19 August 2010

Giant spider crabs on the move

Helen Lockhart
Giant spider crabs on the move!

On 16 August, two male giant spider crabs were successfully relocated from the Two Oceans Aquarium in Cape Town to the East London Aquarium in the Eastern Cape. They were flown to their new home courtesy of 1time airline, the Aquarium’s official animal airline carrier.

Because of their delicate long legs and fragile bodies, the crabs had to be carefully packed. “We first had to secure their legs with twine to immobilise them, so that they wouldn’t injure themselves. Then we covered them in moss to cushion and protect the rest of their bodies. To keep the crabs cool for the duration of the trip, each container was lined with ice packs,” said Tinus Beukes, the Aquarium’s operations manager.

In June this year we received nine female spider crabs from Tokyo Sea Life Park in Japan. They were introduced to the spider crab exhibit in the Oceans of Contrast: Atlantic Ocean Gallery, which already housed several male spider crabs. Unfortunately, during mating, these animals tend to be aggressive toward one another, resulting in injuries such as the breaking of the crabs’ long, delicate legs.

“In order to keep our crabs in pristine condition, we decided to send the males to the East London Aquarium,” said Assistant Curator Claire Taylor. “However, due to the fact that spider crabs live in low temperatures, the staff at the East London Aquarium needed to set up a chiller system on their exhibit before they could accept the animals into their new home. As a temporary measure, we kept the males in the Tristan Exhibit, which, at 13˚C, is the second coldest in our Aquarium.”

Spider crabs are the largest crustaceans in the world – males grow to approximately one metre in length, with a four-metre leg span. They live at depths of approximately 400m, in temperatures between 11 and 14ºC, and very little is known about their biology. It is virtually impossible to determine their age and we do not know when they reach sexual maturity. Giant spider crab breeding habits are also a mystery to marine biologists.

A giant spider crab gets covered in moss

As with all crustaceans, continual growth is impossible in giant spider crabs because of their hard exoskeleton. To grow, the crabs have to periodically shed their exoskeleton by moulting. This is a complicated process and can take up to two days. Each moult is potentially life-threatening as the crab can become entrapped in its old shell. Even if the moult is successful, the sheer effort is sometimes so exhausting that the crab dies soon afterward.

Once the moulting is complete, the crab draws water into its new exoskeleton, making it swell rapidly. As this covering is still soft and elastic, the crab is vulnerable to predation, and it is only over time, and with a combination of enzymes and calcium carbonate, that the new exoskeleton hardens. When it does so, the water is then released and the crab literally “grows” into the space it has made for itself. 

blog comments powered by Disqus