Monthly Archives: September 2014

Oahu’s upside-down jellyfish came in ships’ ballast water

Published September 22, 2014 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2014 Susan Scott

A beached Cassiopea, or upside-down jellyfish, has frilly “arms” that face up to provide food for the animal. Courtesy Jan Dettweiler

A reader recently came across what she described as pulsating gelatinous creatures on the Kaiwi shoreline.

“Anxious to know what they are,” Jan wrote, and sent two pictures, one taken from each side of the animal.

Jan’s find was an alien creature with a cosmic name: Cassiopea. Most of us, though, call it an upside-down jellyfish.

Upside-down jellyfish live in the reverse position of most jellyfish, with bell on the seafloor and frilly arms facing up. That’s because those lovely lacy limbs contain algae that, like reef corals, contribute to the jellies’ food supply.

Like all plants, algae need sunlight to grow, and that’s what turns the world upside down for these creatures. The bell in this case works as a gentle suction cup to hold the animal in position on the bottom.

The algae give the bushy arms their color of brown, green or blue.

Upside-down jellyfish are not native to Hawaii. Oahu hosts two species (there are eight worldwide), delivered here by accident in ships’ ballast water, probably in the 1940s.

The underside of a beached Cassiopea, or upside-down jellyfish. Courtesy Jan Dettweiler

One of our species is native to the Red Sea and Atlantic Ocean. The jelly grows about 12 inches across and lives in shallow lagoons, sand flats and around mangroves (not native to Hawaii, either) on the leeward side of the island.

Years ago the Duke Kahanamoku Lagoon, adjacent to the Hilton Hawaiian Village, was a good place to watch these elegant jellyfish pulsing in the shallows like flowers with heartbeats. The pulses direct animal plankton toward stinging cells around the jellies’ hundreds of mouths tucked in folds of the frills.

When their water is disturbed, upside-down jellies release loads of free-floating stinging cells. For most people the stings are just prickles on areas of tender skin. Large numbers of stings, though, can get your attention. I paid for my snorkeling excursions in the lagoon with mild, itchy stings to my face and neck.

To me, watching those out-of-this-world jellies was worth some discomfort, but others didn’t see it that way. In 2006 the lagoon owners drained the water and installed a new circulation system. Alas, the upturned jellyfish are now gone.

Oahu’s other kind of upside-down jelly is in Kane­ohe Bay and other windward areas, including, apparently, some places on the Kaiwi Coast. DNA studies suggest that this species came from the Western Pacific, possible New Guinea.

Cassiopea may not look like much lying on a beach, but in their element, the jellies dance like the stars. See one at

Marine biologist Susan Scott writes the newspaper column, “Ocean
Watch”, for the Honolulu Star-Advertiser,

©2014 Susan Scott

Fantail filefish populations ebb and flow over the years

Published September 29, 2014 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2014 Susan Scott

Fantail Filefish. Courtesy Russell Gilbert

When Craig and I moved to Hawaii in 1983, we saw so many fantail filefish, we thought the species, found only in Hawaii, might be the state fish. The 7-inch-long fantails were easy to see and not just because of their striking colors.

The little omnivores were everywhere, nibbling on coral, picking algae off rocks and grazing on dead things.

You didn’t even have to go snorkeling to see fantail filefish. They washed up on Hawaii beaches by the thousands, lying in bright lines of yellow, orange and blue.

A few years later they were gone — so gone that seeing one on the reef was a noteworthy event.

And now they’re back. Fantail filefish are once again a common sight on island reefs.

This boom and bust cycle is normal for fantail filefish, a fact we know because ancient Hawaiians noted the blooms, believing that when the fish, oili uwi­uwi, washed up on beaches, an alii, or chief, would die.

After the filefish dried, people burned them as fuel.

No one knows how often fantail filefish populations exploded in old Hawaii. The first recorded year of high abundance was 1903; the next, 1944. The mid-’50s had a flood of these fish, with another in 1975.

During my early years in Hawaii, the fantails flourished for years on end, starting in the Northwestern Hawaiian Islands in 1982, moving to the main islands in 1983 and lasting until 1987.

No one knows why filefish numbers fluctuate so extremely, but one guess is that it involves conditions offshore. A local researcher in the past observed that one year when Hawaii waters were cooler than normal, and the tuna catch was poor, the filefish population surged.

It’s possible, he speculated, that lower numbers of tuna resulted in a higher rate of filefish larval survival because in addition to fish and squid, tunas also eat animal plankton.

Filefish and triggerfish are similar in shape, and the two families are closely related. Members of both have one stout spine on their backs that the fish raise when threatened. Filefish get their name not from the spine, though, but from their sandpapery scales.

