What’s so special about this fish? Not much, really.

The Hawaiian Rock Damselfish is a dowdy little fish. No bright colors, no interesting morphological features. Just a shy little fish. What it is, though, is uncommon. Enough so that when I tried to enter a sighting of this fish into a citizen-science database the computer flagged my entry.

The nonprofit REEF (Reef Environmental Education Foundation) runs an extensive, worldwide network of volunteer fish surveyors. Volunteers are required to take a range of fish ID tests and are given proficiency ranks based on the difficulty of tests they’re passed and how many surveys they’ve conducted. Having only done five surveys to date, I’m still rated as a novice, so red flags went up when I claimed that I’d seen Hawaiian Rock Damselfish at Mahukona. I got an email from the REEF volunteer coordinator telling me my observation had been flagged. The email asked if I was sure it was really a Rock Damsel or if perhaps it was a similar-looking but much more common Hawaiian Gregory. Apparently the Rock Damsel had never been recorded at Mahukona. Fortunately I was able to provide photos.

This fish shows all the standard features of Hawaiian Rock Damsels: pale, indistinct vertical bars; slightly purplish coloration; brown, not yellow, eyes.

This one is a bit less obvious. The vertical bars are pretty much absent and there’s hardly any purple.

Here’s a Hawaiian Gregory photographed on the same day as the Rock Damsel shown above. There are a handful of less obvious differences: the rear lobe of the Gregory’s dorsal fin is more elongated than that of the Rock Damsel; the tail is less deeply forked; and the eye is clearly yellow. Nonetheless, it’s easy to mistake the two species, largely because they—especially the Rock Damsels—never stand still.

Juvenile Rock Damsels are easier to identify that the adults. The distinct dark spot (ocellus) on the rear of the body is missing on the Gregory.

I’ve actually gotten pretty good at identifying the Rock Damsels by their behavior. They spend most of their time in dark recesses between rocks, with brief, nervous forays into the open. (This makes them really hard to photograph.) Gregories tend to behave this way too, but less so than the Rock Damsels. The difference is subtle but quite consistent. By the way, both of these species are endemic.

 

 

Diving Dog Pee Beach

Marla and I have been feeling that our scuba skills were getting a bit rusty. Neither of us had dived for almost  year, so the other day we booked a single tank dive with the friendly folks at Jack’s Diving Locker.

We went to a dive site I’d been wanting to visit for a long time. It was a very short boat ride—just a few hundred yards outside Honokohau Harbor where Jack’s keeps their boats. The site has a lot of different names, including Alula Beach, Crescent Beach, Manta Cove, and Dog Beach. The last of these comes from its popularity with dog walkers. So popular that the beach can smell of dog urine. Which is why we, in our typical coarse fashion, call it Dog Pee Beach. The site can be accessed from shore, but that involves a rather long walk over lava to reach the beach, so doing it by boat, while a bit costly, was our preferred option.

We had a great dive. The site had lots of fish, and lots of variety. Here are a few highlights:

The numerous large Yellowfin Surgeonfish at the site seemed very interested in us, sometimes to the extent of interfering with my attempts to photograph other types of fish. I often see these guys while snorkeling at Hapuna Beach, where they’re much harder to approach. I wonder if someone’s been feeding them here.

Another large surgeonfish, the Eyebstripe, or Dussumier’s. These did not seem as interested in us as the Yellowfins. I think these are the handsomest of Hawaiian surgeonfish.

For me, the best fish of the dive was this gorgeous Bicolor Anthias—only the second I’d ever seen. This solitary male was skittish and difficult to photograph.

Lots of Gilded Triggerfish at this site. This one’s a female.

And here’s a male, so you can tell how this species got its name.

I wish I could say I took this photo, but I can’t. It was taken by our most excellent divemaster, Keller. He blew this bubble ring and shot through it to capture one of the numerous spinner dolphins that swam above us during the dive. I gotta learn how to blow those rings.

A Twospot Wrasse, probably not very interesting except to us geeks. The wedge-shaped tail and (I think) red and black triangle at the front of the dorsal fin indicate that this attractive little fellow is a male. This species is one of several small, nervous, deep water wrasses I’m always trying to get a decent photo of. 

