Aquarists were shocked to find a young Horseshoe Crab (Limulus polyphemus) in the Stingray Bay touch tank this week. It was removed and placed in a small tank in the quarantine room.
Many facilities regularly breed these animals. So, why were aquarists so surprised to discover this quarter-sized crab?
To begin, our male crab (who could often be seen hitching a ride on the back end of the carapace of one of the female crabs, waiting to fertilize eggs) passed away several months ago. Apparently, before we lost him he fertilized some eggs.
The female crab can lay 15,000-65,000 eggs at a time. Horseshoe Crab eggs are extremely small and would be vulnerable to predation by every single animal in the tank. Some would also get pulled into the strong flow of the exhibit’s 420 gallon-per-minute filtration system.
If by chance some eggs did not get eaten or filtered out, they could hatch. At this point the young animals are still in a very tiny larval stage, swimming for five to seven days. Any larval Horseshoe Crabs would remain very vulnerable to being gobbled up by other animals in the touch tank and would still be prone to being caught in the filtration system. They would also struggle to find food that would be small enough to eat.
And yet, one tiny crab managed to overcome these odds.
After the larval stage, the baby Horseshoe Crab settled to the bottom and began growing and looking like a miniature version of the adults. At this point it was less likely to be eaten by the smaller fish in the tank, but it would appear more and more like a snack for a stingray or shark. Our tiny crab would also have the same issue of finding food small enough to eat.
And yet, this tiny crab avoided predators and a strong filtration system, scrounged up enough food to be nourished and grew.
The fact that this little crab survived long enough to attain the size of a quarter in an exhibit packed with its natural predators is nothing short of mind boggling!