The Ross Sea is the largest continental shelf ecosystem in the Southern Ocean. This means most of the ecosystem is situated above the relatively shallow continental shelf. The Ross Sea is on roughly 5-600m deep, shallow compared to the 2-3000 meters deep the Southern Ocean surrounding it. Because of this more mixture between different layers of water can take place bringing nutrients from the deeper parts to the surface where they can be used by phytoplankton and be part of the start of the food chain. Even though the Ross Sea only makes up for 2% of the total Southern Ocean, 28% of the total primary production of the Southern Ocean takes place in it. This high primary production forms a solid base for a, for Polar regions, unusual rich food web.
Most of this food web is connected to sea ice. This far south sea ice is plentifully available. Even late in the season, there is still a lot of it around. But there is also always open water possible, which is a necessity for the marine mammals like seals and whales. They need open water to surface to breath. Strong katabatic winds coming from the Ross Ice Shelf (not to be mistaken for the continental shelf which is something completely different) push the ice away from the ice shelf creating a polynya for most of the year. Because of this marine mammal like Ross Sea Orca and Ross Seals can stay in the area year round. And being the southernmost sea in the world, the effects of climate change are (yet) less pronounced. It is likely that the Ross Sea might turn out into a refuge for Antarctic species who are driven out of their normal areas by the changing climate. For a while at least, if we continue behaving like we do now, the Ross Sea will change as well of course.
All these factors make the Ross Sea an unusual rich ecosystem and well worth protecting.