Is it a rock crab or a Dungeness? Would you be able to tell the difference? These differences are often subtle, but some obvious physical indicators will help tell them apart. In this article, we analyze what it takes to correctly identify both types of crab, using some tell-tale qualities that distinguish one from the other. So, stick around to unwrap the rock crab vs. Dungeness crab mystery.
Comparing Rock Crab vs. Dungeness Crab
|Rock Crab||Dungeness Crab|
|Scientific Name||Cancridae /Malacostraca class||Metacarcinus magister/ Crustacea class|
|Identification||Reddish brown in color. Shell is round and flat, chunky with large, pointed claws. Black on the tips of its claws.||Purple-tinged, grayish-brown backs with a lighter, maroon-colored underside. Large blunt claws with white tips.|
|Size||6 inches||10 inches|
|Food||Mainly hard-shelled prey but also worms and sea cucumbers.||Both hard-shelled and soft-bodied prey|
|Market Value||Less pricey||More expensive|
|Majority of Edible Flesh||The claws||The body|
|Habitat/Location||Near rocks, tide pools, and rocky marine areas. Native to the Pacific Ocean.||Rocky reefs. Most places of the West Coast. Originally from Dungeness Spit, a sandy stretch of land in Northwest Washington.|
The Key Differences Between a Rock Crab and Dungeness Crab
The primary difference between a Dungeness crab and rock crab is that Dungeness crabs are generally much larger. In addition, there are physical differences such as the black tips on the claws of rock crabs, their value to commercial fisheries, and preferred habitats.
Let’s dive into the main differences between Dungeness and rock crabs in detail!
Rock Crab vs. Dungeness Crab: Size
The size difference between rock and Dungeness crabs is an essential distinction between the two types. In contrast to Dungeness crabs, rock crabs are typically smaller, with a maximum carapace width of around 6 inches. Conversely, the Dungeness crab can reach up to 10 inches in carapace width. As such, when considering crab size, it is important to know with which kind of crab you are dealing.
Consequently, those who harvest crabs for food may prefer the larger Dungeness crab over the smaller Rock crab. In addition, the different sizes may make it easier or more challenging to prepare each type of crab for food. For example, removing the meat from a larger Dungeness crab may be easier than from a smaller Rock crab.
Rock Crab vs. Dungeness: Claw Variation in Relation to Diet
In contrast to the Dungeness crab, the rock crab typically has slenderer and pointed claws. This variation is because their diet consists mainly of hard-shelled prey. Therefore, to effectively puncture and tear through the exoskeletons of their food, they need sharp, strong claws.
The Dungeness crab diet consists of a wider variety of food, including hard-shelled and soft-bodied prey. As a result, their claws are less specialized for puncturing and more adapted for power grips and crushing. These two crab species illustrate how claw shapes adapt to different dietary needs.
Color in Relation to Protection from Predators
In contrast to the rock crab, the body of a Dungeness crab is usually darker red or maroon. This color distinction is because Dungeness crabs typically live in deeper waters, where they are less exposed to sunlight.
As a result, their bodies contain more pigment, which helps to protect them from predators such as humans, sea otters, octopuses, and Pacific halibut. In addition, the darker color helps camouflage the crabs when they hide among the rocky reefs of their habitats. Alternately, the Rock crab’s brownish red shell blends well with the more sandy, rocky areas of its natural environment.
Eyes, Antennae, and Carapace
The placement of a crab’s eyes and antennae can help determine its species. For example, rock crab eyes are closer to the front of the carapace, while Dungeness crab eyes are farther back. In addition, the antennae of a Rock crab are usually located closer to the mouth, while those of a Dungeness crab are typically further down on the head.
On the other hand, the Dungeness crab has longer legs and claws than the Rock crab. Alternately, Rock crabs have a smoother carapace, while Dungeness Crabs have a rougher carapace. Knowing these characteristics can help you determine the type of crab you observe.
Rock Crab vs. Dungeness: Legs in Relation to Survival
A rock crab’s legs are typically covered in tiny spines, while those of a Dungeness crab are spine-free. This spiny feature is a key disparity between the two types of crabs. The purpose of the spines is to provide defense against predators. The lack of spines on the legs of a Dungeness crab makes them more vulnerable to predators, but their large size helps make up for this lack of additional armor.
The spines on the legs of a Rock crab can also help it to grip onto rocks and other substrates, versus the Dungeness crab, which alternately relies on its claws for locomotion. In short, the presence or absence of spines on the legs of these two crab species is indicative of their contrasting ecological niches.
Rock Crab vs. Dungeness: Swimming Ability
Rock crabs are better swimmers than Dungeness crabs. They are often seen in tidal pools and estuaries, whereas Dungeness crabs are more commonly found in bays and along the coastline. Rock crabs alternately use all eight legs for swimming, whereas Dungeness crabs only use six. This gives rock crabs an advantage in speed and agility in the water. Consequently, they are better able to escape predators and find food.
In addition, the rock crab shell is narrower and more streamlined than the Dungeness crab shell, streamlining its shape so it is easier to move through the water. They can also hold their breath for more extended periods. Dungeness crabs, on the other hand, are better at digging and burrowing. They are also more resistant to cold water temperatures. Ultimately, these characteristics make rock crabs better swimmers than their Dungeness counterparts.
Rock Crab vs. Dungeness: Gender Identification
It is relatively easy to identify the gender of a rock crab as the male has large, flat-topped claws. However, it can be more challenging to determine the gender of a Dungeness crab. The best way to tell them apart is by looking at the underside of the crab’s body – males have a sizeable sternal plate, while females have a smaller one.
You can also look at the crab’s gonopods on the fifth pair of legs. The male’s gonopods are curved, while the females are straight.
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