Kelp forests create some of the ocean’s most vibrant ecosystems, stretching up to 150 feet from the seafloor toward sunlight. These underwater forests support an intricate food web where numerous marine animals depend on kelp as their primary food source.
From tiny invertebrates grazing on holdfasts to large marine mammals seeking shelter and sustenance, you’ll discover how kelp-eating animals maintain the delicate balance of coastal marine environments.
Understanding these relationships reveals why kelp forests rank among the most productive ecosystems on Earth.
1. Sea Urchins
Sea urchins (Echinoidea) serve as the primary herbivores in kelp forest ecosystems, with species like the purple sea urchin (Strongylocentrotus purpuratus) and red sea urchin feeding heavily on these underwater plants. You’ll find these spiny creatures grazing directly on kelp holdfasts, the root-like structures that anchor kelp to the ocean floor. Purple sea urchins inhabit shallow coastal waters of the Pacific Ocean off western North America, where their diet consists primarily of bull kelp and giant kelp.
When sea urchin populations grow unchecked by natural predators like sea otters and sunflower sea stars, they can devastate entire kelp forests. This overgrazing creates “urchin barrens,” barren areas where kelp has been completely removed, leading to significant biodiversity loss. The balance between sea urchins and their predators remains critical for maintaining healthy kelp forest ecosystems.
2. Snails
Various snail species graze on kelp in coastal waters worldwide, using specialized feeding structures to consume both kelp tissue and the microalgae growing on kelp surfaces. These gastropods scrape algae and kelp fragments using their radula, a ribbon-like structure covered with tiny teeth. You’ll commonly find snails moving slowly across kelp fronds, methodically feeding on available plant material.
Snails play an important role in kelp forest health by controlling microalgae growth and processing decomposing kelp matter. While they consume kelp at a much slower rate than sea urchins, their consistent grazing contributes to nutrient cycling within the ecosystem. Many snail species find both food and protection within the complex three-dimensional structure of kelp forests.
3. Limpets
Limpets are small, cone-shaped mollusks that attach firmly to rocks and kelp surfaces in intertidal and subtidal zones. These specialized grazers use their strong radula to scrape algae, microorganisms, and small pieces of kelp from rocky substrates. You’ll often see limpets clustered on kelp holdfasts or nearby rocks, where they feed during high tide.
These mollusks exhibit remarkable homing behavior, returning to the exact same spot after each feeding session. This consistent grazing pattern helps prevent excessive algae buildup on kelp surfaces, which could otherwise block sunlight and reduce photosynthesis. Limpets demonstrate how even small herbivores contribute to the overall health and productivity of kelp forest ecosystems.
4. Abalone
Abalones are large marine snails that primarily consume algae and kelp throughout their lives. When young, abalones (Haliotis species) graze on plankton, but as they mature, they shift their focus to various kelp types found in coastal waters. These mollusks use their radula to scrape kelp off rocks, processing substantial amounts of plant material to support their growth.
Both black and white abalone species have become endangered due to overharvesting by humans, who prize their nutritious meat and beautiful shells. Sea otters in the Pacific Ocean heavily depend on abalone as a food source, creating a direct link between kelp forests, abalone populations, and sea otter survival. Without healthy kelp forests, abalone populations decline, which in turn affects the predators that rely on them for sustenance.
5. Crabs
Multiple crab species feed on kelp and seaweed, with the kelp crab (Pugettia productus) relying most heavily on seaweed for its diet. Ranging along western North America’s coastal waters, kelp crabs almost exclusively eat bull kelp, sea cabbage, and rockweed during warm months. When seaweed becomes dormant in winter across much of their range, these crabs switch to an omnivorous diet.
Crabs use their powerful claws to tear off pieces of kelp for consumption, though they generally don’t pose a significant threat to kelp forests due to their moderate consumption rates. You’ll find various crab species inhabiting kelp forests, where they serve multiple roles as both herbivores and scavengers, helping to process both living and decomposing plant material.
