Toby Edelstein, 9 years old, stood Sunday evening before a synagogue audience of about 350 to talk about his grandmother. The details were few, but they were enough.

Grandma, Aviva Rohloff Zylberberg, was a child herself during the Holocaust, that cataclysm of cataclysms in the blood-soaked 20th century. A Jew in Germany, she survived by passing as a Christian. Other young people — some in their 30s but most in their teens — also rose at the Park Avenue Synagogue, on East 87th Street, to recount in a few unadorned sentences how a grandmother or a grandfather eluded the Nazis’ industrialized slaughter of Europe’s Jews.

Cara Levine told of Anne and Saul Celnik, who hid in Warsaw after escaping from that city’s ghetto. Jennifer and Matt Balaban spoke of Irene Anshelewitz Schwadron, who endured through concentration camps and a death march. “Our two great-aunts were killed,” Matt Balaban said, “but the bullets somehow missed our grandmother.” Michael Silverstone talked about Henry Vogelstein, who fled Nazi Germany in 1939, emigrated to the United States and returned to Germany as an American combat soldier.

If an event may be said to possess a commodity, then, by definition, memory is the principal one for Holocaust Remembrance Day. But it is a perishable commodity. Preserving it requires work.

The day was observed in various ways around the city. As usual, the largest event was a ceremony at Temple Emanuel. At the Jewish Community Center in Manhattan, on the Upper West Side, there was a daylong recitation of names of the dead. In Lower Manhattan, some survivors went to the Museum of Jewish Heritage — A Living Memorial to the Holocaust, to relate their experiences to visiting schoolchildren.

More and more, though, survivors are not the principal bearers of their own stories. That responsibility is falling with greater urgency to their children and, as the Park Avenue Synagogue ceremony underscored, to their grandchildren. The war, after all, ended 65 years ago. Holocaust survivors are not getting any younger. Worse, one by one they are not getting any older.

“This has long been considered one of the looming events in Holocaust education: What are we going to do when the last survivor passes,” said David G. Marwell, director of the heritage museum. “Survivors are an irreplaceable resource. Anyone who says ‘You’ll be able to do the same kind of education’ is wrong, I think.”

Relegating the Nazis’ crimes solely to textbooks is not enough, Mr. Marwell said: “We rely increasingly on the second generation to tell their parents’ stories, so that there is still the human factor.”

A shift of this sort is never sudden; the torch-passing has been under way for a while. And it isn’t as if the generation of survivors has disappeared.

Selfhelp Community Services, a nonprofit organization that has long assisted sufferers of Nazi persecution, puts the number in the five boroughs at about 33,000, with two-thirds of them living in Brooklyn, many below the poverty line. In 15 years, Selfhelp says, that number is expected to be cut in half. Even so, that would leave about 16,500 survivors.

“It’s important to remember those who are still alive,” said Elihu Kover, the organization’s vice president for Nazi Victims Services.

But the emphasis on a new generation is inexorable. That “transfer of memory” was behind Park Avenue Synagogue’s reliance on grandchildren, said Menachem Z. Rosensaft, a lawyer, who organized the program with a cantor at the synagogue, Elana Rozenfeld.

Interlaced with the stories of ordeal and endurance were songs in Yiddish, written for the most part during the Holocaust. They drew attention to “the inner and spiritual strengths required to survive,” Mr. Rosensaft said. “That’s a core ingredient of the human condition. Focusing on it doesn’t get old.”

Cantor Rozenfeld movingly sang tunes like “Yisrolik,” about a tough yet caring boy of that name in the Vilna Ghetto, and “S’Brent” (“It Is Burning”), written in Poland in 1938. “Ugly winds are blowing,” it warned prophetically.

One song written after the war was a sad, sweet number called “Mayn Shvester Chaye” (“My Sister Chaye”). This was a tribute by a Yiddish poet, Binem Heller, to his sister, who raised him in their house “with tumbledown steps.” Chaye, with the green eyes. Chaye, with the black braids. Chaye, who died in the Treblinka extermination camp, not quite 10 years old.