Herbivory Has a Major Influence on Structure and Condition of a Great Barrier Reef Subtropical Seagrass Meadow
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SPECIAL ISSUE: SEAGRASSES TRIBUTE TO SUSAN WILLIAMS
Herbivory Has a Major Influence on Structure and Condition of a Great Barrier Reef Subtropical Seagrass Meadow Abigail L. Scott 1,2
&
Paul H. York 1 & Michael A. Rasheed 1,2
Received: 20 April 2020 / Revised: 25 October 2020 / Accepted: 5 November 2020 # Coastal and Estuarine Research Federation 2020
Abstract Grazing by all members of an herbivore community can act to structure the ecosystems they feed on. The outcome of this grazing pressure on the plant community also depends on the interaction between different herbivore groups that are present. We carried out a three-month multi-level field exclusion experiment to understand how different groups of herbivores act both individually and interactively to structure a subtropical seagrass meadow in the Great Barrier Reef. Megaherbivore grazing had the largest impact on this seagrass meadow, significantly reducing aboveground biomass and shoot height, whereas there was no measurable impact of meso- or macroherbivores on seagrass metrics or epiphyte biomass. Megaherbivores here grazed broadly across the meadow instead of targeting grazing in one area. The principal seagrass-herbivore dynamic in this meadow is that megaherbivores are the main group modifying meadow structure, and other grazer groups that are present in lower numbers do not individually or interactively structure the meadow. We demonstrate that herbivory by large grazers can significantly modify seagrass meadow characteristics. This has important implications when designing and interpreting the results of monitoring programs that seek to conserve seagrass meadows, the ecosystem services that they provide and the herbivores that rely on them. Collectively, our results and those of similar previous studies emphasize there is unlikely to be one seagrass and herbivory paradigm. Instead, for individual meadows, their unique species interactions and differences in biotic and abiotic drivers of seagrass change are likely to have a strong influence on the dominant seagrass-herbivore dynamic. Keywords Plant-herbivore interactions . Mesograzer . Megagrazer . Green turtle . Dugong
Introduction Seagrass meadows are some of the most productive ecosystems in the marine environment, providing a food source for a range of herbivores as well as a suite of other ecosystem functions and services (Heck and Valentine 2006; Nordlund et al. 2016). Grazing by the herbivore community can structure seagrass meadows. The impact of this grazing depends on the numbers and types of herbivore present, and how these Communicated by Masahiro Nakaoka * Abigail L. Scott [email protected] 1
Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER), James Cook University, QLD, Cairns 4870, Australia
2
College of Science and Engineering, James Cook University, QLD, Cairns 4870, Australia
different herbivore groups interact (Scott et al. 2018). The community of herbivores that graze in seagrass meadows is diverse in terms of the species, body sizes and foraging str
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