Abstract
Ecosystem functioning and services have provided a rationale for conservation over the past decades. Intertidal muddy sediments, and the microphytobenthic biofilms that inhabit them, perform crucial ecosystem functions including erosion protection, nutrient cycling and carbon sequestration. It has been suggested that predation on sediment macrofauna by shorebirds may impact biofilms, and shorebirds are known to consume biofilm, potentially causing significant top-down effects on mudflat ecosystem functioning. We carried out an exclusion experiment on the Colne Estuary, Essex, to examine whether shorebird presence significantly affects sediment erodibility measured with a Cohesive Strength Meter (CSM) and microphytobenthos biomass measured using PAM fluorescence (Fo) and chlorophyll a content. We also tested for treatment effects on sediment-water nutrient fluxes [nitrate, nitrite, ammonia, phosphate and dissolved organic carbon (DOC)] during periods of both dark and light incubation. Excluding shorebirds caused statistically significant changes in regulating and provisioning ecosystem functions, including mudflat erodibility and nutrient fluxes. The presence of shorebirds lowered the sediment critical erosion threshold τcr, reduced nitrate fluxes into the sediment under illumination, lowered nitrate efflux, and reduced phosphate uptake, compared to sediments where birds were excluded. There were no significant differences in macrofauna community composition within the sediment between treatments after 45 days of bird exclusion, suggesting a direct link between shorebird presence or absence and the significant differences in biofilm-related variables. This study introduces previously unknown effects of shorebird presence on ecosystem functions within this system and highlights an area of shorebird science that could aid joint conservation and human provisioning action.
Highlights
Ecosystem functioning and ecosystem services have provided a rationale for conservation over the past decades (Cabello et al, 2012)
Orders of magnitude changes in the scale of some fluxes were flux into/out of the sediment is considered to be ecologically observed. significant. These results suggest that shorebirds significantly Despite not being formally significant, the reversal of phosphate alter ecosystem functioning associated with nutrient cycling
Limitations are acknowledged regarding the link between Fo measurements and actual Chl a content, the end effect of shorebird presence on erodibility and nutrient fluxes was found to be significant, and a large amount of existing literature indicates that MPB are highly likely to drive this effect
Summary
Ecosystem functioning and ecosystem services have provided a rationale for conservation over the past decades (Cabello et al, 2012). Intertidal mudflat ecosystem functions include nutrient cycling, erosion protection and carbon sequestration, which mediate associated services (Foster et al, 2013). Shorebirds and Ecosystem Functioning polymeric substances (EPS) (Underwood and Paterson, 2003). These biofilms have a stabilizing effect on surface sediments, reducing erodibilty and aiding in the accumulation of particles and microbes (Gerbersdorf and Wieprecht, 2015). Nitrogen loading into marine systems can lead to eutrophication and decline in water quality, making its source and removal pathways of high interest (Burgin and Hamilton, 2007) and changes in nutrient loads can impact benthic communities (Culhane et al, 2019). Dissolved organic carbon (DOC) may provide an important part of both global and coastal carbon sinks (Maher and Eyre, 2010; Legge et al, 2020), making effects on DOC fluxes in this environment relevant to anthropogenic climate change effects and mitigation (McKinley et al, 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
