Register      Login
Marine and Freshwater Research Marine and Freshwater Research Society
Advances in the aquatic sciences
RESEARCH ARTICLE

Swan grazing on seagrass: abundance but not grazing pressure varies over an annual cycle in a temperate estuary

Gary E. Choney A C , Kathryn McMahon A , Paul S. Lavery A and Neil Collier B
+ Author Affiliations
- Author Affiliations

A School of Natural Sciences & Centre for Marine Ecosystems Research, Edith Cowan University, 270 Joondalup Drive, Joondalup, WA 6027, Australia.

B Faculty of Health, Engineering and Science, Edith Cowan University, 270 Joondalup Drive, Joondalup, WA 6027, Australia.

C Corresponding author. Email: gchoney@our.ecu.edu.au

Marine and Freshwater Research 65(8) 738-749 https://doi.org/10.1071/MF13126
Submitted: 19 May 2013  Accepted: 9 November 2013   Published: 16 June 2014

Abstract

Herbivorous waterfowl such as black swans are significant grazers in temperate waterbodies; their abundance, distribution and grazing rates vary over seasonal cycles. The present study examined spatial and temporal variation in the abundance and grazing rates of black swans in the Lower Swan River estuary, Western Australia, using visual surveys over 1 year (2009), and potential drivers of this variation, food sources and disturbance factors were assessed. We predicted that swan abundance and grazing pressure would be greater in summer and autumn when seasonal wetlands dry and the abundance of food sources would positively influence their distribution, whereas the level of disturbance would have a negative effect. Plant–grazer interactions are dynamic and complex; the present study revealed new findings on the seasonality of this relationship, where swan abundance but not grazing pressure varied over an annual cycle. Maximum swan abundance occurred in autumn (185) with minima in spring (53) but the swan grazing pressure did not vary between seasons, ranging from 6% to 25% of seagrass production consumed. Swan abundance was a function of season and the cover of seagrass. Key hot spots for swan abundance were identified where management efforts could be targeted by minimising human disturbances and protecting seagrass.

Additional keywords: black swan (Cygnus atratus), Halophila ovalis, Lower Swan River estuary, Western Australia.


References

Altmann, J. (1974). Observational study of behaviour: sampling methods. Behaviour 49, 227–266.
Observational study of behaviour: sampling methods.Crossref | GoogleScholarGoogle Scholar | 1:STN:280:DyaE2c7mtlWmsQ%3D%3D&md5=0d0f4a02e4983544a92b029791637aacCAS | 4597405PubMed |

Baldwin, J. R., and Lovvorn, J. R. (1994). Expansion of seagrass habitat by the exotic Zostera japonica, and its use by dabbling ducks and brant in Boundary Bay, British Columbia. Marine Ecology Progress Series 103, 119–127.
Expansion of seagrass habitat by the exotic Zostera japonica, and its use by dabbling ducks and brant in Boundary Bay, British Columbia.Crossref | GoogleScholarGoogle Scholar |

Bates, D., Maechler, M., Bolker, B., and Walker, S. [Computer software] (2013). ‘lme4: Linear Mixed-effects Models using Eigen and S4. R Package Version 0.99999911-5.’ Available at http://lme4.r-forge.r-project.org/ [verified October 2013].

Bolker, B. M., and R Development Core Team (2013). ‘bbmle: Tools for General Maximum Likelihood Estimation. R Package Version 1.0.13.’ Available at http://CRAN.R-project.org/package=bbmle [verified October 2013].

Braithwaite, L. W. (1982). Ecological studies of the black swan IV.* The timing and success of breeding on two nearby lakes on the Southern Tablelands of New South Wales. Australian Wildlife Research 9, 261–275.
Ecological studies of the black swan IV.* The timing and success of breeding on two nearby lakes on the Southern Tablelands of New South Wales.Crossref | GoogleScholarGoogle Scholar |

Brearley, A. (2005) ‘Swanland, Estuaries and Coastal Lagoons of South-Western Australia.’ (UWA Press: Perth.)

