Monthly Archives: April 2015

Rock-boring sea urchins excavate homes in reefs

Published April 27, 2015 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2015 Susan Scott

urchin

Rock-boring sea urchins are vegetarians. ©2015 Susan Scott

Rock-boring sea urchins have riddled the reef in so many parts of my favorite snorkeling area, it’s a wonder there are any rocks left at all.

Some of the bowl-shaped caves that the urchins call home are so enclosed, it looks as if the spiky little creatures, which come in pink, green, cream and black, can’t possibly get out. If hemmed in a hollow for life, what do the rock-borers eat? And how did they manage to get in so deep?

They chewed their way in.

Rock-boring urchins have thick, stubby, nonvenomous spines sticking out from their spheroid skeletons except at the bottom. In the center of the flat space beneath is the urchin’s mouth containing five sharp teeth fused together in a circle called Aristotle’s lantern.

The name comes from Aristotle himself, who described sea urchin teeth (all species are similar) as looking like a five-sided lantern with the panes left out.

When you live in the shallow ocean and grow to only 2.5 inches across, including spines, most waves would bowl you over. To hang on against such force, rock-borers use their round set of teeth to gnaw into limestone or volcanic rock, and thus create their own personal tsunami shelters.

Chewing rocks sounds hard on the teeth, but sea urchin teeth are renewable, growing with built-in breaking points. When a tooth gets worn down, it snaps off at the weak point, exposing a sharp new edge.

The rock-boring urchin also uses its bottom and side spines to scour and scrape. That’s why, in most individuals, the working lower spines are shorter than the slackers on top.

Rock-boring urchins get no nutrients from rocks.

The animals are vegetarians that, when able, come and go from their caverns to graze on algae. Even as the urchins grow bigger and dig deeper, their movable spines allow them to elbow their way in and out of their holes.

Some rock-borers excavate tunnels with open ceilings of various widths. The urchin can get in and out at the wide spots and hunker down where the skylights narrow.

Other urchins grow too big to get out the door. Housebound urchins simply eat in, which is how they get too large to leave. The individuals eat algae that grow in their cave, plus waves and currents offer free delivery.

Rock-borers are a central part of natural erosion cycles. Because urchin predators are mostly reef fish, in areas of heavy fishing, rock-boring urchins cause far more damage to the reefs than they would normally.

Now that I know how remarkable these urchins are, I see them in a hole new light. (Sorry.) Rock-boring urchins are anything but boring.


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

©2014 Susan Scott

 

Scorpionfish can be tough to spot, even inches away

Published April 20, 2015 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2015 Susan Scott
Plover

A scorpionfish matches its surroundings well. ©2015 Susan Scott

The trouble with taking pictures of scorpionfish, called nohu in Hawaiian, is that I often delete the photos thinking I missed whatever fish I was trying to shoot. Then later I wonder what happened to my scorpionfish pictures and find them in the recycle bin.

Not this time. While snorkeling recently, I found a devil scorpionfish sitting right out in the open, exceptionally noticeable in all its bumpy beauty. When I drew close to snap photos, the 12-inch-long fish held its ground. Go ahead, those bulging eyes seemed to say as the fish fanned out its scalloped side fins. Touch me. See what happens.

I knew what would happen. Scorpionfish belong to a large family of fish that get their name from venomous fin spines.

Some scorpionfish match their surroundings so well that they’re hard to spot even when right in front of your face. These types grow algae and fleshy flaps on their skin for camouflage. When this invisibility cloak gets overly fuzzy, the fish molts and starts over.

Other scorpionfish family members, lion fish and turkey fish, use the opposite defense strategy. Their flamboyant colors and conspicuous fins are like big guns warning would-be predators to back off or be sorry.

The two diverse scorpionfish forms are clues to these fishes’ hunting methods. The camouflaged species are ambush predators, lying as motionless as the rocks they mimic while waiting for passing prey. With a lightning-speed lunge, the scorpionfish swallows the unsuspecting fish or invertebrate whole.

Lion fish and turkey fish use their delicate-looking fins to wave sand and debris off creatures on the ocean floor. The fanlike fins also trap prey in corners and against walls of coral and rocky reefs.

The most notorious of all stinging fish are the South Pacific’s stonefishes, but those species belong to a different family not found in Hawaii. Although stings from stonefish cause the rare death, fatalities usually occur in people who have other medical conditions. When supported in modern medical facilities, most people with stonefish stings survive.

Hawaii’s scorpionfish stings won’t kill you, but they hurt like the devil. Immersing the wound in hot water often relieves the pain.

Scorpionfish use their venomous spines for defense only. Leave them alone and they’ll return the favor.

I took several pictures of the little limestone impersonator and back home immediately downloaded my memory card. Even so, when organizing pictures recently, I wondered what I was thinking to have saved a photo file of rocks.


