More nudibranch procreation and another record

We saw a couple of noteworthy nudibranch (or if you prefer, sea slug) events on our recent trip. Kawaihae Harbor of course.

A couple of Goniobranchus alboputulosus mating on a piling in the harbor. Like most nudibranchs, the species is hermaphroditic. Also like a lot of nudibranchs, there’s no broadly accepted common name for this species; Hoover calls it “Purple-edged Nudibranch” in the 1998 edition of Hawaii’s Sea Creatures, but changes that to the to me less useful “White-bump Nudibranch” in the 2006 edition. Neither of these helps to distinguish it from the similar Trembling Nudibranch, but that’s the way common names go. This species, while not endemic to Hawaii, has a fairly limited distribution, occurring only in Hawaiian archipelago and the remote Marshall Islands.

This is another species with no agreed-upon common name. Two,” Mourning Nudibranch” and “Funeral Nudibranch,” seem appropriate. More boring is “Polka-dot Nudibranch.” The Latin name is Jorunna funebris—I’m guessing the second term refers to funerals. Anyway, this specimen is in the process of laying eggs, that stippled ribbon to the slug’s left. A lot of nudibranchs deposit their eggs in these looped ribbons. Why loops? As Geoffrey Rush would say, “it’s a mystery.” I was with Hai and Wendy when we found these nudis—there were several of them scattered on the pilings. Hai being Hai noticed that some were kind of big, so he took a photo one with a dive knife next to it to serve as a measurement reference. Sure enough, the animal measured about 70mm compared to the 50mm maximum length posted on the authoritative seaslugsofhawaii.com. Cory Pittman, primary curator of the site, and invaluable resource for us amateurs, has since updated the site with the new maximum. Another obscure record! This species is broadly distributed in the tropical Pacific. It’s unclear if it’s native to Hawaii or introduced.

I’m far from alone in my fascination with nudibranchs—the web is full of nudi fanciers. A lot of it is the phantasmagoria of colors and color schemes, but to me it’s also the hostile, alien environment these little slugs inhabit. They go about their colorful, sluggish business in a world full of stinging hydroids and poisonous sponges (both of which the nudibranchs eat), noxious bristle-worms, and sundry other unlikely creatures. Someone please pass the mushrooms…wait, no need.

Whatcha doing down here?

We’ve returned from Hawaii only to be laid low by Covid. Got lots of good water time in and saw a lot of good stuff. We’re isolating for a few more days, so a good time for some posts.

Reef fish generally ignore snorkelers and divers—as long as they’re not toting spearguns, and as long as they don’t get too close. The definition of too close varies greatly among different species and different locations, and the diver’s behavior—like us, fish don’t like being rushed at or chased. Unlike most of us, they’re often less than thrilled about having a camera pointed at them, either. I’ve crudely categorized fish’s responses when you start to get a little too close thusly:

• Outright flight, rapidly swimming off into the distance—terminal males of the large wrasse species come to mind.
• Darting into holes in the coral and not reappearing—blennies, some hawkfish.
• Nervous hide and seek among the coral branches—the majority of smaller fish, including immature wrasses, parrotfish, butterflyfish, angelfish, many damselfish.
• Casually drifting away, keeping just beyond good photo distance—larger butterflies, parrots, wrasses. These fish are pretty confident they can outdistance the intruder in an instant.
• And then there are those brave little fish, the photographer’s friends, that don’t take off at all. They stick around to inspect the intruder out of what looks a lot like plain old curiosity. Like these little fellows:

This bold little Three-spot Chromis wouldn’t stop trying to size me up, offering a nice photo opportunity. The behavior is common among various damselfish species. Oddly, though, numerous other damselfish—such as the Blue-eye—are extremely shy. This juvenile Three-spot was at about fifty feet off North Kohala. (The name comes from three barely white spots near the tail, barely visible here.)

Ewa Fang Blennies seem to know no fear. They make a living by sneaking up on larger fish and taking nips out of their skin. They’ll try to do the same to divers, but you can barely feel it. The hidden fangs for which the species is named are not part of the fish’s feeding strategy. They’re used for defense. When a larger fish tries to swallow the blenny it uses the fangs to hang onto the would be predator’s esophagus, forcing it to regurgitate its catch. No wonder these fish are so fearless. North Kohala, 50 ft.

This subadult Oval Chromis was not as outgoing as the Three-spot above, but still amenable to having its portrait taken. The iridescent blue and yellow color scheme disappears in adults. This beautiful coloration always reminds me of our dive trips to Samoa and Bali, where several common Chromis species show this pattern into adulthood. Those with southern Indopacific experience will know what I mean—they’re almost emblematic of the region. Once again, this fish was at about fifty feet—a nice depth.

All three of the fish in this post are endemic to Hawaii. All three under three inches long.