The Role of Herbivory in Structuring Tropical Seagrass Ecosystem Service Delivery

Abstract

Seagrass meadows support key ecosystem services, via provision of food directly for herbivores, and indirectly to their predators. The importance of herbivores in seagrass meadows has been well-documented, but the links between food webs and ecosystem services in seagrass meadows have not previously been made explicit. Herbivores interact with ecosystem services – including carbon sequestration, cultural values, and coastal protection. Interactions can be positive or negative and depend on a range of factors including the herbivore identity and the grazing type and intensity. There can be unintended consequences from management actions based on a poor understanding of trade-offs that occur with complex seagrass-herbivore interactions. Tropical seagrass meadows support a diversity of grazers spanning the meso-, macro-, and megaherbivore scales. We present a conceptual model to describe how multiple ecosystem services are influenced by herbivore pressure in tropical seagrass meadows. Our model suggests that a balanced ecosystem, incorporating both seagrass and herbivore diversity, is likely to sustain the broadest range of ecosystem services. Our framework suggests the pathway to achieve desired ecosystem services outcomes requires knowledge on four key areas: (1) how size classes of herbivores interact to structure seagrass; (2) desired community and management values; (3) seagrass responses to top–down and bottom–up controls; (4) the pathway from intermediate to final ecosystem services and human benefits. We suggest research should be directed to these areas. Herbivory is a major structuring influence in tropical seagrass systems and needs to be considered for effective management of these critical habitats and their services.

Overfishing and the ecological impacts of extirpating large parrotfish from Caribbean coral reefs

“…This increased bite size may also result in the incidental removal of non‐target species, such as unpalatable macroalgae, that smaller fishes avoid, as the feeding morphology of large herbivores can physically constrain their ability to selectively target individual resources (Pollard and Cooke , Scott et al. ). In fact, many parrotfish species appear to be microphages that target cyanobacteria and other autotrophic microorganisms living on or within the algae and substrate they consume, suggesting the majority of macroalgae consumption by parrotfishes may be incidental (Clements et al.…”

Habitat complexity influences the structure of food webs in Great Barrier Reef seagrass meadows

“…Baseline size spectra can be used to assess the health and value of different types of meadows, providing a tool for management to understand how different meadows might provide for ecosystem services such as fisheries (Scott et al. ). Size spectra may also be indicative of the dynamic stability of food webs (Law et al.…”

“…Seagrass loss means a loss of a wide range of important ecosystem services, including food web support for endangered fauna (Scott et al. , Sievers et al. ), and a greater understanding of how seagrasses provide these services is required to manage impacts on seagrass (Unsworth et al.…”

Positive Ecological Interactions and the Success of Seagrass Restoration

“…Alternatively, seagrass can be directly grazed upon. Seagrass herbivory by macrograzers (i.e., fish) and megagrazers (i.e., turtles and dugongs) are important to maintaining ecosystem function and reproduction in balanced ecosystems (i.e., systems with predators, grazers, and seagrasses) (Tol et al, 2017;Scott et al, 2018). With the loss of predators and conservation of large herbivores without habitat consideration, it is suggested that seagrass ecosystem functions could be lost from uncontrolled rates of grazing (Burkholder et al, 2013;Christianen et al, 2014;Heithaus et al, 2014;Scott et al, 2018).…”