Scientist have observed many types of tropical fish moving beyond their traditional ocean ranges into water that have historically been more temperate. These fish compete for food with native fish, consuming much from the kelp forest and beds of sea grass. The expansion of the ranges of tropical fish was most likely caused by: agriculture runoff that contributes to dead zones in the ocean agriculture runoff that contributes to dead zones in the ocean global droughts that raise the salt concentration of ocean waters global droughts that raise the salt concentration of ocean waters the rising temperatures of ocean waters the rising temperatures of ocean waters acid rain pollution that lowers the pH of ocean waters