Population regulation, population dynamics and competition amongst mobile epifauna associated with seagrass

Edgar, Graham J.

doi:10.1016/0022-0981(90)90029-c

Cited by 95 publications

(71 citation statements)

References 37 publications

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“…3B). Other experimental studies have also demonstrated interference competition among grazing isopod species (Franke and Janke 1998), and we have found experimental evidence of interspecific competition among grazing amphipods in this system (Duffy and Harvilicz, in press), as have other authors for epifauna inhabiting both seagrasses (Edgar 1990A) and macroalgae (Edgar and Aoki 1993). In this regard our results are similar to those of Hooper and Vitousek (1997), who found that competition among plant species in a California grassland strongly reduced total Notes: Separate regressions used grazer abundance and grazer biomass as the independent variables.…”

Section: Grazer Functional Diversity and Ecosystem Processes In Seagrsupporting

confidence: 86%

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

Duffy

Macdonald

Rhode

et al. 2001

Ecology

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Abstract. Concern over the accelerating loss of biodiversity has stimulated renewed interest in relationships among species richness, species composition, and the functional properties of ecosystems. Mechanistically, the degree of functional differentiation or complementarity among individual species determines the form of such relationships and is thus important to distinguishing among alternative hypotheses for the effects of diversity on ecosystem processes. Although a growing number of studies have reported relationships between plant diversity and ecosystem processes, few have explicitly addressed how functional diversity at higher trophic levels influences ecosystem processes. We used mesocosm experiments to test the impacts of three herbivorous crustacean species (Gammarus mucronatus, Idotea baltica, and Erichsonella attenuata) on plant biomass accumulation, relative dominance of plant functional groups, and herbivore secondary production in beds of eelgrass (Zostera marina), a dominant feature of naturally low-diversity estuaries throughout the northern hemisphere. By establishing treatments with all possible combinations of the three grazer species, we tested the degree of functional redundancy among grazers and their relative impacts on productivity.Grazer species composition strongly influenced eelgrass biomass accumulation and grazer secondary production, whereas none of the processes we studied was clearly related to grazer species richness over the narrow range (0-3 species) studied. In fact, all three measured ecosystem processes-epiphyte grazing, and eelgrass and grazer biomass accumulation-reached highest values in particular single-species treatments. Experimental deletions of individual species from the otherwise-intact assemblage confirmed that the three grazer species were functionally redundant in impacting epiphyte accumulation, whereas secondary production was sensitive to deletion of G. mucronatus, indicating its unique, nonredundant role in influencing this variable. In the field, seasonal abundance patterns differed markedly among the dominant grazer species, suggesting that complementary grazer phenologies may reduce total variance in grazing pressure on an annual basis. Our results show that even superficially similar grazer species can differ in both sign and magnitude of impacts on ecosystem processes and emphasize that one must be cautious in assuming redundancy when assigning species to functional groups.

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Section: Grazer Functional Diversity and Ecosystem Processes In Seagrsupporting

confidence: 86%

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

Duffy

Macdonald

Rhode

et al. 2001

Ecology

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“…In fact, the presence of epiphytes on host seagrass meadows raised habitat complexity, creating new attachment sites and shelter as well as increasing food supply for the associated fauna (Hall and Bell 1988;Martin-Smith 1993). Epiphytes also favour detritus accumulation and amplify surface area for the colonization of bacteria and microalgae (Hacker and Steneck 1990;James and Heck 1994;Leber 1985;Russo 1990), thus beneWting species that consume these food resources (Edgar 1990). In several seagrass ecosystems, algal epiphytes are found to be more attractive food for herbivores than the leaves themselves (Kitting et al 1984;Van Montfrans 1984, Van Montfrans et al 1984).…”

Section: Discussionmentioning

confidence: 99%

Community structure of amphipods on shallow Posidonia oceanica meadows off Tunisian coasts

2010

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The structure, diversity and spatial distribution of the amphipod fauna associated with Posidonia oceanica meadows were studied along the Tunisian coasts in 2007. Samples were collected in nine diVerent meadows at 2 m depth. A total of 44 species belonging to 12 families were collected. The most common species in terms of abundance were Ampithoe helleri, Hyale camptonyx and Ericthonius punctatus. The highest values of abundance and species richness and the lowest values of diversity and equitability were found in meadows with high epiphyte biomass. Multivariate analyses of data indicated that epiphyte biomass and geographical position were major determinants of the distribution and composition of amphipod assemblages along Tunisian coasts. The presence of two lessepsian amphipod species in one of the southern Posidonia oceanica meadows modiWed the structure of assemblage.

