Testing for biological molecules — practice question

In some ecosystems, particular species carry out vital roles in keeping communities biodiverse. These species are often referred to as keystone species. The sea otter, Enhydra lutris, occurs in the waters off the northern and eastern Pacific coasts, where it has a predator niche. These coastal waters contain abundant kelp communities. Kelp are very large seaweeds that create ‘underwater forests’. During the 19th century, sea otters were hunted for their fur, so population sizes fell. One effect of this decline was that much of the kelp disappeared. Conservation action in the 20th century increased sea otter numbers again. Fig. 6.1 gives the food web for this ecosystem.