MBL SciShoots: Horseshoe Crab Biology
We call them crabs, but did you know that horseshoe crabs are more closely related to spiders and scorpions? In the inaugural video of our new digital learning initiative MBLSciShoots, Dave Remsen, Director of the MBL Marine Resources Center, talks horseshoe crabs, their unique physiology, and what makes them so important in biological research.
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Questions from the Audience
How do hatched babies (larvae) make it back to the ocean since they are above the high tide mark? Can they walk already? Horseshoe crabs time their egg laying and hatching to the highest tides of the lunar month. These occur during the full moon and the new (dark) moon, which are approximately two weeks apart. On these nights the tides are the highest of the month. Horseshoe crab eggs hatch anywhere between 14 to 30 days after laying. At these times, there will be a new set of high lunar tides on the new or full moon that will flood the nest area and allow the hatchlings to escape. The hatchlings are able to swim and make their way into the deeper water away from the inter-tidal zone to begin their lives.
For each sex, how has the behavior changed in 5-decades relative to the amazing set of second eyes? Has its brain size changed in that time given UV changes? We can extend the known history of horseshoe crabs back about 445 - 500 million years. New research coming out of the fossil records by researchers in Poland may be even older than that. Horseshoe crabs have quite stubbornly stuck to the basic form we see today for hundreds of millions of years, so it wouldn’t surprise me if there hasn’t been much change in the past fifty. A few years ago we sent some preserved horseshoe crabs to some researchers in France. They wanted to compare their internal anatomy to those of some very well preserved fossils. They later reported to me that, as far as they could tell, there was no difference between the fossils they examined and the modern horseshoe crabs of today.