Great and small: Horseshoe crabs of the Aquarium
New horseshoe crabs have arrived in the Primorsky Aquarium. They are from 5 to 30 cm in length, selected specially to show their developmental stages. “Horseshoe crabs grow very slowly. The smallest, 5 cm long, is 4 or 5 years old, and the largest, 30 cm long, is over 25 years of age,” tells Marat Haidarov, Head of the Exotic Aquatic Species Department. “They live long, grow continuously throughout life and may reach 30 to 40 cm in diameter.” Horseshoe crabs are featured in the “Evolution of Live in the Ocean” exhibit. These arthropods appeared about 450 million years ago in the Paleozoic and have hardly changed in their appearance since then. Instead of common red blood, these animals have blue hemolymph. This fluid is widely used in pharmacology and medicine due to its unique defense system: if harmful bacteria or toxins appear, special very sensitive cells clot around them, thus protecting the internal organs from damage. This property of horseshoe crab’s blood is applied in testing medicines, including vaccines: if clots occur after adding of the crab’s blood extract to the samples of the drug produced, the whole batch is destroyed. More than half a million of horseshoe crabs are round up annually to harvest the blood and then released back to the sea. Many years the process seemed more or less safe for the animals. However, recent research have shown that the mortality of the bled crabs reaches almost 30% and their population significantly decreases. Despite the fact that scientists have already developed a synthetic alternative to the unique blue blood, it is considered not yet adequately tested, and horseshoe crabs still die for the humankind. The coronovirus pandemic only worsened the situation, as even more crab blood was used for testing millions of doses of COVID-19 vaccines.