Decadal Monitoring in Bermuda Shows a Widespread Loss of Seagrasses Attributable to Overgrazing by the Green Sea Turtle Chelonia mydas

Recovery of a large herbivore changes regulation of seagrass productivity in a naturally grazed Caribbean ecosystem

“…Our results emphasize the need for caution when interpreting seagrass response to grazing based primarily on measures of mass growth or blade morphology (e.g., Hernández and van Tussenbroek 2014, Fourqurean et al 2019). Use of P:B and measures of in situ grazing intensity, in addition to mass growth, are critical to understanding effects of green turtle grazing as meadows are returned to a natural grazed state.…”

“…3d) observed at our study site provide compelling evidence that T. testudinum coevolved with green turtles under a consistent grazing regime and can sustain increases in grazing pressure by recovering green turtle populations. Thalassia testudinum in shallow habitats has been shown to exhibit decreased blade width, aboveground biomass, and shoot density under consistent grazing pressure by green turtles (Williams 1988, Moran and Bjorndal 2005, Fourqurean et al 2010, Hernández and van Tussenbroek 2014, Holzer and McGlathery 2016, Fourqurean et al 2019). However, these responses may not be consistent across all seagrass meadows, particularly over gradients of depth and grazing intensity as demonstrated by our study (Tables 2, 3).…”

“…However, populations of green turtles are now recovering in many areas as a result of long‐term conservation efforts (Chaloupka et al 2008, Weber et al 2014, Mazaris et al 2017), offering a unique opportunity to understand the ecological role of these large herbivores and how seagrass ecosystems once functioned under a consistent grazing regime. Green turtle recovery and the return of many seagrass meadows to a natural grazed state have raised concerns that ecosystem services provided by ungrazed seagrasses may be lost (Heithaus et al 2014, Atwood et al 2015, Maxwell et al 2017) and that meadows may become overgrazed (Fourqurean et al 2010, 2019, Christianen et al 2014). A historical perspective and an understanding of how green turtle grazing affects the productivity of naturally grazed ecosystems are necessary to evaluate the potential impacts of the current green turtle recovery while avoiding the “shifting‐baseline syndrome,” the use of inappropriate baselines to assess population change (Pauly 1995, Pitcher 2001).…”

Habitat Partitioning in the Marine Sector of Karst Subterranean Estuaries and Bermuda's Marine Caves: Benthic Foraminiferal Evidence

“…Colored ellipses correspond to 95% confidence intervals around the mean values for selected groups. The values of δ 13 C org and the C:N ratio of other organic carbon pools are compiled from the literature (Lamb et al, 2006;Kennedy et al, 2010;Fourqurean et al, 2019). openings (i.e., exits) to the forest landscape is clearly impacting organic matter delivery to the benthos.…”

Effects of Epiphytes and Depth on Seagrass Spectral Profiles: Case Study of Gulf St. Vincent, South Australia

“…Seagrasses are underwater angiosperms (flowering plants) that tend to form dense beds in shallow, subtidal marine and estuarine benthic seafloors that could be optically clear [1,2,3]. The development and maintained existence of these seagrass beds as a natural resource helps create a substratum and provide shelter, and food sources for epiphytic algae, mollusks, invertebrates, fishes, and sea turtles [4,5,6,7,8]. This, in turn, also allows for the trapping and stabilization of sediments, which helps in maintaining water clarity [1,9,10,11,12].…”