Multicolor Sea Urchin (Tripneustes gratilla) 9 cm

Overview

The Multicolor Sea Urchin, Tripneustes gratilla, is a distinctive and hardworking marine invertebrate prized for its attractive appearance and algae-grazing habits. Typically sold at around 9 cm, this species is a useful addition to established saltwater aquariums where natural algae control and a fascinating display animal are both desired. Its rounded body, short spines and varied colouration give it a unique look that stands out in reef and fish-only systems alike.

Although generally peaceful, this is not a beginner invertebrate. Like most sea urchins, it requires a mature aquarium with stable water chemistry, plenty of live rock and careful aquascaping. It is best suited to aquarists who already have experience keeping marine livestock and who can provide a secure environment free from unstable decorations or loose corals that could be dislodged. In the right conditions, Tripneustes gratilla can be a long-lived and rewarding addition to the tank.

At Tropical Fish Co, we select healthy livestock and pack with care for fast UK delivery. Every order is covered by our live arrival guarantee, giving you added confidence when purchasing marine invertebrates online.

Care at a Glance

Origin & Natural Habitat

Tripneustes gratilla is found across tropical Indo-Pacific waters, including reef flats, lagoons, seagrass beds and sheltered coastal areas. In the wild, it lives on hard substrates and among vegetation where it can graze continuously on algae and detritus. This natural behaviour is important to understand when keeping the species in captivity, as it spends much of its time moving slowly across rockwork and glass while feeding.

Its habitat preference explains why it does best in a mature aquarium with abundant grazing surfaces and stable salinity. It is adapted to environments with good water movement and high oxygenation, and it should never be kept in a tank that is still cycling or lacking in biological maturity. A well-established reef system with natural algae growth closely mirrors the conditions this species expects.

Tank Setup & Water Parameters

A secure marine aquarium of at least 200 litres is recommended, with a larger footprint preferred if you plan to keep it with corals or other delicate invertebrates. Sea urchins are strong and surprisingly capable of moving loose items, so rockwork should be stable and firmly seated. Avoid precarious stacks, unsecured frags and ornaments that could topple as the urchin explores the tank.

Provide plenty of live rock and open grazing areas. A mix of rock, sand and some sheltered crevices will allow the urchin to move naturally. Because Tripneustes gratilla may carry shells, rubble or bits of algae on its spines, ensure there are no sharp objects or small loose items that could become trapped or cause injury. Strong filtration, regular water changes and consistent salinity are essential. As with all marine invertebrates, avoid copper-based treatments and any medication not explicitly marked safe for invertebrates.

Recommended parameters are a temperature of 23–27°C, salinity around 1.023–1.025, and pH between 8.1 and 8.4. Ammonia and nitrite must always be zero, and nitrate should be kept as low as practical. Stable alkalinity and calcium levels are beneficial in reef systems, especially where coralline algae growth is desired. Good water movement will help replicate its natural habitat and support healthy grazing behaviour.

Feeding Guide

The Multicolor Sea Urchin is primarily herbivorous and should be fed with a diet rich in marine algae. In a mature aquarium it will graze on film algae, microalgae and biofilm, but this should not be relied upon as its only food source. Supplement with dried seaweed sheets, algae wafers, blanched marine vegetables and other suitable herbivorous marine foods. Offering food after lights out can be helpful, as many urchins feed actively in lower light conditions.

Do not assume that a reef tank alone provides enough nutrition. A well-fed urchin is less likely to overgraze desirable coralline algae or wander excessively in search of food. If the tank is very clean, increase supplemental feeding accordingly. Remove uneaten food before it breaks down and affects water quality.

Tank Mates / Compatibility

Tripneustes gratilla is generally peaceful and can be kept with a wide range of calm marine fish and invertebrates. Suitable companions include clownfish, gobies, blennies, wrasses of appropriate temperament, chromis, and many reef-safe shrimp and snails. It can also work in mixed reef systems where fish are not prone to nipping or harassing invertebrates.

However, care is needed with very active or aggressive species. Large puffers, triggerfish, some wrasses and other inquisitive fish may nip at the spines or disturb the urchin. Avoid keeping it with species that are known to prey on echinoderms. Also be cautious with delicate coral frags, unsecured rockwork and very small ornamental items, as the urchin may move them while travelling across the tank.

Because sea urchins are excellent climbers, make sure the aquarium has a secure lid or safe top edge, and check overflow areas and pump intakes. A peaceful community with stable conditions is the best match for this species.

Why Buy from Tropical Fish Co

When you order from Tropical Fish Co, you get more than just a marine invertebrate. You get carefully selected livestock, expert packing and support from a UK specialist who understands the needs of saltwater aquariums. We offer fast UK delivery so your livestock arrives promptly and in the best possible condition, and our live arrival guarantee provides extra peace of mind when buying online.

We aim to supply healthy, well-acclimated animals with clear care guidance, helping you set up for success from day one. If you are looking for a striking, useful and genuinely interesting reef inhabitant, the Multicolor Sea Urchin is an excellent choice for a mature marine system.