Fantails can rapidly change color to blend in with a background.

One quirk of this species is that two sometimes swim head to tail, sides nearly touching, while moving the back spines up and down and fanning their orange tails.

It’s common these days to see this odd pairing, a behavior that could be a flirtation or a claim to territory. Craig’s theory is that the fish are like dogs, sniffing each other to say hello. Only the fish know for sure.

Since the 1980s I’ve learned a lot about Hawaii’s fish. Now I know that when fantail filefish appear, I should get out there and enjoy them while they last.

Marine biologist Susan Scott writes the newspaper column, “Ocean
Watch”, for the Honolulu Star-Advertiser,

©2014 Susan Scott

7-11 crab gets its name from its array of spots

Published September 15, 2014 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2014 Susan Scott

This 7-11 crab was found in a Waia­lua tide pool. The crab is named for its spots — 11 total, with seven in front and on top, and four in back. ©2014 Susan Scott

I recently received an email with the subject “Crab on V-land beach.” (V-land, or Velzyland, is a North Shore surf spot.) Reader Bill Quinlan wrote, “I have attached two photos of a dead crab we found this afternoon. A lady we showed the crab to said she was from Kauai and they call that type of crab a 7-11 crab. She did not explain why.”

Oahu people call them 7-11 crabs, too. The striking species ranges throughout the Indian and Pacific Oceans on reefs from tide pools to 50 or so feet deep. Other names are spotted reef crab and dark finger coral crab. In Hawaii, though, and for many people around the world, it’s a 7-11 crab.

A common story about the unusual name is that it’s a reference to the crab’s maroon spots. Although some individuals have more, most crabs have seven spots across the shell’s front and top, and four across the lower back, totaling 11.

This logic would make it a 7-4 crab, but the words “seven-11” have more of a ring. A convenience store chain called Tot’m liked the rhyming words, as well.

In 1946 the name was changed to 7-Eleven to reflect its long (for the ’40s) operating hours, 7 a.m. to 11 p.m.

Two days after Bill’s email, I received another 7-11 crab email from my friend Mary. “This morning I found the remnants of a huge 7-11 crab on the reef at Ala Moana. His shell was about 8 inches across. First one I ever saw, living or dead. I understand from other locals there that about two years ago a lot of juveniles washed ashore. What an interesting world!”

It sure is. For unknown reasons, in July 2012 thousands of blueberry-size creatures washed ashore on Oahu. Being in their larval stage, the creatures didn’t look much like adult 7-11 crabs, but that was an expert’s conclusion. Check out the baby crabs at

I also found a 7-11 crab, but it was alive and well in a Waia­lua tide pool. After I took this picture, I put the little crab back in its pool to grow up and make more crabs. In Singapore the species is considered threatened due to pollution and over-collecting.

Seven-11 crabs grow to about 6 inches across, so the crab Mary found was as big as they get. She took it home to let the ants clean it outdoors before giving it a place of honor in the house.

Bill considered his crab a gem, too. “My wife, Rita, and I have been dive buddies for almost 40 years and have dived in numerous countries,” he wrote. “We both feel this is the most special crab we have ever seen. A graphic designer couldn’t come up with a design anywhere close to as good.”

I agree. A certain convenience store would do well to make this crab its logo.

Marine biologist Susan Scott writes the newspaper column, “Ocean
Watch”, for the Honolulu Star-Advertiser,

©2014 Susan Scott

Ocean’s power transforms glass from litter into glitter

Published September 8 2014 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2014 Susan Scott
Glass Beach, Fort Bragg, CA. ©2015 Scott R. Davis

Glass Beach, Fort Bragg, CA. ©2015 Scott R. Davis

Last spring in Tahiti, while preparing my sailboat for a South Pacific cruise, I took a break to go snorkeling with a little girl I met in the marina. The 9-year-old and I had a fine swim, and afterward we walked the beach, looking at the variety of objects the ocean had washed up.

Our beachcombing led us in opposite directions, and later the girl came running to show me her finds. I watched her dump her plastic cup onto a concrete park step, expecting to see snail shells, crab claws and sea urchin tests. Instead, I saw bottle shards.

A few of her green, brown and clear pieces were slightly milky and rounded, but most were transparent with jagged edges. They weren’t dangerously sharp, but clearly the glass hadn’t been in the ocean long. Some stamped-in logos were clear. These were broken beer bottles.

As I watched the girl sort her treasures, she said, “I just love how the ocean makes glass.”

Oh, dear. Should I tell her where beach glass really comes from? To this child, the cup contained gemstones. It seemed wrong to spoil her day.

I remembered that moment with my young friend vividly last week when a friend emailed me a story and pictures of a place called Glass Beach in California’s MacKerricher State Park.

