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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps13657

High rates of herbivory in remote north-west Australian seagrass meadows by herbivorous rabbitfish and green turtles

Mathew A Vanderklift*, Richard D Pillans, Marlee Hutton, Lisa De Wever, Gary A Kendrick, Andrea Zavala-Perez, Adriana Verg├ęs, Ruby Garthwin, Daniel Oades, Phillip McCarthy, Kevin George, Trevor Sampi, Dwayne George, Chris Sampi, Zac Edgar, Kevin Dougal, Azton Howard

*Corresponding author:

ABSTRACT: Herbivory is a key ecological process that often determines the composition and abundance of plants. Estimates of herbivory in seagrass meadows are typically lower than those in other vegetated coastal ecosystems, but herbivory can be intense when large herbivorous vertebrates are abundant. We surveyed rates of herbivory on 2 species of tropical seagrasses (Thalassia hemprichii and Enhalus acoroides), the abundance of herbivorous vertebrates, and the diet of 2 abundant herbivorous vertebrates (the green turtle Chelonia mydas and the rabbitfish Siganus lineatus) in lagoons adjacent to remote islands off north-western Australia. Rates of herbivory in some deployments of tethered seagrass were more than a thousand times higher than rates of production and were among the highest recorded. Consumption exceeded production in half the deployments (9 of 18). Remote underwater video revealed that S. lineatus was the most abundant herbivore. Stomachs of S. lineatus contained mostly seagrass, and models based on stable isotopes indicated that seagrass was the primary source of nutrition. Stomach contents of C. mydas were more variable, containing seagrass and macroalgae (although sample size was low), but models based on stable isotopes indicated that seagrass was likely the primary source of nutrition. Multiple lines of evidence suggest that the high rates of herbivory on the seagrasses T. hemprichii and E. acoroides are mainly due to direct consumption by the abundant S. lineatus, and perhaps also C. mydas. Seagrass is the primary contributor to nutrition of both species.