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What Is a Star Polyp?

Ray Hawk
Ray Hawk

A star polyp is a thumb-shaped individual example of a star coral colony, a species of stony corals which are round or boulder-shaped. Sea anemones and jellyfish also have a polyp stage, and all produce a medusa stage. Medusas are free swimming or floating versions of a coral’s star polyp that break off from the main body at sea, and can be tendril or disc-shaped. Corals universally undergo a polyp stage, but the medusa stage may be dominant, such as in the class Scyphozoa, without the presence of the polyp stage at all.

Growing star polyps in an aquarium is pretty easy as they are non-invasive and spread out rapidly from a central core. Common names used to describe the expanding shapes of star corals include Eight Tentacle, Brain, Daisy, and Starburst, and they are usually white or brown in color, but can also be green and blue. The great star coral can grow to over 5 feet in diameter (1.52 meters) and is composed of green star polyps, which can change to a bright red or orange color during the daytime.

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Woman holding a book

The structure of an individual polyp is an upright sac-shape with eight tentacles at the top, and a cylindrical wall composed of two layers of cells, with a basal plate that attaches to a hard surface. The tentacles surround a mouth and serve both as sensory organs and as an array of fingers used to capture food. The star polyp typically reproduces by asexual budding, but, in the marine environment, they are also known to utilize sexual reproduction by releasing sperm and eggs into the water that merge far off from the initial coral colony.

Caring for star polyps requires that they have significant water flow over the surface and they need to be kept separate from other corals that can dominate the local environment. The algae Zooxanthellae must be introduced into the water as they host it within their bodies and they can then derive the majority of their nutrition from it. Algae generates energy through photosynthesis and for this reason a star polyp needs to be elevated in the tank to a point where it has good exposure to a light source. Introducing micro-plankton and fish larvae into the water will also serve as an extra food source for a star polyp.

Propagating a star polyp colony is easily done if they are started on pieces of broken rock, that can then be separated and moved to several different sections of a tank as they grow. In order to keep new colonies healthy and thriving, it’s important not to overstock the tank with fish or invasive algae. A small amount of phosphate in the water will help them grow, but it will also encourage nuisance algae growth for a star polyp. Snails in the clade of sea slugs known as Nudibranchia can act as predators for a star polyp and should not be included in the tank.

Frequently Asked Questions

What exactly is a star polyp?

A star polyp, belonging to the genus Pachyclavularia, is a type of soft coral commonly found in reef aquariums. They are known for their vibrant colors and star-shaped polyps that extend from a mat-like base. These corals are photosynthetic, hosting symbiotic algae called zooxanthellae, which help provide nutrients through photosynthesis.

How do star polyps reproduce?

Star polyps can reproduce both sexually and asexually. Sexual reproduction occurs when they release sperm and eggs into the water column, leading to the formation of free-swimming larvae. Asexually, they can propagate through fragmentation, where a piece of the coral breaks off and develops into a new colony, a process often used by aquarists to propagate them.

What kind of environment do star polyps need to thrive?

Star polyps require a marine environment with stable water conditions, including a temperature range of 72-78°F, a pH of 8.1-8.4, and specific gravity of 1.023-1.025. They need moderate lighting and water flow to flourish. Proper calcium levels are also crucial for their growth, as they build a calcium-based structure beneath their mat.

Are star polyps easy to care for in an aquarium setting?

Yes, star polyps are considered one of the easier corals to care for, making them popular among beginner and experienced reef aquarists alike. They are hardy and can tolerate a range of conditions, but they do best with consistent water quality, appropriate lighting, and regular feeding of planktonic foods.

Can star polyps be harmful to other corals in a reef aquarium?

Star polyps are generally peaceful, but they can overgrow and overshadow other corals if not managed properly. They have the potential to outcompete slower-growing corals for space and light. Regular pruning and careful placement within the aquarium can prevent them from encroaching on the territory of other corals.

What are the signs that a star polyp is healthy?

A healthy star polyp will display vibrant colors, with its polyps fully extended during the day when the lights are on, indicating active photosynthesis and feeding. The base should be firmly attached to a surface, and there should be noticeable growth over time. A lack of polyp extension or receding tissue may indicate poor health or water quality issues.

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