Glass Beach got its start in the early 1900s when area residents threw their garbage over the cliff into the ocean. The household trash included cars, appliances and, of course, glass bottles and jars.

By 1949 the beach area below the cliffs had become the public dump with trash in some places piling up three stories. It wasn’t until 1967 that officials closed the area to dumping.

Cleanup efforts over the years removed most of the big stuff from the beach, but the ocean kept the glass.

Since then the Pacific surf has been pounding, scouring and rounding the glass trash, resulting in tons of smooth, frosted multicolored chips that the waves cough up on the beach.

The phenomenon became known as Glass Beach and was so remarkable that the property’s owner sold it to the state in 2002 to include in California’s park system. Today Glass Beach is a tourist attraction, drawing thousands of summer visitors to view the rainbow-colored shore and listen to the tinkling of the pieces as the waves roll them.

Today, after years of continual motion, the pieces are wearing down, some to mere granules, making some parts of the beach sparse in glass. In addition, although park officials discourage the taking of glass, people collect it for souvenirs and to sell. Sea glass is prized for jewelry, furniture inlays and other creative artwork.

As the little girl sorted her colored chips, I decided it was wrong to let her believe that the ocean made the glass. I broke it to her gently: Sea glass is the result of people littering.

She took it well, because we talked about how even though the ocean doesn’t create glass, it works marine magic by turning something ugly into something beautiful.

To see some stunning photos of Glass Beach, check out

Note: Susan and her web guy Scott visited Glass Beach in February of 2015 during her West Coast book tour. Pictures from that later trip have been added to this post from 2014.

Susan at Glass Beach in 2015. ©2015 Scott R. Davis

At Glass Beach in 2015. ©2015 Scott R. Davis

Marine biologist Susan Scott writes the newspaper column, “Ocean
Watch”, for the Honolulu Star-Advertiser,

©2014 Susan Scott

Fish reproduction an intriguing process

Published September 1, 2014 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2014 Susan Scott

In 1958 my mother went into labor during a Labor Day picnic. The pandemonium that ensued, ending with the delivery of a healthy baby boy, made such an impression on my 10-year-old mind that since then I’ve linked Labor Day with the labor of giving birth.

Today, given my interest in marine life, I’ve extended that link to include the birth of fish.

Fish don’t deliver live babies in the way of us mammals (sharks and seahorses being exceptions), but in a massive ocean teeming with predators, fish have methods of producing offspring that are a category of labor all its own.

The most common kind of fish reproduction is called broadcast spawning, a system in which males and females release sperm and eggs into the water. And that’s the end of it for the potential parents. Spew and split. Job done.

The chances of free-floating eggs and swimming sperm connecting on a coral reef is small, and offshore even smaller. But fish have ways of upping the odds. One is to produce an enormous number of eggs and sperm. This is where labor comes in. When it’s time, as dictated by moon phase, day length, water temperature or something we don’t know, female reef fish produce tens of thousands of eggs and males manufacture millions of sperm.

Open ocean species churn out even more.

The queen of egg production is the ocean sunfish (scientific name Mola mola, hence the common name, mola). In one 4.5 foot-long female, researchers found an estimated 300 million eggs in her one ovary, several orders of magnitude greater than the average broadcast spawner. Since molas grow to about 6 feet long, it’s likely that a full grown female would have even more eggs.

Broadcast spawners’ tiny floating eggs and sperm become part of the drifting plant and animal soup known as plankton, the beginning of the food web. Plankton eaters gobble up most of those sex cells, but some fulfill their destiny of continuing of the species.

Researchers measure a fish’s reproductive effort by comparing the size of its gonads to the size of its body. Charles Darwin proposed the idea that because fish ovaries are considerably larger (30 to 70 percent of the female’s weight) than testes (5 to 12 percent of body weight), female fish invest more energy in reproduction than males.

Today, however, males get more credit. Because random spilling of sperm is a waste, males expend considerable energy to attracting females, establishing territories and running off trespassers.

Some male fish send out pheromones that cue a female to begin egg maturation. Others signal their fitness by turning bright colors or performing lively dances. And when the going gets tough, the tough change sex. Wrasses, parrotfish and anemonefish change sex as circumstances demand.

Studies show that larger female fish of all species produce more and bigger eggs, resulting in higher offspring survival.

That’s why it’s crucial in this era of depleted fish stocks to leave some of the biggest fish in the ocean.

Most people don’t associate Labor Day with reproduction like I do. But in nature, it’s the only labor that counts.

Marine biologist Susan Scott writes the newspaper column, “Ocean
Watch”, for the Honolulu Star-Advertiser,

©2014 Susan Scott