Cacao Gorgonian, Muricea cacao

Cacao Gorgonian, Muricea cacao. Underwater photograph taken in coastal waters of the greater Los Cabos area, Baja California Sur, May 2018. Photograph courtesy of Bob Hillis, Ivins, Utah. Identification courtesy of Greg Timms, youtube.com/@Coral-masterdivesPuertoVallarta/videos.

Phylogeny: The Cacao Gorgonian, Muricea cacao (Hernández, Gómez-Gutiérrez, Galván-Tirado & Sánchez, 2023), is an octocoral member of the Plexauridae Family of Gorgonians. The Muricea Genus is one of five genera in the Plexauridae Family and there are thirty-three species in the Muricea Genus. The Cacao Gorgonia is a species within the Muricea fruticosa Group – all the species in this group are distinguished by having shelf-like calyces (cups that hold polyps). Separating species within this group can be difficult in the field and may require laboratory analysis. The species name cacao comes from the color similarity between the gorgonian and the cacao food product (similar to cocoa, which is derived from the Theoboma cacao tree). They are also known as the Cacao Sea Fan and in Mexico as the Gorgonia Cacao.

Morphology: The Cacao Gorgonian is a colonial organism that is composed of thousands of individual polyps. Gorgonians have flexible branches that often sway with the currents, unlike stony corals. Cacao Gorgonians generally grow as multiple branches in a planar, fan-like structure. The branches do not simply radiate from a central axis, but they repeatedly branch laterally,  filling the plane, suggesting a “woven” appearance. The branches are 3 mm (0.118 inches) in diameter and have blunt tips. The branches are reddish-brown or chocolate brown in color. The polyps are in overlapping (imbricate) rows. The polyps are flower-like, with eight tentacles around the oral disk. The polyps have white stalks and white or clear heads. The polyp cups (calyces) reach about 1 mm in height.  Cacao Gorgonian colonies reach a maximum of  55 cm (21.7 inches) in height. The similar looking Brown Gorgonian, Muricea fruticosa, has more irregular, bushy, branches.

Habitat and Distribution: Cacao Gorgonians are found attached to hard surfaces such as coral, pilings, rocks, and wreckage. Because this species is so new, there is limited documentation of distribution. It appears that all the scientifically documented observations were made at 15 m (49 feet). Unreferenced sources state that the species ranges from 2 m (6.5 feet) to 30 m (98 feet). Cacao Gorgonians are a tropical Eastern Pacific species that is ENDEMIC to the northwestern coastal waters of the Mexican Pacific. They are found as far north as Midriff Archapelago in the Sea of Cortez, and along the west coast of the Baja Peninsula, as far north as Magdalena Bay, Baja California Sur. They have not been documented in coastal waters of Mainland Mexico.

Diet: The Cacao Gorgonian is a sessile suspension feeder that captures drifting food in the water column by individual polyps with small tentacles. These nutrients will reach all members of the colony through channels in the gastrovascular cavity. The Cacao Gorgonian’s diet consists of water-borne prey like eggs, coral spawn, larvae and plankton. They are an azooxanthellate coral.

Predation: Documentation of Cacao Gorgonian predators is very limited. Other similar species in the Muricea Genus are preyed upon by butterfly fishes, damselfishes, gastropods and sea stars.

Reproduction: Cacao Gorgonian colonies are gonochoric (male or female for life). They can reproduce asexually through budding, and sexually through broadcast spawning. During spawning, mass amounts of eggs and sperm are released into the water and fuse into gametes. The gametes become planktonic planula larvae. These larvae will eventually settle on a substrate and begin to form a polyp. From here, a colony grows through budding. They can also reproduce asexually through fragmentation.

Ecosystem Interactions: Cacao Gorgonians are a poorly studied and documented species. Their commensal, mutualistic and parasitic relationships have not been formally documented. Other species in the Muricea Genus have microbial corallicolids living in their cells. It is thought that these corallicolids are parasitic, but they may be commensal. Many invertebrates species, such as amphipods, brittle stars, copepods, and polychaetes find shelter in the branches of Cacao Gorgonians.

Human Interactions: Cacao Gorgonians have a very limited impact on human activities. From a conservation perspective they have not been formally evaluated. Regional threats to the species include coastal development, water pollution, and increased sedimentation from coastal activities from human development.

Synonyms: None