Unraveling the mystery behind crown-of-thorns starfish outbreaks and their devastating impact on coral ecosystems
Imagine an army of spines and tentacles slowly advancing across your favorite tropical paradise. As they move, they leave behind a ghost town of skeletal white structures where vibrant, colorful communities once thrived. This isn't science fiction—it's the reality of crown-of-thorns starfish (CoTS) outbreaks, ecological disasters that are decimating coral reefs from the Great Barrier Reef to French Polynesia .
During population explosions, CoTS densities can skyrocket from less than one per hectare to over 1,000 individuals in the same area 3 .
Each adult can consume an astonishing 10 square meters of coral per year 3 .
Recent research has uncovered a fascinating and terrifying aspect of these outbreaks: when these starfish run low on their preferred food, they don't just stay put and starve. Instead, they undergo dramatic behavioral changes, forming massive aggregations that migrate across reefs in search of better feeding grounds. Understanding this link between food scarcity and starfish behavior may hold the key to protecting our precious coral ecosystems from these spiny invaders.
Crown-of-thorns starfish may seem like indiscriminate destroyers, but scientists have discovered they're actually quite picky eaters. When given a choice, they strongly prefer certain coral species, particularly Acropora corals—the branching, table-shaped species that provide critical habitat for many reef creatures 1 3 .
In a detailed study tracking individual starfish feeding habits, researchers found that despite consuming 17 different coral genera, Acropora alone accounted for 51% of all colonies eaten and a whopping 82% of the total surface area consumed 1 . This preference isn't just a matter of taste—Acropora corals are both highly nutritious and structurally complex, allowing the starfish to maximize their meal with each feeding bout.
If you've ever wondered how much a crown-of-thorns starfish eats, the answer might surprise you. Using advanced 3D modeling techniques to precisely measure feeding scars, scientists discovered these starfish don't actually feed every day. They observed that:
Advanced photogrammetry reveals true consumption rates
| Measurement Type | Average Daily Consumption | Equivalent For Perspective |
|---|---|---|
| Colonies consumed | 1.35 colonies per day | 1 coral head per feeding |
| 2D planar area | 198.4 cm² per day | Size of a smartphone screen |
| 3D surface area | 998.83 cm² per day | Size of a kitchen towel |
This "feast and famine" approach to eating suggests CoTS may consume large meals and then need time to digest before hunting again. But what happens when the pickings get slim across an entire reef?
When CoTS populations explode and locally preferred corals become scarce, these normally solitary creatures begin to exhibit dramatically different behavior. Research from Moorea in French Polynesia documented one of the most intense and methodic outbreaks ever recorded .
Scientists observed that outbreaks don't appear randomly across reefs. Instead, they typically originate in restricted areas confined to ocean-exposed reef bases, then progressively spread to adjacent shallower locations . The starfish migrate in aggregative waves that eventually affect the entire reef system, methodically moving from one coral patch to another.
Starfish gather in restricted areas at reef bases
Aggregations spread to adjacent shallower locations
Reef is methodically consumed in predictable sequence
As the starfish advance, they don't just randomly consume corals. The Moorea study revealed they feed in a predictable sequence, consuming coral species in order of their feeding preferences . This results in a systematic alteration of the coral community structure, often eliminating the most architecturally and ecologically important species first.
The migrating aggregations leave behind a clearly visible path of destruction—fresh white feeding scars on the coral skeletons where living tissue has been stripped away. Over time, these scars get covered by algae, changing color from bright white to dark green and brown. By monitoring these scars, scientists can track the progression, timing, and intensity of outbreaks.
| Coral Type | Preference Level | Percentage of Diet | Ecological Impact |
|---|---|---|---|
| Acropora | High | 51% of colonies, 82% of surface area | Loss of complex habitat |
| Pocillopora | High | Commonly consumed | Reduced structural diversity |
| Porites | Low | Rarely consumed when alternatives available | Community shift to less-preferred species |
| Merulinidae | Low | Rarely consumed | Community shift to less-preferred species |
To truly understand CoTS feeding behavior during outbreaks, a research team conducted an intensive tracking study at Lizard Island on Australia's Great Barrier Reef in late 2023 1 . Their goal was simple but ambitious: closely monitor individual starfish over an extended period to collect precise data on their daily feeding habits.
