Coral Reefs- Focus on Farmerfish

(modified from Moorea Coral Reef LTER Education "Focus on Farmerfish")

Lesson at a Glance: Students will gain a deeper understanding of the relationships between abiotic factors and organisms adaptations through focusing on the farmerfish.

Goals: Students will be able to look critically at different organisms in a habitat and hypothesize about the influence of abiotic/biotic factors on physical and behavioral adaptations through the process of natural selection.

Estimated Time: One class period

Materials:

  • Coral Reef Organism Cards from Coral Reef Introduction lesson
  • Farmerfish Powerpoint (see bottom of page)
  • Farmerfish game board (see bottom of page)
  • Farmerfish game cards (see bottom of page)
  • Farmerfish game rules (see bottom of page)

Teacher Background:

The names for the 2 species of farmerfish in this lesson are Stegastes nigricans, the Dusky Farmerfish, and Stegastes punctata, the Farmerfish. They are found on coral reefs in many parts of the world.

These fish fill a unique niche in the coral reef habitat. Farmerfish live in various sized patches of staghorn corals (Acropora sp.), but on the upper branches of the coral have living polyps. The lower branches of the coral are no longer alive, but are covered by strands of filamentous algae. As the name suggest, farmerfish actually promot the growth of this algae by grooming territorial patches on the dead staghorn coral branches. These "farmed" algae are then consumed as food, making the Stegastes sp. a primary consumer on the trophic chart.

The farmerfish expend a good deal of energy grooming their algal patches, energy that would be wasted if other fish were able to graze freely on the carefully tended gardens. For this reason, Stegastes sp. aggressively defend their territories from other farmerfish as well as from other species of fish that pose a threat to their algal patches.

Defensive behaviors range in aggressiveness. Sometimes a farmerfish will merely lift its dorsal fin and wave its pectoral fins in an intimidating display, like a dog's hackles rising. If the farmerfish believes the competitot is a greater threat, it will actually chase the offending fish as far as a meter from the precious algae. Stegastes sp. have even been observed going so far as nipping fish that stray too near. Some competitors that illicit the aggressive defenses of farmer fish include brushtail tangs, brown surgeon fish, striped surgeonfish, speckled butterfly fish, and other primary consumers within the coral reef.

Since female farmerfish lay their eggs in male algal patches, male Stegastes sp. also guard their territories from fish species that might snack on their developing offspring. Egg predators that are often chased by farmer fish include 6-bar wrasse and PIcasso triggerfish.

Fish that pose less of a threat to the algae or the eggs within a farmerfish's territory often time are ignored. These include carnivors that eat crustaceans and small fish like trumpetfish and slingjaw wrasse.

Most fish species that would prey on farmerfish hunt in the darkness of night, when Stegastes sp. hide down in the branches of the coral, so interactions between these species have not been observed. Predators capable of making a meal out of farmerfish include blacktip reef sharks, moray eels, and large honeycomb groupers.

The aggressive actions of farmerfish toward potential competitors and/or egg predators are behavioral adaptations that have developed over many generations through the process of natural selection. Fish that successfully deterred competitors from eating their algae had more food, most likely lived longer, and therefore fertilized more eggs to produce more offspring with similar traits. Over many generations, the majority of the farmerfish population has inherited the genes for these beneficial behavioral adaptations.

Reources:

Background information for this lab was gathered from teh following:

  • Steagstes nigricans,global range www.aquamaps.org
  • Michele Johnson, M.A. Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara

Activity:

Review:

As students sit down they should fill out a trophic level chart with at least on example of coral reef organism for each trophic level. The organism cards from the previous lesson can be on the desks to aid students. Have students share out.

Engage:

Begin the powerpoint and get them through slide # 8, "What do the do?" The goal is to just get students excited and engaged about the Farmerfish.

Explore:

Have the students become Stegastes! They will play the Farmerfish board game to explore interactions with competitor and predator species. Students should play in groups of 4. Give each group the rules of the game, explain and answer any questions. Distribute the materials.

Explain:

Have the students explain what they observed from participating in the game. As students describe the adaptations, create two columns on the board, "Behavioral" and "Physical." When a student shared a new adaptation observed during the game, have them classify it as a behavioral or physical adaptation.

Complete the rest of the slides from the Powerpoint to affirm their observations from the game and provide additional clarification.

Elaborate:

Using either a classroom tank, tank at the aquarium, etc. have students complete observations of fish behavioral and physical adaptations. They can do this a couple of different ways:

  1. Have students complete observations and investigations of different fish in a classroom tank or at the aquarium. Have them develop a field guide that distinguishes between the physical and behavioral adaptations that allow it to flourish in its environment. Have them do some web or library research to insure that their individual observations are supported by the greater body of science knowledge about that species.
  2. Have them conduct an ethogram of when they see different behaviors and have them answer an inquiry question. For example:
  • Which types of fish do the clown fish interact most often?
  • Which types of fish chase the sea horses most often?
  • During what time of day are guppies most active?

Evaluate:

Have students reflect in their science notebook to the following:

  • How do Stegastes sp. and other species develop such adaptations?
  • Which adaptations are the most advantageous? Why?
  • How does Stegastes sp. contribute to the health of the coral ecosystem?