Researching Crab Development
The stone crab fishery is very important in Florida, contributing close to $25 million a year to local economies. It is considered a renewable fishery because adult crabs are harvested only for their claws. Fishermen remove the claws at their joint and then throw the crab back into the ocean in hopes that the claws will regenerate and the crab will re-enter the fishery in future years.
Documenting embryonic development
I have been researching the larval biology of the Florida stone crab for the last several years as part of my dissertation research. I have documented their embryonic development, which takes about two weeks. During the two weeks, the female preens and aerates her eggs (~one million) with her abdomen to oxygenate and keep parasites from settling on the eggs. During this time, you can notice distinct changes in the embryo. Below I have outlined some of the key embryonic development stages that take place during the stone crabs’ development.
Crab Development: A female stone crab with an orange egg mass. The orange color is the yolk of the egg, which is similar to the yolk you see in an egg you would eat for breakfast.
Crab Development: This egg cluster was removed from the female about three to four days after she put the eggs onto her abdomen. The eggs are in embryonic development stage three. Stage three is when the eye spot becomes visible. In some of the eggs, you can see the yolk starting to be consumed (clear poles).
Crab Development: This shows embryo stage four. The yolk is about 50 percent absorbed by the embryo and the eye spot has started to become triangular in shape and position.
Crab Development: This shows the fifth embryonic development stage. During this stage, the pigment cells become apparent throughout the egg. The eye spot also starts to become more rounded. The yolk is about 60 to 70 percent absorbed.
Crab Development: During the sixth embryonic development stage, the pigment cells become apparent throughout the egg/embryo’s body. You can also begin to see the abdominal segments along the periphery of the egg in some of the embryos (uppermost embryo on the bottom side of the egg). The eye spots become rounded and elongated, and the yolk is now only surrounding the eye spot. The yolk is around 80 percent absorbed and in two days, the embryos will hatch.
Crab Development: The seventh development stage is the last embryonic stage before hatching. Hatching almost always occurs the next morning. The eyes are now kidney bean or watermelon seed shaped. There is also little to no yolk present. The pigment cells are also well defined.
After hatching, the new crab (larvae or zoea) are released into the water column. Hatching occurs when the female vigorously pumps her abdomen until the embryo membrane breaks. The larvae then swim out of the embryo toward the surface, where they feed. Development continues in the water column for the next month before molting into the next development stage (megalopae – small tadpole-like crab). The larval stages are alien-like with spines used for protection from predators (fish larvae). They use their fan-like arms and forked tail to help them swim. Upon hatching, they are about 2 mm in size. This larva was photographed at 25x.
(Featured Photo Credit: Jax Shells)