Horseshoe Crabs too Cold to Spawn
In May of 2017, horseshoe crabs would not spawn. Shorebirds came to the bay in mid-May as usual, but they found too few eggs to remain. With unique leg flag codes, Red Knots were seen in NJ one day and would turn up in Massachusetts the next. The cause for the delay – the bay’s water temperature refused to climb to the threshold necessary for cold-blooded crabs to get hot bloodied enough to spawn -59 degrees.
The bay water heats and cools counterintuitively, building hopes and then with the next tide extinguishing them. It falls in the day ( after a night of cooling) and goes up at night ( after a day of warming). It would warm with a cool northwest wind (slowing down incoming cold ocean water at the bay’s mouth) and get cold with a warmer southeasterly wind ( by pushing in cold ocean water). Without crabs spawning, the knots and other shorebirds were going to have a tough breeding season.
A Deadly Storm Pushed Crabs to their Death
Eventually, warmer weather brought rising water temperatures. A modest daytime spawn on the 17th promised a better spawn during the subsequent higher nighttime high tide. That evening as the tide rose higher and higher, a storm loomed ominously in the distance. Crabs came ashore in tremendous numbers, and the beach finally started to fill with eggs. Eventually, the storm hit in the dead of night with a gale-force westerly wind slamming against the Cape shoreline and whipping up waves usually seen on the Atlantic Coast. Although it lasted only 30 minutes, the storm caught crabs just at the wrong time.
The following day we saw the storm had overturned thousands of crabs on the beaches. Fortunately, teams from the volunteer group, Return the Favor, acted quickly to rescue many of the crabs from suffocation and dehydration by carrying them to the shoreline. But the storm had far more significant impacts. The onshore winds hit just exactly at high tide as horseshoe crabs gathered to spawn, and in places where the sea has eroded gaps in the dune, the wind pushed water and crabs into the marsh behind the beach. When the tide fell, the crabs remained, trapped in the tall reeds piled atop each other
Fixing the Gaps
The worst overwash of crabs occurred on South Reeds Beach. There was a happy ending for those crabs because we trapped the beach that day and saw the carnage. Quickly the NJ Shorebird Team organized a bucket brigade and rescued over 5000 crabs.
For all the other places, crabs just died. And this is the focus of the American Littoral Society and Wildlife Restoration Partnership restoration work. Last year, the National Fish and Wildlife Foundation granted our group funds to fix the eroded gaps in the Bayshore’s low dunes, where crabs will most likely overwash and die. The work carried out by JR Heun of H4 Enterprises will place 5000 tons of sand into four gaps known to strand horseshoe crabs: Reeds Beach, Kimble Beach, and Pierce point. Follow this gallery of pictures to understand the work.
( see next post)