Role of sea urchin Lytechinus variegatus grazing in regulating subtropical turtlegrass Thalassia testudinum meadows in the Florida Keys (USA)

Valentine, John F.; Heck, Kenneth L.; Kirsch, Kevin D.; Webb, D. P.

doi:10.3354/meps200213

Cited by 49 publications

(25 citation statements)

References 8 publications

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“…Heck & Valentine (1995) predicted that season of initiation would be a significant factor in the effect of sea urchin grazing in the northeastern Gulf of Mexico. Both of these studies were based on shorter trials (3 to 4 mo) and in areas with greater temperature fluctuations than our study (Heck & Valentine 1995, Valentine et al 2000.…”

Section: Effects Of Season When Clipping Was Initiatedmentioning

confidence: 80%

“…On the x-axis, monthly tick marks represent the first day of each month The long duration of the experiment may have been responsible for the lack of importance of the season when clipping was initiated. Effects of sea urchin grazing on Thalassia testudinum productivity in the Florida Keys were significantly different when clipping was initiated in spring or summer (Valentine et al 2000). Heck & Valentine (1995) predicted that season of initiation would be a significant factor in the effect of sea urchin grazing in the northeastern Gulf of Mexico.…”

Section: Effects Of Season When Clipping Was Initiatedmentioning

confidence: 99%

“…Some studies report that grazing increases productivity in T. testudinum. Aboveground primary production increased in response to grazing by the sea urchin Lytechinus variegatus in the northeastern Gulf of Mexico and during the summer in the Florida Keys (Valentine et al 1997(Valentine et al , 2000. The former increase in productivity was a result of a significant increase in shoot density in response to grazing, which is opposite to both the trend in our study for a decrease in shoot density and the significant decrease in shoot density in T. testudinum grazed by L. variegatus during winter in Biscayne Bay, Florida (Maciá 2000).…”

Section: Effects Of Grazing On Structure and Productivity In Thalassimentioning

confidence: 99%

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Simulated green turtle grazing affects structure and productivity of seagrass pastures

Moran¹,

Bjorndal

2005

Mar. Ecol. Prog. Ser.

120

118

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The seagrass Thalassia testudinum evolved under much greater grazing pressure than exists today because overexploitation by humans caused the severe decline of green turtles Chelonia mydas, the major seagrass herbivore in the Caribbean. Understanding the effects of grazing on the structure and function of seagrass ecosystems is critical to evaluating how ecosystem processes have changed since the major herbivore was essentially removed from modern Caribbean seagrass systems. We evaluated effects of grazing on the structure and productivity of T. testudinum pastures by simulating green turtle grazing in 3 × 3 m plots for 16 mo in the central Bahamas and comparing these clipped plots to adjacent control (unclipped) plots. Simulated grazing affected the physical structure of T. testudinum plots, resulting in a system with reduced structural complexity. Simulated grazing resulted in compensatory growth in T. testudinum. Clipped plots maintained levels of growth comparable to unclipped plots over the 16 mo clipping trial, and specific mass growth was significantly elevated in clipped plots, even without simulating the nutrient return from green turtle feces and urine. The green turtle grazing pattern of re-cropping T. testudinum plots is sustainable for long periodsat least 16 mo. We estimated a range of carrying capacities of T. testudinum for green turtles of 1567 to 3748 kg turtle ha -1. Our study provides a foundation for reconstruction models and restoration plans for Caribbean seagrass ecosystems.

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Section: Effects Of Season When Clipping Was Initiatedmentioning

confidence: 80%

Section: Effects Of Season When Clipping Was Initiatedmentioning

confidence: 99%

Section: Effects Of Grazing On Structure and Productivity In Thalassimentioning

confidence: 99%

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Simulated green turtle grazing affects structure and productivity of seagrass pastures

Moran¹,

Bjorndal

2005

Mar. Ecol. Prog. Ser.

120

118

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“…This partial refuge from consumption may allow seagrasses to quickly overcome grazer-induced damage to aboveground tissues (cf. Valentine et al 1997Valentine et al , 2000. It is noteworthy, however, that when meristems are exposed, grazers can dramatically reduce seagrass density and biomass (Maciá & Lirman 1999, Rose et al 1999.…”

Section: Introductionmentioning

confidence: 99%

Parrotfish grazing on turtlegrass Thalassia testudinum: evidence for the importance of seagrass consumption in food web dynamics of the Florida Keys National Marine Sanctuary

Kirsch¹,

Valentine

Heck³

2002

Mar. Ecol. Prog. Ser.

