Agassiz’s Sea Fan, Pacifigorgia agassizii
Agassiz’s Sea Fan Pacifigorgia agassizii. Underwater photographs taken in Bahía de Banderas, Puerta Vallarta, Jalisco, July 2026. Photographs and identifications courtesy of Greg Timms, youtube.com/@CoralmasterdivesPuertoVallarta/videosThe two photographs just above also feature the Rigid Gogonia, Leptogorgia rigida.
Phylogeny: The Agassiz’s Sea Fan Pacifigorgia agassizii (Verrill, 1864), is an octocoral within the Gorgoniidae Family of Soft Corals. It was formally described by A.E. Verrill in 1864, who named the species in honor of legendary naturalist Louis Agassiz. The species has surfaced under a vast array of historical generic combinations in early literature, but was definitively consolidated as a valid, stable species during the modern monographic revisions of Breedy & Guzman (2002). The Pacifigorgia Genus is one of thirteen genera in the Gorgoniidae Family, and there are thirty-seven species in the Pacifigorgia Genus. It is known in Mexico as Coral Blando.
Morphology: Agassiz’s Sea Fans are colonial organisms, with polyps that have 8-fold radial symmetry. Their eight tentacles are pinnate (having a feather-like appearance). The polyps have a flower-like appearance, a hollow digestive cavity, and specialized stinging structures in tentacles surrounding the mouth. As octocorals, they have tiny spine-like hard parts in their bodies called sclerites (or spicules) that give them some degree of support. The branches have a central core, which is made of a horn-like substance called gorgonin. Gorgonin is a protein which is exclusive to the gorgonians and which contains significant amounts of iodine and bromine. The sclerites are located in the solid core. The polyps are embedded in a gelatinous material (called the coenenchyme) which surrounds the core. The material surrounding the openings in the coenenchymes (from which the polyps emerge) are called calyces (singular calyx). The branches are arranged in a fan-shaped plane. They reach 40 cm (16 inches) in height and width.
Colony Architecture: Mature colonies of Agassiz’s Sea Fan are unique because they routinely grow away from a strict single-plane fan structure. Instead, they form dense, three-dimensional clusters of multiple smaller fans that overlap, fuse, and radiate out from a centralized lower base.
Mesh Metrics: Agassiz’s Sea Fan has a fine-to-medium reticulated network averaging 15 to 19 meshes per square centimeter. The individual branches are relatively fine, averaging 1.0 mm to 1.2 mm in diameter.
Midrib Development: Agassiz’s Sea Fan haves faint, thin, poorly-defined principal midrib lines radiating into the lower portions of the main fan network. These midribs do not flatten out or visibly slice the colony into distinct, heavily isolated lobes.
Polyps & Calyces: The polyps of Agassiz’s Sea Fan are distributed in tight longitudinal rows along the sides of the branches. They retract completely into flat, flush, or only slightly elevated oval coenenchymal rings.
Coloration Profiles: Agassiz’s Sea Fan has historically been described as possessing a greenish-brown, olive-drab, or greenish-gray coenenchyme, often featuring orangish-beige polyps. However, color variations remain highly descriptive rather than a strict taxonomic diagnostic metric.
Field Identification Key: The color of Agassiiz’s Sea Fan is highly variable and our identifications ignore the “greenish” descriptions in favor of structural metrics. Colonies of this sea fan exhibits a dense mesh screen but resolves into a crowded cluster of multiple smaller, overlapping fans arising from a shared base and features faint with thin starter lines near the bottom.
Habitat and Distribution: Agassiz’s Sea Fans are found firmly attached to solid, wave-exposed, rocky substrates, volcanic boulder fields, and deep structural shipwrecks. They typically live at depths between 5 m (16 feet) to 25 m (82 feet). They rely on a broad, encrusting, holdfast to attach to the substrate. Agassiz’s Sea Fans are often found in dense populations. They are a foundational species native to the Tropical Eastern Pacific (Panamic Province), with deep evolutionary ties to the Mexican Pacific coast. They are present in all Mexican waters of the Pacific, with the exception that they are absent from north of La Paz, Baja California Sur, in the Sea of Cortez, and from the west coast of the Baja Peninsula.
Diet: Agassiz’s Sea Fans are azooxanthellate suspension feeders. The tiny octocoral polyps rely entirely on moving water currents to deliver micro-zooplankton (such as copepods and microscopic invertebrate larvae), phytoplankton, and organic particulate matter (marine snow). They lacks the polyp size and stinging capability to consume macro-organisms like amphipods or fish larvae.
Predators: Predation studies specific to Agassiz’s Sea Fans are poorly documented. Their tissue is subject to opportunistic, localized grazing by browsing omnivorous reef fish, specialized Panamic corallivores, including ovulid gastropods, and specialized nudibranchs.
Reproduction: Agassiz’s Sea Fans are gonochoric (male or female for life) and reproduce sexually through synchronized broadcast spawning events. External fertilization produces a free-swimming, planktonic planula larval stage before settlement. They also reproduce asexually through continuous tissue budding to expand the fan network, fragmentation recovery, and occasional stolonization (sending out horizontal runners that bud into new polyps).
Ecosystem Interactions: Agassiz’s Sea Fans, with their unique, multi-layered cluster of overlapping fans, create an exceptional benthic microhabitat sanctuary. It acts as a highly effective current baffle, hosting an expansive community of associated micro-crustaceans, caprellid amphipods, specialized microbial biofilms, brittle stars, symbiotic copepods, and commensal shrimp.
Human Interactions: Agassiz’s Sea Fans have a limited direct human interaction. Historically, they were occasionally harvested from the wild for the commercial aquarium trade and also sold dried in curio markets. Today, its primary human relevance is as a vital indicator species for regional rocky reef monitoring and conservation assessments. From a conservation perspective, they have not been formally evaluated.
Synonyms: Rhipidigorgia agassizii, Gorgonia (Litigorgia) agassizii, Gorgonia agassizii, Litigorgia agassizii, and Leptogorgia agassizii.