Starfish and sharks – two of the most intriguing marine animals that capture our imagination. But do these enigmatic creatures ever cross paths? Can sharks feast on starfish or do the spiny marine invertebrates have defenses against ocean predators?
If you want a quick answer – sharks do eat starfish when food is scarce or the starfish are small enough to swallow. However, starfish have several defenses that make dining on them tricky and their diet is not a preferred staple for most shark species.
In this detailed guide, we’ll explore the factors surrounding sharks eating starfish including starfish defenses, shark feeding behavior, instances of sharks successfully hunting starfish, and which species are most likely to make a meal of these funky echinoderms.
Starfish Defenses Against Predators Like Sharks
Spines
Many species of starfish have spines covering their upper surface that help protect them against predators like sharks. These spines can be short and rounded, or long and sharp, depending on the species.
Some starfish like the crown of thorns starfish have very long, venomous spines that can cause severe pain and injury if touched by predators. The spines make it harder for predators to swallow or bite starfish, causing them to reject the starfish as prey after an initial attempt at attacking it.
Additionally, injury from venomous spines may teach predators to avoid that species of starfish in the future.
Ability to Regenerate
Another amazing defense that starfish have against predators like sharks is their ability to regenerate lost arms or even their entire bodies from just a portion of a remaining arm. If a shark bites off part of a starfish, the starfish can regrow that missing section in a matter of months.
This makes starfish very resilient against attacks, as they can recover after being bitten and survive to regrow. Even if a starfish is cut into several pieces, those pieces can each regrow into entirely new starfish, making them extremely hard prey for sharks to actually kill and consume.
This incredible regenerative capacity allows starfish to persist and thrive even with regular predation attempts from sharks and other predators.
Toxic Saponins
Many starfish species have saponins in their bodies – compounds that are toxic to predators like sharks. These saponins give the starfish a soap-like, frothy quality. When a starfish is attacked, these saponins are released into the water, creating a noxious substance that deters the predator.
Sharks and other predators find the taste and toxicity of these saponins highly unpleasant. In animal studies, starfish saponins have been shown to cause significant gastrointestinal distress and even convulsions and paralysis.
So the saponins act as a powerful chemical defense against predators, making starfish an undesirable and toxic meal.
Shark Hunting and Feeding Behavior
Opportunistic Feeders
Sharks are opportunistic predators that are constantly on the hunt for food. They have evolved excellent senses that allow them to detect prey from great distances. Their sense of smell is exceptional – they can detect tiny amounts of blood or chemicals in the water from up to a mile away.
Their vision is adapted for detecting movement and their lateral line system allows them to sense vibrations in the water. Sharks will eat just about anything they can capture, which makes them opportunistic feeders.
Although sharks are formidable hunters, hunting success rates are actually quite low. For every 100 hunting attempts, estimates indicate that sharks are only successful about 33% of the time. This means they need to be constantly on the prowl for the next meal and will eat just about anything they can find.
Sharks are not picky eaters! They will consume fish, seals, dolphins, turtles, sea birds, squid, crabs and even smaller sharks. Basically if it swims or walks near the ocean, a shark will eat it.
Varied Diets
Different species of sharks have evolved to take advantage of different food sources, leading to varied diets. For example, the enormous whale shark mainly feeds on plankton and small fish by filtering huge volumes of water through its enormous mouth as it swims.
Contrast this with the great white shark which focuses on hunting seals, dolphins and even small whales. The tiger shark has a reputation for eating just about anything, including turtles, birds, smaller sharks and even license plates or clothing that falls into the ocean!
Most sharks are generalist predators, not picky eaters, which takes advantage of whatever prey is commonly available. But some species have specialized diets. The basking shark has specially adapted gill rakers to filter zooplankton from the water.
The cookiecutter shark takes non-lethal circular bites out of large prey like whales or tuna. The goblin shark has protrusible jaws that snap up deep sea fish.
Hunting Strategies
Different sharks employ different hunting strategies suited to their diet, habitat and body type. Large open ocean predators like the great white shark and mako shark rely on speed, acceleration and the element of surprise to catch swift prey like seals or tuna.
They gather momentum with powerful tail beats and launch fast surprise attacks from below. Nearshore bottom dwellers like angel sharks bury themselves in sediment and ambush unsuspecting prey that swim close by.
