Endangered Spotlight: Black Abalone (Haliotis cracherodii)

Black Abalone. Photo courtesy of UCSD

By Peter Winch

Black Abalone are a medium sized mollusk that live in rocky habitat from intertidal areas down to depths of 120 ft.  They are distributed over an area from just north of San Francisco to Baja California, Mexico.

The mollusks are distinguishable by a smooth black / slaty blue shell with a pearly white interior, as opposed to the rougher surfaces of other abalone species and their more silvery mother of pearl color interior.

Physical Characteristics

The abalone has two eyes, a mouth and two tentacles. The mouth has a long, rasp-like tongue called the radula, an organ which grinds kelp small enough so it can be ingested.

Abalone have a muscular foot with strong suction power allowing the animal to grip tightly to rocky surfaces. The foot is surrounded by a fleshy mantle, which is fringed by the epipodium, a sensory structure that has tentacles that can feel and taste for food.

A stack of shell muscles link the animal to its shell.  On a microscopic level, the shell is composed of calcium carbonate bricks that slide and spread the blow horizontally when struck, making the shell exceptionally strong.

Food Chain

Abalone are an important prey item for many animals. Their larvae and eggs are ingested by filter-feeding animals, and juveniles are preyed upon by lobsters, octopuses, sea stars, fish and predatory snails. Sea otters use rocks as tools to remove adult abalone from their vacuum hold on the rocks.

Endangered Status

Once abundant, black abalone are now being proposed to be added to the endangered species list due to their drastic decline in numbers. Their reduction in population has been attributed to a number of reasons.

A bacterial infection called withering disease has reduced numbers by 90%.  This pathogen inhibits digestive enzymes leading to starvation, which is manifested in atrophy of the muscular foot. 

The bacteria requires warmer water (16 degrees Celsius), and has been found as far north as Pedro Point.  With increasing sea temperatures, it is likely that withering disease will continue to be a persistent problem to black abalone populations.

In addition, black abalone have long been a much sought after delicacy for both commercial and recreational abalone divers, and over-fishing has definitely taken its toll.  

Despite stringent rules on harvesting, abalone poaching is a serious undocumented threat to their populations.

History

Abalone has had a long cultural link with the indigenous peoples of this area.  The Miwok and Alone people harvested them from intertidal areas using their meat for food and shells as utensils and decoration.  Shells from Central California abalone were traded with tribes from the Pacific Northwest who treasured them for their size (abalone decrease in size in their northern range).

The Gulf of the Farallones National Marine Sanctuary Visitor Center currently has a live red abalone in its aquarium, courtesy of NOAA Marine GIS Analyst Tim Reed.