An area with a large population of valuable ocean organisms is called a fishing ground.

Here's why:

* Fishing grounds are areas where fish and other marine life are abundant enough to support commercial fishing. They are often characterized by specific environmental conditions that support a thriving ecosystem.

* Other terms like "marine sanctuary", "protected area" or "biodiversity hotspot" could also apply depending on the specific context, but "fishing ground" is the most common term for an area valued for its abundance of resources.