Grazer Diversity, Functional Redundancy, and Productivity in Seagrass Beds: An Experimental Test

Duffy, J. Emmett; Macdonald, Kenneth S.; Rhode, Jennifer M.; Parker, John D.

doi:10.2307/2679926

Cited by 30 publications

(40 citation statements)

References 38 publications

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“…Fish predation, migration and space limitations contribute to limit the amount of small grazers Norderhaug et al 2005. All these factors and a possible high functional redundancy (see Duffy et al 2001) among the kelpassociated flora and fauna increase the persistence and stability of the kelp ecosystem.…”

Section: System Stability and Shifts Between Kelp Forests And Sea Urcmentioning

confidence: 99%

Sea urchin grazing and kelp re-vegetation in the NE Atlantic

Norderhaug

Christie

2009

Marine Biology Research

125

114

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Small-scale grazing events where sea urchins have grazed kelp forests to barren grounds have been reported all along the NE Atlantic coast. One large-scale event has been reported where kelp forests along the Norwegian and Russian coast were grazed by sea urchins during the early 1970s. The barren ground area has persisted since. Different theories to explain the grazing event have been presented. This paper seeks to sort and summarize earlier published papers and national reports and to critically examine the most important theories presented to explain the grazing event. The conclusion is that the reason for the event is unknown and it is too late to find causes 40 years after it took place. However, new data and new geographical analysis tools provide insight into the extent and consequences of this dramatic event, and show re-vegetation of kelp forests in the southernmost area. Emphasis in future studies should be given to understand the reasons for shifts between the two ecosystem states and take advantage of the ongoing shift. Such basic ecological knowledge could provide an important basis for better understanding the system and further, to understand the extent to which other observed largescale changes (e.g. climatic changes, fish stock reductions) affect kelp forestÁsea urchin interaction.

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Section: System Stability and Shifts Between Kelp Forests And Sea Urcmentioning

confidence: 99%

Sea urchin grazing and kelp re-vegetation in the NE Atlantic

Norderhaug

Christie

2009

Marine Biology Research

125

114

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“…Thus, it has been suggested (7) that top-down control via trophic cascades may be an idiosyncratic attribute of simple, aquatic systems that are not buffered from run-away consumer effects by multiple predators and͞or omnivory and are characterized by weedy, poorly defended primary producers. Recent evidence from temperate (8) and tropical (9) seagrass systems, however, suggests that communities dominated by higher, more heavily defended plants, are also susceptible to cascading consumer effects.…”

mentioning

confidence: 99%

A trophic cascade regulates salt marsh primary production

Silliman

Bertness

2002

Proc. Natl. Acad. Sci. U.S.A.

436

307

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Nutrient supply is widely thought to regulate primary production of many ecosystems including salt marshes. However, experimental manipulation of the dominant marsh grazer (the periwinkle, Littoraria irrorata) and its consumers (e.g., blue crabs, Callinectes sapidus, terrapins, Malaclemys terrapin) demonstrates plant biomass and production are largely controlled by grazers and their predators. Periwinkle grazing can convert one of the most productive grasslands in the world into a barren mudflat within 8 months. Marine predators regulate the abundance of this plant-grazing snail. Thus, top-down control of grazer density is a key regulatory determinant of marsh grass growth. The discovery of this simple trophic cascade implies that over-harvesting of snail predators (e.g., blue crabs) may be an important factor contributing to the massive die-off (tens of km 2 ) of salt marshes across the southeastern United States. In addition, our results contribute to a growing body of evidence indicating widespread, predator regulation of marine macrophyte production via trophic cascades (kelps, seagrasses, intertidal algae).

