Dead Man’s Fingers, Codium fragile subsp. californicum

Dead Man’s Fingers, Codium fragile subsp. californicum. Underwater photograph taken in coastal waters off La Jolla, California, August 2016. Photograph and identification of Bob Hillis, Ivins, Utah.

Phylogeny: Dead Man’s Fingers, Codium fragile subsp. californicum (J. Agardh) Maggs & J.Kelly, 2007, is a member of the Codiaceae Family of Green Macro Algae.  The genus Codium is one of three genera in the Codiaceae Family , and the are one hundred fifty-eight species in the Codium genus. Species in this genus exhibit no calcification. They may appear as mats, spheres, or grow erect. They may be unbranched and finger-like, or branched with cylindrical or flattened branches. The branches are also known as siphons. The genus name Codium comes from both the Greek and Latin and means “soft” or “fleece-like”, referring to the plant’s surface texture. This species is a subspecies of Codium fragile (Suringar) Hariot, 1889. Currently, there are eleven accepted subspecies of this plant.  There are multiple common names for this species including: Branched Felt-algae, Felty Fingers, Green Fleece, Green Sea Fingers, Green Sponge, Oyster Thief, Sea Staghorn, Sponge Seaweed, Spongeweed, Stag Seaweed, and Sputnik Weed.

Morphology: Dead Man’s Fingers has thick, tubular, soft, branches (siphons), which extend from an irregular holdfast. The holdfast consists of intertwined root-like threads (rhizoids). The branches may be finger-like or branching (dichotomous). The tips of the branches are tapered. Densely-packed hairs cover the branches giving them a felty appearance and a slimy texture. The plant produces oxygen as a byproduct of photosynthesis. This oxygen is trapped in the branches, making them buoyant. If they attach to a small bivalve or other small anchor, their buoyancy can sometimes float the anchor and carry it away. Their tendency to attach to oysters and float them away is what gives them the name Oyster Thief. The older branches are darker green, while the tips and newer growth are bright green. Dead branches turn white. Dead Man’s Fingers reach 40 cm (15.7 inches)  in height.

Habitat and Distribution: Dead Man’s Fingers grows on rocks, shells, pilings, seawalls, and other hard surfaces.  It lives in the lower intertidal zone and to depths of 22 m (72 feet). This species is dependent on sunlight so most plants are found in shallow water.  Dead Man’s Fingers is a temperate to subtropical Eastern Pacific species  that has a limited range in Mexican waters of the Pacific Ocean being found from Bahía Asuncion, Baja California Sur, northward along the central and northwest coasts of the Baja Peninsula. The very similar looking species Codium fragile (Suringar) Hariot, 1889, that is also known as Dead Man’s Fingers, that is a highly invasive species and can now be found worldwide in temperate to tropical seas including both coasts of Mexico in the Atlantic and Pacific Oceaans. In the Atlantic it is found in the Gulf of Mexico south to Playa del Carmen, Quintana Roo; in the Pacific is is found north of Chamela, Jalisco. Where these califoricum subspecies overlap it is difficult to differentiate between them, and many sources lump them together.

Predators: Dead Man’s Fingers is preyed upon by amphipods, crabs, mollusks, and sea urchins. In addition, Saccoglossan Slugs that belong to the clade Heterobranchia known as sacoglossans, which are green algae specialists, do well feeding on this plant.

Reproduction: Dead Man’s Fingers are monecious (each plant having male and female reproductive organs {hermaphrodites}). They reproduce sexually through the production and release of  zoospores (flagellated swarmers).

Ecosystem Interactions: Dead Man’s Fingers  provides shelter and structure for various species of crustaceans, fish, mollusks, and other invertebrates. It often hosts  filamentous red algae as an epibiont.

Human Interactions: This subspecies of Dead Man’s Fingers has no direct human impact. From a conservation perspective Dead Man’s Fingers has not been formally evaluated. It is fairly common, with a wide range, and should be considered  to be of Least Concern.

Synonyms: Codium fragile var. californicum and Codium mucronatum f. californicum.