6. Sea Hares
Sea hares (Anaspidea) are seaweed-eating marine snails found in coastal waters with dense vegetation worldwide. These fascinating creatures occur in sheltered temperate and tropical waters, where they actively graze on various seaweed species including kelp. The color of a sea hare often reflects the type of seaweed it consumes, displaying red, green, or brown hues depending on its diet.
The California brown sea hare (Aplysia californica) feeds mainly on red and brown seaweed, processing significant quantities of plant material daily. These soft-bodied mollusks move slowly through kelp forests, using their sensory tentacles to locate preferred food sources. Sea hares play an important role in controlling seaweed populations and contributing to nutrient cycling in coastal ecosystems.
7. Fish (Such as Kelp Perch and Opaleye)
Numerous fish species consume kelp as part of their diet, with kelp perch and opaleye representing prime examples of fish that directly feed on these underwater plants. The opaleye (Girella nigricans) is a perch-like fish living off North America’s western coast, inhabiting tide pools, kelp forests, and rocky intertidal zones depending on its life stage. As juveniles, opaleye feed almost entirely on seaweed in tide pools, while adults become omnivorous, consuming kelp, other seaweed forms, and small invertebrates.
Kelp bass (Paralabrax clathratus) plays a crucial role in kelp forest health, particularly during its juvenile stage. Young kelp bass primarily eat kelp-associated invertebrates and may occasionally consume kelp itself, helping maintain the delicate ecological balance. As adults, this species switches to feeding on benthic and pelagic fish such as anchovies and perches. Many rockfish species, including black rockfish, blue rockfish, olive rockfish, and kelp rockfish, inhabit kelp forests and rely on these ecosystems for food and protection from predators.
8. Sea Otters
Sea otters (Enhydra lutris) represent one of the most important mammals in kelp forest ecosystems, though they don’t directly consume kelp. Instead, these charismatic marine mammals feed heavily on sea urchins, abalone, and other invertebrates that eat kelp. By controlling sea urchin populations, sea otters indirectly protect kelp forests from overgrazing and destruction.
Kelp forests provide sea otters with refuge from sharks and storms, while the otters help maintain forest health through their predation on kelp grazers. When sea otters were hunted to near extinction in the 18th and 19th centuries, sea urchin populations exploded, leading to widespread kelp forest degradation that still affects some coastal areas today. Sea otters also display adorable behavior by wrapping themselves in kelp to stay together while floating, demonstrating their intimate connection to these underwater forests.
9. Sea Stars
Sea stars, also known as starfish, feed on kelp and other submerged plants throughout the world’s oceans. More than two thousand starfish species exist worldwide, though none possess brains or blood. These intricate creatures use their tube feet to move across the ocean floor and kelp surfaces, feeding on both living kelp and decayed plant material.
The sunflower sea star (Pycnopodia helianthoides) plays a particularly crucial role in kelp forest ecosystems by preying on sea urchins at rates that help restore kelp forest health. While sea otters prefer the most nutritious sea urchins, sunflower stars eat different urchin species, including smaller, less optimal ones that otters leave behind. Unfortunately, sea star wasting disease has devastated sunflower star populations across the Northeastern Pacific coast since 2013, with over 95 percent dying. This collapse has contributed to increased sea urchin grazing and kelp forest decline in many areas.
10. Marine Amphipods
Marine amphipods are small crustaceans that inhabit kelp forests, feeding on various organic materials including kelp fragments and the microorganisms growing on kelp surfaces. These tiny creatures often measure just a few millimeters in length but exist in massive numbers throughout kelp forest ecosystems. You’ll find amphipods crawling across kelp fronds and among holdfasts, where they process both fresh and decomposing plant material.
