Mariner Books, a division of Houghton Mifflin Harcourt, was established in 1997 as a publisher of fiction, non-fiction, and poetry in paperback. Mariner is also the publisher of the Harvest imprint backlist, formerly published by Harcourt Brace/Harcourt Brace Jovanovich.
Mariner Books is smaller than Houghton Mifflin Harcourt.
Mariner Books is a division of Houghton Mifflin Harcourt; that relationship implies it is part of something bigger. The algorithm may not know this relationship.