You never know what you will discover while walking along a beach during an outgoing tide. A sandy shoreline with an ebbing tide is always full of surprises.
The unexpected find of the day took place on Christmas day. I was walking along the water’s edge of Raritan Bay in Union Beach, NJ. The remains of Atlantic rock crabs (Cancer irroratus) were everywhere, washing ashore with every wave. Bits of shells, claws, and other body parts, some attached to seaweed or tender fragments of algae, strewn on the sand amid pebbles and trash.
What could have slaughtered these little crabs? Obviously it’s a dangerous and stressful world underneath the waves. Food can be found, but only at the risk of being a meal for a larger or faster sea creature.
With so many rock crab relics, though, these little critters were most likely not leftovers from lunch.
Many washed in from currents of the estuary, probably due to environmental extremes, such as a quick change in salinity or water temperature. The rock crabs could be an indicator of colder waters coming in after a few months of mild temperatures. Change is ensuing along the subtidal area of the bay or around jetties and under and around rocks where rock crabs commonly call home.
Rock crabs are one of the most common crabs in the subtidal zone of New York Harbor. It’s the area just below the low tide line and which is always covered by water. Critters that live here often cannot tolerate long exposure to air or sun, such as sea stars, shrimp, fish, and crabs.
Not sure why, but the rock crabs I found lying around were all males. Maybe the females had migrated to deeper waters of the bay before the upturn. If so, they got lucky.
After looking at one lifeless crab after another lying on the beach, it was a delightful surprise to see a few still alive. The hardiest endure.
Holding one in my hand, I could feel nine flat projections on top of its carapace. I could see the characteristic purplish brown spots sprinkled over its upper exoskeleton. It had two short, stubby front claws that are normally powerful, but heavy and slow, perfect for crushing shells of mussels or crabs for food.
The rock crab was about five inches across, approximately the length of a moderate sized blue crab. Unlike blue crabs, though, this crab was no pincher and in no mood to be touched. It was weak and stunned from being splashed around along the water’s edge.
Normally, rock crabs would be active and animated foraging one last time for small seaweeds, worms, mollusks, and crustaceans before winter’s arrival. Perhaps scurrying around from crevice to crevice this time of year was what caused the demise for many.
After taking a few pictures and some video, I released the poor rock crabs back into the bay. Good luck little crabs. I hope you survive a little longer the life-and-death struggle that takes place every day underneath the waters in New York Harbor.