Honolulu Star-Advertiser © Susan Scott
August 25, 2018
We Hawaii residents welcome strong winds in summer because they cool us off. But some of us like persistent trades and storm winds for another reason: They drive offshore marine life to island shorelines.
Two weeks ago, while I snorkeled in Waimea Bay looking for a species of crab my friend told me about, clumps of baby crabs washed ashore in Kailua Bay. Except they didn’t look like crabs. Several readers emailed pictures of masses of tiny pink bodies with big black eyes lying in the sand on Bellows, Lanikai and Kailua beaches.
Flat rock crabs in Waimea Bay.
©2018 Susan Scott
Crabs and lobsters begin life as eggs held to their mothers’ bellies by a short, wide tail that folds underneath the body. (Male tails are narrow.) After a male fertilizes her eggs, the mother crab holds them under her tail until they hatch. Then the kids are on their own.
Crab hatchlings, called zoea, look like tiny space aliens, each having two black eyes embedded in a rounded body, spikes jutting here and there, a tail and feathery legs. At this stage of life, the baby crab must swim constantly to keep from sinking. It also must eat constantly, gobbling up any kind of plankton it comes across.
To grow, all crabs molt, forming new, larger shells beneath their too-small ones, and then casting those off. Depending on species, crabs at the zoea stage molt from one to eight times before graduating to the next stage, called a megalopa, meaning huge eyes. All crabs have at least one swimming megalopa stage before they sink to the bottom and become adults.
I don’t know what kind of immature crabs died on our windward shores. One knowledgeable reader wrote that she found a 1-inch-long slipper lobster in the mix with what looked like juvenile snapping shrimp. They might have been crab larvae, she wrote, but lacking a microscope, she couldn’t be sure.
In the meantime I found several of the crabs I was looking for in Waimea Bay, colorful little things with shells only an inch wide. These are flat rock crabs, Hawaiian name papa, scientific name Percnon planissimum.
The active little crabs were scooting around the boulders in an area called Bowling Balls, so named because those smooth rocks roll around during Waimea’s famous winter surf.
Of the 4,500 or so crab species in the world, Hawaii hosts about 190. Crabs range in size from one-sixteenth-inch across (a species that lives on sand dollars) to 12 feet across (the outstretched legs of the Japanese spider crab). The sideways walkers live on land, in the ocean and in fresh water, and eat nearly every kind of dead plant and animal they can find.
When the storm clears, I’ll be walking the beaches to see what the wind blew in. But I’ll have to act fast. What I call treasures, ghost crabs call food.
Have a crabby weekend.