Spiny Sea Stars: The Prickly Reef Dwellers

Reef ecosystems are home to a dazzling array of marine life, each species contributing to the intricate web of interactions that sustain these vibrant environments. Among the many fascinating inhabitants of coral reefs, spiny sea stars stand out with their unique appearance and ecological roles. This comprehensive guide will cover various species of spiny sea stars, their characteristics, and their essential role in reef ecosystems.

What Are Spiny Sea Stars?

Spiny sea stars belong to the class Asteroidea within the phylum Echinodermata. They are characterised by their rigid bodies covered with spines or tubercles, giving them a distinctive prickly appearance. These sea stars are found in various marine habitats, including coral reefs, where they play crucial roles in maintaining ecological balance.

Key Characteristics:

• Appearance: Spiny sea stars have a central disc and multiple arms (usually five, but sometimes more). Their surfaces are adorned with spines, which can vary in length, density, and arrangement depending on the species.
• Size: They range in size from a few inches to over a foot in diameter, depending on the species.
• Habitat: Spiny sea stars inhabit rocky substrates, coral reefs, and sandy bottoms, often hiding in crevices or under rocks during the day.

Species of Spiny Sea Stars

Several species of spiny sea stars are commonly found in reef ecosystems. Each species has unique characteristics and adaptations that make them well-suited to their specific environments.

1. Crown-of-Thorns Starfish (Acanthaster planci)

• Description: This infamous sea star is known for its numerous long, venomous spines. It has a broad, central disc and multiple arms that can reach up to 21.
• Habitat: Found in coral reefs across the Indo-Pacific region.
• Role: While they play a role in reef ecology by controlling coral populations, outbreaks can cause significant damage to coral reefs.

2. Chocolate Chip Sea Star (Protoreaster nodosus)

• Description: Named for the dark, cone-shaped spines that resemble chocolate chips, this sea star has a striking appearance with a range of colours, including shades of red, orange, and brown.

• Habitat: Commonly found in shallow, sandy, and seagrass areas of the Indo-Pacific.
• Role: An important scavenger, feeding on detritus, algae, and small invertebrates.

3. Horned Sea Star (Protoreaster linckii)

• Description: This species features large, prominent spines on its arms and central disc. It typically has a reddish or orange coloration with contrasting spine colours.
• Habitat: Prefers shallow reef environments and sandy bottoms.
• Role: Acts as a scavenger and predator of small invertebrates, helping to keep the reef clean.

4. Spiny Cushion Star (Culcita novaeguineae)

• Description: Unlike the typical star shape, this species is more cushion-like with short, stubby arms and a heavily spined body.
• Habitat: Found in coral reefs and lagoons throughout the Indo-Pacific.
• Role: Primarily a detritivore, consuming organic material and contributing to nutrient cycling.

Role in Reef Ecosystems

Spiny sea stars are integral to the health and stability of reef ecosystems. Their behaviours and interactions with other organisms contribute to the complex dynamics of these environments.

Ecological Roles:

1. Predation and Population Control:

• Some spiny sea stars, like the crown-of-thorns starfish, feed on coral polyps, helping to control coral populations and promote diversity. However, when their populations are unchecked, they can cause significant coral damage.

2. Scavenging and Nutrient Cycling:

• Many spiny sea stars are scavengers, feeding on detritus, dead organisms, and algae. This scavenging behaviour helps recycle nutrients within the reef, supporting the growth of other organisms.

3. Habitat Formation:

• By burrowing and moving through the substrate, spiny sea stars help aerate the seabed, promoting healthy sediment turnover and providing habitats for other small marine creatures.

4. Biodiversity Enhancement:

• Their presence contributes to the overall biodiversity of the reef, supporting a wide range of interactions and ecological processes. Diverse reef systems are more resilient to environmental changes and stressors.

Care Requirements in Reef Aquariums

Keeping spiny sea stars in a reef aquarium can be rewarding, but it requires careful attention to their specific needs and environmental conditions.

Tank Setup and Environment:

1. Tank Size:

• Provide a sufficiently large tank to accommodate the size and activity level of the sea stars. A minimum of 50 gallons is recommended for smaller species, while larger species may require much bigger tanks.

2. Substrate and Rockwork:

• Offer plenty of live rock and a suitable substrate to mimic their natural habitat. Ensure there are hiding spots and crevices where they can seek shelter.

3. Water Parameters:

• Maintain stable water conditions with temperatures between 72-78°F (22-26°C), salinity levels of 1.023-1.025 specific gravity, and a pH of 8.1-8.4.
• Regular water changes and efficient filtration are crucial to prevent the buildup of waste and maintain high water quality.

4. Lighting:

• Moderate lighting is sufficient for spiny sea stars. They do not rely on light for photosynthesis but benefit from a stable light cycle that supports the overall health of the tank.

5. Water Flow:

• Provide moderate water flow to ensure proper oxygenation and nutrient distribution. Avoid strong currents that could dislodge the sea stars from their preferred locations.

