Patch dynamics and species shifts in seagrass communities under moderate and high grazing pressure by green sea turtles

Molina‐Hernández, Ana; Tussenbroek, Brigitta I. van

doi:10.3354/meps11068

Cited by 63 publications

(97 citation statements)

References 40 publications

(61 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Seagrass meadow characteristics such as shoot density, canopy height and above‐ground biomass are likely to be more variable among ungrazed areas than grazed areas, as green turtle grazing results in similar canopy morphometry across meadows in the Greater Caribbean region (e.g. Bjorndal, ; Hernández & van Tussenbroek, ; Williams, ). Given the strong relationship between NEP and above‐ground biomass (Figure a), high variability in NEP would be expected across ungrazed meadows (e.g.…”

Section: Discussionmentioning

confidence: 99%

Seagrass ecosystem metabolic carbon capture in response to green turtle grazing across Caribbean meadows

et al. 2019

View full text Add to dashboard Cite

1. Increasing green turtle abundance will lead to increased grazing within seagrass habitats-ecosystems that are important for carbon sequestration and storage.However, it is not well understood how carbon dynamics in these ecosystems respond to grazing and whether a response differs among meadows or locations.2. We measured seagrass ecosystem metabolism in grazed and ungrazed areas of Thalassia testudinum meadows with established green turtle foraging areas across the Greater Caribbean and Gulf of Mexico. We sampled meadows from five locations that differed in seagrass and environmental characteristics. Established meadows of the invasive seagrass Halophila stipulacea were also present at two of these locations, and we measured ecosystem metabolism in these meadows for comparison to grazed and ungrazed areas of the native T. testudinum.3. Across all individual sites, rates of net ecosystem production (NEP) ranged from 56% to 96% lower in grazed areas than ungrazed areas of T. testudinum meadows.Rates of NEP were also strongly, positively correlated with above-ground seagrass biomass across sites. While metabolic carbon capture rates were lower in grazed areas, heterotrophic respiration was not stimulated, and grazing therefore did not result in significant metabolic remineralization of carbon in these meadows. NEP in H. stipulacea meadows was similar to rates in T. testudinum meadows at all three sites, suggesting that metabolic carbon capture may remain similar in Caribbean meadows where this invasive seagrass is replacing native species. Synthesis.Our results show that there is a consistent response in metabolic carbon dynamics to green turtle grazing in T. testudinum meadows across the Greater Caribbean region. An increase in grazing will not likely stimulate remineralization of carbon as these important habitats are returned to a natural grazed state. K E Y W O R D Scarbon dynamics, grazing, green turtle, Halophila stipulacea, invasive, metabolism, plantherbivore interactions, Thalassia testudinum

show abstract

Section: Discussionmentioning

confidence: 99%

Seagrass ecosystem metabolic carbon capture in response to green turtle grazing across Caribbean meadows

et al. 2019

View full text Add to dashboard Cite

show abstract

“…In the Caribbean, green sea turtles typically consume large amounts of turtle grass (Thalassia testudinum, henceforth referred to as "native" seagrass). Grazing patches in Thalassia meadows are easily recognized, as turtles crop seagrass leaves in specific patches or zones that they maintain and revisit to stimulate the production of new, highly nutritious leaves (Hernandez & van Tussenbroek, 2014;Preen, 1995), comparable to "grazing lawns" in terrestrial systems. Turtle grazing further results in shorter leaves, lower shoot density, and lower below-ground biomass (Christianen et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Megaherbivores may impact expansion of invasive seagrass in the Caribbean

et al. 2018

View full text Add to dashboard Cite

Abstract1. Our knowledge of the functional role of large herbivores is rapidly expanding, and the impact of grazing on species coexistence and nonnative species expansion has been studied across ecosystems. However, experimental data on large grazer impacts on plant invasion in aquatic ecosystems are lacking.2. Since its introduction in 2002, the seagrass species Halophila stipulacea has rapidly expanded across the Eastern Caribbean, forming dense meadows in green turtle (Chelonia mydas)-foraging areas. We investigate the changes in seagrass species coexistence and the impacts of leaf grazing by green turtles on nonnative seagrass expansion in Lac Bay (Bonaire, Caribbean Netherlands).3. Green turtle grazing behaviour changed after the introduction of nonnative seagrass to Lac Bay in 2010. Field observations, together with time-lapse satellite images over the last four decades, showed initiation of new grazing patches (65 ha, an increase of 72%). The sharp border between grazed and ungrazed seagrass patches moved in the direction of shallower areas with native seagrass species that had previously been ungrazed. Green turtles deployed withFastloc-GPS transmitters confirmed high site fidelity to these newly cropped patches. In addition, cafeteria experiments indicated selective grazing by green turtles on native species. These native seagrass species had significantly higher nutritional values compared to the nonnative species. In parallel, exclosure experiments showed that nonnative seagrass expanded more rapidly in grazed canopies | INTRODUC TI ONLarge herbivores, whether aquatic or terrestrial, can have strong impacts on associated species and can be critical ecosystem engineers as they alter plant productivity, modify geomorphology, and influence nutrient cycling, habitat structure and plant coexistence (Bakker et al., 2016;Poore et al., 2012;Wood, Armstron, & Richards, 1967). Megaherbivores can impact plant species coexistence and species composition via multiple mechanisms. Preferential grazing on dominant plant species can promote species diversity by releasing competitors (Olff & Ritchie, 1998), or reduce diversity by selectively removing nondominant species (Hidding, Bakker, et al., 2010).Grazing can also precipitate species shift from long-lived, slow growing species, to faster growing pioneer species that are better adapted to grazing (Kelkar, Arthur, Marba, & Alcoverro, 2013;Knapp et al., 1999). Additionally, grazing on below-ground plant parts can enhance species diversity by creating regeneration niches through sediment disturbance (Hidding, Nolet, Boer, Vries, & Klaassen, 2010).The impact of herbivory on plant coexistence has been shown across diverse ecosystems, including examples from terrestrial and aquatic systems (Augustine & McNaughton, 1998;Bakker, Pagès, Arthur, & Alcoverro, 2015). This being the case, there is a potential for grazers to increase the success of invasive plants. Evidence of interactions between grazing and invasive plants go both ways.Nonnative species may come to dominate ...

