FeedingGuilds

Feeding Guilds and Trophic Levels

Feeding Guilds

As Merriam-Webster dictionary defines it, a feeding guild is “a group of organisms that use the same ecological resource in a similar way." In simpler terms, feeding guilds can be described as groups of living things that get their energy necessary to survive from the same source. Feeding guilds do not have to be made up of the same or similar species; they can be completely unrelated, only alike in the fact that they acquire resources from their surroundings in similar ways. Because members of a guild use the same resources, competition is common within that guild. A feeding guild is composed of three major categories: autotrophs, heterotrophs, and detritivores.

Autotrophs

Autotrophs are "self-nourishing organisms capable of absorbing solar energy and photosynthetically building high-energy organic substances." Because these organisms need light to survive, they are most commonly found within the top 70 meters of water in marine environments. Since most coral reefs reside in shallower waters, they provide a great environment for autotrophs. Two examples of autotrophs in coral reef ecosystems are seaweed and zooxanthellae, a type of algae that makes up part of the coral and gives it color.

Heterotrophs

Heterotrophs are consumers, they obtain their energy necessary to survive from other organisms. Heterotrophs can be broken down into seven different subcategories: herbivores, carnivores, omnivores, filter feeders, planktivores, oppurtunistic feeders, and parasites.

Herbivores

Herbivores feed only upon autotrophs. There is a large guild of herbivores in coral reef environments. Two examples are the Green Sea Turtle, which eats sea grass, and a sea urchin, which eats algae.

Carnivores

Carnivores feed only upon other animals. In coral reefs, they range from top predators such as barracudas and eels to smaller predators such as lobsters.

Omnivores

Omnivores consume both autotrophs and other heterotrophs.An example of an omnivore in coral reefs are anglefish which feed algae, smaller fish, and shrimp.

Filter/Suspension feeders

Filter/suspension feeders primarily consume organic material (pseudo-plankton) floating in the water column. Suspension feeders capture particles of food from the water using tentacles while filter feeders use a filtration system to filter out dissolved particles after pumping in water. Zooplankton and sponges are good examples of these in coral reef environments.

Planktivores

Planktivores eat the small organisms (collectively known as plankton) that drift in the water. They can herbivorous and consume primarily phytoplankton, or they can be zooplanktivores that consume suspended animals. The whale shark, which feeds primarily on plankton, is an example of planktonivores in coral reef ecosystems.

Opportunistic feeders

This group targets prey based on what is available at the time. Scavengers and cannibals, such as some species of crabs, are included in this group.

Parasites

Parasites "live on or in another organism", taking their nutrition from the host organism while giving nothing in return. A common example seen on coral reef fish is the cymothoid isopod which can deplete energy and even leave bone deformations to the affected fish's facial area.

Detritivores

Detritovores are decomposers that feed upon the waste products and dead remains of other organisms. They are extremely important to coral reef ecosystems because the break down the dead waste, convert it to energy they can use, and then return important materials back into the environment. For coral reefs, the main decomposers are bacteria. Bacteria play an essential role in the nitrogen cycle to provide the environment with necessary nutrients, such as nitrate, while also keeping toxic waste levels low.

Trophic Levels

Trophic levels describe

Trophic levels

Why It's Important: Imbalances in the System

“Coral reefs are complex ecosystems that require a balanced trophic structure to function properly and efficiently. Imbalances can occur in this intricate trophic cascade from the top down or the bottom up.”

An example of bottom up effect imbalances that illustrates why feeding guilds and trophic levels are important to the coral reef ecosystem comes from an incident in the Great Barrier Reefs. Coral in the Great Barrier Reefs is now being threatened not only by coral bleaching but an even bigger predator, the Crown of thorns starfish. Agricultural runoff containing fertilizer has caused an excess of phytoplankton to be present in the waters around the reefs. The Crown of thorn starfish larvae feed on this phytoplankton and thus caused a population explosion in the area. The problem is that the crown of thorn starfish feeds on coral and can eat up to 10 square meters of tissue a year. This bottom up effect has taken its toll on the reefs surrounding Australia, with 42% of coral reef decline in the area due to the crown of thorns invasion.