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“…to respond rapidly to the nutrient conditions among algae, the grazers never increased to densities where macroalgal beds were destructively affected . Edgar (1990) postulated that grazing macroinvertebrates in seagrass ecosystems were exposed to food limitation, and that food availability regulated these mobile epifauna populations. Fucoids have not been observed to be eaten by amphipods by Vassallo and Steele (1980), but a majority of common seaweeds are found to serve as food for grazers in other studies (Denton and Chapman, 1991;Costa and Costa, 1999;Cruz-Riveira and Hay, 2000a, b).…”

Section: Introductionmentioning

confidence: 99%

Mechanisms regulating amphipod population density within macroalgal communities with low predator impact

Christie¹,

Kraufvelin²

2004

Sci. Mar.

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SUMMARY: In eight mesocosms (land based basins) macroalgae communities with associated fauna were transplanted from the sea and established during two years. Then, different doses of nutrients (N and P) were added to the basins throughout the following three years. During the period of nutrient addition, macroinvertebrate grazers showed seasonal fluctuations with densities usually between 500,000 and 1 million individuals per mesocosm during summer and to a level of about 100,000 during winter. The macroinvertebrate grazers mainly consisted of about 10 species of amphipods and isopods, among which the amphipod Gammarus locusta dominated strongly by biomass. Although the number of predators was very low, the grazer populations never reached a density where considerable grazing impact could be found on the macroalgae. No increase in grazer density was found in the basins with improved nutrient conditions. Thus food quality may be insufficient for further population growth, or density dependant regulation mechanisms may have prevented the grazers from flourishing and overgrazing the system. In aquarium experiments we showed that G. locusta could grow and reproduce on Fucus serratus, Ulva lactuca, periphyton and detritus, and that cannibalism by adult G. locusta on juveniles may have great impact on the population growth. The basins were run with a water flow through system. Nets were placed in front of the inflow and outflow tubes to measure immigration and emigration. Only few individuals (and no Gammarus sp.) were recorded in the inflowing water, while high numbers of both amphipods and isopods were found in the outflowing water. Emigration reached peak values during night-time, and it was then two to three times as high as during day-time. Emigration of mobile grazers from the basins amounted to 1-2% of the standing stock daily. These mechanisms that regulate grazers do contribute to maintenance of the seaweed dominance and thus the stability of the seaweed community.Key words: Mesocosm, macroalgae, grazers, Gammarus locusta, population regulation, eutrophication. RESUMEN: MECANISMOS QUE REGULAN LA DENSIDAD DE POBLACIONES DE ANFÍPODOS EN COMUNIDADES DE MACROALGAS CONBAJO IMPACTO DE DEPREDACIÓN. -En ocho mesocosmos (depósitos situados en tierra) se trasplantaron comunidades de macroalgas con fauna asociada procedentes del mar y se establecieron durante dos años. Posteriormente se añadieron diferentes dosis de nutrientes (N y P) a los depósitos a lo largo de los tres años siguientes. Durante el período de adición de nutrientes, los macroinvertebrados herbívoros mostraron fluctuaciones estacionales con densidades que por lo general se encontraban entre 500.000 y 1 millón de individuos por mesocosmos durante el verano y hasta un nivel de unos 100.000 ind. en invierno. Los macroinvertebrados herbívoros eran principalmente unas 10 especies de anfípodos e isópodos, entre los cuales el anfípodo Gammarus locusta dominaba mucho por la biomasa. Aunque el número de depredadores fue muy bajo, las poblaciones de herbívoros no...

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Population regulation, population dynamics and competition amongst mobile epifauna associated with seagrass

Cited by 95 publications

References 37 publications

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

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

Community structure of amphipods on shallow Posidonia oceanica meadows off Tunisian coasts

Mechanisms regulating amphipod population density within macroalgal communities with low predator impact

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