Some amphipod species prefer eating aged, decomposing kelp rather than fresh material, as bacterial colonies make the kelp easier to digest and increase its nutritional value. These crustaceans serve as an important food source for many fish species and contribute significantly to nutrient cycling within kelp forests. Their role in breaking down dead kelp helps return nutrients to the ecosystem, supporting new growth.
11. Isopods
Isopods are crustaceans closely related to amphipods, though they possess distinct anatomical features. These animals inhabit kelp forests where they feed on kelp fragments, decomposing plant material, and the organisms growing on kelp surfaces. The isopod Ligia pallasii, like some amphipods, prefers eating aged, decomposing algae rather than fresh material.
Isopods use their mouthparts to tear small pieces of kelp, processing organic matter at a gradual but consistent rate. You’ll find various isopod species throughout kelp forest ecosystems, from the seafloor to the upper canopy. These crustaceans help maintain ecosystem health by breaking down dead organic material and serving as prey for larger animals like fish and sea stars.
12. Marine Worms
Bristle worms represent one of the most commonly found invertebrates in kelp forests, with the Polychaeta family including at least 10,000 species inhabiting practically every ocean habitat. These segmented worms feed on kelp holdfasts, the root-like structures securing kelp to the seafloor. You’ll find bristle worms actively consuming both living holdfast tissue and decomposing organic matter.
Marine worms play an essential role in nutrient cycling and decomposition within kelp forest ecosystems. By feeding on holdfasts and dead kelp material, they help break down complex organic compounds and return nutrients to the water column. While some species can damage kelp by consuming holdfasts, their overall contribution to ecosystem function remains beneficial for maintaining healthy nutrient cycles.
13. Green Turtles
Green sea turtles (Chelonia mydas) are the only primarily herbivorous sea turtles as adults, feeding extensively on algae, seaweed, and seagrasses. These large marine reptiles possess finely serrated beaks specially adapted to their vegetarian diet, allowing them to easily scrape seaweed off marine rocks and tear kelp from the seafloor. A 2021 study found that green sea turtles in the northwestern Gulf of Mexico consume 33 species of red seaweed, 12 species of green seaweed, and eight species of brown seaweed.
As juveniles, green sea turtles are mostly carnivorous, but they transition to plant-based diets as they mature. You’ll find these turtles grazing in shallow coastal waters where kelp and seaweed are abundant. Green sea turtles can consume substantial quantities of marine vegetation daily, playing an important role in controlling seaweed and kelp populations in tropical and subtropical waters.
14. Manatees
Manatees are large marine mammals that consume enormous quantities of aquatic vegetation daily, including various forms of seaweed and kelp when available. As adults, manatees weigh between 800 and 1,200 pounds, eating the equivalent of 4 to 9 percent of their body weight in wet vegetation every single day. Their diet consists of various algae, marine grasses, leaves, and aquatic plants.
These gentle herbivores use their flexible lips to grasp vegetation and their molars to grind plant material thoroughly. While manatees primarily inhabit warm coastal waters, rivers, and estuaries where seagrasses are abundant, they will consume kelp and other seaweeds when encountered. Manatees demonstrate how large marine mammals can significantly impact aquatic plant communities through their substantial daily consumption rates.
15. Dugongs
Dugongs are marine mammals closely related to manatees, sharing similar herbivorous feeding habits and massive daily vegetation requirements. These animals primarily feed on seagrasses in shallow coastal waters of the Indo-Pacific region, but they also consume various seaweed species including kelp when available in their habitat range. Dugongs use their muscular upper lips to uproot seagrasses and tear seaweed from substrates.
You’ll find dugongs in tropical and subtropical coastal waters where they graze extensively on underwater vegetation. Like manatees, dugongs must consume large quantities of plant material daily to meet their energy needs, sometimes eating up to 88 pounds of vegetation per day. These peaceful marine mammals play an important role in shaping seagrass and seaweed communities through their intensive grazing behavior, though their populations face significant threats from habitat loss and human activities.