Bunn, S. E., and Arthington, A. H. (2002). Basic principles and ecological consequences of altered flow regimes for aquatic biodiversity. Environmental Management 30, 492–507.
Basic principles and ecological consequences of altered flow regimes for aquatic biodiversity.Crossref | GoogleScholarGoogle Scholar | 12481916PubMed |

Burnham, K. P., and Anderson, D. R. (2002). ‘Model Selection and Multi-model Inference. A Practical Information-theoretic Approach.’ 2nd edn. (Springer-Verlag: New York.)

Chambers, L. E., and Loyn, R. H. (2006). The influence of climate variability on numbers of three waterbird species in Western Port, Victoria, 1973–2002. International Journal of Biometeorology 50, 292–304.
The influence of climate variability on numbers of three waterbird species in Western Port, Victoria, 1973–2002.Crossref | GoogleScholarGoogle Scholar | 16435107PubMed |

Clarke, K., and Gorley, R. (2006). ‘PRIMER v6: User Manual/Tutorial.’ (PRIMER-E: Plymouth, UK.)

Congdon, R. A., and McComb, A. J. (1981). The vegetation of the Blackwood River Estuary, south-west Australia. Journal of Ecology 69, 1–16.
The vegetation of the Blackwood River Estuary, south-west Australia.Crossref | GoogleScholarGoogle Scholar |

Creed, K. E., and Bailey, M. (2009). Continuing decline in wader populations at Pelican Point, Western Australia, since 1971. Stilt 56, 10–14.

Dennison, W. C. (1990). Rhizome/ root production. In ‘Seagrass Research Methods’. (Eds R. C. Phillips and C. P. McRoy.) pp. 81–82. (UNESCO: Paris.)

Department of Conservation and Land Management (1999). ‘Swan Estuary Marine Park and Adjacent Nature Reserves, Management Plan 1999–2009.’ (CALM: Perth.)

Dingle, H. (2008). Bird migration in the southern hemisphere: a review comparing continents. Emu 108, 341–359.
Bird migration in the southern hemisphere: a review comparing continents.Crossref | GoogleScholarGoogle Scholar |

Dos Santos, V. M., Matheson, F. E., Pilditch, C. A., and Elger, A. (2012). Is black swan grazing a threat to seagrass? Indications from an observational study in New Zealand. Aquatic Botany 100, 41–50.
Is black swan grazing a threat to seagrass? Indications from an observational study in New Zealand.Crossref | GoogleScholarGoogle Scholar |

Eklöf, J. S., McMahon, K., and Lavry, P. S. (2009). Effects of multiple disturbances in seagrass meadows: shading decreases resilience to grazing. Marine and Freshwater Research 60, 1317–1327.
Effects of multiple disturbances in seagrass meadows: shading decreases resilience to grazing.Crossref | GoogleScholarGoogle Scholar |

Fournier, D. A., Skaug, H. J., Ancheta, J., Ianelli, J., Magnusson, A., Maunder, M., Nielsen, A., and Sibert, J. (2012). AD Model Builder: using automatic differentiation for statistical inference of highly parameterized complex nonlinear models. Optimisation Methods and Software 27, 233–249.
AD Model Builder: using automatic differentiation for statistical inference of highly parameterized complex nonlinear models.Crossref | GoogleScholarGoogle Scholar |

Gyimesi, A., de Vries, P. P., de Boer, T., and Nolet, B. A. (2011). Reduced tuber banks of fennel pondweed due to summer grazing by waterfowl. Aquatic Botany 94, 24–28.
Reduced tuber banks of fennel pondweed due to summer grazing by waterfowl.Crossref | GoogleScholarGoogle Scholar |

Hamilton, A. J., Taylor, I. R., and Hepworth, H. (2002). Activity budgets of waterfowl (Anatidae) on a waste-stabilisation pond. Emu 102, 171–179.
Activity budgets of waterfowl (Anatidae) on a waste-stabilisation pond.Crossref | GoogleScholarGoogle Scholar |

Hay, J. G. (1906). The visit of Mr Charles Fraser, colonial botanist of New South Wales, with Captain Stirling, in HMS Success, to the Swan River in 1827, with his report on the botany, soil, and capabilities of the locality. Journal of the Western Australian Historical Society 2, 16–35.

