This is the molted shell of an a’ama crab, seen on the North Kohala shore. A’ama crabs are numerous around the Big Island and they scuttle away when disturbed. But while these crabs are black, their molted shells turn red in the sun, as this one has.
A bright-eye damselfish guards its territory, which includes this red pencil urchin, against intruders.
Back in the fall of 2014, Hawaiian waters experienced temperatures up to 86°F. This very warm water resulted in a major coral bleaching event statewide. Since that time, water temperatures have been in a more normal range and the coral has stabilized and even shown signs of recovery in places.
In August of this year, the National Oceanic and Atmospheric Administration (NOAA) issued a warning that another major bleaching event was likely to happen this fall. Last month, NOAA reported that bleaching was already occurring. And I’ve noticed that the water does seem warmer, sometimes disturbingly so.
Because of the bleaching threat, I’ve been looking at the coral when I go snorkeling. There are a few very white patches, but by and large it doesn’t look too bad. This patch of purple coral still looked quite healthy and was host to a saddle wrasse (at right) and three unidentified fish (above).
A little snapshot of things tucked into the rocks along the Big Island. There’s a red pencil urchin and blue-black urchin, a patch of cauliflower coral, and a cowry, probably a reticulated cowry. And if you look closely, there’s a bright-eyed damselfish swimming between the coral and red pencil urchin.
Until I moved to Hawaii, I was not aware that lobsters molt. I only learned this when a local diver presented my wife with a lobster molt he’d recovered.
I’d seen live lobsters here, scuttling around on the sea floor, and others looking like the one in the photo. This one was moving, but only because of the action of the water on it. I used to think these were either dead or resting lobsters. In part this was because adult lobsters, which molt once or twice a year, discard a remarkably complete exoskeleton. It then takes them a few weeks for their new exoskeleton to fully harden.
This is probably a molt from a banded spiny lobster. True lobsters and their relatives have enlarged pincers on their front pair of legs. Spiny lobsters (family Palinuridae) are among the lobster varieties that don’t have those enlarged pincers.
This week’s Sunday Stills challenge theme is ‘Fifth.’ (See more offerings here.) I was stumped as to what to post until I thought about looking back to see what photos I’d taken on the fifth of a given month. As it happened, these somewhat strange photos were taken just one month ago, on April 5th, and I was now ready to run them.
I was out snorkeling and was drawn to some black triggerfish, which were gathered in a very tight group. I took some photos and as I maneuvered around the group I became aware of something very close by.
The thing was at least two feet long and six inches or so in diameter. It was translucent, but with short lines of purple dots, and a milky central line through the tube. It was floating just below the water, changing shape, though not appearing to propel itself, but more being moved by the water. I thought it was some kind of egg sac, but really had no idea what it might be.
I wasn’t even sure I could get a photo of it, since I thought my camera might not ‘see’ it and instead focus on the fish beyond. I was also leery of getting too close. Perhaps it was some form of jellyfish or some other creature loaded with toxins.
When I got home, I was thrilled to find that some of the photos had turned out and registered what I’d seen, but I had no idea what it was. It didn’t really look like an egg sac, but what were the alternatives?
I had a browse in John Hoover’s Guide to Hawaii’s Marine Invertebrates and the closest thing I found was a prickly pyrosoma (pyrosoma atlanticum), but while the general shape was similar, the surface looked much less smooth than the thing I saw. So I shared the photos with some local snorkelers and divers and asked if they had any idea what it was. A couple of ideas were floated but nothing definitive. No one had seen anything like this before.
I looked online and found a few images that bore some resemblance. One of those links was to John Hoover’s website so I thought, ‘Why not ask someone knows about these things?’ and sent him an email with the photos. He quickly responded that it looked like a pyrosoma, a type of tunicate, and referred me to the listing in his book.
As we exchanged emails about a definitive identification, he noted, ‘Often microscopic examination is required to definitely identify tunicates, so unless you can get a piece of one, preserve it properly, and send it to a specialist we’ll probably never know exactly what it is.’
So what is this pyrosoma in the photos? Well, the name means ‘fire body’ and it can light up at night. It’s a colonial tunicate that can be 30 feet or longer (search online for pyrosoma and diver to see examples). Tunicates are filter-feeding creatures that either attach to hard surfaces or float free in the oceans. The colony is made up of zooids, individuals animals that are embedded in a gelatinous tube, which is open at one end and, apparently, is quite hard to the touch. One end of each zooid opens to the outside of the tube, the other end to the inside. Each zooid filters tiny cells from the water outside and expels filtered water to the inside of the tube.
Now, every time I get in the water, I’m looking around for another one. I probably won’t see one, but if I do get lucky, I just want to poke it, gently of course, to see what it feels like.
The photos show the shape and general composition of the pyrosoma. Some people have said it must have been huge because it dwarfs the fish in the photos, but the pyrosoma was only a couple of feet away. The fish were 20 or more feet beyond.
My wife spotted this crab scuttling quite rapidly along the floor of the bay where we were snorkeling. It was clearly some kind of hermit crab, but it was quite deep and this was the best photo I got.
When we got home, I looked through my copy of John P. Hoover’s Hawaii Sea Creatures and the jeweled anemone crab seemed the most likely identity. As can be seen in the photo, the shell is covered with anemones which is a feature of these crabs. Since these crabs are mostly night feeders, we were lucky to see one still active in the early morning. Possibly it had been disturbed and was headed to a new hiding place.
Crown-of-thorns sea stars (Acanthaster planci) feed on coral and, because of this, are considered a menace to the health of coral reefs. Up to a foot-and-a-half across, they can have as many as 19 arms and are covered by venomous spines. If this all sounds like this creature is a nasty piece of work, the good news is that it has not caused extensive damage to the reefs here in Hawaii.
The crown-of-thorns does have predators, one of which is triton’s trumpet (Charonia tritonis). These large triton snails, up to 20 inches long, feed on echinoderms including crown-of-thorns sea stars. When they scent prey, they will take off after it and are considered speedy for a snail. When a triton’s trumpet catches its prey, it grips it with its foot and applies saliva that causes paralysis, which allows the snail to consume its meal without further drama.