Competition
Competition

Sessile organisms

Competition in sessile reef organisms takes 3 forms: 1) preemptive, where through its presence one organism prevents another from occupying the same space, 2) overgrowth, where one organism, like a seaweed, grows over or otherwise crowds out and kills another organism like a coral, and 3) chemical, where through release of a toxic material one organism prevents another from settling and surviving. Access each type via the icons. hot button for preemptive competition part of Biology of Caribbean Coral Reefs website hot button for preemptive competition part of Biology of Caribbean Coral Reefs hot button for overgrowth competition part of Biology of Caribbean Coral Reefs hot button for chemical competition part of Biology of Caribbean Coral Reefs

Sessile organisms: overgrowth competition

hot buttons for overgrowth competition hot button for fire-coral overgrowth competition hot button for sponges-overgrowth competition hot button for coral/zoanthid overgrowth competition hot button for tunicate-overgrowth competition hot button for algae/cyanophyte-overgrowth competition
Overgrowth by fire corals is considered here, while information on other taxa can be accessed via the icons.

Sessile organisms: overgrowth competition: fire corals


seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of fire coral taken from a video "Fire coral seem to be able to overgrow almost everything, but it seems particularly successful with gorgonians." - Turks & Caicos 2005

Fire coral is not a coral; rather, it is a type of hydroid known as an hydrocoral. It is a strong competitor and commonly overgrows gorgonians and other sessile organisms. It also overgrows rocks and other inanimate objects:
photo collage of different growth forms and habitats of fire coral Millepora

photograph of fire coral Millipora overgrowing and killing a gorgonian
Like other hydroids, the nematocysts (stinging cells) of fire coral Millepora spp. are potent. Their high toxicity greatly enhances the overgrowth aggressiveness of fire corals.

 

 

 

 

To the eye, it appears that the gorgonian is offering
no defense against the encroaching fire coral 0.8X

photograph of fire coral showing finger-like growth
Studies in Jamaica show that a fire coral can detect and actively redirect its growth towards arborescent gorgonians and overgrow them. Attack branches of the fire coral resemble fingers or hands as they reach towards the target gorgonian. Wahle 1980 Science 209: 689.

NOTE tree-like in shape or growth; branching form

 

 

 

 

 

Characteristic finger-like growth form
of fire coral Millepora sp. as it seeks for
new substrata on which to grow 2X

Here is an experiment to test the effect of gorgonian proximity on direction of growth in fire corals. Wahle 1980 Science 209: 689.
drawing 1 in a series of 3 showing an experiment on "finger" development in fire corals drawing 2 in a series of 3 showing an experiment on "finger" development in fire corals drawing 3 in a series of 3 showing an experiment on "finger" development in fire corals
We start with 2 equal-sized stalks cut from a single colony
of a sea-rod gorgonian, mounted on a tray with a piece of
fire coral inserted between

The assembly is lowered into the sea in an area of
the reef known to sustain good growth of both
gorgonians and fire corals

After 6mo the assembly is removed and . All pieces are in good health and have grown in size. Moreover, the fire coral has developed fingers reaching to the right

What is the best explanation of the results? Think about the possibilities below then CLICK HERE.

Water current is from the right.

More metabolites are being produced by the larger-sized right-hand individual.

The right-hand gorgonian species is more susceptible to being overgrown by fire coral.


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