Why Are Horseshoe Crabs Important?

Horseshoe crab eggs are a major source of food for migratory shorebirds. Upwards of 1 million birds stop in the Delaware Bay region to gorge themselves on these eggs at their last stop before continuing on to the Arctic for breeding.  The Delaware Shorebird Project has made a short film to highlight the importance of this connection - Feast on the Beach: The Delaware Bay Horseshoe Crab/Shorebird Connection.
Horseshoe crab blood is 1 million times more sensitive than ours and because of this, an extract of their blue blood called Limulus amebocyte lysate, or LAL, is used to test the sterility of all equipment and injected drugs in the medical industry today. If you have ever gotten a vaccine or had a medical procedure done, you can thank the horseshoe crab for ensuring the equipment used is clean.
Horseshoe crabs are used as bait in the eel and whelk fisheries, which makes them important to our local economy. Additionally, horseshoe crabs and their relationship with the shorebirds attract many visitors and tourists who are interested in helping with the spawning survey, birding surveys, or just enjoying the wonders of nature, which boosts local ecotourism, a major source of Delaware's income.
Delaware and New Jersey Horseshoe Crab Spawning Activity in May
The figure above shows the relationship between spawning activity and average water temperature during the month of May. It is important to note average water temperature changes may affect the timing of horseshoe crab spawning. This can also impact the incubation of the eggs and the survival rate of the juveniles.
Monitoring the percentage of spawning in May is specifically valuable because this is the time period that overlaps with the shorebird stop-over. Timing of peak horseshoe crab spawning and the arrival of shorebirds provides insight for decision-making and species management. One particular shorebird that visits the region, the red knot (Calidris canutus rufa), is federally threatened in the United States and is listed as near threatened globally, which makes this work particularly important.
Note: the graph above does not include water temperature data for 2017 because of lack of availability from the NOAA weather station in Lewes, DE for the month of May.

Page reviewed 3/5/19