Category Archives: Marine Invertebrates

Lobster molt

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.

Pyrosoma

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.

Jeweled anemone crab

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.

A mackerel scad school draws attention

Mackerel Scad shoal

Mackerel Scad shoal over coralMackerel scad are schooling fish, the kind that make ‘bait balls’ which end up being decimated by large predators. They’re members of the jack family, not that this does them much good. Some of those large predators are other members of the jack family such as greater amberjacks and almaco jacks.

I came across this school not far from shore. There were probably two or three hundred fish in the school and it was fun watching them twirl and circle in harmony. They encircled me, went past and I popped out the other side. It was then I noticed they weren’t alone. One the other side of the school, a medium-sized great barracuda cruised around.

The barracuda came toward me to take a look, but I was clearly less interesting than the scad and it moved away again. The barracuda can be seen in the bottom photo. See if you can spot it.

Mackerel Scad shoal and a great barracuda

Brown water

Brown water

After something of a dry spell, during which I was able to drive my truck out of the yard without sliding about, there’s been a lot of rain lately. My truck is back to sliding, but that’s a minor issue compared with what happens to all that rainfall.

What happens is that the rain hits the land and runs downhill. It channels into dry gullies. If the rain is heavy enough, flash floods occur and wash all before them – dirt, rocks, trees. But any kind of heavy or prolonged rain will wash earth and debris down the gullies. All those gullies lead to the ocean, channeled under roads by culverts (bottom photo).

When the runoff reaches the ocean, it forms a distinct area of dirty brown water in the blue Pacific Ocean (top photo). The contrast is striking and easily visible from miles away. Over time, the brown and blue water will begin to mix until the delineation is gone, but part of that process is the dirt from the brown water settling to the ocean floor.

This kind of runoff is one of many threats to coral reefs around the Big Island. It’s not just dirt in the runoff, but also pesticides and other chemicals that can be washed down into the reefs, damaging the coral. There are hundreds of gullies and only a few places have erosion prevention measures to help mitigate this pollution.

So while Hawaii may be considered paradise, it has its share of challenges. And the problems associated with runoff and pollution are more visible and obvious than most.

Posted in response to this week’s Friendly Friday challenge on the theme of ‘Contrasts.’ See more responses here.

Brown water and culvert

Crown-of-thorns sea star and its nemesis

crown of thorns

giant triton snailCrown-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.

Redbarred hawkfish

redbarred hawkfish

Redbarred hawkfish, like other hawkfish, spend most of their time perched motionless on a rock or coral head, waiting to dart out at passing prey, usually little fish or small crustaceans. On some fish, the bars are more of a brick red, similar to the color of the red pencil urchin on the left of the photo.