And, oh yeah, I almost forgot to mention, Marla and I were attacked by a large shark. Luckily, we escaped.

 

More tales from the pilings—a patriotic nudibranch

Hai and I spent yesterday morning poking around the pilings at Kawaihae. Lots of interesting nudis.

How about this red(-dish)-white-and-blue nudi for Independence Day? This is one of many nudibranch species with no common name. The scientific name is Caloria species #3. This one, a little less than an inch long, has its mouth parts curled around the hydroid it’s crawling on and eating. (Hydroids are tiny, colonial relatives of jellyfish.) The erect appendages on the animal’s head are rhinophores—sensory organs possessed by most nudibranchs. Most nudis lack the longer, curved appendages you see here. Those are called “cephalic tentacles.”

This majestic (for a sea slug) Gloomy Nudibranch bucks a head current on an exposed piling. Gloomies are the most conspicuous nudibranchs at Kawaihae.

Here’s another nudi with no common name. Scientifically, it goes by Doto species #2. These tiny guys—only about 5 mm long—have only been observed at Kawaihae. They live on, and likely dine on, a different hydroid, probably Pennaria disticha. (I got all this from http://www.seaslugsofhawaii.com.)

 

An improbable shrimp—the blind watchmaker strikes again

Back in May, Hai and I saw a tiny, leggy creature hiding among the branches of a large cauliflower coral in Kawaihae harbor. It was clearly some sort of crustacean, but it was too small—a little over half an inch in total length—and too far down in the coral to tell exactly what type. I, with my presbyopic  eyes, thought it was a hermit crab. Hai, despite his better vision, wasn’t sure what it was, but he took a few photos and we moved on. Later that day Hai emailed me the amazing photo posted below. It was an Eyespot Shrimp, a reclusive species widely distributed through the indopacific. It appears to be rather rare throughout its range, or at least rarely observed.

We’ve revisited the spot several times since that first encounter, hoping to get better—or at least additional—photos. Turns out there are two of these shrimp living in our coral head, but we’ve not been able to get any more decent photos. The camera-shy little guys retreat deep into the coral when we come by. I’d been delaying posting this until we’d gotten a few more photos, but I’ve gotten tired of waiting, so here it is:

Hai’s Eyespot Shrimp. How (and for that matter, why) did nature come up with this design? The wild array of antennae, furry forelegs, and googly eyes; the crazy-striped walking legs; the polka-dotted body; and that vivid eyespot on the tail! Any one of these would make this shrimp an outstanding find; the unlikely combination is mind-blowing.

Here’s the best I could do since that first day. The shrimp taunts me from deep in the coral. Is that its tongue sticking out at me?

Eighteenth century theologian William Paley postulated the “watchmaker analogy” to support the idea that an intelligent creator was responsible for our unimaginably complex natural world. The argument goes that if one finds a watch lying in the sand at the beach it can be assumed that someone or something had intentionally created it, since it is too complex to have arisen by accident. Variations of this argument still live among the creationist crowd. The argument is robustly (at least to me) rebutted in Richard Dawkins’ 1986 The Blind Watchmaker. Dawkins shows with considerable mathematical rigor how the simple process of natural selection can produce results that appear to be impossibly unlikely. No watchmaker is needed. Or, if there is a watchmaker, she is blind. I won’t belabor the point further, but rather refer you to Dawkins. So do you think a watchmaker created this unlikely shrimp? Not me.

Look what drifted in at Hapuna

Most reef fish begin their lives as planktonic larvae, drifting in the open ocean. Most perish before settling down to adult life on the reef. Some are undoubtedly scooped up into the cavernous mouths of passing mantas, many are consumed by smaller predators, and many more are probably just lost at sea. Research has shown that a surprising number are somehow able to return to their natal reefs*. How they accomplish this, along with most other aspects of the planktonic lives of reef fish, is a mystery. But return they do.

Last week we saw several groups of small juvenile Oval Chromis, an endemic damselfish, at the north end of Hapuna Beach. They weren’t there a couple of weeks earlier, so it was clear they’d just settled in from their open ocean journey. Welcome back, little guys!

