Monthly Archives: February 2018

Breathing gets bubbly while crabs are on land

Published February 10, 2018 in the
“Ocean Watch” column, Honolulu Star-Advertiser ©2018 Susan Scott

A reader spotted this rock crab, or aama, blowing bubbles at Maunalua Bay.

A lot of us beach walkers are crabby, and I mean that as a compliment.

Last week a reader spotted two rock crabs, or aama, at Maunalua Bay that gave her pause. Barbara emailed, “Do the crabs blow bubbles? I came across a crab with fine white bubbles on its eye area. … The bubbles seemed to dissipate within a few minutes and then the crab scuttled away.”

Crabs that spend part of their lives in the water, and part out, can blow bubbles. This foaming-at-the-mouth might look like the crab is in distress, and sometimes it is, but in healthy crabs, mouth bubbling comes from the crab breathing air instead of water.

All crabs have gills, and all gills need to be wet to work properly. Crab veins bring carbon-dioxide- loaded blood to the gills. There the blood offloads this gas, a waste product of metabolism, and gets a fresh hit of oxygen. Arteries carry the recharged blood away from the gills, delivering it through the body.

Crab blood carries its oxygen with copper molecules rather than iron and, therefore, is blue instead of red.

Crab gills come in pairs, each housed in a chamber beneath the top shell near the creature’s front. To keep respiratory current flowing, the crab beats a tiny paddle, called a bailer, at the base of each of its two front claws. The water or air exits through two holes, one on each side of the mouth.

You might say, then, that a crab breathes in through its legs and out through its own version of nostrils.

When it comes to getting oxygen, the aama is flexible, extracting the essential gas from water or air, depending on where the creature is scavenging. When an aama is on a rock pushing air past its gills, because they’re wet, the exhaled breath comes out in bubbles.

Barbara saw another aama with a bulging lower flap holding a spongy egg mass, and wondered whether rock crabs give birth to live crabs.

Sort of. Females of this genus (there are eight species, one being the red Sally Lightfoot) carry fertilized eggs under the belly flap for about three weeks and then drop the hatchlings in the water.

Crab hatchlings don’t look like crabs, but rather are larvae that drift around as plankton. Survivors go through several molts before they look like crabs.

Hawaii hosts about 200 crab species in a wide variety of shapes, colors and habitats. They have one trait in common: pluck. If they can run and hide, most crabs will do so. If cornered, though, crabs defend themselves, raising their claws like little boxing gloves to fight even enormous monsters like humans.

Hawaii’s shoreside crabs can breathe air or water, run sideways, eat most anything and fight for their lives with remarkable courage. In my view, calling someone crabby is a good thing.

Clinger crabs are members of wind drift community

Published February 3, 2018 in the
“Ocean Watch” column, Honolulu Star-Advertiser ©2018 Susan Scott

A pregnant clinger crab fits in the palm of a hand. ©2018 Susan Scott

When the wind is howling and the surf is busy salting everything in my house, I hit the beach. Those aren’t the best conditions for soaking up sun or playing in the water, but for us avid walkers it’s prime time for finding marine treasures.

Because I make mosaics from litter I find in albatross nests at Midway and on beaches in the Pacific, my gems are usually bits and pieces of colored plastic. Last week, though, my prize was alive. When I got home and dumped my junk in a colander for rinsing, there on a barnacle- and algae-encrusted toy truck clung an offshore crab.

This species of crab is a member of the wind drift community, a diverse bunch of animals that float on the surface eating anything they run into, including each other. They’re called wind drifters because they are indeed adrift, their direction and speed controlled entirely by current, wind and waves.

Common jelly-type critters floating offshore are Portuguese men-of-war (Physalia), by-the-wind sailors (Velella) and blue buttons (Porpita).

You might not expect snails to be members of this community, but two species are common: violet snails (Janthina) and snails-without-shells called nudibranchs (Glaucus).

Another unlikely offshore mariner is a little crab I call the clinger crab because it doesn’t have its own float system, as the others do, nor does it swim. Rather, the clinger crab spends its life hanging onto a piece of wood or debris. (I can’t find a common or scientific name for this little crab. If you have one, please write.)

Clinger crabs are about the size of a quarter and come in shades of blue or brown, depending on which object they’ve chosen to call home. This clinger was brown, a perfect match to the brown seaweed that grew on its floating toy.

You can tell a male crab from a female by the flap on the center of its underside. Narrow is male; females have wide flaps that hold their eggs.

When I examined my crab’s belly, I discovered, with some excitement, that I had a female with eggs. Hoping to raise some baby clingers, I rushed back to the ocean for a bucket of water, half filled my rescue tank and gave my pregnant crab her tiny truck, a pile of rocks to reach it and some frozen brine shrimp for energy.

A pregnant clinger crab fits in the palm of a hand. The eggs are the yellow mass under the flap. ©2018 Susan Scott

Alas, a tank being the utter opposite of her natural habitat, she did not survive. Even so, I was happy to have had a wind drift pet, even if just for a day.

During my beach walks I sometimes forget to bring a bag, and have to go trash-can diving for containers. Failing at both those things last week, I called Craig to come get me in the car, because I couldn’t walk home. After stuffing my pockets full of flotsam, I then filled my Crocs.

I have lived in Hawaii long enough that I sometimes think it’s too cold to go snorkeling. Never, ever, though, is it too cold for beachcombing.