Galapagos Crabs

Galapagos Sally Lightfoot Crab

 

Sea Lions and boat, Galapagos

 

Galapagos Sally Lightfoot Crabs

 

With all the magnificent sights on the shores of the Galapagos Islands, crabs are not usually the first creature our eyes behold. But the Galapagos crabs, like other crab species, are fascinating.

 

The two species we saw most were the Sally Lightfoot and hermit crabs.

 

Sally Lightfoot Crabs are most prevalent, seen on beaches and rocks on all the islands. The legend is that they were named after a Caribbean dancer, for their agility.

 

They have great speed and are very difficult to capture, moving swiftly in four different directions. Charles Darwin jokingly wrote of them: “…perhaps because of their rapid reaction time, they appear to read the mind of their hunter.” 

 

Like other saltwater crabs, Grapsus grapsus are equipped with five pairs of legs, including a pair of pincers. The hard exoskeleton is an acquired feature.

 

When born, they hatch in the water. At that early point they are larvae and swim deeper into the waters, feeding on phytoplankton. They undergo a series of molts, each time adding more body segments and appendages, eventually developing into juveniles. They then swim to shore, and begin scavenging.

 

Juveniles are dark-colored, camouflaging in the lava rocks; they also stay in groups, for safety. As the young crab ages, each molt provides a harder and more colorful skeleton.

 

This photo captured both adult and juvenile crabs.

Sally Lightfoot Crabs. Juveniles are black, adults are bright-colored.

Like all of Earth’s scavengers, the crabs add enormously to our environment by keeping it clean and providing a healthy seaside ecosystem.

 

In addition, the Sally Lightfoot Crabs are known to eat ticks on marine iguanas.

 

Sally Lightfoot Crab with four Marine Iguanas

 

Sally Lightfoot Crab Wikipedia

 

Hermit crabs are another species you see on the Galapagos.

 

This species has evolutionarily adapted to their soft body by finding hard, discarded shells to live in.

 

This one, below, has chosen a sea snail shell for its protective body covering. The tip of the abdomen can clasp strongly onto the shell. When the crab outgrows its shell, it finds a new one.

 

Galapagos Hermit Crab

 

Hermit Crab Wikipedia

 

All crabs are especially vulnerable creatures. Predators from the water and land abound, including humans.

 

American Oystercatcher, Galapagos Islands. They can pry open crab shells with that powerful red bill.

 

For protection: the hard shell helps, they can surrender and regenerate a leg if necessary, and they quickly scamper, hiding in rocks and crevices. Their sideways motion is also an aid.

 

We don’t usually think about the locomotive ways of living creatures, but for most it is forwards and backwards. Crabs are different.

 

If you quietly stand still on the shoreline, you may have the opportunity to observe a crab skitter sideways. Watching this brilliant, bright creature effortlessly zip sideways is like watching a marine superhero.

 

Written by Jet Eliot.

All photos by Athena Alexander.

Marine Iguana, Galapagos. Photo: A. Alexander