A school of newly-recruited Oval Chromis. The little fish, none over an inch long, huddle in a recess in the reef, which they are very reluctant to leave. This allows fairly good photo opportunities despite the fact that the fish are in constant motion. The vivid yellow and iridescent blue color scheme is quite common among Indopacific damselfish, but this is the only Hawaiian species with these showy colors. As is the case with many reef fish, the adults are much duller. (See April 13, 2018 post.)

Members of another school. The fish on the right is clearly younger than the other two, indicating that it’s joined the school more recently. How did this one find the others?

*https://www.cell.com/current-biology/comments/S0960-9822(05)00712-8 https://www.pnas.org/content/104/3/858/

Kahalu’u’s friendly fish

Kahalu’u Beach Park in Kona has always been one of my favorite snorkeling spots. It’s got a lot of fish, it’s uniformly shallow, and it’s often calm and clear. One thing it’s usually not is uncrowded. The park is widely touted in books and web sites as one of the best sites in Hawaii, so sometimes it seems like every tourist in Kona is there, chasing fish, walking all over the reef, and crashing into one another. The fish don’t seem to mind the human crowds. In fact the fish here are more approachable than at most other sites I’ve snorkeled, owing largely to the fact that spearfishing is prohibited.

Due to the State’s coronavirus lockdown the park has been closed for a while, but has recently reopened. You have to walk in though. No loitering or socializing—just swim, shower if desired, dry off, and scram. Between the loitering restrictions and the current lack of tourists, the reef here is now very uncrowded. Surf was calm yesterday and weather was fine, so Jeff and I decided to take advantage of the conditions with a nice long morning snorkel. We were well-rewarded.

This pair of Lined Butterflyfish trailed me for the entire hour and a half I was in the water. The stately beauties approached very closely, apparently looking for a handout. This behavior contrasts sharply with this species’ shy behavior at Mahukona and every other site I’ve seen them. Someone has clearly been feeding them here.

The Lined Butterflies followed us like dogs. They seemed to be particularly interested when I dove to the bottom. Maybe whoever’s been feeding them was doing so by diving and breaking open urchins’ hard, spiny shells. Broken urchins, as I’ve noted in earlier posts, attract all sorts of fish, eager to cash in on the newly-exposed, soft insides. That’s Jeff in the background, trying to get a shot of a little hermit crab.

A mature female Yellowtail Coris boldly approaches the camera. Look at those snaggly teeth! These fish feed largely on hard-shelled invertebrates, breaking a lot of teeth in the process. Luckily for them, lost teeth are regrown.

Threadfin Butterflyfish were abundant and easy to approach. That’s Mound Coral (Porites lutea) in the background—the area is full of large, healthy heads of this species.

Jeff spotted this pair of large Yellowmargin Morays being groomed by a juvenile Hawaiian Cleaner Wrasse. I didn’t manage to get a photo of the shy little wrasse, so settled for this eel portrait. Morays tend to be solitary creatures, so it was quite unusual to see this pair. My guess is that the pairing is coincidental—”hey, what are you doing in my coral head?”

Two morays

Fish will often tip you off to the presence of other fish. Yesterday I was snorkeling off the Kawaihae breakwater when I spotted a group of Blue Goatfish and Bluefin Trevally excitedly swarming around a small, mostly dead coral head. I knew that these goats and jacks often hunt cooperatively with moray eels, so I swam closer to see if there was an eel hiding in the coral. I was surprised to find two gorgeous morays. Not just two eels, but two different species.

An unusually handsome Whitemouth Moray. I’ve posted about the variable coloration of this species here: https://onebreathkohala.wordpress.com/2019/07/18/a-rare-morph-of-a-common-fish/. In this photo the strong backlighting gives a pink cast to the white mouth interior.

Stout Morays are even more variable than Whitemouths. They can superficially resemble Whitemouths, but they have narrower, more curved jaws and the inside of the mouth is often speckled, but rarely, if ever, all white. Both this species and the Whitemouth are quite common on Hawaiian reefs, but the Stout is more secretive and less often seen.

