Final answer:
Urchin barrens can survive without kelp because sea urchins eat detritus, making them omnivorous grazers with diverse diets that include algae and decomposing organic matter.
Step-by-step explanation:
Urchin barrens can persist without the presence of kelp because urchins have alternative food sources. The freshly dead or partially decomposing remains of organisms that urchins consume are known as detritus. Sea urchins are considered omnivorous grazers and can feed on algae, as well as a variety of dead or decomposing matter such as fish, mussels, sponges, and barnacles. This diverse diet allows sea urchins to survive in environments without kelp, ultimately contributing to the persistence of urchin barrens. Ecosystems like kelp forests, intertidal zones, and deep-sea vent communities demonstrate the complex interactions and adaptations of marine organisms, including the feeding strategies of various echinoderms such as sea urchins.