Giant kelp (Macrocystis pyrifera) forms dense underwater forests along temperate coastlines and is one of the fastest-growing organisms on Earth. Its long, buoyant fronds can reach from the seafloor to the ocean surface, creating a complex three-dimensional habitat for fish, invertebrates, marine mammals, and seabirds. However, marine heatwaves, intense grazing by sea urchins, pollution, and the loss of predators can rapidly reduce these forests and shift them toward persistent urchin barrens.

Purple sea urchins (Strongylocentrotus purpuratus) are important grazers in eastern Pacific kelp forests, but when predators decline and warming weakens kelp, they can transform forests into urchin barrens. In these food-poor habitats, the urchins survive by reducing their metabolism and resorbing their own gonadal tissue for energy. Even after their gonads have greatly diminished, they can remain alive and graze newly emerging kelp, helping to prevent the forest from recovering.

The California sheephead (Semicossyphus pulcher) is a large wrasse found on rocky reefs and in kelp forests from California to the Gulf of California. Using powerful jaws and prominent teeth, it feeds on hard-shelled animals such as sea urchins, crabs, and mollusks, helping regulate reef grazers. California sheephead begin life as females, and some later transition into males, developing a black head and tail, a reddish body, and a prominent forehead. This life history also makes their populations sensitive to fishing that selectively removes the largest individuals.

The branching anemone (Lebrunia neglecta) is distinguished by six highly branched pseudotentacles that resemble algae or soft corals and help it blend into the reef. Its true tentacles are largely concealed beneath these structures and contain stinging cells used to capture and guide prey toward the mouth. When disturbed, the anemone withdraws deeper into its rocky shelter, while the pseudotentacles may remain visible.

The American whitespotted filefish (Cantherhines macrocerus) has a strong, prominent spine on its back that can be raised when the fish feels threatened. This spine can be locked upright, allowing the filefish to wedge itself securely into reef crevices. The mechanism helps protect it from predators by making the fish difficult to remove from its shelter. Reaching up to about 40 cm in length, it feeds mainly on soft corals, hydroids, sponges, algae, and other reef-dwelling organisms.

The spotfin frogfish (Abantennarius nummifer) is a well-camouflaged ambush predator. Its modified first dorsal spine functions like a fishing rod, with a small fleshy lure that it moves in front of its large mouth to attract unsuspecting prey. Once a fish or crustacean comes within reach, the frogfish rapidly expands its mouth and swallows it. Its rounded body, textured skin, and slow movement help it blend into reefs and remain almost invisible while hunting.