A research ship is due to return from a voyage to the marine monument in the Northwestern Hawaiian Islands.

The Hiialakai is due to arrive at Pearl Harbor today after spending 30 days among the remote string of atolls that make up the Papahanaumokuakea Marine National Monument.

The scientists studied deep coral reef fish and new species of coral.

They also took samples to measure ocean acidification — which refers to the phenomenon affecting oceans as they absorb rising volumes of carbon dioxide emitted by humans.

Rising levels of carbon dioxide are making the oceans more acidic, which can harm corals and otherwise affect sea life.

The Hiialakai is a National Oceanic and Atmospheric Administration vessel.