Food (or trophic) webs show who eats whom in the ecological community. Thus, food webs (which are made of interconnected food chains) help us understand changes in ecosystems. For example, the disappearance of a top predator affects many different species, both directly and indirectly.
Algae and phytoplankton are the basis of aquatic food webs. They are the food of primary consumers, such as small fish and crustaceans. Primary consumers, in turn, are eaten by larger fish, such as sharks, baleen whales or even corals. Thus, the main ocean predators are large sharks, billfish, dolphins, toothed whales and large seals. Finally we, human beings, find ourselves at the top of this entire network.
Producers
Primary producers, such as bacteria, phytoplankton, and algae, form the lowest trophic level. That is, they are the basis of the aquatic food web. Primary producers get their own energy without the need to eat. Many photosynthesize, using energy from the Sun to produce carbohydrates. However, some primary producers are able to create energy without sunlight through a process called chemosynthesis.
Predators
Some zooplankton, including copepods, rotifers, and some fish and invertebrate larvae, are herbivores and drift through water. Larger animals such as sea snails, fish, reptiles, and mammals eat algae. On the other hand, filter-feeding animals (that is, feeding on plankton and debris directly from the water) include tubeworms, sponges, bivalves, and even baleen whales and stingrays.
Predators, on the other hand, feed on other animals. There are many types of predators that feed on a wide variety of prey. Thus, ambush predators such as some octopuses, some eels and scorpion fish, often capture their prey by hiding and attacking by surprise.
Animals that have few or no predators are called top predators. Among them are killer whales, leopard seals, large sharks, sunflower starfish and other migratory species.
Scavengers
When an animal dies without being eaten, it sinks to the bottom, where it can be eaten by scavengers that live on the seabed (such as crabs and lobsters). The organic material that remains is decomposed by bacteria, and the resulting waste is converted into nutrients for the producers. Therefore, when a whale dies, it becomes a source of food for an entire ecosystem.
Opportunistic feeders
Some consumers are opportunistic eaters, so they can eat anywhere in the food web. In fact, they can be a combination of any of the types mentioned, and sometimes they even eat each other.
