Coastal food webs

(peaceful music) - [Woman] Let's visit an underwater forest near Monterey, California, where kelp grows over 100 feet tall, reaching towards the sunlight above. It's fallen blades litter the sea floor below, providing nutrients for a host of creatures including these spiny purple sea urchins which move slowly in search of food. Sea urchins make a tasty mean for this marine mammal. Sea otters help keep the sea urchin population in check. Too many sea urchins will devour living kelp, destroying the forest. We consider otters a keystone species. As active predators they protect kelp from hungry herbivores like sea urchins and help maintain diversity and balance and this ecosystem. But we're seeing just one small part of an intricate network. Sunflower stars also prey on sea urchins and may become dinner for a hungry sea otter. But otters prefer abalone and crabs. From the smallest microbes to the largest animals these species take part in a diverse food web that links more than a thousand species. The connections in the web represent the transfer of energy with every meal. At the California Academy of Sciences, paleontologist Peter Rutenrein studies both modern day food webs, like this one, and those from the past. - [Peter] Basically a food web is a map of all of the interactions, what we call the trophic interactions, in an ecosystem or community. And those are predator prey interactions. Who eats whom, who eats you, what do you eat, and so on. The food web is one of, if not the most important representation of interactions that we have in an ecosystem because it's a main passage of energy. Through that system energy is produced, it's consumed, and everything else runs on that. - [Woman] Let's take a closer look at our marine ecosystem off the coast of California. What connections do you see in this food web? Can you predict the flow of energy between otters, urchins, and kelp? From primary producers to top predators, this dynamic ecosystem supports a diverse set of species. Small changes, however, can have big impacts across the entire community. Imagine you're a citizen scientist exploring marine ecosystems on the California coast. You visit the same kelp forest every year and observe seat otters, sea urchins, and kelp populations. Looking over your field notes now, what trends do you see? How are otters, urchins, and kelp connected? Take a moment to pause the video and examine your graph. Here we see the impact sea otters have as a keystone species. When otters are present, urchin and kelp populations are stable. When absent though, urchins boom and kelp beds are reduced. Let's take another look at our coastal food web. Can you predict how a removal of sea otters would impact the flow of energy through the system? Which species would be negatively impacted? Would any be positively impacted? Pause the video to take a closer look. Removal of a keystone species, the sea otter, has cascading effects, impacting populations across multiple trophic levels and disrupting the flow of energy through the entire system. Understanding ecosystems and the various threads that connect species together in food webs can help us better direct resources for conservation efforts and, most importantly, come to sustain these diverse networks of life.