Each crab has its own way of life.
Date posted: 2026.03.29
Update date: 2026.03.29
What image comes to mind when you hear the word "crab"? You might imagine various kinds of crabs, such as the delicious king crab or snow crab, the large Giant Spider Crab that lives in the deep sea, or the mitten crab or red-clawed crab that you can see in familiar places like waterways and along rivers.
Today, we'll introduce two types of crabs at Tokyo Sea Life Park look similar but are actually quite different.
In the "Tokyo Sea" area and the "Ogasawara Sea 2" tank, Blenny are actively leaping around on the rocks. If you look closely at the crevices of these rocks, you might spot a crab, encased in an orange shell, sitting still.
This is a large rock crab (Giant Rock Crab), belonging to the family Grapsidae. It is a terrestrial crab that lives in rocky areas where waves break. It usually moves slowly, but it can also exhibit swift and sharp movements when hunting for food.
Now, if you look underwater, you can see false frogfish and surgeonfish swimming around, and crabs crawling on the surface of the rocks.
This crab, called the spiny spider crab, also belongs to the Grapsidae family, just like the giant rock crab. As its name suggests, it is characterized by sharp spines on its legs, and unlike the giant rock crab which moves slowly on land, it moves busily in the water. It constantly moves its claws as if cleaning the surface of rocks, bringing algae to its mouth.
When fish pass overhead, they can sometimes be observed exhibiting a threatening behavior, raising both of their claw-like appendages.
Although they differ in whether they live in or out of water, these two species of crabs inhabit rocky areas. They share some similarities, such as their orangish body color and rounded torso, but if you compare them closely, you can find differences as well.
Whether on rocks or in the water, each species has adapted to its respective environment. The large rock crab has a sturdy body and legs, while the spiny spider crab has a smaller body and long, slender spiny legs. The large rock crab also has a thick body, while the spiny spider crab has a flatter body.
Despite belonging to the same family, these two species exhibit significant differences in behavior and appearance, separated only by the water's surface. We encourage you to observe these crabs, paying attention to their differences and considering why they are different.
[Tokyo Sea Life Park]
(March 29, 2026)