The crew will stage off the San Pedro harbor at 7:30 a.m. Thursday before heading out. The site was chosen for the presence of the USS Moody, which was split into two pieces and sunk as part of the 1933 movie “Hell Below,” a World War I submarine thriller from MGM starring Robert Montgomery and Walter Huston. “Since the local fishermen may not know about the wreck, it is a huge obstacle that catches ghost nets from time to time,” said Christina Wiegers, project manager for Healthy Seas. “The wreck is home to a few species of rockfish,” she added, “as they like rocky reef habitats and it provides a valuable nursery for them.”