Self Cite

111

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The widespread occurrence and persistence of modern day seagrass habitats has led many to hypothesize that grazing on seagrasses is minimal. On a global scale this may well be true as the numbers of large vertebrate herbivores (e.g. sea turtles, manatees and dugongs) and waterfowl, grazers that can greatly alter seagrass density, have been dramatically reduced in coastal ecosystems. Nonetheless, numerous observations indicate that smaller herbivores (e.g. the bucktooth parrotfish Sparisoma radians), grazers that may not be able to reduce seagrass density substantially, still commonly feed on seagrasses in the subtropical and tropical western Atlantic Ocean. These observations led us to quantify the role that seagrass herbivory plays in modern-day seagrass food webs. In the first phase of this study, digitally scanned seagrass leaves were clipped to ropes and placed at 3 sites in Hawk Channel, in the northern Florida Keys (USA). Areal loss from the tethered leaves provided a daily estimate of seagrass grazing rates. These losses, coupled with local estimates of net aboveground primary production, allowed us to determine the proportion of seagrass production consumed at our study sites during 4 separate seasons. We found that seagrass grazing varied greatly both spatially and seasonally at our sites but, on average, grazers consumed virtually all of the aboveground production at 2 of the 3 sites. When experiments were repeated in the summer of a second year at 6 sites, seagrass grazing again varied greatly among sites, but at 3 of the sites most of the daily production of seagrass shoots was consumed by small herbivorous fishes. These results suggest that while it is undoubtedly true that modern day grazing by mammals, turtles and waterfowl on seagrass is reduced, small vertebrate grazers consume substantial amounts of seagrass production in the northern Florida Keys.

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“…In high nutrient environments, macroalgal blooms increase the sensitivity of seagrasses to grazing as light availability affects carbohydrate storage in rhizomes and therefore the energy available to compensate for grazing disturbances (Macia 2000, Valentine et al 2000 or higher summer productivity (Lee & Dunton 1997). Studies considering herbivores in conjunction with eutrophication are of particular importance as coastal ecosystems worldwide are increasingly impacted by anthropogenic disturbances (Waycott et al 2009) and interactions of grazers with nutrient-replete systems becomes more common.…”

Section: Introductionmentioning

confidence: 99%

Herbivore and Nutrient Impact on Primary Producer Assemblages in a Tropical Marine Environment

Lacey¹

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Globally, human populations are increasing and coastal ecosystems are becoming increasingly impacted by anthropogenic stressors. As eutrophication and exploitation of coastal resources increases, primary producer response to these drivers becomes a key indicator of ecosystem stability. Despite the importance of monitoring primary producers such as seagrasses and macroalgae, detailed studies on the response of these benthic habitat components to drivers remain relatively sparse.Utilizing a multi-faceted examination of turtle-seagrass and sea urchinmacroalgae consumer and nutrient dynamics, I elucidate the impact of these drivers in Akumal, Quintana Roo, Mexico. In Yal Ku Lagoon, macroalgae bioindicators signified high nutrient availability, which is important for further studies, but did not consistently follow published trends reflecting decreased δ 15 N content with distance from suspected source. In Akumal Bay, eutrophication and grazing by turtles and fishes combine to structure patches within the seagrass beds. Grazed seagrass patches had higher structural complexity and productivity than patches continually grazed by turtles and fishes.v Results from this study indicate that patch abandonment may follow giving-up density theory, the first to be recorded in the marine environment. As Diadema antillarum populations recover after their massive mortality thirty years ago, the role these echinoids will have in reducing macroalgae cover and altering ecosystem state remains to be clear.Although Diadema antillarum densities within the coral reef ecosystem were comparable to other regions within the Caribbean, the echinoid population in Akumal Bay was an insufficient driver to prevent dominance of a turf-algal-sediment (TAS) state. After a four year study, declining coral cover coupled with increased algal cover suggests that the TAS-dominated state is likely to persist over time despite echinoid recovery. Studies on macroalgal diversity and nutrients within this same region of echinoids indicated diversity and nutrient content of macroalgae increased, which may further increase the persistence of the algal-dominated state.This study provides valuable insight into the variable effects of herbivores and nutrients on primary producers within a tropical coastal ecosystem. Results from this work challenge many of the currently accepted theories on primary producer response to nutrients and herbivory while providing a framework for further studies into these dynamics.vi Significant differences between winter and summer ungrazed samples were assessed with a student's t-test. Significant differences between summer ungrazed and turtle grazed were assessed with student's t-test (t-test) or Mann-Whitney t-test (M-W), depending on normality of data from the small sample size. Samples sizes are summer, winter: ungrazed (4, 11), fish grazed (0, 0) and turtle grazed (0, 4An additional driver is through herbivore grazing disturbance. In the absence of herbivory, areas experiencing high nutrient loads would be expected to shif...

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Role of sea urchin Lytechinus variegatus grazing in regulating subtropical turtlegrass Thalassia testudinum meadows in the Florida Keys (USA)

Cited by 49 publications

References 8 publications

Simulated green turtle grazing affects structure and productivity of seagrass pastures

Simulated green turtle grazing affects structure and productivity of seagrass pastures

Parrotfish grazing on turtlegrass Thalassia testudinum: evidence for the importance of seagrass consumption in food web dynamics of the Florida Keys National Marine Sanctuary

Herbivore and Nutrient Impact on Primary Producer Assemblages in a Tropical Marine Environment

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