The researchers selected eight adult crown-of-thorns starfish, each separated by at least 50 meters to ensure independent movement patterns. Each starfish was carefully tracked for 9-13 days during a 13-day survey period. Rather than physically tagging the starfish (which could alter their behavior), the team identified individuals based on a combination of body size, distinct morphological features, and their precise spatial position on the reef.
The researchers employed cutting-edge scientific techniques to obtain unprecedented accuracy in their measurements. Using structure-from-motion photogrammetry—the same technology that creates 3D models from multiple photographs—they generated high-resolution, three-dimensional maps of each feeding scar 1 .
This approach represented a major advancement over previous methods that used simple linear measurements or two-dimensional projections. By capturing the full three-dimensional complexity of corals, the team could calculate the actual surface area consumed, rather than just the two-dimensional projection. This gave a much more accurate estimate of how much coral tissue the starfish were actually ingesting and digesting.
Additionally, the team monitored how quickly the feeding scars became overgrown with algae—critical information for interpreting feeding activity during large-scale reef surveys where researchers count fresh scars to estimate outbreak activity.
3D modeling from multiple photographs for precise measurements
The results revealed striking patterns that earlier, less precise methods had missed:
| Measurement Method | Average Daily Consumption | Advantages | Limitations |
|---|---|---|---|
| Traditional 2D planar | 198.4 cm² | Quick, easy field measurement | Misses complex surfaces |
| 3D photogrammetry | 998.83 cm² | Captures true surface area | Requires specialized equipment |
| Linear measurements | Varies widely | Very fast, no equipment needed | Least accurate, high error |
Understanding crown-of-thorns starfish behavior requires specialized equipment and techniques. Here are some key tools scientists use to unravel the mysteries of these coral killers:
High-resolution cameras used to create 3D models of feeding scars for precise measurement of coral consumption 1 .
Advanced genomic analysis helps track population connectivity and determine outbreak origins 5 .
"Scooter-assisted large-area diver-based" technique for rapid assessment of feeding scars across large reef areas 1 .
Emerging technology that detects genetic traces in water samples for early outbreak detection.
While CoTS outbreaks are natural phenomena in many coral reef ecosystems, there's growing concern that human activities and climate change may be making them more frequent and severe. Recent distribution modeling studies paint a worrying picture for the future.
Using species distribution models that incorporate both abiotic factors and the distribution of their preferred Acropora coral prey, scientists have projected significant range expansions for CoTS, particularly in the Southern Hemisphere 3 . New Zealand, previously unsuitable for these tropical starfish, might experience invasions as ocean temperatures continue to warm.
The complex relationship between climate change and CoTS outbreaks involves several worrying mechanisms:
May enhance larval development and survival rates
Could reduce coral resistance to predation
Creates weakened corals that may be more vulnerable
May alter larval dispersal patterns to previously unaffected areas 3
Genomic analyses support an anthropogenic influence on CoTS populations, showing that current starfish populations have the highest effective sizes of the last million years, suggesting human or climate factors may be driving population increases 5 .
Additionally, laboratory studies on related sea star species have demonstrated that elevated temperatures and food restriction significantly reduce fecundity 2 . While this might seem like good news, the complex interplay of these factors in natural ecosystems makes predicting outbreak patterns increasingly challenging.
Current CoTS populations are the largest in a million years, suggesting human or climate influences 5 .
The detailed understanding of crown-of-thorns starfish behavior—their feeding patterns, migration triggers, and population dynamics—provides crucial insights for coral reef management. By recognizing that outbreaks are typically locally derived rather than spreading through oceanic dispersal 5 , scientists can help managers focus on local intervention strategies.
Identifying initial aggregations allows for targeted removal before mass migration begins
Tracking preferred coral patches helps predict movement patterns and intervention priorities
Identifying self-seeding reefs versus those receiving external larvae informs management strategies
While crown-of-thorns starfish will always be part of coral reef ecosystems, the recent scientific advances in understanding their response to food limitation gives us a fighting chance to prevent the complete destruction of our precious coral reefs. The next time you see a picture of a healthy, vibrant coral reef, remember the army of spiny invaders waiting in the depths—and the scientists working tirelessly to keep them in check.