Texas Invasive Species Institute

Texas Invasive Species Institute

Titan Acorn Barnacle

Megabalanus coccopoma

Class: Maxillopoda
Order: Sessilia
Family: Balanidae

Megabalanus coccopoma

Photographer: Sarah Stephenson, FWC-FWRI Source: Bugwood.org Copyright: CC BY-NC 3.0 US


This pink barnacle is large, being over 2 inches in width and height. The pink plates of the barnacle are smooth and fused together, and separated by a narrow purple or white radii. The opening (aperture) at the top is small. These sessile creatures like to attach themselves to other structures in marine waters, varying from boats, rocks, reefs, docks, buoys, and even other animals like clams.

Ecological Threat

Its expansive settlement, rapid growth, and large size are factors that make it an aggressive species. This large barnacle is able to out compete native barnacles for habitat and food sources due to their size. In South Carolina can gain a body mass 100 times greater than native barnacle species. It has also been observed to out-compete with other intertidal suspension and filter feeders for space and food, completely altering the marine ecosystems. It can also impede recreational, navigational and commercial activities by clogging boat propellers, drive shafts, and smothering coastal navigation buoys.


These barnacles are suspension feeders that extend modified arms through their opening to catch plankton. This is a similar concept for reproduction, which is typical of other barnacles. Sperm is passed to a neighboring barnacle through a long tube, into the mantle of the other barnacle, to fertilize internally. The motile larvae go through several growth phases over three weeks. They then settle and metamorphose into adults.


El Niño events have allowed Megabalanus coccopoma to travel up the California coast to San Diego in 1985, expanding its distribution in the Pacific. However, it wasn’t found in the Gulf of Mexico or Atlantic waters until the 2000s. Collected from Louisiana in 2001, Port Aransas, Texas in 2002, and Cape Canaveral, Florida in 2006. Soon afterwards it was found on the coasts of Georgia, North Carolina and South Carolina. With cooler water temperatures being limiting factor, these pests will probably not extend farther than North Carolina.

Native Origin

Pacific coasts of Central and South America

Current Location

U.S. Habitat: Tropical to subtropical marine habitats

U.S. Present: CA, FL, GA, LA, NC, TX and SC.


In the Pacific Ocean Megabalanus coccopoma can be confused with the native species Megabalanus californicus. However, the native species is a darker, with a wider aperture and wider rays between the plates.


With invasive aquatic species, management can be very costly and ineffective. The best method is prevention. Cleaning boats before leaving one site, and dry-docking boats can help prevent the spread of this barnacle. If removing specimens from boat hulls or other marine equipment, be sure to throw them away in a trash receptacle and not back into the ocean.


McPherson B.F., Sonntag W.H., and M. Sabanskas. 1984. Fouling Community of the Loxahatchee River Estuary, Florida, 1980-81. Estuaries 7:149-157.
Newman, W.A., and R.R. McConnaughey. 1987. A tropical eastern Pacific barnacle, Megabalanus coccopoma (Darwin), in southern California, following El Ni–o 1982-83. Pacific Science 41:31-36.
Perreault, R. T. 2004. An exotic tropical barnacle, Megabalanus coccopoma (Darwin, 1854), in Louisiana: its probable arrival and environmental implications. Proc. Louisiana Acad. Sci. 66:13-16.

Powers A., Mitchell M., Walker R., Posey M., Alphin T., and C. Belcher. 2006. Baseline Port Surveys for Introduced Marine Molluskan, Crustacean and Polychaete Species in the South Atlantic Bight. NOAA's National Sea Grant Aquatic Nuisance Species Program. Project Number R/HAB-15; Grant number NA06RG0029. 310 pgs

Internet Sources





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