Epiphyte grazing enhances productivity of remnant seagrass patches

Mirella P C Verhoeven, Brendan P. Kelaher, Melanie J. Bishop, Peter J. Ralph

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Anthropogenic nutrient enrichment is increasingly modifying community structure and ecosystem functioning in terrestrial and aquatic ecosystems. In marine ecosystems, the paradigm is that nutrient enrichment leads to a decline of seagrasses by stimulating epiphytic algal growth, which shades and overgrows seagrasses. This ignores the potential for herbivores, which graze upon epiphytic algae, to partially or wholly counter such nutrient effects. We conducted a field experiment to assess the role that the trochid gastropod Calthalotia fragum plays in reducing nutrient impacts on the seagrass, Posidonia australis, in an urbanized Australian estuary, Botany Bay, Sydney. In a field experiment, where nutrient loading and grazer density were orthogonally manipulated, nutrient enrichment failed to promote epiphyte biomass or diminish growth and primary productivity of P.australis. To the contrary, nutrient enrichment enhanced photosynthesis of the seagrass in plots where the grazer was present at higher density. Epiphytic growth was negatively affected by increased C.fragum density, while P.australis shoot growth was positively influenced. Thus, in this study system, grazing appears to play a much greater role in determining seagrass primary productivity and above-ground growth than moderate nutrient loading, suggesting that the interaction between grazers and nutrients depends on the relative levels of each. Our study contributes to a growing body of literature suggesting that effects of nutrient loading on benthic assemblages are not universally negative, but are dependent on the biotic and abiotic setting.

LanguageEnglish
Pages885-892
Number of pages8
JournalAustral Ecology
Volume37
Issue number8
DOIs
Publication statusPublished - Dec 2012

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epiphyte
seagrass
eutrophication
pollution load
grazing
nutrient enrichment
productivity
nutrient
algae
primary productivity
nutrients
botany
Gastropoda
shade
community structure
herbivores
estuaries
shoot growth
photosynthesis
terrestrial ecosystem

Cite this

Verhoeven, Mirella P C ; Kelaher, Brendan P. ; Bishop, Melanie J. ; Ralph, Peter J. / Epiphyte grazing enhances productivity of remnant seagrass patches. In: Austral Ecology. 2012 ; Vol. 37, No. 8. pp. 885-892.
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Epiphyte grazing enhances productivity of remnant seagrass patches. / Verhoeven, Mirella P C; Kelaher, Brendan P.; Bishop, Melanie J.; Ralph, Peter J.

In: Austral Ecology, Vol. 37, No. 8, 12.2012, p. 885-892.

Research output: Contribution to journalArticleResearchpeer-review

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