Cancer magister, Dungeness crab

Reproduction

Sexual Reproduction

The male embraces the female belly to belly and clasps onto her to ensure she will mate with him.  He may clasp on for several days softly stroking her with his chelipeds.  Then finally when she molts, she will signal the male by nibbiling his eyes.  Once her exoskeleton is off he will insert his sperm.  The male is not monogamous and will go onto other females.  Interestingly, the sperm can be viable inside the female for several months, and she may use the viable unused sperm on her second molting.  The fertilized eggs are attached under the abdomen of female for several months until they hatch as free-swimming zoea.

 Once out of the free-swimming larval stage the Cancer magister grows through molting.  All arthropods have an exoskeleton made of chitin which offers support and protection.  The exoskeleton does not grow with the organism and must be shed periodically for a new larger one.  It is during these times of molting that the crab is very vulnerable to predation and cannibalism. Below is a picture of the molting process.

Typical life cycle

First stage: free swimming larval zoea which will last for about 2-3 months which is variable on temperature(explained below in greater detail).  The image shows how small the zoea really are.

Second Stage: megalope, where the zoea form has turned into something that resembles a small crab. The megalope will eventual molt into a juvenile crab which takes about a year.  The image shows the megalope form.                   

Last two Stages: These include being a juvenile for 1-2 years and then a sexually mature adult for 2-6 years. On average the whole life cycle of the Dungeness crab taking about 8 years. The image shows the adult crab.

    Temperature and latitudinal location

The reproductive events for the Cancer magister vary based on their latitudinal location.  Reproduction occurs earlier for southern populations than for the northern.

In southeast Alaska, the Dungeness crab extrudes eggs from September to November which will hatch during May and June. 

The Dungeness off the coasts of California hatch from late December to March.

Climate changes such as El Niño in 1997-98 and local cold events in 2002 had dramatic effects on the embryonic rate of development.  Studies have shown that temperature is directly proportional to how fast the larvae will develop.  The warmer the water the faster and the colder the longer it takes.

Conveyor Belt Theory  

Many adult Dungeness crab move very little and live with in relatively the same habit their whole life.  However, the Cancer magister has a long larva stage of about 3 months where they are moved by water currents or winds.  This allows for long distance dispersal of the crabs ranging from north to south.  This transportation or called the conveyor belt, allows for gene flow between the northern and southern populations of crabs.

Next, look at the Interactions of the Dungeness crab.