Every summer, my dad teaches a science class about sea turtles in the atlantic ocean.

Every summer, my dad teaches a science class about Sea Turtles in the Atlantic Ocean

Explanation:

The word every should be capitalized because it is the first word in the sentence and the first word is always capitalized.

Dad should not be capitalized as it comes after a possessive pronoun being my.

Sea Turtles as well as the Atlantic Ocean should be capitalized as you are referring to them directly.