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

©2015 Susan Scott

 

Scientific name for fish doesn’t quite do it justice

Published April 13, 2015 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2015 Susan Scott
Plover

Dascyllus albisella, or, in Hawaiian, aloiloi. ©2015 Susan Scott

While snorkeling last week, I noticed that some Hawaiian dascyllus were mostly gray, some were nearly all white, and further on, they were black with a white spot on each side.

The name Hawaiian dascyllus doesn’t tell you what kind of marine animal I’m talking about, and even if you know Greek, you still don’t get much of a clue. The generic term dascyllus (da-SILL-us) means “a kind of fish.” And the species name of the Hawaiian dascyllus, albisella, is equally nondescript. It means “white.”

Even though I see different colors and patterns in this fish, I know it’s the same species because Hawaii has only one dascyllus. (Eight others occur in the Indian and Pacific oceans.) But the distribution of black, white and gray in individuals varies widely.

The Hawaiian dascyllus, sometimes called the Hawaiian domino damselfish (more descriptive but a mouthful), reminds me of a fish-shaped beverage coaster. The flat, roundish species grows to 5 inches long.

fish

Juvenile dascyllus usually hover in schools just above branching corals, but long-spined sea urchins and crown-of-thorns starfish are also favorite hangouts. At the approach of a predator (or snorkeler), the babies dive to safety inside the coral’s narrow corridors or among the urchin’s or starfish’s sharp toxic spines.

Some adult dascyllus spend their entire lives in the arms of antler coral, venturing out to graze on passing plankton. Other adults throw caution to the current and live in the open, using cracks and crevices in nearby rocks and reefs as emergency shelter.

The juvenile Hawaiian dascyllus is black with a brilliant white patch on each side and a neon-blue spot on the forehead. As the fish gets bigger, it loses the headlight and its white side spots fade.

dascyllus

As an adult, the Hawaiian dascyllus changes patterns to suit the occasion. When courting, the fish’s sides turn bright white, while the head, fins and tail are all black.

Dining calls for different attire. When feeding, the fish’s sides are white, but the edges of the scales there darken, giving the fish a gray mesh look, as if it’s wearing a shirt of chain mail.

When threatened, adult dascyllus revert to their juvenile colors of all black with bright white side spots.

After reading up on dascyllus colors, I went back to my snorkeling site to match patterns with behaviors, but I couldn’t tell what those perky little fish were up to. All I knew as I watched them dart here and there in their assorted black-and-white outfits was that the ancient Hawaiians had it right when they named the fish “aloi­loi.” It means “bright and sparkling.”

fish


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

©2015 Susan Scott

 

Our Pacific golden plovers prepare for Alaska flight

Published April 6, 2015 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2015 Susan Scott

Plover

A male kolea in breeding colors. Courtesy O.W. Johnson

Hawaii’s annual spring pageant is upon us, the superstars dazzling in their April outfits as they prance through backyards, across golf courses, among gravestones and between parked cars. The celebrities are Pacific golden plovers, our much-loved migratory shorebirds known in Hawaii as kolea.

Although kolea start molting into their striking breeding colors here in March, the birds stay single until they reach their Alaska breeding grounds. There males return to the same spot each year and, upon arrival, get busy rebuilding a ground nest of leaves and lichen.

Females, though, aren’t usually faithful to either place or partner. Instead they shop around, looking for the handsomest male with the finest nest.

After choosing a homestead and mating, the female lays four huge eggs, their total weight equaling her own body weight. If a fox, raptor or caribou eats or breaks her eggs, a kolea can lay a replacement clutch in a week or so.

As if this reproductive labor isn’t astonishing enough, it all takes place after the 6-ounce birds have flown 3,000 miles over the Pacific Ocean. Nonstop. In three days.

If a nesting attempt fails due to weather or predation, adults can return to Hawaii as early as June. But if all goes well, the couple takes turns keeping the eggs, and later the chicks, warm and protected.

When chicks fledge, that’s the end of family togetherness. Mother plovers leave for Hawaii first, in early August, with fathers following a bit later. Chicks stay in their Arctic birth areas as long as the bugs and berries last, with most arriving here in October or November.

If you see a scrawny bird in a new place, it’s likely a recently landed chick that survived its first migration (on its own — there’s no adult guidance). But the struggle isn’t yet over. New arrivals must establish their own winter territory, often having to fight established plovers and other bird species for space.

Only about 20 percent of kolea chicks live to reproduce.

If you have a plover pecking and hopping around your yard year after year, it’s almost certainly the same bird, because both sexes return to the same wintering spot. And you could have that feathered friend for a long time. Some kolea live for 20 years or more.

Our grassy Easter parade isn’t going to last much longer. All kolea fit to migrate leave Hawaii within a few days of one another around April 25.

I know that countless Hawaii residents join me in wishing our little superbirds fair winds, strapping chicks and bugs galore. A hui hou.


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

©2015 Susan Scott