Herbivory effects on Thalassia testudinum leaf growth and nitrogen content

Zieman, Joseph C.; Iverson, Richard L.; Ogden, John C.

doi:10.3354/meps015151

Cited by 109 publications

(86 citation statements)

References 17 publications

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“…Leaf widths of fish grazed (4.9-5.4mm) and turtle grazed (5.0-5.9mm) patches in this study were within range of other studies on grazing (5.3-6.3mm, Zieman et al, 1984;5.6-6.3mm, Moran & Bjorndal, 2005;3.3-4.7mm, Williams, 1988;1.4-3.0mm, Fourqurean et al, 2010). These differences in leaf widths further emphasize the detrimental effects of intense grazing to seagrasses, which have less photosynthetic leaf tissue, storage of carbohydrates in their rhizomes, and narrower and shorter leaves when subjected to intense grazing.…”

Section: Discussionsupporting

confidence: 68%

“…Herbivores are important drivers of ecosystem dynamics (Heck & Valentine, 2007;Valentine & Duffy, 2006) and seagrass productivity (Valentine, Heck, Busby, & Webb, 1997;Zieman, Iverson, & Ogden, 1984), reducing canopy cover and freeing space for competitive interactions between macrophytes (Heck & Valentine, 2006). Grazing by herbivores is not uniform as they selectively feed in certain areas depending on abiotic and biotic factors.…”

mentioning

confidence: 99%

“…Based on this theory, decreased soluble carbohydrates may therefore serve as a predictor of herbivore abandonment of particular grazed areas over others. In addition, indices of shoot density, blade width and leaf growth are also used as early indications of chronic stress (Lal, Arthur, Marba, Lill, & Alcoverro, 2010;Lee & Dunton, 1997;Zieman, Iverson, & Ogden, 1984). Decreased food availability for herbivores in a patch may be the cue for grazing patch abandonment.…”

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confidence: 99%

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Morphological and physiological responses of seagrasses (Alismatales) to grazers (Testudines: Cheloniidae) and the role of these responses as grazing patch abandonment cues

Lacey

Collado‐Vides

Fourqurean

2014

RBT

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Green sea turtles, Chelonia mydas, are grazers influencing the distribution of seagrass within shallow coastal ecosystems, yet the drivers behind C. mydas patch use within seagrass beds are largely unknown. Current theories center on food quality (nutrient content) as the plant responds to grazing disturbances; however, no study has monitored these parameters in a natural setting without grazer manipulation. To determine the morphological and physiological responses potentially influencing seagrass recovery from grazing disturbances, seagrasses were monitored for one year under three different grazing scenarios (turtle grazed, fish grazed and ungrazed) in a tropical ecosystem in Akumal Bay, Quintana Roo, Mexico. Significantly less soluble carbohydrates and increased nitrogen and phosphorus content in Thalassia testudinum were indicative of the stresses placed on seagrasses during herbivory. To determine if these physiological responses were the drivers of the heterogeneous grazing behavior by C. mydas recorded in Akumal Bay, patches were mapped and monitored over a six-month interval. The abandoned patches had the lowest standing crop rather than leaf nutrient or rhizome soluble carbohydrate content. This suggests a modified Giving Up Density (GUD) behavior: the critical threshold where cost of continued grazing does not provide minimum nutrients, therefore, new patches must be utilized, explains resource abandonment and mechanism behind C. mydas grazing. This study is the first to apply GUD theory, often applied in terrestrial literature, to explain marine herbivore grazing behavior. Rev. Biol. Trop. 62 (4): 1535-1548. Epub 2014 December 01.

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Section: Discussionsupporting

confidence: 68%

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confidence: 99%

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confidence: 99%

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Morphological and physiological responses of seagrasses (Alismatales) to grazers (Testudines: Cheloniidae) and the role of these responses as grazing patch abandonment cues

Lacey

Collado‐Vides

Fourqurean

2014

RBT

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“…Was this exported out of the system? Studies on leaf-export rates of seagrasses with a leaf morphology resembling that of T. hemprichii (Thalassia testudinum, Enhalus acoroides, Cymodocea rotundata, Posidonia australis, and Zostera marina; Kirkman and Reid 1979;Zieman et al 1979;Josselyn et al 1983;Bach et al 1986) showed values of up to 30% of the produced leaf biomass. Stapel et al (1996b) showed that only ϳ10% of the nitrogen incorporated in seagrass leaves was exported from a coral island seagrass meadow.…”

Section: Discussionmentioning

confidence: 99%

“…Community production and respiration are in balance (Erftemeijer et al 1993b). Grazing by herbivores, potentially capable of removing a considerable amount of nutrients from the seagrass bed (Zieman et al 1984), plays no role of any significance in this system. Sea turtles and dugongs are practically extinct because of severe hunting pressure by the indigenous people (De Iongh 1996).…”

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confidence: 99%

Nitrogen (¹⁵N) retention in small Thalassia hemprichii seagrass plots in an offshore meadow in South Sulawesi, Indonesia

