Mexican Crustose Red Algae, Metapeyssonnelia mexicana
Mexican Crustose Red Algae, Metapeyssonnelia mexicana. Underwater photographs taken in Bahía de Banderas, Puerta Vallarta, Jalisco, July 2026. Photographs and identifications courtesy of Greg Timms, youtube.com/@CoralmasterdivesPuerto-Vallarta/videos.
Mexican Crustose Red Algae, Metapeyssonnelia mexicana. Underwater photograph taken in Bahía de Banderas, Puerta Vallarta, Jalisco, October 2026. Photograph courtesy of Mary Schofield, Puerto Vallarta, Jalisco. Identification courtesy of Greg Timms, you-tube.com/@CoralmasterdivesPuertoVallarta/videos.
Phylogeny: The Mexican Crustose Red Algae, Metapeyssonnelia mexicana (E.Y. Dawson, 1953), is a calcified red algae in the Peyssonneliaceae Family of Encrusting Red Algae. The name Peyssonneliaceae was given to honor the French naturalist and physician Jean-Andre Peyssonnel. The Metapeyssonnelia Genus is one of thirteen genera in the Peyussonneliaceae Family, and there are four species in the Metapeyssonnelia Genus. The genus name Metapeyssonnelia is a Greek prefix added the existing genus name peyssonnelia and together it means “related to peyssonnelia”. The species name indicates that the type specimen for this species was first found in Mexico. This species was first described by botanist E. Yale Dawson in 1953, from a specimen collect from Bahía Acapulco in Guerrero, Mexico. This species is sometimes referred to as Dawson’s Peyssonnelid Algae. Editorial Note: The species identification for the Banderas Bay photographs is a morphology-based working identification supported by a photographic comparison and regional distribution. The distinctive colors described above refer specifically to the photographed specimens and should not be interpreted as the only color form possible for the species. The Mexican Crustose Red Algae can be easily confused with the similar named Mexican Red Algae, Peyssonnelia mexicana.
Morphology: Mexican Crustose Red Algae are a crust-forming marine red algae that grow tightly against hard underwater surfaces. The thallus (main body) is flattened and crustose. Its flattened growth habit allows it to spread across rock and other stable reef substrates, forming irregular patches rather than upright, leafy fronds. The patches reach about 3.0 cm (1.2 inches) to 5.0 cm (2.0 inches) in diameter. They deposit calcium carbonate into their cell walls to make them tough and calcified. Mexican Crustose Red Algae vary in coloration including yellowish, greenish, olive, often with reddish-brown radial markings and margins. These contrasting colors create a striking pattern across the crust. The appearance may vary with illumination, growth conditions, and the condition of the thallus. Color alone is not sufficient to distinguish all crustose red algae. Microscopic characteristics are used in formal taxonomic identification.
Habitat and Distribution: Mexican Crustose Red Algae are found encrusting rocks, reefs, coral rubble, and other hard surfaces. There is very limited published literature related to the depth range for this species, however, we have observed them from the intertidal zone to depths of 6 m (20 feet). They are a subtropical to tropical Eastern Pacific species and are found in all Mexican waters of the Pacific Ocean, with the exception that they are absent from the west coast of the Baja Peninsula.
Predation: The tough crusty texture of Mexican Crustose Red Algae deters many predators. The predators specific to this species have not been formally documented but similar species in the Metapeyssonnelia Genus are preyed upon by fishes, gastropods and sea urchins.
Reproduction: Like other red algae, Mexican Crustose Red Algae have complex reproductive lives. They contain both male and female reproductive structures. The reproductive organs are located in specialized nemathecia (wart-like surface structures). Their reproductive cycles passes through three phases (triphasic or polysiphonia-type). The first phase is a haploid gametetophyte phase, when reproductive structures are formed, the male gameteophytes release spermatia, and the spermatia drift until they contact the hair-like receptors of the female organs. The second phase is a diploid carposporophyte phase when genetically identical clones are formed directly on the female gametophyte, and are then released into the surrounding water. The last phase is a diploid tetrasporophyte phase when they settle to the substrate and undergo meiosis to create haploid tetraspores. When these tetraspores germinate, they cycle back into new male and female gametophytes, to begin again with new genetic diversity.
Ecosystem Interactions: Mexican Crustose Red Algae obtain their energy from photosynthesis and they absorb other needed nutrients from the surrounding water. They are part of a community that different algae and sessile marine organisms occupy and compete for space. They occasionally demonstrate epiphytic commensalism by growing on larger marine plants or hard shelled invertebrates, without harming their host. They provide microhabitats for very small fish and invertebrates. Calcareous red algae also contribute to consolidating and building coral reefs.
Human Interactions: Mexican Crustose Red Algae have a very limited direct impact on human activities. From a conservation perspective, they have not been formally evaluated. They are fairly common and have a wide geographic range, with stable populations and should be considered to be of Least Concern.
Synonyms: Peyssonnelia dawsonii.