 

Social distancing at Kawaihae

We’re lucky here in Hawaii. The Governor is encouraging outdoor water activities, and a few of our favorite swimming holes remain open. Last week Marla, Hai, and I were snorkeling off the Kawaihae breakwater when one of the local mantas stopped by.  She graced us with her presence for about twenty minutes and then wandered off.

Our friend Hai positions himself for a photo.

 

A nudibranch holds its breath

Nudibranchs are endlessly weird. Weird, psychedelic colors; weird diets, including lots of toxic organisms; weird anatomy… No wonder so many of us find them fascinating. The other day I discovered yet another strange thing about these oh-so-strange creatures: some of them can withdraw their gills entirely into their bodies. I kind of think of this as the physiological equivalent of holding their breaths.

Hai took this photo of two presumably mating Painted Nudibranchs. Both have their gills—the tufted plumes in the middle of their backs—fully extended, which is their normal state.

I photographed the same pair a minute later. The gills of the lower animal have started to retract.

A few seconds later the gills have completely disappeared into the nudi’s body. What a cool trick. So how does it breath with retracted gills? A little Googling revealed that these nudibranchs, like many small aquatic animals, can breathe through the surface of their bodies—at least when they’re in well-oxygenated water.

Examining photos I’d taken of a different Painted Nudi, I stumbled onto another strange fact: its anus is located in the middle of its gill plumes. I saw what looked like it might be fecal matter protruding from the gills of this animal, so I Googled nudibranch anatomy and found that the gill-anus association is characteristic of the nudibranch suborder Doridacea. All this is probably not so strange to students of invertebrate biology, but this vertebrate-oriented guy found it pretty weird.

A Painted Nudibranch relieving itself.

Where’s the fish?

Yesterday Hai and I spent the morning poking around under the main loading dock at Kawaihae Harbor. The dock, which is idle most Sundays, is supported by an array of hundreds of concrete pilings. Each piling hosts a miniature ecosystem of encrusting sponges, coral, and miscellaneous small, sessile, so-called fouling organisms. A wide variety of fish are attracted to this jungle, many sheltering among the corals and sponges.

Hai noticed something unusual as we passed one of the pilings: he thought he saw one of the corals move. Looking closer, we discovered that it wasn’t a coral, but a large frogfish. More precisely, a Giant Frogfish, also known as Commerson’s Frogfish. These cryptic ambush predators are sublimely adept at blending into their surroundings. Sometimes they assume a solid color and texture similar to that of a nearby sponge or coral, but sometimes they take on a patchwork appearance to mimic the fish’s background substrate. As you can see below, this individual has chosen the latter option. The effect is enhanced by a partial coat of some sort of grayish organisms that the frogfish has apparently recruited. How can these fish be so good at camouflage? Eons of natural selection can work wonders.

You can kind of make out the shape of a frogfish here. The primary giveaway is the hand-like pectoral fin on the lower right. Frogfish use these and their pelvic fins (hidden here) like limbs to clamber around the reef. The anal fin (to the left of the pectoral fin) and the caudal (tail) fin are also fairly apparent. What is not apparent, or even visible, is the fish’s eye, which is hidden by all the fuzzy growth on the fish’s head. As the name suggests, Giant Frogfish are the largest members of their family. According to Hoover they can reach a foot in length—this one is about eight inches.

Another view of the Giant Frogfish’s left side. This time the eye is visible, but I wouldn’t exactly call it obvious. Can you find it? (Colors here are a bit different from the first photo because the first photo did not use flash, while this one did.)

This is the fish’s right side. Harder to recognize as a fish, but the eye is a little more obvious. Still can’t find it? It’s a third of the way down from the top edge of the photo and a third of the way right from the left edge.

A closeup of the above photo. The eye is the small, round, spoked structure at the dead center. Amazing, huh?

At the other end of the size spectrum is this Reticulated Frogfish. Hai found this little guy—a little over an inch long—hiding in a cauliflower coral on a Kawaihae breakwater a few weeks ago. With those clownish eyes and big, grim, downturned mouth it looks like something out of a horror movie. And that’s what it is to any fish small enough to fit into that mouth that wanders by.