What does Nim's father research in the 2008 adventure film "Nim's Island"?

"Nim's Island" is a 2008 adventure film written and directed by Jennifer Flackett and Mark Levin, and based on the children's story of the same name by Wendy Orr. A young girl alone on a remote island seeks help from an agoraphobic San Franciscan author (Jodie Foster). While the author attempts to overcome her agoraphobia to search for her, Nim tries to overcome her fear of losing her father. It stars Abigail Breslin, Jodie Foster, and Gerard Butler, and was released on 4 April 2008 by 20th Century Fox. The film received mixed reviews from critics and earned $100.1 million on a $37 million budget.

11-year-old Nim (Abigail Breslin) lives with her widower marine biologist father Jack Rusoe (Gerard Butler) on a South Pacific island. Jack takes a boat out for a two-day scientific mission to find Protozoa nim, a new species of plankton he has named after his daughter. He suffers a shipwreck in a cyclone and cannot return on the planned day, nor communicate with Nim.

The next day, Nim starts to cry, reasoning that her ever-successful father would be back by then if he were still alive. Fortunately, Jack reaches the island windsurfing on a makeshift catamaran and all ends well.