When a female crab is described as “pregnant,” the more accurate scientific term is “berried.” This refers to the stage where the crab carries her fertilized eggs externally, attached to her abdomen. Unlike mammals, crabs do not carry their young internally; instead, the developing embryos are housed in a protective mass outside her body. This external brooding strategy allows the female to protect her offspring until they hatch.
Identifying a Berried Crab
Observing a berried crab reveals distinct visual cues, primarily centered around her abdomen. The most noticeable feature is the egg mass, which resembles a spongy cluster. This mass is located underneath the crab’s abdomen, also known as the “tail flap,” and is typically folded tightly against the underside of her body. The eggs are securely attached to small, feathery appendages called swimmerets or pleopods.
The egg mass varies in color, often progressing through different shades as the eggs develop. Initially, the eggs might appear bright orange or yellow due to a high yolk content. As the embryos mature, consuming the yolk and developing eye spots and other pigments, the egg mass can darken, turning brown, grey, or even black just before hatching.
The egg mass is typically granular and clumped, protruding noticeably. A female crab’s abdomen is distinctly wider and more rounded compared to a male’s narrower, triangular abdomen, providing ample space to accommodate the egg mass. She may also fan the eggs with her pleopods, a behavior that helps aerate and clean them, ensuring healthy development.
The Crab’s Reproductive Process
The journey to becoming a berried crab begins with mating, often after the female has molted and her shell is soft. Following copulation, many female crabs can store the male’s sperm for extended periods, sometimes for weeks or months, until environmental conditions are optimal for egg development. When the time is right, the female extrudes her eggs. As they are released, they are fertilized by the stored sperm and immediately attached to the swimmerets on her abdomen, forming the visible egg mass.
The eggs then undergo an incubation period, developing externally. This period ranges from a few weeks to several months, depending on the crab species and environmental factors like water temperature. Warmer temperatures generally lead to shorter incubation times. Once embryos are fully developed, the female releases tiny, free-swimming larvae, known as zoea, into the water column. These larvae are planktonic and undergo several molts and developmental stages before transforming into juvenile crabs.
Variations Among Crab Species
While general characteristics of a berried crab remain consistent across species, certain details vary. The egg mass color, for instance, can differ significantly; blue crabs often have eggs that progress from orange to brown, while other species might display different initial or final colors, including yellow, red, deep grey, or black depending on their developmental stage.
The size and shape of the egg mass are also influenced by the crab’s overall size and species. Larger crabs typically carry more eggs, resulting in a more substantial egg mass, with some species carrying millions. The female’s “tail flap” or abdomen can also show slight species-specific variations, though it consistently remains broader than a male’s to accommodate the eggs. Despite these differences, the fundamental process of carrying and brooding eggs externally beneath the abdomen is a universal trait for berried crabs.