Community Science to the Rescue, One Flipped Horseshoe Crab at a Time

On a beautiful sunny day in early summer, a group of community scientists led by Ron Smith — a Drexel University BEES instructor and high school environmental science teacher — was making the most of the beachy breeze on the Delaware Bay.  Fixing their hats and covering themselves in sunscreen and bug spray, these volunteers were setting off to do some very important conservation work: rescuing horseshoe crabs.  

Horsehoe crabs haven’t always needed human intervention and assistance. More closely related to arachnids such as spiders and scorpions, these ancient creatures, with their iconic shells and long spiny tails, have lived in the coastal waters of the Atlantic Ocean for millions of years. They only emerge from the water to spawn in late spring on high tides from the Gulf of Mexico all the way up the Atlantic Seaboard, with the world’s largest gatherings right in the Delaware Bay.  

Smith and his community science team visit five sites along the Bay once a week during the spawning season for the sole purpose of flipping over or pulling out trapped crabs from rubble, pipes, jetties and sea walls, counting the rescue numbers as they go along. 

“We have been asked by beachgoers, fishermen, why we are flipping them,” Smith says. To many who live or work near the Bay and are used to frequently seeing these prehistoric-looking creatures slowly scuttle across the sands, some are of the opinion that nature should be left alone to take its course.  

“If the only hazard to a spawning crab were to be flipped over during the high tide spawn,” he explains, “then that argument might make sense. Unfortunately, due to a century of human impact — habitat loss, overharvest and now climate change — their population is unstable and much lower than historic levels.”  

Habitat loss, overharvesting and climate change all impact horseshoe crab spawning, and many do not make it.

Horseshoe crabs are harvested for a variety of reasons. Pharmaceutical companies collect them for an extract of their blood which has special properties used in labs to test for impurities in vaccines and drugs, making the crabs an important commodity in a pandemic-stricken human world. While bled crabs are released back into the wild, some die during the process. Further studies are needed to assess alternative measures to their safe harvesting.  

The crabs are also a popular fishing bait, and pressure in the Mid-Atlantic region to increase the harvest of horseshoe crabs for this reason is only increasing.  

Constant beachfront human development also creates a habitat loss issue for the crabs. With climate change and shifting water levels, comes land shape and access changes, too. New developments spring up, while some buildings and roads are abandoned and left as inaccessible rubble. Infrastructure to keep rising tides at bay can also reduce the amount of necessary beach environment available to support their spawning.  

Horseshoe crab eggs are a critical source of food for many estuarine species. For this reason, the Delaware Bay is one of the most important locations in the western hemisphere for migratory shorebirds who visit for a brief few weeks in spring to fuel up for their journey that will take them to the Arctic to breed. For red knots, a migratory shorebird listed as Threatened under the Endangered Species Act, fewer eggs mean reduced chances for survival.  

“Not to put too fine a point on it,” Academy Collection Manager of Ornithology, Nate Rice, says, “but horseshoe crabs are just not going to survive without change and action. What Smith and his team are doing is the most noble work of local conservation efforts that have broad reaching impacts. The horseshoe crabs, the red knots, the many other shorebirds, they all intimately rely on each other, and now on us for a chance of survival.” 

Laughing gulls, Larus atricilla and red knots, Calidris canuta, feeding on horseshoe crab eggs, Delaware Bay, NJ © Doug Wechsler/VIREO

Because red knots time these spectacular global flights around the massive horseshoe crab spawning in the Delaware Bay, specifically to feed on these eggs, horseshoe crabs are the crucial part of a very precarious ecological situation. Without enough crabs laying eggs, the red knots and other migrating birds cannot fuel up properly, which means many of these birds will not make it to their destination or have enough energy to breed if they do arrive.  

Smith recalls when he was a child about 30 years ago, the red knot population that arrived on New Jersey shores were estimated yearly at around 80–100,000 birds. In the last few years, however, scientists have counted only a fraction of that — with numbers as low as 7,000 birds.  

While flipping over horseshoe crabs seems like the least Smith and his community scientists can do, there is actually much more conservation work going on under the surface. For the past 10 seasons, Smith has been collecting immensely important data: counting each and every crab the group interacts with; noting whether it was flipped or rescued from the rubble; documenting details like each crab’s sex or size; and capturing other pieces of environmental information, like the weather, locations and if other animal species, like birds and turtles, were spotted nearby. All this data will help paint the scientific picture of what is going on in these critical tidal ecosystems.  

This effort is coordinated by a group of conservation organizations known as reTURN the Favor, NJ, a multi-partnered program working to rescue horseshoe crabs with other sanctioned volunteer community scientists like Smith. Since 2013, according to their site, reTURN the Favor volunteers have saved over 840,000 horseshoe crabs along the Delaware Bayshore beaches in New Jersey. Meanwhile, hemispheric efforts to save horseshoe crabs are being led by the Horseshoe Crab Recovery Coalition (HCRC). 

“Community scientists play a critical role in efforts to safeguard migratory shorebirds and horseshoe crabs in Delaware Bay and along the entire Atlantic Coast,” says Co-Director of HCRC, David Mizrahi, who is also the vice president of research and monitoring for New Jersey Audubon.  

He explains that these volunteers do quite a lot of simple, practical but enormously impactful science work, in addition to rescuing the horseshoe crabs. “They contribute to assessments of shorebird survival and migration stopover behavior by reporting observations of birds marked with coded leg flags to an online database.  They also participate in horseshoe crab spawning and egg density surveys organized by HCRC, that has partners in many states along the East Coast.”   

Mizrahi believes more efforts like Smith’s work with community scientists are needed in the Delaware Bay and encourages Academy readers to join the mission to save our local horseshoe crab and shorebird populations.  

“The help of these tireless and dedicated volunteers to the conservation of shorebirds and horseshoe crabs is truly immeasurable.” 

Interested in taking action? Join in the efforts of the Horseshoe Crab Recovery Coalition and become a volunteer today with reTURN the Favor, NJ. 

Red knots Calidris canuta, with horseshoe crabs, Delaware Bay, NJ © Doug Wechsler/VIREO

Visual Resources for Ornithology (VIREO), the worldwide bird photograph collection of the Academy of Natural Sciences, can help you identify migratory shorebirds on your next outing in the Delaware Bay. More than 700 photographers from around the world have contributed to VIREO, with over 100,000 images accessible online for educational, scientific and commercial use for students, birders and researchers alike.

One comment

  1. I have been doing that in Atlantic City veterinary Margate longport South Jersey for as long as I can remember ever since I came to United States from Greece in 1970 as a kid and now I’m 63 still doing it still….

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