Hillman, K., McComb, A. J., and Walker, D. I. (1995). The distribution, biomass and primary production of the seagrass Halophila ovalis in the Swan/Canning Estuary, Western Australia. Aquatic Botany 51, 1–54.
The distribution, biomass and primary production of the seagrass Halophila ovalis in the Swan/Canning Estuary, Western Australia.Crossref | GoogleScholarGoogle Scholar |

Jacobs, R. P. W. M., Den Hartog, C., Braster, B. F., and Carriere, F. C. (1981). Grazing of the seagrass Zostera noltii by birds at Terschelling (Dutch Wadden Sea). Aquatic Botany 10, 241–259.
Grazing of the seagrass Zostera noltii by birds at Terschelling (Dutch Wadden Sea).Crossref | GoogleScholarGoogle Scholar |

Kim, G. Y., Kim, J. Y., Ganf, G. G., Lee, C. W., and Joo, G. J. (2013). Impact of over-wintering waterfowl on tuberous bulrush (Bolboschoenus planiculmis) in tidal flats. Aquatic Botany 107, 17–22.
Impact of over-wintering waterfowl on tuberous bulrush (Bolboschoenus planiculmis) in tidal flats.Crossref | GoogleScholarGoogle Scholar |

Kingsford, R. T., and Norman, F. I. (2002). Australian waterbirds – products of the continent’s ecology. Emu 102, 47–69.
Australian waterbirds – products of the continent’s ecology.Crossref | GoogleScholarGoogle Scholar |

Kirkman, H., and Kirkman, J. (2000). Long-term seagrass meadow monitoring near Perth, Western Australia. Aquatic Botany 67, 319–332.
Long-term seagrass meadow monitoring near Perth, Western Australia.Crossref | GoogleScholarGoogle Scholar |

Ma, Z., Cai, Y., Li, B., and Chen, J. (2010). Managing wetland habitats for waterbirds: an international perspective. Wetlands 30, 15–27.
Managing wetland habitats for waterbirds: an international perspective.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC3cXht1GrsL7I&md5=29edcc548b1353ac663951245eb9447fCAS |

Marchant, S., and Higgins, P. J. (1990). ‘Handbook of Australian, New Zealand and Antarctic Birds.’ (Oxford University Press: Melbourne.)

McKinney, R. A., McWilliams, S. R., and Charpentier, M. A. (2006). Waterfowl–habitat associations during winter in an urban North Atlantic estuary. Biological Conservation 132, 239–249.
Waterfowl–habitat associations during winter in an urban North Atlantic estuary.Crossref | GoogleScholarGoogle Scholar |

Mitchell, S. F., and Wass, R. T. (1996). Grazing by black swans (Cygnus atratus Latham), physical factors, and the growth and loss of aquatic vegetation in a shallow lake. Aquatic Botany 55, 205–215.
Grazing by black swans (Cygnus atratus Latham), physical factors, and the growth and loss of aquatic vegetation in a shallow lake.Crossref | GoogleScholarGoogle Scholar |

Nebel, S., Porter, J. L., and Kingsford, R. T. (2008). Long-term trends of shorebird populations in eastern Australia and impacts of freshwater extraction. Biological Conservation 141, 971–980.
Long-term trends of shorebird populations in eastern Australia and impacts of freshwater extraction.Crossref | GoogleScholarGoogle Scholar |

Nienhuis, P. H., and Groenendijk, A. M. (1986). Consumption of eelgrass (Zostera marina) by birds and invertebrates: an annual budget. Marine Ecology Progress Series 29, 29–35.
Consumption of eelgrass (Zostera marina) by birds and invertebrates: an annual budget.Crossref | GoogleScholarGoogle Scholar |