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“…Because seagrasses, macroalgae, and epiphytes differ in their biochemical composition and proportion of structural components, the food preferences of grazing invertebrates may, affect the quantity and lability of organic carbon delivered to the sediments and thus, the quantity and quality of sediment organic carbon (Canuel et al 2007). Such compositional changes need not be dramatic to affect ecosystem properties: small shifts in grazer richness and species composition can significantly affect plant and algal biomass and influence total sediment organic carbon (e.g., Duffy et al 2003;Canuel et al 2007).Because sediment microbial communities are important mediators of carbon and other elemental cycles in coastal environments (Boschker et al 1999;Holmer et al 2001Holmer et al , 2004, changes in aboveground trophic structure and diversity that alter OM delivery to seagrass sediments may have important consequences for carbon cycling and storage. In terrestrial soils, by analogy, microbial community composition and activity are sensitive to changes in aboveground community structure (Setälä et al 1998;Wardle et al 2005).…”

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confidence: 99%

Top‐down and bottom‐up controls on sediment organic matter composition in an experimental seagrass ecosystem

Spivak¹,

Canuel²,

Duffy³

et al. 2007

Limnology & Oceanography

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We tested the singular and interactive effects of resource availability (light) and community composition (food chain length and herbivore species richness) on eelgrass (Zostera marina) ecosystem properties and functioning with an experimental mesocosm system. Food chain length was manipulated through the presence or absence of blue crab (Callinectes sapidus) predators, whereas grazer species richness varied across three levels (zero, two, or four crustacean species). We found important and interacting effects of bottom-up and top-down forcings on sediment organic matter (SOM) composition. Light increased eelgrass and algal biomass and sediment organic carbon and nitrogen content. Increasing grazer diversity generally decreased algal biomass and ecosystem production but interacted with food chain length (i.e., presence of predatory crabs) and light. Predators generally increased algal biomass and ecosystem production through a trophic cascade, which was stronger at high grazer diversity and under ambient light. SOM composition, determined with fatty acid (FA) biomarkers, was sensitive to all manipulated variables. Increasing grazer species richness often decreased the contributions of FAs derived from plant and algal sources, whereas increasing light had the opposite effect. Food chain length was generally a less important determinant of SOM composition than light, although predators did increase FAs representative of heterotrophic bacteria. Overall, resource availability and epibenthic community composition strongly influenced organic matter cycling, SOM composition, and the bacterial community in seagrass-bed sediments.Coastal ecosystems are often affected by multiple disturbances that alter both resource availability and community composition simultaneously. In the Chesapeake Bay, for example, seagrass beds are affected by commercial harvesting of the blue crab, Callinectes sapidus (Stephan et al. 2000), and by suspended sediment and nutrient loading that can lead to reduced light availability (Kemp et al. 2004). Changes in abundance of important predators, such as the striped bass or the blue crab, may precipitate changes in the biomass of lower trophic levels (Hairston et al. 1960;Strong 1992;Pace et al. 1999). These shifting trophic interactions, along with reduced light availability, can affect primary producer abundance and productivity (Heck et al. 2000;Hughes et al. 2004;Borer et al. 2006) and, in turn, sediment organic matter (SOM) content (Canuel et al. 2007). Consequently, cascading changes in animal and plant biomass may alter the rates and pathways by which organic matter (OM) is cycled in an ecosystem (Schindler et al. 1997;Dangles and Malmqvist 2004).Predicting how changing trophic structure affects OM cycling is complicated by the fact that predators induce shifts not only in prey biomass but also in prey community structure. In seagrass systems, for example, grazing invertebrates can consume epiphytic algae, macroalgae, benthic microalgae, and vascular plants (Valentine and Duffy 2006)...

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Grazer Diversity, Functional Redundancy, and Productivity in Seagrass Beds: An Experimental Test

Cited by 30 publications

References 38 publications

Sea urchin grazing and kelp re-vegetation in the NE Atlantic

Sea urchin grazing and kelp re-vegetation in the NE Atlantic

A trophic cascade regulates salt marsh primary production

Top‐down and bottom‐up controls on sediment organic matter composition in an experimental seagrass ecosystem

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