|Chalinula nematifera over-growing encrusting (a) and branching (b) corals. Note the white band at the boundary between the sponge and coral due to the probable production of allelochemical compounds.|
By Gianfranco Rossi, Reef Check Italia onlus
Gianfranco Rossi sends us this summary of a paper that Reef Check Italy and colleagues recently had published in the Italian Journal of Zoology. An encrusting sponge may represent an increasing threat to corals in the Indo-Pacific.
Chalinula nematifera is a common Indo-Pacific encrusting sponge able to overgrow living corals. Distribution data of C. nematifera are fragmentary; its presence is documented as a potential threat for coral reefs in the Mexican Pacific coast (Ávila and Carballo 2009). By standardized visual surveys carried out during April 2012 along 830 nautical miles of the eastern coast of Sulawesi (Indonesia), the presence of the sponge was recorded frequently at different sites in the Strait of Lembeh, Tanjung Flesko, Pangkalsian, Karang Vesuvius, Wakatobi. C. nematifera was observed spreading out over both old dead portions of corals and over living coral colonies. Unlike along the Mexican Pacific coast, where the sponge is almost exclusively reported on the branching coral Pocillopora verrucosa (Ávila and Carballo 2009) and never on massive corals, we found C. nematifera also on: massive-encrusting corals like Mycedium elephantothus, Platygira daedalea, Echinopora sp., Favia sp., Pachyseris sp. and Goniastrea sp.; laminar like Pectinia sp.; branching like Pocillopora sp., Stylophora sp. and Seriatopora sp..
In the early-stage covering phase on live corals, a white rim is very evident at the interface with the sponge. These bands of bare coral clearly suggest the production of allelochemicals able to kill the coral tissue. The slimy mucus produced by the sponge could be involved in this kind of competitive interaction.
The sponge growth evaluated on Acropora branches is fast, about 60 mm per month. These rates are higher than those observed in other sponge species. While this common species is found throughout the Indo-Pacific, its role on coral reefs has not been well studied. Our data suggest C. nematifera may represent a spreading threat to be carefully monitored in the future, to better understand its baseline distribution, growth dynamics, and recruitment in Indo-Pacific coral reef ecosystems.
Ávila E, Carballo JL (2009) A preliminary assessment of the invasiveness of the Indo-Pacific sponge Chalinula nematifera on coral communities from the tropical Eastern Pacific. Biological Invasions 11 (2):257-264
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