Dead horseshoe crabs washed up in Ocean City
Following a spawning event in the Assawoman Bay, a large number of dead horseshoe crabs washed up in the 94th Street canal in Ocean City last week, the Maryland Coastal Bays Program reported.
While the large number of dead crabs caused an inconvenience to those living in the area of the dead-end canal, the incident has been deemed likely a natural event. Due to the stress of spawning on older horseshoe crabs, up to 10 percent of the crabs die during the spawning period.
However, Sandi Smith from the Maryland Coastal Bays Program said other contributing factors could have been at play.
"The thing is, we don't really know how many horseshoe crabs are out there," Smith said. "Say there are a thousand, and it's natural that 10 percent die during spawning, then that's a 100 dead crabs, and that's to be expected. But there were other things that have happened that could have influenced this, namely low DO (dissolved oxygen) as a result of the macro algae bloom earlier this year."
Low dissolved oxygen, which results from the macro algae bloom and its subsequent death and decay, makes for an ecosystem where fish, crabs and other marine life are unable to survive. Evidence pointing toward this factor being at play are carapaces of crabs too young to spawn, as well as blue crabs, being found among the dead, which Smith estimated to be around 300.
Maryland Department of Natural Resources Director of Resource Assessment Service Bruce Michael said state of Assawoman Bay could have contributed to the high number of deaths.
“Water quality data from Assawoman tributaries is indicating relatively low DO reading — less than 2.0 mg/l," Michael said. "DO can go lower in some of these dead end canals, so low DO could have contributed to mortality event.”
Maryland Department of Natural Resources biologist Steve Doctor, while noting that low-DO could have been at play the overall health of the Assawoman Bay ecosystem is good.
"The good news is fish and crabs are recolonizing and macro algae is less," Doctor said. "The overall horseshoe crab population is good."
Smith went on to state, while the cause of the kill is unclear and could potentially have been nothing more than a natural occurrence, it is one for the Coastal Bays Program to keep an eye on.
"It's an event of concern," Smith said. "It could have been an entirely natural, or it could have been the result of something else. We're hoping that no one did anything reckless to cause it."
Horseshoe crabs, more closely related to arachnids than real crabs, are an important asset for medical science. The substance Limulus amebocyte lysate, found in the blood of horseshoe crabs, is used to test for sterility of virtually all medical tools and intravenous drugs. Scientists have also studied the eyes of horseshoe crabs to better understand human vision.
The Coastal Bays Program urges citizens to help protect the quality of the bays by following proper guidelines for disposal of chemicals and lawn fertilizers, which can immense effect on water content and lead to blooms of macro algae.