Captain Caveman and the Teen Angels (1980)

S1E1 The Scarifying Seaweed Secret

Ms. Snowden stands to inherit a vast fortune, but there's a catch—she must remain on the island, or her relatives will claim it instead. When her relatives begin vanishing under strange circumstances linked to a mysterious sea creature, Captain Caveman and the Teen Angels are summoned to uncover the truth behind the disappearances and the sinister seaweed secret lurking in the waters. They must race against time to solve the mystery and protect Ms. Snowden's inheritance.