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Marine Ecology Progress Series

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MEPS 665:63-73 (2021)  -  DOI: https://doi.org/10.3354/meps13657

High rates of herbivory in remote northwest Australian seagrass meadows by rabbitfish and green turtles

Mathew A. Vanderklift1,*, Richard D. Pillans2, Marlee Hutton1, Lisa De Wever1, Gary A. Kendrick3, Andrea Zavala-Perez3, Adriana Vergés4, Ruby Garthwin4, Daniel Oades5, Phillip McCarthy5, Kevin George5, Trevor Sampi5, Dwayne George5, Chris Sampi5, Zac Edgar5, Kevin Dougal5, Azton Howard5

1CSIRO Oceans & Atmosphere, Indian Ocean Marine Research Centre, Crawley, 6009 Western Australia, Australia
2CSIRO Oceans & Atmosphere, Queensland Biosciences Precinct, St. Lucia, 4067 Queensland, Australia
3School of Biological Sciences and Oceans Institute, The University of Western Australia, Crawley, 6009 Western Australia, Australia
4School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, 2052 New South Wales, Australia
5Bardi Jawi Rangers, One Arm Point, 6725 Western Australia, Australia
*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 northwestern Australia. Rates of herbivory in some deployments of tethered seagrass were more than 1000 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 the 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 the nutrition of both species.


KEY WORDS: Siganus · Chelonia · Thalassia · Enhalus · Stable isotope · Tethering


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Cite this article as: Vanderklift MA, Pillans RD, Hutton M, De Wever L and others (2021) High rates of herbivory in remote northwest Australian seagrass meadows by rabbitfish and green turtles. Mar Ecol Prog Ser 665:63-73. https://doi.org/10.3354/meps13657

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