Some small shark species swarm around larger prey in groups and take turns darting in to take quick bites. Thresher sharks use their elongated upper tail lobe to slap and stun small schooling fish. Port Jackson sharks have developed specialized spiral shaped egg capsules they anchor into seaweed beds, allowing the young to hatch close to abundant food sources right from birth.
Sharks have evolved a diversity of specialized hunting mechanisms over hundreds of millions of years. They are highly successful apex predators because of adaptations like speed, sharp senses, stealth, and strategies that maximize encounters with prey.
Their flexible opportunistic diets ensure they can thrive in most marine environments by taking advantage of whatever prey is available. Sharks are beautiful examples of evolutionary adaptation and fine-tuned hunting behavior!
Evidence of Sharks Eating Starfish
Documented Instances
There are several documented cases of sharks preying on starfish in the wild. Here are some examples:
- Tiger sharks are known to eat crown-of-thorns starfish around Australia’s Great Barrier Reef. These dangerous starfish are covered in venomous spines, but tiger sharks can easily swallow them whole.
- Blacktip reef sharks have been observed hunting blue sea stars in coral reefs of French Polynesia. They use their sharp teeth to pry the starfish off the reef before gulping them down.
- Port Jackson sharks off the coast of Australia eat a wide variety of sea stars, including the common cushion star. Researchers found the remains of stars in the shark’s stomach contents.
- Leopard sharks feed on bat stars in California’s kelp forests. Bat stars use their spines for defense, but leopard sharks are unfazed by the spines.
There are also videos and photos of various shark species eating starfish in aquarium settings. For example, horn sharks and swell sharks are often seen eating urchins and sea stars offered as food by aquarium staff.
Likely Species
The shark species most likely to eat starfish are bottom-dwelling coastal sharks found in shallow reef environments where starfish are abundant. This includes:
- Port Jackson sharks
- Wobbegong sharks
- Nurse sharks
- Leopard sharks
- Horn sharks
- Swell sharks
- Bamboo sharks
Larger, more pelagic shark species are less likely to eat starfish. However, tiger sharks and great hammerheads sometimes hunt crown-of-thorns starfish that destroy coral reefs.
Sharks that eat starfish use their strong jaws and sharp teeth to crunch through the starfish’s tough outer skin and spines. They are able to handle the starfish’s venom and swallow them whole. The starfish provide sharks with essential nutrients like protein, vitamins, and minerals.
Factors Impacting Likelihood of Predation
Starfish Size
Research indicates that a starfish’s size significantly influences its chances of getting eaten by sharks. Small juvenile starfish under 2 inches wide are the most vulnerable as they can easily fit inside a shark’s mouth (Florida Museum).
However, even large starfish over 12 inches wide can fall prey if the attacking shark has a big enough jaw span. For instance, tiger sharks and great white sharks have been known to swallow whole sea turtles, so an oversized starfish would not be impossible (National Wildlife Federation).
Food Availability
Sharks are more likely to hunt starfish when their preferred food sources like fish, seals, and sea turtles are scarce. During certain seasons or anomalous environmental events when ocean prey becomes less abundant, some shark species will eat less desirable substitutes like crustaceans and echinoderms to survive.
According to a 2015 marine biology study, over 60% of tiger sharks had starfish remains in their stomachs in the aftermath of a regional tuna shortage.
Location
Geographic area plays a major role in the probability of interaction between sharks and starfish. Regions like coral reefs where both species overlap in habitat provide more opportunity for sharks to run into and consume starfish.
Sharks also patrol the seafloor more often in hunting grounds near seal or sea lion colonies, heightening the chances of encountering bottom-dwelling starfish. Furthermore, some shoreline environments happen to contain higher densities of sharks and starfish simultaneously (NOAA).
For example, a 2021 survey of Australia’s Great Barrier Reef observed 30% more reef shark and starfish sightings compared to the 10-year average.
Conclusion
While starfish have formidable defenses, sharks have proven to be resourceful, opportunistic hunters. During times of scarce food supply, sharks may turn to the slow-moving echinoderms for sustenance. However, the frequency and success likely depends on species as well as environmental factors.
By better understanding these unique marine organisms, we gain appreciation for the interconnectedness of ocean life. We see that sharks play an important role in balancing starfish populations while the starfish’s defenses help maintain biodiversity.
While predator and prey, shark and starfish harmoniously occupy their shared marine habitat.
