The effects of shorebirds on the erodibility, properties and ecosystem functioning of intertidal muddy sediments

Booty, James (2023) The effects of shorebirds on the erodibility, properties and ecosystem functioning of intertidal muddy sediments. Doctoral thesis, University of East Anglia.

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Abstract

We are only beginning to understand the complex interactions between shorebirds and other organisms on intertidal mudflats. Migratory shorebirds are indicators of ecosystem functioning; their distribution and abundance can signal trends at local and global levels. Mudflats support a highly productive community of microphytobenthos (MPB) which are at the interface between sediment and the water column and influence ecosystem functioning. The MPB facilitate nutrient exchange and bind the sediment surface reducing erodibility of the sediment.

A series of manipulative field and laboratory experiments were carried out across three sites in East Anglia, UK, to determine the effects of wintering shorebird presence, density, species composition and bioturbation on MPB biomass and key ecosystem functioning parameters mediated by MPB. Shorebird presence was controlled using exclosures, shorebird density was manipulated using partial exclosures, species assemblage was compared among study sites and bioturbation was manipulated by artificially mimicking shorebird ambulatory movement. Response of chlorophyll a to treatments was measured in situ by proxy using PAM fluorometry and ex situ using laboratory techniques. Ecosystem function responses were sediment erodibility, measured in situ using a Cohesive Strength Meter, and fluxes of oxygen, nutrient and organic matter between the sediment surface and water column. Fluxes were measured ex situ using cores extracted from treatment plots and sampled within controlled mesocosms.

In a single site experiment shorebird presence had a significant effect on the key ecosystem functions of erodibility and fluxes of nitrate, nitrite, ammonium, phosphate and dissolved organic carbon (DOC). Within a multi-site experiment the best fitting LME model found highly significant interactions between shorebird density, species assemblage and site, with effects of density on MPB biomass varying among sites and depending on species assemblage. Principal component analysis demonstrated that nitrite flux was positively correlated with shorebird density and negatively correlated with bird assemblage scores across all three sites. The artificial manipulation experiment identified surface bioturbation by shorebirds as a process by which the observed effects described above were driven; i.e. that ‘low level’ shorebird ambulatory bioturbation significantly increased MPB biomass and erosion resistance, with significant effects on fluxes of ammonium, nitrate and DOC. These findings indicate that due to top-down effects on MPB, the primary producer on intertidal mudflats, shorebirds can be considered ecosystem engineers.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Chris White
Date Deposited: 03 Jan 2024 14:26
Last Modified: 03 Jan 2024 14:26
URI: https://ueaeprints.uea.ac.uk/id/eprint/94062
DOI:

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