Monthly Archives: October 2017

Sea snakes seen sunning amid Great Barrier Reef

Published October 28, 2017 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2017 Susan Scott

Sea snakes, which carry venom used to paralyze prey, can make for good swimming and snorkeling companions, if one doesn’t fear them. ©2017 Susan Scott

KELSO REEF, AUSTRALIA >> After sitting out a week of rain in Magnetic Island Marina, we’re back in flat water, moored on another of the Great Barrier Reef’s pristine outer reefs. Snorkeling here at Kelso Reef is as good as it gets, but even so, we don’t have to get in the water to be thrilled. We just stand on the deck.

While sailing between the mainland and the outer reefs these last few weeks, we’ve seen four sea snakes sunbathing on the water’s surface. Three dived before we could turn the boat around for pictures, but one, a tan-colored beauty with dark saddles on its back, totally ignored us, continuing to nap as we circled.

The 15 species of sea snakes that live on Australia’s reefs are bold, because they’re packing. All carry cobra-type venom stored in cheek glands connected to two front fangs. Injected toxin paralyzes muscles almost immediately, handy for halting fast-swimming prey, such as the bottom-dwelling fish that most snakes like to eat.

The good news is that sea snakes don’t waste their venom on snorkelers or divers. Australia reports no deaths from sea snake bites.

Even though we’ve seen sea snakes basking on the water’s surface this month, I’ve not seen a single one while snorkeling. That’s partly by chance, but it may also be because some sea snakes don’t like to travel.

In a study of olive sea snakes, the Great Barrier Reef’s most common species, researchers found the snakes’ foraging areas were only half an acre. When workers moved some individuals from their home reef to an adjacent one 200 yards away, none crossed the sandy channel to get back.

Sea Snake. New Caledonia 2006

That might explain why sea snakes are common on some reefs and absent on others, but it makes me wonder about the snakes we see basking on the surface miles from the nearest coral reefs. Maybe like us humans, some sea snakes are wanderers and others are homebodies.

All sea snakes are air breathers, but because they have one cylindrical lung nearly as long as their bodies, they can stay submerged for up to two hours.

Olive sea snakes come in shades of solid green, gray or golden yellow. Our first three snake sightings were olives. The species has light sensors on its flat, paddlelike tail, a feature that tells the snake whether its rear end is sticking out. When you’re 6 feet long, eye spots on your tail are handy for hiding under a coral head.

For us sailors, though, eyes peering through polarized sunglasses are all we need to spot a sea snake snoozing on the water’s surface.

I know I’ll never convince people who fear snakes that they’re fun snorkeling companions. But even those with phobias might appreciate seeing, from the deck of a boat, a rare marine animal in its natural element.

Or not, if it’s a snake.

Banded Sea Snake on land, New Caledonia, 2006. Courtesy Scott R. Davis

Underwater ‘banquets’ are a feast for the eyes

Published October 21, 2017 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2017 Susan Scott

A giant clam sits on a bed of coral in Britomart Reef in Queensland, Australia. ©2017 Susan Scott

ORPHEUS ISLAND, AUSTRALIA >> After nearly a week of snorkeling on the outer reefs of the Great Barrier Reef Marine Park, stormy weather forced Craig and I to sail our 37-foot boat, Honu, back to the shelter of this island. Although Orpheus is also a national park with its own charming beaches, birds and reefs, we missed our giant clams.

While anchored on the reef, we had discovered a several-acre area that looked like the site of a mermaid’s banquet. Table after table was set with pink, green and lavender plate corals sitting between runners of gold and tan leather corals. In the midst of these place settings sat dazzling centerpieces: blue, green and gold giant clams.

A major downfall of these beautiful bivalves is that they’re sitting ducks, big pieces of meat that can’t run away and have only minimal defense. (They can close their shells somewhat but don’t slam shut like they do in cartoons.) Because the colorful algae in their soft tissues need sunlight to thrive, the clams grow mostly in clear, shallow water, making them easy to find, kill and eat.

Like stony corals, giant clams host algae in their tissues that grow sugars for the clams. If conditions are prime and the algae get too dense, the clam simply eats them, too.

A giant clam gathers fertilizer for its algae directly from the seawater that bathes it. Covering the soft, gaping lips of the creature is a type of tissue that can absorb ammonia, nitrate and phosphates, nutrients crucial for plant growth.

The clam breathes, and gets nutritional supplements, by inhaling water through a round siphon on one end of its soft body and sifting out tiny plants, animals and oxygen. The filtered water exits out another siphon on the clam’s opposite end.

Because giant clams grow well in tanks, aqua-farmers in Palau, the Philippines, the Cook Islands and other areas grow them for food, for the aquarium trade and to replenish reefs where people have overharvested.

Giant Clams being grown in a tank in the Cook Islands. ©2006 Scott R. Davis

Just when Craig and I were reminiscing about our amazing experience in what we named the Super Duper Royal Clam Garden, we made a joyful discovery. Near the James Cook University’s marine science center in Orpheus Island’s Pioneer Bay, researchers had planted a giant clam garden in the 1970s.

We found the man-made plot by accident while going ashore in our dinghy. From the surface we could see the 3-foot-long creatures smiling up at the sun, their oval bodies resembling iridescent place mats, and their siphons projecting from the flesh like white porcelain cups. Today 40 to 50 (my guess) mature clams thrive there.

Swank dinner parties aren’t Craig’s and my usual thing, but last week we attended two and we didn’t get a bite to eat. In giant-clam gardens the feast is for the eyes.

