With over 120 film and television credits to her name, Dowse has steadily appeared on screen since 1989.
The actor was "peacefully taken off life support" nine days after a car crash, a family spokesperson said.
Seymour and Newton-John, who died on Monday at age 73, had been in each other's lives for over 40 years.
Mosley played helicopter pilot T.C. alongside Tom Selleck in the 1980s series.
Saldana, who took over the "Star Trek" role Nichols made famous, said the late actor "blazed a trail" for women of color.
"We had such a chemistry on the show," Discovery Channel castmate Jeremy McCaa said.
The actor was best known for his role as Sonny Corleone in "The Godfather."
She appeared in "Ray Donovan," "Dexter" and "ER" among scores of credits.
"I must be kind to myself and remember that nothing is permanent," the actor wrote on Mother's Day.
"She fought hard against her demons," her father said.