If you have been a student of biology, you must be aware of horseshoe crabs. These creatures, hailed as ‘living fossils’, inhabited the Earth some 445 million years ago. The surprising thing is they are not crabs, not even crustaceans, and are classified under chelicerates, a subphylum that also includes arachnids.
So, how on earth did they manage to survive without getting extinct? This question had opened a whole new field of research into these creatures and what was found was most astounding. Here are some highlights:
● The horseshoe crab blood color is bright blue. This is because horseshoe crabs rely on hemocyanin to transport oxygen throughout the body. This contains copper, which turns bluish-green when it oxidizes. In the case of vertebrates, it is the haemoglobin that transports oxygen and contains iron that makes blood’s color red.
● The blood of a horseshoe crab has remarkable antibacterial properties. It has amebocytes, instead of white blood cells, to fight infection.
● So effective are amebocytes in fighting bacterial contamination that it takes only 45 minutes to coagulate around one part in a trillion of bacterial contamination. The white blood cells in vertebrates, on the other hand, take two days for the same feat.
These properties of horseshoe crab’s blood are of immense medical interest. A million crabs are harvested each year for blood use. At present, the amebocytes in the blood are used for testing medical equipment and vaccines prior to use. For this, the amebocytes are introduced into a sample.
If the cells coagulate, it indicates the presence of bacteria and the product is not ready for use as yet. However, the synthesis of crab’s blood is still in its infancy.
The declining crab population due to over harvesting in North America has prompted the authorities to focus on their conservation. Now, instead of killing the horseshoe crabs for their blood, harvesters draw only 30 percent of their blood and return them to the ocean to be harvested again.
It has been found that a horseshoe crab manages to survive on 70 percent blood, but not lower than this. One downside is a reduction in breeding in females who have been bled. Despite this, the temptation to bottle this horseshoe crab blood, priced at $15,000 per-litre, is too great to resist.
Horseshoe crabs are rightly hailed as life savers. Had it not been for the miraculous properties of its blood, millions of people might have died from germ-infected injections.