Does Anything Eat Crown of Thorns Starfish? Understanding Natural Predators of a Reef Threat
While the infamous crown of thorns starfish (COTS) poses a significant threat to coral reefs, the good news is that yes, some marine species do prey upon them, especially during their vulnerable larval and juvenile stages. However, their effectiveness in controlling COTS outbreaks is limited.
Introduction: The Crown of Thorns Starfish and its Impact
The crown of thorns starfish (Acanthaster planci) is a large, venomous starfish that feeds on coral polyps. In moderate numbers, they are a natural part of the reef ecosystem. However, outbreaks can decimate coral reefs, leaving behind barren landscapes. Understanding their natural predators is crucial for developing effective management strategies. This article explores what eats crown of thorns starfish, examining their life cycle and the role of different predators at different stages.
Natural Predators of COTS
Several marine species have been observed preying on crown of thorns starfish, particularly during their early life stages. The list of known predators includes:
-
Larval Stage:
- Filter-feeding organisms: These consume COTS larvae as they drift in the water column. While not specific to COTS, their collective impact helps regulate larval populations.
- Planktivorous fish: Similar to filter-feeders, these fish consume COTS larvae incidentally while feeding on plankton.
-
Juvenile Stage:
- Harlequin shrimp (Hymenocera picta): These specialized shrimp are known to feed almost exclusively on starfish, including juvenile COTS.
- Pufferfish: Some species of pufferfish will consume juvenile COTS.
- Triton snails (Charonia tritonis): This giant marine snail is a well-known predator of adult COTS, but its populations are often too low to effectively control outbreaks.
-
Adult Stage:
- Triton snails (Charonia tritonis): Considered the most significant natural predator of adult COTS.
- Humphead wrasse (Cheilinus undulatus): This large fish has been observed feeding on adult COTS, though its impact on large outbreaks is limited.
The Role of the Triton Snail
The giant triton snail stands out as a significant predator of adult crown of thorns starfish. They are large, visually striking snails that actively hunt and consume COTS. The snail uses its proboscis to inject a paralyzing venom into the starfish before consuming it. However, triton snail populations have been significantly reduced due to over-collection for the shell trade, diminishing their ability to control COTS outbreaks. Conservation efforts focused on protecting triton snails could aid in natural COTS control.
Harlequin Shrimp: A Specialized Predator
Harlequin shrimp are fascinating creatures known for their vibrant colors and their exclusive diet: starfish. They typically attack COTS by flipping them over and consuming their tube feet, eventually leading to starvation. While effective predators of juvenile COTS, their small size and limited numbers mean they cannot control large-scale outbreaks.
Limitations of Natural Predation
While some species prey on crown of thorns starfish, natural predation alone is often insufficient to prevent or control outbreaks. Several factors contribute to this limitation:
- Overfishing: Many COTS predators, such as the humphead wrasse and triton snail, are targeted for fishing or the shell trade, reducing their populations and, consequently, their ability to control COTS numbers.
- Habitat degradation: Pollution and habitat destruction can negatively impact the populations of COTS predators.
- COTS outbreaks overwhelm predators: During large-scale outbreaks, the sheer number of COTS overwhelms the capacity of natural predators to control them.
- Larval survival rates: Even with predation on larvae, a significant number still survive to adulthood, contributing to future outbreaks.
Management Strategies Beyond Natural Predation
Given the limitations of natural predation, other management strategies are necessary to address COTS outbreaks effectively. These include:
- Manual removal: Divers manually remove COTS from reefs, either by injecting them with a lethal substance (like vinegar or bile salts) or by physically removing them.
- COTSbots: Underwater robots are being developed to autonomously detect and inject COTS, making manual removal more efficient.
- Improved water quality: Reducing nutrient runoff from land can help limit algal blooms that provide food for COTS larvae, reducing their survival rates.
- Marine protected areas: Establishing marine protected areas can help conserve populations of COTS predators, allowing them to play a more significant role in controlling COTS numbers.
Research and Future Directions
Ongoing research is focused on better understanding COTS biology, ecology, and behavior. This includes:
- Identifying key factors that trigger COTS outbreaks.
- Developing more effective and environmentally friendly methods for controlling COTS populations.
- Assessing the long-term impacts of COTS outbreaks on coral reef ecosystems.
- Studying the genetics of COTS populations to understand their dispersal patterns.
Frequently Asked Questions (FAQs)
What causes crown of thorns starfish outbreaks?
Crown of thorns starfish outbreaks are complex events influenced by several factors. Increased nutrient runoff from land, which promotes algal blooms that feed COTS larvae, is a significant contributor. Other factors include overfishing of COTS predators and natural fluctuations in ocean currents.
How can I tell the difference between a healthy number of COTS and an outbreak?
A healthy reef system typically has a low density of COTS. An outbreak is generally defined as more than 15 COTS per hectare, where the starfish are actively consuming coral at a rate that exceeds the coral’s ability to recover.
Is it safe to swim near crown of thorns starfish?
While not aggressive, crown of thorns starfish possess venomous spines that can cause painful stings. It’s best to avoid touching them. If stung, seek medical attention as needed.
Are crown of thorns starfish native to coral reefs?
Yes, crown of thorns starfish are native to coral reefs in the Indo-Pacific region. They play a natural role in reef ecosystems in low numbers. However, their populations can fluctuate dramatically, leading to outbreaks.
Are there any efforts to breed triton snails for release onto reefs?
Yes, research and pilot programs are underway to breed triton snails in captivity and release them onto reefs to help control COTS populations. These efforts are still in the early stages, but show promise.
How effective is manual removal of COTS?
Manual removal can be an effective short-term solution for controlling COTS outbreaks on localized areas of reefs. However, it is labor-intensive and costly, and requires trained divers. It’s most effective when combined with other management strategies.
What are the environmental impacts of injecting COTS with vinegar?
Vinegar injection is considered a relatively environmentally friendly method of COTS control. The vinegar breaks down quickly and does not appear to have significant negative impacts on other marine life. Bile salts are also used but require greater caution.
Do COTS have any other natural predators besides triton snails, harlequin shrimp, and humphead wrasse?
While those listed are the most well-known predators, other species, such as some species of triggerfish, pufferfish, and sea stars (other than COTS!) may occasionally prey on juvenile or small adult COTS.
Can COTS reproduce asexually?
No, crown of thorns starfish reproduce sexually. Females release millions of eggs into the water column, which are then fertilized by males. This high reproductive rate contributes to their ability to form large outbreaks.
What is being done to address nutrient runoff into the ocean?
Various initiatives are underway to reduce nutrient runoff, including improving wastewater treatment, promoting sustainable agriculture practices, and restoring coastal wetlands.
How are outbreaks of COTS monitored?
COTS outbreaks are typically monitored through a combination of underwater surveys conducted by divers and aerial surveys using drones or aircraft. These surveys help to track the size and location of outbreaks.
Does anything eat crown of thorns? (As adults)
Yes, the Giant Triton Snail is the adult Crown of Thorns’ most effective predator. However, due to over-collection, these snail populations are too low to impact COTS outbreaks significantly. Therefore, while there are predators, their effectiveness in controlling populations is limited.