This isn’t an astronomical observation, but it is astronomy related. Today I went out to Orchard Beach where the Urban Park Rangers were holding a horseshoe Crab hunt. The crabs come ashore to breed at sunset on a spring high tide. So the parks department scheduled the hunt at 1000 EDT on a rising tide a week after apogee. The rangers didn’t even know what time the walk was supposed to take place.
I walked out to the beach and arrived 45-30 minutes early and walked along the beach to the ranger station. Along the way I found a lot of nest sites and a few stranded crabs as well as other interesting things.
Sea Lettuce,
Ulva lactuca
Sea Lettuce is one of the most familiar shallow-water seaweeds. It grows in a variety of places ranging from exposed rocks to quiet, semistagnant, brackish pools, where huge detached sheets carpet the muddy bottoms. Tolerant of or actually thriving in moderate pollution. Eddible.
Snails
A conch shell with limpets or slipper shells inside and parts of a crab – probably a common spider crab,
Libinia emarginata.
Clams
Green Crab,
Carcinus maenas, probably dead.
A common British and n. European crab, also reported from Brazil, Panama, Suez Canal, Australia, and Hawaii, presumably by accidental transport. Tolerates salinities as low as 6%. Found under stones and in pools intertidally, also in crevices in sea walls and jetties.
to 3 in. (75 mm).
N.J. to Nova Scotia. Unknown north of Cape Cod in the 19th century; now probably the most common New England shore crab at least as far north as Bay of Fundy. South in N.J. at least to Manasquan Inlet but absent from Delaware Bay. Intertidal to subtidal at shallow depths.
Rockweed,
Fucus sp. and Razor Clam,
Ensis directus (and Styrofoam cup).
Burrows vertically in sandbars, and the speed with which it can sink down out of sight in wet sand is astonishing. Also a successful if somewhat erratic swimmer. The long foot is extended out and folded back against the shell, then suddenly straightened out as if it were a steel spring, and the clam is propelled like an arrow for 3 or 4 feet. Razor clams are tender if not too large and have an excellent flavor.
Snails scavenging in the shell of a Common Razor Clam,
Ensis directus amid Sea Lettuce,
Ulva lactuca and clam shells.
Flat-clawed Hermit Crab,
Pugurus pollicaris
Our largest hermit; chiefly subtidal but may be cast ashore by storm tides. Occupies large moon shells and werlks. Latin name credits it with a thumb, perhaps an allusion to thumblike angle of movable finger on great claw.
This guy pulled into the shell when I picked him up so I know he was alive but he gave no sign of it when I touched his feelers.
Half of an oyster shell
My first Atlantic Horseshoe Crab,
Limulus polyphemus
Identification: Unmistakable! Females reach 2 ft. (600 mm) including the tail spike [I had one that was that big across the body of the shell when I spent a summer on Long Island]; first 4 pairs of legs similar. Males smaller, 1st pair of legs hevier and different from other 3 pairs. Hatchlings lack tail spike; after 1st molt they resemble adults.
Where Found: Bar Harbor, Maine to Gulf of Mexico. Intertidal to subtidal down to about 75 ft. (22.5 m).
Remarks<: Adults migrate into shallow water in late spring and lay greenish eggs – 1/8 in (3 mm) in diameter – in upper intertidal zone. Sand-colored young remain near shore, moving gradually into deeper water as they grow older and darker. Horseshoe crabs can swim, awkwardly and upside down, but spend most of their time rummaging through bottom sand and muck for the worms and mollusks that are their main food. They were once harvested for fertilizer, and a few are still taken to be chopped up for lobster bait. Despite their armament of spines, tail spike, and wriggling, weakly clawed feet, horseshoe crabs are harmless.
Family: Limulidae.
This is the view from the front end. You can see an eye just under a protective spine. They eye has a hard, transparent covering and no lid.
This is the back end. The tail can move to some extent in all directions. It is used, most successfully in the water, by the crab to turn itself over when upside down.
There about a half-dozen shallow depressions in this image where crabs have laid their eggs. The depressions can be up to 8" deep and there doesn’t appear to be any attempt to fill them in, that being left to the tide and waves.
More horseshoe crab nests.
Crab nests with Great Egrets,
Casmerodius albus in the background.
You can see the shape of the crab’s shell in this nest.
We didn’t find any eggs but didn’t disturb the nests to make a thorough search.
The Egrets
Northern Moon Shell,
Lunatia heros sand collar.
Moon shells are common on beaches. “Sand collars” containing their eggs are also found ashore. (Note: Sand collars are very fragile when dried.) Live shells are often seen plowing along, half-buried, on wet beach flats. They are predatory on other mollusks, which they drill neatly, making a beveled hole. The foot is enormous but can be completely retracted.
If you look closely you can follow this crab’s curving track clockwise from its nets at the top of the image.
One that didn’t make it.
A pair of buried crabs that have been partially dug up. Some of these crabs we dug up so we could see the difference between males and females.
This is a female crab. The first pairs of claws from the front of the shell back are all the same.
This is a male crab. The first pair of claws has is boxing glove-like and is used by the male to hold onto the back edge of the female’s shell when she comes ashore.
The crabs, at least on land, seem to walk in curved tracks. This one turned a couple of loops and never got into the water while we were watching even though she was no more than a yard away.
After a while on the beach the rangers took us over to the bay side where we looked for other types of crabs.
[I tried uploading videos but haven't gotten that figured out so will have to include links to the videos instead.]
The fiddler crabs are very skittish and scurry to their holes as soon as they notice any movement. But if you stand still and start looking far away you notice movement on the sand.
As I stood there crabs closer to me started coming out. I noticed some sort of a display behavior. The crabs rear up on their hind legs and splay out their claws. One will do it and then other will join in. I am assuming that this is supposed to make them look bigger to the others and establishing a pecking order.
The crabs climb into their holes and gather up sand which they form into a ball and pull out of the hole in their trailing feet. They take this ball some distance from their hole and drop it, often right next to the hole of a crab with a smaller claw. The object appears to be to keep the area around their hole clear of obstructions so they can scurry into it easily when an emergency arises.
There are blue muscle beds along the high tide line.
The sea gulls eat the muscles and the some of the area is covered with broken shells. I found it interesting that the large intact shells were farthest from the water
while the smallest broken fragments were in the intertidal zone.
I would have expected the reverse to be the case. There isn't that much wave action here but my hypothesis is that when the waves come onshore they carry the shells up the beach and after the wave has expended most of its energy it can't carry the intact shells back down to the water's edge so only the fragments end up there.
I went back to the sound side and walked the length of the beach (1.1 mile) and found very few more horseshoe crabs.
This one was apparently just digging itself into the sand, probably to prevent dessication before it gets covered by the incoming tide but possibly on a nest. I didn't disturb it.
There were more gulls (a.k.a. dump ducks) at this end of the beach.
Mostly there are immature Ring-billed Gulls,
Laurus delawarensis, (the brownish mottled birds) a few adult Ring-billed Gulls (the gray and white birds) and one Great Black-Backed Gull,
Larus marinus, (the gull with the black back).
And a few Bonaparte's Gulls,
Larus philadelphia.