Colorful Giant Clams-Bora Bora, French Polynesia. ©2006 Scott R. Davis

Coral-eating starfish have their place in healthy reefs

Published October 14, 2017 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2017 Susan Scott

A crown-of-thorns starfish eats live coral bodies, leaving their white skeleton cups intact. ©2017 Susan Scott

BRAMBLE REEF, AUSTRALIA >> On our sailboat, Honu, no wind means using the boat’s loud, hot motor to go somewhere, something we sailors resist. Last week, though, the lack of breeze and Honu’s diesel engine were a godsend, allowing us to explore sections in the outer area of the Great Barrier Reef Marine Park.

Being out in the Coral Sea, anchored in striking white sand patches surrounded by city-block-size coral heads and boulevard-wide reef flats was a wilderness experience like no other. We snorkeled for hours on end, and each time we rested, the same word came to both Craig and I in describing what we saw: pristine. These reefs are among the few remaining places on Earth that show no sign of human disturbance.

In some areas, though, nature had wielded a heavy hand. Massive coral heads lay on their sides, and car-size table corals stood upside down, tipped over by cyclone-­driven waves.

We also saw crown-of-thorns starfish, the largest of all starfish species, slurping the soft bodies out of corals’ hard cup skeletons. The starfish everts its stomach through its mouth, oozes digestive juices onto the live coral body and sucks it up, leaving only the white calcium carbonate cup.

Crown-of-thorns starfish, COTS for short, have 10 to 20 arms, grow to 20 inches across and are a normal part of healthy coral reefs. Coral deaths open space for juvenile plants and animals to settle, thus giving reefs variety in shapes, surfaces and species that can withstand, and recover from, natural damage, including starfish blooms. Of the reefs we visited, however, in two places COTS were clearly more numerous than a healthy reef can handle.

COTS blooms have been a threat to the Great Barrier Reef since the 1970s. Researchers once thought that human collecting of the giant triton snail, called Triton’s trumpet, was to blame, since the snail eats COTS. The outbreaks, however, aren’t caused by a shortage of starfish predators, but rather by the survival of exceptional numbers of the starfish’s babies.

River runoff causing algae blooms that feed drifting starfish larvae is another suspect. But COTS outbreaks also occur off remote islands where there’s no such runoff.

Of the 100-some COTS research papers published over the decades, the cause of the blooms remains the same: unknown. It may be a normal part of reef evolution.

Just when we started to worry about COTS destroying these pristine reefs, the starfish vanished. The next acres of reef had zero COTS, and the corals, fish and giant clams sparkled with such beauty, I felt happy to be alive.

Sailboats might need the wind to sail, but sitting becalmed on the Great Barrier Reef, sunny day after sunny day, landed us smack in the middle of ocean paradise. Now that’s a godsend.

Crown of Thorns starfish, French Polynesia, 2006. Courtesy Scott R. Davis

Colorful ocean plant also reeks of dead fish

Published October 7, 2017 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2017 Susan Scott

Sea sawdust blooms in the Coral Sea, forming strips of growth so large that they’re visible in satellite photos. ©2017 Susan Scott

TOWNSVILLE, AUSTRALIA >> Last week a Tahitian snapper made itself known to me by opening its own page in my fish book. This week an ocean plant I didn’t know called attention to itself by floating around Honu’s hull in swirls of yellow, purple and pink. With the plant came its signature smell, the nose-wrinkling stink of dead fish.

The alga — scientific name Trichodesmium (trick-o-DEZ-me-um) — is commonly called sea sawdust. Australian boaters know this marine alga well because it occasionally blooms in the Coral Sea, forming strips of growth so large they’re visible in satellite photos.

The streaks the alga sometimes forms on the ocean’s surface spooked Capt. James Cook and his crew in 1770. In his log Cook wrote, “The sea in many places is here cover’d with a kind of brown scum … upon our first seeing it, it alarm’d us thinking that we were amongst Shoals.”

They were not, however, in shallow water, but were sailing through miles of one of the most vital marine plants in our planet’s oceans.


Trichodesmium is a blue-green alga that grows as tiny filaments, like miniature grains of rice. Usually, the barely visible seaweed lives in the water column where endless tiny animals eat it. During blooms, though, thousands of alga strands stick together and float to the surface in miles-long lanes of sea sawdust.

Sometimes the alga produces substances that are toxic to fish and irritating to human skin. Other times, depending on conditions, the plant produces red, pink and purple pigments. The Red Sea got its name from a red strain of this alga.

Sea sawdust is key in keeping the nutrient-poor tropical and subtropical oceans around the world productive by converting nitrogen from the air to fertilizers crucial to other marine plants.

Blooms of sea sawdust during periods of calm seas are common inside the Great Barrier Reef. People here accept the colorful alga mats and their pungent odor as part of life on Australia’s tropical coast.

Trichodesmium films smell fishy because when each plant dies, its cell wall breaks down and the insides spill out. Bacteria eat the spillage, a meal that gives them gas. Called dimethyl sulfide or DMS, the gas is one of several fishy odors we associate with the ocean.

As we set about provisioning Honu for our latest voyage in the Great Barrier Reef Marine Park, Craig and I marveled over the colorful eddies around the boat, a vision worthy of an exhibition in a modern art museum. And the odor? Well, learning the chemistry of the plant, knowing the significance of it to the world’s oceans and remembering that bacteria pass gas like everyone else took the smart out of the smell.

I’m in no hurry to sail Honu out of this marina, because it’s in the central part of the Great Barrier Reef Marine Park, pure heaven for us oceangoers. All I have to do is open my eyes, breathe in deep and, like the Tahitian snapper, let the marine life come to me.