O’Connell, T. J., Jackson, L. E., and Brooks, R. P. (2000). Bird guilds as indicators of ecological condition in the central Appalacchians. Ecological Applications 10, 1706–1721.
Bird guilds as indicators of ecological condition in the central Appalacchians.Crossref | GoogleScholarGoogle Scholar |

Paracuellos, M., and Telleria, J. L. (2004). Factors affecting the distribution of a waterbird community: the role of habitat configuration and bird abundance. Waterbirds: The International Journal of Waterbird Biology 27, 446–453.
Factors affecting the distribution of a waterbird community: the role of habitat configuration and bird abundance.Crossref | GoogleScholarGoogle Scholar |

Quinn, G. P., and Keough, M. J. (2002). ‘Experimental Design and Data Analysis for Biologists.’ (Cambridge University Press: Melbourne.)

R Core Team (2013). ‘R: a Language and Environment for Statistical Computing.’ (R Foundation for Statistical Computing: Vienna.) Available at http://www.R-project.org/ [verified October 2013].

Roshier, D. A., Robertson, A., and Kingsford, R. T. (2009). ‘The Availability of Wetland Habitat for Waterbirds in Arid Australia.’ (Johnstone Centre, School of Science and Technology, Charles Sturt University: Wagga Wagga, NSW.)

Skaug, H., Fournier, D., Nielsen, A., Magnusson, A., and Bolker, B. [Computer softare]. (2013). ‘Generalized Linear Mixed Models using AD Model Builder. R Package Version 0.7.7.’

Smith, A. N., Vernes, K. A., and Ford, H. A. (2012). Grazing effects of black swans Cygnus atratus (Latham) on a seasonally flooded coastal wetland of eastern Australia. Hydrobiologia 697, 45–57.
Grazing effects of black swans Cygnus atratus (Latham) on a seasonally flooded coastal wetland of eastern Australia.Crossref | GoogleScholarGoogle Scholar | 1:CAS:528:DC%2BC38Xht1Cgt7%2FN&md5=c67b91a933f686e21cac7053dde68c04CAS |

Sodhi, N. S., Bickford, D., Diesmos, A. C., Lee, T. M., Koh, L. P., Brook, B. W., Sekercioglu, C. H., and Bradshaw, C. J. A. (2008). Measuring the meltdown: drivers of global amphibian extinction and decline. PLoS ONE 3, e1636.
| 18286193PubMed |

Valentine, J. F., and Duffy, J. E. (2006). The central role of grazing in seagrass ecology. In ‘Seagrasses: Biology, Ecology and Conservation’. (Eds A. W. D. Larkum, R. J. Orth and C. M. Duarte.) pp. 463–501. (Springer: New York.)

Van den Bergh, E., Ysebaret, T., and Meire, P. (2005). Water bird communities in the Lower Zeeschelde: long-term changes near an expanding harbour. Hydrobiologia 540, 237–258.
Water bird communities in the Lower Zeeschelde: long-term changes near an expanding harbour.Crossref | GoogleScholarGoogle Scholar |

Wen, L., Rogers, K., Saintilan, N., and Ling, J. (2011). The influences of climate and hydrology on population dynamics of waterbirds in the lower Murrumbidgee River floodplains in southeast Australia: implications for environmental water management. Ecological Modelling 222, 154–163.
The influences of climate and hydrology on population dynamics of waterbirds in the lower Murrumbidgee River floodplains in southeast Australia: implications for environmental water management.Crossref | GoogleScholarGoogle Scholar |

Williams, M. (1979). Status and management of black swans Cygnus atratus, Latham at Ellesmere since the ‘Wahine’ storm, April, 1968. New Zealand Journal of Ecology 2, 34–41.

Wood, K. A., Stillman, K. A., Coombs, T., Mcdonald, C., Daunt, F., and O’hare, T. (2013). The role of season and social grouping on habitat use by mute swans (Cygnus olor) in a lowland river catchment. Bird Study 60, 229–237.
The role of season and social grouping on habitat use by mute swans (Cygnus olor) in a lowland river catchment.Crossref | GoogleScholarGoogle Scholar |