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Ocean Watch

Last week, I joined a boatload of friends on an excursion to the Sand Bar in Kaneohe Bay. This famous area of fine white sand near the center of the bay emerges during low tide, making a unique playground.

Often, especially on weekends, boats line up on the downwind side of this bar like puppies at a saucer of milk. Boaters usually set their anchors in the sand by hand, then let their boats float in the deep water off the edge.

When we arrived at the area, the tide was in, meaning two to three feet of water covered the sand. To me, this also meant we would have a great day of snorkeling.

Snorkeling over sand in shallow water is not most people's idea of a good time, but it's worth it. Sand bottoms, even ones left high and dry at low tide, host entire ecosystems of marine animals.

We found our first item of interest floating just beneath the water's surface. A friend handed me the greenish thing, shaped like a hard hat with the texture of rubber bands. "Any idea what this is?" he asked.

I did have an idea because I wrote about it two weeks ago. The dense mass was a seaweed from the Philippines accidentally released in Kaneohe Bay in the 1970s. Currently the pesky stuff is growing like mad, and some researchers think it may be smothering the bay's coral.

It's a good bet. After seeing and feeling these compact caps of growth, it's hard to imagine coral surviving beneath them.

Soon after that I heard, "Here are three baby cornetfish."

I swam to the spot, and sure enough, three pale, pencil-size fish with barely visible filaments streaming from their tails hovered just above the sand. I followed the little cornetfish for a while, but they turned so light against the white sand, they were difficult to keep in sight.

I knew these fish could change color to blend into their surroundings because as luck would have it, I wrote about cornetfish last week. I was on a roll.

"Come quick," two other friends called a little later. I raced to the site, but when I looked down, I saw nothing but sand. Slowly, one friend pointed a finger near the bottom, and a cloud of sand appeared, but not before I spotted what made it. "It's a flounder," I said, and then explained these remarkable fish.

A flounder starts out life like a regular fish, swimming with its back up, belly down and an eye on each side of its head. But as the flounder matures, one eye migrates over the top of the head to join the other eye, and the body begins to spread out. At maturity the fish is flat as a pancake with both eyes on the top.

Like cornetfish, flounders also change color to match the ground beneath them. Also, with a little wiggle of their fins, they can partially cover themselves with sand. All that remains visible of the hiding flounder is the fish's two eyes, poking through the sand like little periscopes.

Once you've found one, flounders are easy to observe because their method of escape is to lie still and blend. But these fish can disappear even while you're watching them. When a flounder is startled, it darts forward a few feet, then flutters backward into the sand. This places the fish a few feet away from where you expect it to be.

Then, just when my friends were thinking I knew all the answers, my sister burst the bubble. Curious about the countless holes pocking the sand beneath us, she said, "Who dug these holes?"

I didn't know. But I found out. The answer is in next week's column.