Feeding and Nutrition:

1. Diet:

• Depending on the species, spiny sea stars may feed on a variety of foods, including algae, detritus, small invertebrates, and carrion. Supplement their diet with high-quality marine pellets, flakes, and frozen foods like mysis shrimp or chopped seafood.
• Ensure a varied diet to meet their nutritional needs and support their health.

2. Feeding Frequency:

• Feed spiny sea stars several times a week, providing enough food to keep them healthy without overfeeding the tank.

Compatibility with Other Tank Inhabitants:

1. Fish:
• Spiny sea stars are generally peaceful and can coexist with a variety of reef-safe fish. Avoid housing them with aggressive or predatory fish that may harm them.
2. Invertebrates:
• They can be compatible with other reef-safe invertebrates, such as shrimp, snails, and non-aggressive crabs. Monitor interactions to ensure harmony in the tank.
3. Corals:
• Some species, like the crown-of-thorns starfish, can pose a threat to corals. Carefully research and select species that are compatible with your coral types and monitor their behaviour.

Spiny Sea Stars and Their Coral Compatibility

Spiny sea stars, with their unique and often striking appearances, can be a fascinating addition to a reef aquarium. However, ensuring they are compatible with the corals in the tank is crucial for maintaining a healthy and balanced ecosystem. Below is a list of spiny sea stars and the types of corals they are typically compatible with:

1. Crown-of-Thorns Starfish (Acanthaster planci)

• Coral Compatibility: Not compatible. This species feeds on coral polyps and can cause significant damage to coral reefs.
• Notes: Best kept out of coral reef aquariums due to their destructive feeding habits.

2. Chocolate Chip Sea Star (Protoreaster nodosus)

• Coral Compatibility: Not reef-safe. Known to feed on soft corals, anemones, and other invertebrates.
• Notes: Best suited for fish-only tanks or FOWLR (Fish Only With Live Rock) setups.

3. Horned Sea Star (Protoreaster linckii)

• Coral Compatibility: Not reef-safe. May prey on soft corals and other small invertebrates.
• Notes: Should be housed in fish-only or non-coral environments.

4. Spiny Cushion Star (Culcita novaeguineae)

• Coral Compatibility: Mostly reef-safe, but caution is advised. Generally, they feed on detritus and organic matter but can occasionally consume small corals or polyps.
• Notes: Monitor interactions with corals closely.

5. Blue Linckia Sea Star (Linckia laevigata)

• Coral Compatibility: Reef-safe. Compatible with most types of corals, including soft corals, LPS (Large Polyp Stony) corals, and SPS (Small Polyp Stony) corals.
• Notes: Requires a well-established tank with plenty of live rock for grazing.

6. Fromia Sea Star (Fromia spp.)

• Coral Compatibility: Reef-safe. Suitable for tanks with soft corals, LPS corals, and SPS corals.
• Notes: Prefers tanks with ample live rock and algae to feed on.

7. Brittle Starfish (Ophiuroidea)

• Coral Compatibility: Reef-safe. Compatible with all types of corals.
• Notes: Excellent scavengers; avoid housing with aggressive species like the green brittle star, which can be predatory.

8. Sand Sifting Sea Star (Astropecten polycanthus)

• Coral Compatibility: Reef-safe, but with caution. They can deplete beneficial sand-dwelling organisms, which might impact the sand bed ecology.
• Notes: Best suited for larger tanks with deep sand beds.

9. Red Knobby Sea Star (Protoreaster linckii)

• Coral Compatibility: Not entirely reef-safe. May feed on soft corals and other invertebrates.
• Notes: Best kept in fish-only or non-coral environments.

By carefully selecting the appropriate species of spiny sea stars and monitoring their interactions with corals, reef keepers can maintain a harmonious and thriving reef aquarium. Always research specific needs and behaviours of each species to ensure a balanced and healthy environment for all inhabitants.

Challenges and Considerations

While spiny sea stars offer numerous benefits, there are a few challenges and considerations to keep in mind:

1. Sensitivity to Water Quality:
• Spiny sea stars are sensitive to changes in water quality and can be negatively affected by poor conditions. Regular monitoring and maintenance are essential to prevent stress and health issues.
2. Feeding Needs:
• Ensuring spiny sea stars receive adequate nutrition can be challenging, especially in tanks with low natural food availability. Consistent supplementation is necessary to meet their dietary requirements.
3. Predation Risk:
• Small or juvenile sea stars may be at risk of predation from larger tank inhabitants. Provide ample hiding spaces to reduce this risk.
4. Molting:
• Like other echinoderms, spiny sea stars undergo molting. During this time, they may be more vulnerable and require stable water conditions to support healthy molting cycles.

Conclusion

Spiny sea stars, with their unique appearance and ecological roles, are a fascinating addition to reef ecosystems. Their contributions to predation, scavenging, nutrient cycling, and biodiversity enhancement highlight their importance in maintaining healthy and balanced reef environments.

By understanding their specific needs and providing appropriate care, aquarists can enjoy the beauty and functionality of spiny sea stars in their reef tanks. Whether you are an experienced reef keeper or new to the hobby, incorporating spiny sea stars into your aquarium can enhance its diversity, resilience, and aesthetic appeal.