marine Conservation Area. They can be found in shallow water, in as little as 15 feet to depths of 368 feet on the sea floor. This hydrocoral prefers the rocky reefs, often colonizing in areas of a strong current.

In their habitats, they range from small individuals to heavy colonization, depending on food sources and potential damage to the reefs.

This species shares its habitat with many other important fish species, including the Dwarf-red Rockfish, the Squarespot Rockfish, the Rosy Rockfish, the Blackeye Goby, many species of sea anemones, and other soft corals.

Diet

Unlike other corals, this Hydrocoral does not need sunlight to survive and feed. Rather they are carnivorous and need zooplankton and other small organic matter found in the water currents to feed.

This species houses minuscule pores along its external structure that contain polyps. These polyps are surrounded by long tentacles that have nematocysts or stinging cells. Each of those individual polyps houses a feeding polyp that has its own set of four short tentacles surrounding its mouth. The long tentacles exist to protect the polyp and to catch prey, which passes to the shorter tentacles at the mouth.

Reproduction

Purple Hydrocoral colonies contain both male and female specimens. They can reproduce in two ways. The first way is asexually through fragmentation. This is when segments of the hydrocoral break off from the parent, and a new organism grows from the fragment.

The second way is through sexual reproduction, where the male releases sperm into the water column, and the female houses eggs that then become fertilized. The eggs hatch into larvae that leave the female between late October through November.

Threats

Ecological observations have shown that anchor drops from visiting boats are one of the main threats to the Purple Hydrocoral. In places where this species can be found in the largest colonies, like Farnsworth Bank (an ecological reserve by the California Fish and Game Commission.) Surrounded by sand, the walls, valleys and crevices of Farnsworth Bank create an intriguing dive site for underwater explorers.

Hydrocoral species compete for space and resources with algae, sponges, anemones & zooanthids and other coral species.

In its native habitats, large amounts of marine debris, including large amounts of debris from commercial fishery waste, such as lines and nets, were found in data observations.

During the 1960s, this Hydrocoral was so abundant that divers tell stories about being able to see a purple glow from the water’s surface. It was shortly thereafter that the populations were decimated in the Farnsworth Bank, off Catalina Island, from divers taking the corals for the tourist and jewelry trades. Sadly, due to its delicate nature, this Hydrocoral did not make good candidates for those trades and was often broken before it could reach the public.

Facts about Purple Hydrocoral

1. Purple Hydrocoral is in the phylum Cnidaria, along with all other hydro corals, jellyfish, corals, and sea anemones. This species falls into the Class Hydrozoa.
2. There are at least 48 species in the Stylaster Genus.
3. Technically the California Hydrocoral has tentacles with specialized cells that can sting, but they are so small humans cannot feel the sting.
4. Due to its range along the California coast, this Hydrocoral is often called the California Hydrocoral.
5. The most abundant fish species wait amongst this Purple Hydrocoral for commensal species that serve as prey items.
6. Encrusting species often form flat, sheet-like colonies that closely follow the contours of rocks, corals, or other hard substrates.

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