Help Ocean Climate change

Species are highly connected to one another. The changing climate can alter their relationships. To understand how these relationships change, let’s look at how we divide organisms in a food web. Different levels of the food web, or food chain, are called trophic levels. “Trophic” just means related to eating. So let’s look at the different eating levels of a web.

A food web showing the feeding relationships among organisms in the Canadian arctic. Note that some species have more than one food choice (e.g. narwals eat fish (cod) and benthic, or ground dwelling, invertebrates). Also note that some species are a common food choice to more than one predator (e.g. cod are eaten by seabirds, seals, and some whales). Image from "Current State and Trends in Canadian Arctic Marine Ecosystems II," by Darnis et al., in Climatic Change.

Primary producers (like plants) are at trophic level one. They use sunlight to make sugars to feed themselves. The next level has herbivores, or plant eaters. These include large animals like deer, and tiny animals, like zooplankton. The third level is filled by animals that eat other animals. For example, small fish eat zooplankton. Some food webs have a higher levels, with predators that eat animals from the level below.

In these feeding relationships, the energy stored in prey flows to predators, up through trophic levels. This is known as a trophic flow. And because each organism may have multiple food choices, a food web is created, instead of just specific food chains.

Humans are part of marine food webs, as marine organisms, like fish, are part of our diet. Billions of people depend on fish for nearly one-fifth of the animal proteins they eat. With such a dependence on marine food webs, we need to understand how the changing climate may affect the oceans.