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

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 sponges is considered here, while information on other taxa can be accessed via the icons.


seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of competition involving sponges taken from a video "This green encrusting sponge takes many forms, but it's a common overgrower of gorgonians. Look how carefully it spaces itself from the other sponge. The pink sponge probably has its own defenses." - Grand Cayman 2001

photograph of sponge/gorgonian competition for space
photograph of red sponge overgrowing lace coralSponges readily seem to overwhelm the defenses of most corals and gorgonians. Most often the sponge appears unaffected, but death of the overgrown parts of the affected organism is often inevitable.


The brown encrusting sponge Ectoplasia ferox is overgrowing a
gorgonian Pseudopterogorgia bipinnata, but is meeting fierce chemical
resistance from the gorgonian 0.5X



A rose-lace coral Stylaster roseus is being overgrown
by a red encrusting sponge Diplastrella sp. 1X




photograph of space competition among a red sponge, mound coral, and tunicate
Sponge-coral interactions are complex enough, but the complexity is increased even more when other organisms are involved. Based on our knowledge of the aggressiveness of red boring-sponges Cliona sp. the specimen featured here should dominate the mound coral, but another unrelated species, a mat tunicate Trididemnum solidum, appears to be overgrowing both the coral and the sponge.



The red boring-sponge Cliona delitrix actually
penetrates its coral host through secretion of
a dilute acid. The large openings on Cliona are
its exhalent siphons or oscula 0.6X

photograph of a chicken-liver spong overgrowing some fire coral
Chicken-liver sponges Chondrilla nucula are superior overgrowth competitors. In the Florida Keys it is involved in about one-third of all coral-sponge interactions and, in Caribbean reefs in general, in up to one-half of these interactions. Were it not for spongivorous fishes (mainly angelfishes), this sponge species would soon overgrow the majority of corals with which it interacts. Hill 1998 Oecologia 117: 143.

NOTE lit. "eater of sponges"



The fire coral Millepora sp. is itself a strong
overgrowth competitor, but the chicken-liver
sponge Chondrilla nucula is making short work of it 1X

photo collage showing sponge-competition standoffs
Interactions of boulder corals with sponges in Columbia lead often to "standoffs"; that is, ones in which there is no clear winner. Such standoffs may actually be quite dynamic, with repeated reversals of dominance and changing distances between the protagonists. Aerts 2000 Mar Ecol 21: 191.

photograph of standoff competition between a boring sponge and a coral
In addition to overgrowing corals, certain sponges also parasitise them by boring holes with secreted acid that dissolves the coral's calcareous skeleton. At least 19 species of Caribbean sponges do this. Through their excavating activities, the sponges weaken the structural integrity of the corals and contribute to sedimentation. The sponges are enabled to do this through their superior competitive abilities. Diaz & Rutzler 2001 Bull Mar Sci 69: 535.



The exhalent chimney of a boring sponge Siphonodictyon
extends from the surface of a coral. Food
and oxygen-bearing water enters the sponge via the small
pores and leaves via the large exhalent siphon on top. Note
the white coloration of the coral, indicating that its defenses
against the sponge are mobilised, but to no seeming effect 3X

NOTE lit. "siphon-extending coral-eating"

photograph of boring sponge infesting a boulder coral
In the accompanying photograph, a boring sponge Siphonodictyon coralliphagum is parasitising a boulder coral Montastrea cavernosa. Note the standoff distance maintained by the coral polyps from the siphons of the sponge. Note also that other protagonists are involved, a mat tunicate Trididemnum solidum (see also detail) and some seaweeds, the latter having adventitiously settled and grown on the damaged coral.
photo collage of sponge/coral mutualism
Finally, orange-icing sponges Mycale laevis envelop entire coral colonies without boring. The relationship is mutualistically beneficial, with the coral being provided protection by the sponge and the sponge being given a place to live above the sea bottom in clean "uncompetitive" sea water.

photos and schematic showing interaction between cup-coral Tubastrea coccinea and a potentially overgrowing spongeOrange cup-coral Tubastrea coccinea was introduced into the Curacao area from the Pacific some time in the 1940s and has since spread widely. Part of its success may owe to its propensity to spread via “runners”, thin tissue extensions that grow away from the main colony up to 10cm per year and usually end with production of a terminal new polyp. Growth of such runners is common and, as they have been observed sometimes to be in directions away from encroaching encrusting sponges that tend to overgrow corals, may help explain the overall success of the species in invading Caribbean reefs. Vermeij 2005 Coral Reefs 24: 442.



Left: mature polyps of a Tubastrea coccinea colony.
Right: a new polyp (at 8 o'clock) senses the presence of
an encrusting sponge coming from the Right, extends
a tissue path away from the threat, and produces a new polyp.
The threatening sponge is the yellow tissue on the Right