show abstract

“…The drastic declines of large herbivores, like green turtles, manatees, and dugongs, caused by human overexploitation (Jackson 1997;Jackson 2001;Hughes et al 2004;Valentine & Duffy 2006) has contributed to the undervaluation of top-down controls in seagrass communities. In recent decades, conservation strategies have led to local increases in abundance of green turtles (Chelonia mydas), with noticeable impacts of turtle grazing on seagrass communities Kaladharan et al 2013;Kelkar et al 2013;Molina-Hernández & van Tussenbroek 2014). Herbivores, particularly large herbivores such as green turtles, can alter plant species composition and community structure (Lal et al 2010;Kelkar et al 2013;Molina-Hernández & van Tussenbroek 2014).…”

Section: Introductionmentioning

confidence: 99%

“…In recent decades, conservation strategies have led to local increases in abundance of green turtles (Chelonia mydas), with noticeable impacts of turtle grazing on seagrass communities Kaladharan et al 2013;Kelkar et al 2013;Molina-Hernández & van Tussenbroek 2014). Herbivores, particularly large herbivores such as green turtles, can alter plant species composition and community structure (Lal et al 2010;Kelkar et al 2013;Molina-Hernández & van Tussenbroek 2014).…”

Section: Introductionmentioning

confidence: 99%

“…In the Caribbean, climax seagrass communities are dominated by the robust latesuccessional species Thalassia testudinum (slower-growing), which is the preferred food source for green turtles (Bjorndal 1980;Thayer et al 1984;Molina-Hernández & van Tussenbroek 2014). Green turtles feeding on T. testudinum use a cultivation or rotational feeding strategy (Molina-Hernández & van Tussenbroek 2014), which is also used by roaming wild ungulates in terrestrial systems (Vavra & Ganskopp 1998;Bakker et al 2016). Green turtles create grazing patches within T. testudinum meadows which are easily recognized as they graze seagrass leaves in specific areas or patches that they maintain and revisit (Bjorndal 1980;Molina-Hernandez & van Tussenbroek, 2014).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Peer Review #2 of "Nutrient availability induces community shifts in seagrass meadows grazed by turtles (v0.1)"

2019

View full text Add to dashboard Cite

In the Caribbean, green turtles graze seagrass meadows dominated by Thalassia testudinum through rotational grazing, resulting in the creation of grazed and recovering (abandoned) patches surrounded by ungrazed seagrasses. We evaluated the seagrass community and its environment along a turtle grazing gradient; with the duration of (simulated) grazing as a proxy for the level of grazing pressure. The grazing levels consisted of Short-term (4 months clipping), Medium-term (8 months clipping), Long-term grazing (8 months of clipping in previously grazed areas), 8-months recovery of previously grazed patches, and ungrazed or unclipped patches as controls. We measured biomass and density of the seagrasses and rhizophytic algae, and changes in sediment parameters. Medium-and Long-term grazing promoted a shift in community species composition. At increasing grazing pressure, the total biomass of T. testudinum declined, whereas that of early-successional increased. Ammonium concentrations were highest in the patches of Medium-term (9.23 + 0.78 µM) and Long-term grazing levels (10.96 + 2.16 µM) and were lowest in the control areas (4.65 + 1.48 µM). T. testudinum is a late-successional species that maintains sediment nutrient concentrations at levels below the requirements of earlysuccessional species when dominant. When the abundance of this species declines due to grazing, these resources become available, likely driving a shift in community composition towards a higher abundance of early-successional species.

show abstract

Patch dynamics and species shifts in seagrass communities under moderate and high grazing pressure by green sea turtles

Cited by 63 publications

References 40 publications

Seagrass ecosystem metabolic carbon capture in response to green turtle grazing across Caribbean meadows

Seagrass ecosystem metabolic carbon capture in response to green turtle grazing across Caribbean meadows

Megaherbivores may impact expansion of invasive seagrass in the Caribbean

Peer Review #2 of "Nutrient availability induces community shifts in seagrass meadows grazed by turtles (v0.1)"

Contact Info

Product

Resources

About