Marine Isopod (Pentidotea) Feeding Preferences for Healthy and Wasting Eelgrass (Zostera marina)

Abstract

Despite increasing concerns over infectious wasting diseases among marine macroalga and plants, little is known about preferential herbivory patterns in indicator marine invertebrates like Pentidotea isopods in the face of reduced healthy eelgrass thalli. This study tested whether two marine isopod species, Pentidotea wosnesenskii and Pentidotea montereyensis, prefer to consume healthy vs. wasted eelgrass blades. Individuals from each species were experimentally subjected to feeding trials comparing their consumption of healthy vs. wasted blades. Photographic analysis of blade surface areas pre- and post-feeding were used to quantify the amount consumed by each isopod. When given an option between healthy and wasted blades, both P. wosnesenskii and P. montereyensis consumed significantly more healthy eelgrass surface area than wasted eelgrass (t = -2.69, p = 0.01; t = -2.69, p = 0.001 respectively). These findings support the hypothesis that healthy eelgrass blades are a crucial and preferred food source for marine herbivores over wasted blades, as seen in species within the Pentidotea genus. This pattern of preferential feeding has important disease dynamics and competition implications as Eelgrass Wasting continues to infect new blades in the San Juan Island region.