1. They study the sea animals in Antarctica.
2. They study all the sea animals in Antarctica.
3. They study sea animals in Antarctica.
4. They study some sea animals in Antarctica.
[Does #1 mean #2? Does #3 mean #4? What is the difference between 'the sea animals' and 'sea animals'?]
1 and 2 mean the same.
3 implies that they only study of the sea animals.
4 is different than the other three.