MEPS 549:79-88 (2016)  -  DOI: https://doi.org/10.3354/meps11708

Linking nitrogen sources utilised by seagrass in a temperate marine embayment to patterns of seagrass change during drought

A. J. Hirst1,*, A. R. Longmore2, D. Ball3, P. L. M. Cook4, G. P. Jenkins5

1Centre for Integrative Ecology, School of Life and Environmental Science, Deakin University, Waurn Ponds, Victoria 3216, Australia
2Centre for Aquatic Pollution Identification and Management, School of BioSciences, University of Melbourne, Parkville, Victoria 3010, Australia
3Independent Consultant, PO Box 457, Frankston, Victoria 3199, Australia
4Water Studies Centre, School of Chemistry, Monash University, Clayton, Victoria 3800, Australia
5School of BioSciences, University of Melbourne, Parkville, Victoria 3010, Australia
*Corresponding author:

ABSTRACT: Reductions in the extent of seagrass Zostera nigricaulis coverage in Port Phillip Bay (PPB), Australia, between 2000 and 2011 coincided with a prolonged period of drought (1997 to 2009) characterized by decreases in freshwater and nutrient inputs. This led us to hypothesize that patterns of seagrass expansion and decline in PPB may be linked to nutrient availability. Seagrasses in PPB can make use of a range of different nitrogen (N) sources depending on their relative availability. Accordingly, there is a need to identify the origin of the N utilised by seagrasses in order to understand how changes in the availability of nutrients from various sources may influence seagrass growth. This study used stable isotope analysis to estimate the contribution of different sources of N to seagrass growth in different parts of PPB. Source modelling indicated that regional patterns of N source utilisation matched changes in seagrass extent from 2000 to 2011. Regions in which seagrass declined contained a similar array of sources, including significant contributions from the catchment area, whereas regions where seagrass areas remained unchanged were largely dependent on a single N source (either fixation/recycled or sewage-derived). We propose that reductions in N from the catchment during the drought may have contributed to the decline of seagrasses in regions where N from the catchment is an important source. This finding is likely to have implications for the growth, distribution and resilience of Z. nigricaulis seagrass in PPB as well as in other parts of its range in southern Australia.


KEY WORDS: Zostera nigricaulis · Climate change · IsoSource model · Seagrass decline · Port Phillip Bay


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Cite this article as: Hirst AJ, Longmore AR, Ball D, Cook PLM, Jenkins GP (2016) Linking nitrogen sources utilised by seagrass in a temperate marine embayment to patterns of seagrass change during drought. Mar Ecol Prog Ser 549:79-88. https://doi.org/10.3354/meps11708

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