Why Are Some Lobsters Blue? Rare Lobster Colors Explained

How do lobsters get their color?

The key pigment in a lobster shell is astaxanthin, a red-orange carotenoid in the same family as the pigments that color carrots and flamingos. Lobsters cannot make carotenoids from scratch. They get them through the food chain, which starts with tiny algae that produce the pigments, and then store them in the shell.

On its own, astaxanthin is red. In a living lobster, much of it is locked inside crustacyanin. When the protein holds the pigment, it changes the way astaxanthin absorbs light. Instead of absorbing blue-green light and looking red, the bound pigment absorbs orange and yellow light and looks slate blue. In 2002, scientists who worked out the structure of the protein in detail showed that it grips pairs of astaxanthin molecules tightly and holds them close together, which helps explain this dramatic color shift.

A normal American lobster has a blend of free and bound pigments arranged in its shell, with yellow and red pigments mixed in. The result is the usual olive green to greenish brown, often with orange, red or black speckles and bluish joints. The same protein system gives the blue crab the blue on its claws and legs.

Why are blue lobsters blue?

A blue lobster’s shell contains an unusually large amount of crustacyanin, so far more of its astaxanthin is held in the blue form. The cause is genetic: blue lobsters inherit a variation that leads to overproduction of the protein. Apart from the color, blue lobsters are normal, healthy American lobsters, not a separate species or a sick animal.

Diet can also play a part. NOAA notes that lobsters kept in labs and fed mostly one kind of food can turn bluish, and lobsters that get few carotenoids from their food can become pale. In the wild, however, a bright blue lobster is usually a genetic rarity.

Blue is only rare in the American lobster. Its close relative, the European lobster, is normally dark blue with yellowish markings, so a “blue lobster” caught off Britain or France is simply an ordinary one.

Why do lobsters turn red when cooked?

Heat destroys the shape of crustacyanin. Once the protein unfolds, it lets go of astaxanthin, and the freed pigment shows its true red-orange color. Because the shell holds plenty of astaxanthin, almost every lobster turns the same bright red when cooked, including blue, yellow and calico ones. Shrimp, crabs and crayfish change color for the same reason.

The only exceptions are lobsters that lack pigment altogether. Albino lobsters have little or no astaxanthin in the shell, so they cannot turn red.

How rare are blue and other lobster colors?

The odds below are the figures most often repeated in news stories, largely traced to the Lobster Institute at the University of Maine. They apply to American lobsters and are rough estimates.

Calico lobsters are blotched with orange or yellow and black or brown. “Cotton candy” lobsters are a pale mix of blue, pink and purple; some scientists suspect they lack carotenoids from their food, while others group them with white lobsters.

How reliable are the odds?

Not very. No one has counted colors across a large, random sample of lobsters, and most of the figures are educated guesses that have been repeated so often they look official. Rare lobsters are also only noticed when someone bothers to report them.

Statistician David Spiegelhalter of the University of Cambridge has pointed out that roughly 200 million lobsters are caught in the North Atlantic each year. If the odds of a blue lobster really were 1 in 2 million, about 100 blue lobsters would turn up every year, so finding one is not as astonishing as headlines suggest. Reports of unusual colors have risen since the early 2010s, which may reflect larger catches, smartphones and social media rather than any real change in lobsters.

Colorful lobsters may also be rarer among adults than at hatching. A bright blue or yellow lobster may stand out more to fish and other predators, although this has not been measured in the wild.

Split-colored and white lobsters

Split-colored lobsters are among the strangest. Each half of the body is a different color, often orange on one side and brownish black on the other, divided by a sharp line down the middle. Scientists think this happens very early in development, so that the two halves of the body develop differently. Some split lobsters also show male features on one side and female features on the other.

White lobsters are either albino, with no colored pigment at all, or leucistic, with only traces of color. They are sometimes called “crystal” or “ghost” lobsters because the shell can look almost translucent.

What happens to rare-colored lobsters?

Fishers who catch an unusually colored lobster often donate it to a public aquarium or science center, where it can be seen by visitors and studied. Others are returned to the sea. Blue lobsters have been displayed at the New England Aquarium in Boston and many other aquariums in North America.

A lobster’s shell color should not be confused with its blood. Lobster blood carries oxygen with hemocyanin, a copper-based protein that looks pale blue when it picks up oxygen, as in other animals described in why is horseshoe crab blood blue? Rare colors also do not affect size: for the giants of the species, see how big do lobsters get?