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Brown Algae of Zihuatanejo

CLASS PHAEOPHYCEAE

-Kelp, Diatoms, and Allies (Kingdom Chromista)

-Phylum Ochrophyta

-Brown Algae (Class Phaeophyceae)

-Subclass Fucophycidae

-Order Ralfsiales

-Family Ralfsiaceae

-Ralfsia (Genus Ralfsia)


Ralfsia is a genus of brown algae in the class Phaeophyceae, known for forming thin, crust-like patches tightly adhered to rocks in the intertidal zone. Unlike the familiar leafy or branching seaweeds, Ralfsia grows as a flat, encrusting film, often appearing as brown, olive, or dark greenish patches that can look like a stain or coating on the rock surface. These algae are especially common in wave-exposed shorelines, where their low profile helps them withstand strong surf and desiccation during low tide.

Range

  • The genus Ralfsia is distributed in temperate and tropical oceans worldwide.

  • In the eastern Pacific, species occur from Alaska south through the Gulf of California, the Pacific coast of Mexico, Central America, and South America.

  • Several species are found along the Pacific coast of Guerrero, including the Zihuatanejo region, where they occur on rocky intertidal shores.

Habitat

  • Grows firmly attached to rocks, boulders, reef platforms, shells, and other hard substrates.

  • Most common in the upper and mid-intertidal zones, where it withstands regular exposure to air, intense sunlight, and wave action.

  • Often forms extensive dark brown crusts on exposed rocky shorelines and may grow beneath or alongside other seaweeds.

Size

  • Crust thickness: 0.5–2 mm

  • Individual patches: Usually 2–20 cm (0.8–8 in) in diameter, although neighbouring patches often merge to form much larger continuous mats.

Ralfsia Brown Algae
(Ralfsia) (Genus)
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