Oceanography: Create Your Own Tide Pool Creature

My oldest had an assignment in her Oceanography class to create her own Tide Pool creature. I think she did a fantastic job and her drawing is terrific!! She gets her talent from her mom :) Here is what she came up with...


Pagurus gruvati  The Pagurus gruvati or Groovy Crab, as it is commonly known, lives mainly in the Middle Tide Zone of tidal pools. Even though it lives in the middle tide zone, it usually ventures out into other areas of the tide pool and onto the land to gather food and to visit. Although it is a cousin of the Hermit crab and does share some of its characteristics, it is indeed a creature set apart.

Description... The Groovy Crab will grow to an average size of between 8 to 13 cm in length, with the females being slightly smaller. They are born already having a strong shell about their body to protect them. As they mature, the Groovy Crab will molt its shell and then find another to call home, which will occur until the Groovy Crab reaches maturity. As this time approaches, they will find a small cave near the bottom of the tidal pool and remain there until they grow their final shell.

Artwork courtesy of Katie Hicks

 This process can take as long as four weeks and it is during this time that they are the most vulnerable to predators. To help in their defense, they use a special gland located at the base of their throat to secrete a strong acid, which they can shoot into the face of an enemy. So that the acid does not immediately disassociate when it hits the water, it is encased in a protective film, which bursts on impact. This way, the enemy will get the full power of the acid. Once they have grown their adult shell, the gland will no longer produce this acid, but will serve another purpose. Mobility: The Groovy crab has four legs, which it uses to get around the tidal pool; with two larger claws on the front. These strong claws are used to get food, dig in the sand, general hygiene, and for defense. Yet, these claws also serve a more fanciful function: they can make music. Using their front claws, the Groovy crab can produce some rather complex musical sounds, which it uses for communication and entertainment. This music can be heard up to a mile away under water, and even further, when they are on land.

Extra features: The Groovy crab also has two antennae on the top of its head, which can move in any direction. Strangely, the crab has a light producing organ, which can produce a bioluminescence chemical in all the primary colors. They emit these colors through their antennae, often in conjunction with their music. When there are several Groovy crabs in the area, it can have quite a strobbing effect. The acid sack that protected them throughout their most vulnerable period of life no longer produces acid, but it does have another function. The Groovy crab is able to squeeze air through the sack and manipulate it in such a way as to produce an audible sound. Scientists studying the Groovy crab state that when activated, they can hear what sounds like the word, "Dude."

Another interesting fact about the Groovy crab, is the fact that not only can they produce bioluminescence chemicals through their antennae, but also through their shell. As they cling to the rocks in the tidal pool, they can change their shell color to match their surroundings, just like a chameleon. However, it has also been observed that they can create many patterns, in varying colors.

Breathing: The Groovy Crab is at home both in and out of the water. While in the water, they breathe through a series of gills, which allows them to extract oxygen from the surrounding water. When they come onto land, they are able to close-off the gills using a watertight membrane and breathe using a pair of lungs. Eating: They like to eat just about anything they can get their claws on. They travel the bottom of the tidal zone and eat whatever dead fish may be present. As they prefer not to kill living fish, when it comes to "flesh foods," they eat carrion. However, they will eat most any type of plant, although they do seem to prefer rock algae and seaweed. They have also been known to eat the occasional Twinkie left behind by a careless beach goer.

Reproduction: Once they are mature (about 1 year old), the Groovy crabs will meet their mates at the Sand Bar and when the females lay their eggs, the males will then fertilize them. The gestation period for the eggs is approximately one month. During this time, the female will carry the eggs and protect them. Once they are ready, she will deposit them in the water, where the salt in the ocean will dissolve the shell and the Groovy crab is born.

Predators: Until they reach maturity, just about every creature would love to get their fins on the tasty Groovy Crab. However, once they are grown and have their "adult shell," their only natural predator is the Copper fish. These fish run in packs, called squads, and tend to round-up the Groovy fish and eat them.

Life span: The Groovy crab has a life span averaging about 40 years.

Lifestyle... The Groovy Crabs are social creatures and live in groups called Communes. These communes can have as many as 50 crabs in them. They do everything together as a group and during the day, seem to enjoy just hanging-out on the rocks. When night falls, they gain their second wind and venture to the beach to scrounge for Twinkies and any other tid-bits left over by visiting humans. This is also the time that they seem to "break out of their shells" and have fun. If you are lucky enough to be on the beach when they arrive, you will be a welcomed guest to one of their concerts and light shows. Beach goers have been known to plan nighttime bon fires near where the Groovy crabs gather. In exchange for some choice morsels of food, the crabs provide the music and light show and the humans and crabs dance the night away.