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dc.contributor.authorDos Santos, Virginie
dc.contributor.authorMatheson, Fleur E.
dc.contributor.authorPilditch, Conrad A.
dc.contributor.authorElger, Arnaud
dc.identifier.citationDos Santos, V. M., Matheson, F. E., Pilditch, C. A., & Elger, A. (2012). Is black swan grazing a threat to seagrass? Indications from an observational study in New Zealand. Aquatic Botany, 100, 41-50.en_NZ
dc.description.abstractIn New Zealand, the black swan (Cygnus atratus) is the only large grazer of intertidal seagrass (Zostera muelleri). The present study examined spatial and temporal variations in black swan grazing activity in a large temperate estuary to estimate potential site-specific and estuary-wide impacts on seagrass biomass. We monitored diel swan grazing activities, their seasonal abundance, estimated the rate at which swans consumed seagrass and measured changes in the standing stock of seagrass biomass at four sites in Tauranga Harbour. Black swans foraged primarily at high tide (both during the day and night) and were more numerous at sites with larger meadows, particularly during autumn. Grazing created circular devegetated patches (average size ∼0.28 m²) with 92% of shoots, 25% of roots and 99% of rhizomes removed. We measured an average seagrass consumption rate of 394 g dry mass (DM) swan⁻¹ d⁻¹ in line with consumption rates of other Zostera-feeding waterfowl. At sites where grazing was most intense (annual removal of 19–20% of the average seagrass biomass), we observed a substantial decline (43–69%) in plant biomass in the subsequent growing season. These results suggest that black swan grazing could constitute a threat to seagrass under high grazing pressure.en_NZ
dc.relation.ispartofAquatic Botany
dc.subjectwaterfowl herbivoryen_NZ
dc.subjectCygnus atratusen_NZ
dc.subjectconsumption rateen_NZ
dc.subjectgrazing pressureen_NZ
dc.subjecttemperate estuariesen_NZ
dc.subjectZostera muellerien_NZ
dc.titleIs black swan grazing a threat to seagrass? Indications from an observational study in New Zealanden_NZ
dc.typeJournal Articleen_NZ
dc.relation.isPartOfAquatic Botanyen_NZ

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