Stapel

Hemminga

Bogert

et al. 2001

Limnology & Oceanography

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Nitrogen retention was investigated during 240 d in 1 ϫ 1 m field plots of the tropical seagrass Thalassia hemprichii. Shoots were enriched with 15 N by brief exposure of the leaves to an elevated concentration of 15 N ammonium in the water column. Hereafter, the 15 N absorbed in the seagrass system declined rapidly. The decline was initially dominated by the loss of 15 N in detached leaf fragments. Of the lost leaf fragments, 19% were recovered within the boundaries of the experimental plots, and 25% were deposited outside these boundaries but inside the seagrass meadow. Of the remaining 56%, the fate could not be resolved, but export from the meadow is probably limited to ϳ10%. During the course of time, the 15 N half-life increased from 1 to ϳ2 months because of 15 N accumulation in compartments from which it was not easily exported (roots, rhizomes, and sedimentary detritus). The limited nitrogen retention in the seagrass plots is ascribed to the combined effects of a major allocation of nitrogen to leaf production, restricted nitrogen resorption from senescent leaves (28% of the gross N demand), and a dynamic environment facilitating detachment and export of leaf fragments from the experimental plots. At the scale of the whole meadow, however, nitrogen conservation via the detrital pathway could be of considerable significance. We found indications for a rather efficient reabsorption by the plant of nitrogen regenerated from seagrass leaf litter, with a meaningful role for the leaves, and postulate that increasing patch size may coincide with increasing nitrogen conservation in the system as a whole.Seagrasses are the only descendants of terrestrial angiosperms that have been able to invade the marine environment. The plants form extensive submarine meadows that can be found in oligotrophic and mesotrophic shallow marine waters all over the world (Den Hartog 1970). A comparison among different plant communities shows that the primary production of seagrass meadows ranks among the highest established, being in the range of tropical forest and swamps and marshes (Duarte and Chiscano 1999). The generally high productivity of seagrasses, which is logically paralleled by a high nutrient demand, often in nutrient-poor environments, has attracted attention since the expansion of seagrass research in the early 1970s. Nutrient-limited growth appears to be a quite common phenomenon in seagrass ecology, despite the capacity of seagrasses to exploit the nutrient reservoirs of both the sediment and the water column (Iizumi and

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Growth and flowering responses of eelgrass to simulated grazing and fecal addition by Brant Geese

et al. 2021

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Seagrasses provide a wide range of ecosystem services and are prioritized in conservation planning. Management of this dynamic community requires describing seagrass responses to repeated grazing by dependent herbivores. Using two experimental randomized block designs in Humboldt Bay, California, we tested responses of eelgrass (Zostera marina) to separate and combined effects of simulated Brant Goose (Branta bernicla) grazing (clipping to a uniform height) and fecal pellet addition, and then to medium (MED) and severe (SEV) intensities of simulated Brant flock visitation. In Experiment 1, clipping with fecal addition (FC) stimulated more clonal addition of shoots than controls or clipping and fecal addition alone (standardized β = 0.26 relative to control). The FC treatment also had the largest positive, delayed effect (β = 0.135) on density of flowering shoots. In Experiment 2, the MED intensity treatment had positive effects on shoot density (β = 0.149), rates of leaf extension (β = 0.16), and leaf productivity (β = 0.20). These MED treatment responses resulted in the highest measures of above-ground (β = 0.099) and below-ground (β = 0.32) biomass. Whole shoot (β MED = 0.33, β SEV = −0.36) and landscape (β MED = 0.34, β SEV = −0.23) levels of productivity for the MED treatment reflected the parabolic shape predicted by the compensatory regrowth hypothesis, likely because light and nutrient resources were available to the eelgrass and meristems that were not damaged. Meristem injury in the SEV treatment likely explained why productivity was low, but the high SEV resource levels allowed these plants to recover to control levels in approximately eight to 10 weeks after the last treatment applications. The MED level of shoot and landscape productivity would optimize low intertidal accessibility for Brant to the most nutritiously valuable leaves. Brant grazing and detrital pathways of carbon flow are likely linked with Brant-induced productivity contributing to the detrital pathway when Brant are present and after the birds leave the estuary. The effect of Brant grazing on eelgrass sexual reproduction may increase long-term resilience of estuarine ecosystems.

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Herbivory effects on Thalassia testudinum leaf growth and nitrogen content

Cited by 109 publications

References 17 publications

Morphological and physiological responses of seagrasses (Alismatales) to grazers (Testudines: Cheloniidae) and the role of these responses as grazing patch abandonment cues

Morphological and physiological responses of seagrasses (Alismatales) to grazers (Testudines: Cheloniidae) and the role of these responses as grazing patch abandonment cues

Nitrogen (¹⁵N) retention in small Thalassia hemprichii seagrass plots in an offshore meadow in South Sulawesi, Indonesia

Growth and flowering responses of eelgrass to simulated grazing and fecal addition by Brant Geese

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Herbivory effects on Thalassia testudinum leaf growth and nitrogen content

Cited by 109 publications

References 17 publications

Morphological and physiological responses of seagrasses (Alismatales) to grazers (Testudines: Cheloniidae) and the role of these responses as grazing patch abandonment cues

Morphological and physiological responses of seagrasses (Alismatales) to grazers (Testudines: Cheloniidae) and the role of these responses as grazing patch abandonment cues

Nitrogen (15N) retention in small Thalassia hemprichii seagrass plots in an offshore meadow in South Sulawesi, Indonesia

Growth and flowering responses of eelgrass to simulated grazing and fecal addition by Brant Geese

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Nitrogen (¹⁵N) retention in small Thalassia hemprichii seagrass plots in an offshore meadow in South Sulawesi, Indonesia