Interaction between schools of fish and mysids

Summary A long-term daily census of 20 small patch reefs along the backreef of Tague Bay barrier reef, U.S. Virgin Islands, established that recently recruited postlarval French grunts, Haemulon flavolineatum, form mixed schools with at least two species of mysids (genus Mysidium). The formation of these taxonomically unrelated animals into socially interacting groups probably occurs because of the striking resemblance of postlarval grunts to mysids. Over a period of 5 d and as the postlarval grunts grow, these mixed associations break down, only to reform every 14–15 d as new postlarval grunts periodically recruit from the plankton. The fleeting but persistent formation of these mixedspecies schools is believed to initially provide protection to the grunts and, as the grunts grow, limited protection to the mysids. In additions, the grunts benefit trophically from the associations because they prey on the mysids.