Ocean Watch: Abundant lugworms use their sacs as nurseries

HAZARD BAY, ORPHEUS ISLAND, AUSTRALIA >> The blustery southeast tradewinds finally let up enough to allow us to sail Honu to the Palm Islands, one of our favorite island groups in the Great Barrier Reef Marine Park. Here we happily discovered new reef markers and mooring floats. Boaters tie up to the floats, and if they’re all taken, the markers show us where it’s safe, coral-wise, to drop an anchor.

As usual, the island’s reefs revealed their eye-popping color and diversity, the soft corals waving in the current and the hard corals showing off their symbiotic blue, pink and gold algae.

While Craig and our visiting friends enjoyed the corals and fish in over-the-head deep water, I snorkeled to the shallows over sand and seaweed. This looks boring to most snorkelers, but for me it’s a constant source of entertainment.

Among my multiple sand-flat favorites are lugworms, animals I’ve never even seen. But in their sand depressions, castings and jellylike pouches protruding from their holes, they show me their great abundance.

Several Hawaii readers have described and sent photos of these floppy, tan bags attached to the sand, one woman’s son nicknaming them beach boogers. The sacs, however, are not waste products. They’re lugworm nurseries.

Lugworms, found worldwide, are active diggers, using muscle contractions to dig U- or J-shaped burrows. The worm’s downward wiggles drive water into the burrow, where the creature’s frilly gills, located outside its soft body, extract oxygen. The water then percolates up through the sand.

In its forward movement the worm swallows the sand before it, digesting bacteria and dead plant and animal material mixed in the sand. Often the worm’s sand-consuming creates depressions, and sometimes holes, on the surface.

When it’s full, sometimes in a little as 14 minutes, the worm backs up to the opening where it started and expels the sand, leaving it in distinct piles called castings.

Mature male lugworms release sperm into the water, and some find their way into the burrows of females bearing eggs. After her eggs are fertilized, the female makes a jellylike balloon containing the offspring and releases it to the surface, keeping one end attached to her tube dwelling.

These fragile cases hold the hatchlings until the babies have grown several body segments. The youngsters then break free to grow up and dig in.

We can help keep our sand flats clean by not disturbing these little bundles of life we find swaying in the current.

Marine worms don’t get much attention because we can’t usually see them. But finding worms’ squiggly sand piles and seeing their bags of babies reminds me how much life exists down there below the ocean floor, and how connected it all is. Snorkeling coral reefs is grand, but I take time to love the worms, too.

To reach Susan Scott, go to www.susanscott.net and click on “Contact” at the top of her home page.