The Marshfield Council on Aging offers a lifelong learning course exploring the town's coastal shoreline.

MARSHFIELD -- When the Marshfield Council on Aging began offering a lifelong learning course exploring the town's coastal shoreline a few years ago, the senior center had tapped into an interest expressed by the seniors it serves.

On Wednesday, 28 people showed up for the first of six sessions in the "Coastal Explorations with Mass Audubon" course that will teach them about tides, ocean bay 'critters," estuaries, barrier beaches, mud flats and salt marshes.

One of the goals is to make people appreciate how critical the coastal environment is to their lives.

Doug Lowry and Jacqui Shuster, teacher naturalists for the Mass Audubon South Shore Sanctuaries, promised that as many as possible of the six sessions would be held outdoors, weather permitting.

The first class at Duxbury Beach found the students learning about how tides rise and fall in winter and summer, the effect of low pressure and high pressure on water movement, what makes for an incoming tide's velocity, how to use a compass to read a ocean chart and how oysters and other mollusks filter the water to benefit the environment.

"If a storm comes in at a particular strategic point in the tidal cycle, its impact is much greater," Lowry explained, using small stones gathered by the students to create an educational graph on the ground. Duxbury Beach is a barrier beach, protecting the town's shoreline from the Atlantic Ocean, and it has been severely damaged in recent years by large storms and a portion was rebuilt last year in a new configuration.

He also asked the group to consider the life of a small, shelled critter on an August day -- You'd dry out real fast unless you could close up," Lowry said, or move very quickly into the receding water.

The students also searched the tide line for remains of sea life they might find. Shuster carefully pulled apart and examined an owl ball or owl pellet, which contains material eaten and then regurgitated, by an owl. The soft, small brown ball was  found by a student on the tide along along Duxbury Beach's inner harbor. The inside was found to have tiny skeletal parts, skulls and bones, of small animals an owl likely ate.

The field trips will return to Duxbury Beach and also take the students to the South River. They will learn about salt tolerant plants, boring sponges, herons that actually fish and horshoe crabs that haven't changed much in the 445 million years they have been on the coast.

Future programs will include Steve French, South Shore Bird Club leader Sally Avery and others.