title: Detecting Subtle Shifts in Ecosystem Functioning in a Dynamic Estuarine Environment.
abstract: Identifying the effects of stressors before they impact ecosystem functioning can be challenging in dynamic, heterogeneous 'real-world' ecosystems. In aquatic systems, for example, reductions in water clarity can limit the light available for photosynthesis, with knock-on consequences for secondary consumers, though in naturally turbid wave-swept estuaries, detecting the effects of elevated turbidity can be difficult. The objective of this study was to investigate the effects of shading on ecosystem functions mediated by sandflat primary producers (microphytobenthos) and deep-dwelling surface-feeding macrofauna (Macomona liliana; Bivalvia, Veneroida, Tellinidae). Shade cloths (which reduced incident light intensity by ~80%) were deployed on an exposed, intertidal sandflat to experimentally stress the microphytobenthic community associated with the sediment surface. After 13 weeks, sediment properties, macrofauna and fluxes of oxygen and inorganic nutrients across the sediment-water interface were measured. A multivariate metric of ecosystem function (MF) was generated by combining flux-based response variables, and distance-based linear models were used to determine shifts in the drivers of ecosystem function between non-shaded and shaded plots. No significant differences in MF or in the constituent ecosystem function variables were detected between the shaded and non-shaded plots. However, shading reduced the total explained variation in MF (from 64% in non-shaded plots to 15% in shaded plots) and affected the relative influence of M. liliana and other explanatory variables on MF. This suggests that although shade stress may shift the drivers of ecosystem functioning (consistent with earlier investigations of shading effects on sandflat interaction networks), ecosystem functions appear to have a degree of resilience to those changes.
authors.affiliation: National Institute of Water and Atmospheric Research, P.O. Box 11-115, Hillcrest, Hamilton, New Zealand.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Pratt
authors.affiliation: National Institute of Water and Atmospheric Research, P.O. Box 11-115, Hillcrest, Hamilton, New Zealand.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Lohrer
authors.affiliation: National Institute of Water and Atmospheric Research, P.O. Box 11-115, Hillcrest, Hamilton, New Zealand; Institute of Marine Science, University of Auckland, Private Bag 92019, Auckland, New Zealand.
authors.forename: Simon F
authors.initials: SF
authors.lastname: Thrush
authors.affiliation: National Institute of Water and Atmospheric Research, P.O. Box 11-115, Hillcrest, Hamilton, New Zealand.
authors.forename: Judi E
authors.initials: JE
authors.lastname: Hewitt
authors.affiliation: National Institute of Water and Atmospheric Research, P.O. Box 11-115, Hillcrest, Hamilton, New Zealand.
authors.forename: Michael
authors.initials: M
authors.lastname: Townsend
authors.affiliation: National Institute of Water and Atmospheric Research, P.O. Box 11-115, Hillcrest, Hamilton, New Zealand.
authors.forename: Katie
authors.initials: K
authors.lastname: Cartner
authors.affiliation: Department of Biological Sciences, University of Waikato, Hamilton, New Zealand.
authors.forename: Conrad A
authors.initials: CA
authors.lastname: Pilditch
authors.affiliation: Department of Biological Sciences, University of Waikato, Hamilton, New Zealand.
authors.forename: Rachel J
authors.initials: RJ
authors.lastname: Harris
authors.affiliation: Marine Biology Group, Biology Department, Ghent University, Krijgslaan 281-S8, Ghent, Belgium.
authors.forename: Carl
authors.initials: C
authors.lastname: van Colen
authors.affiliation: CIIMAR, Interdisciplinary Centre of Marine and Environmental Research, University of Porto, Rua dos Bragas 289, Porto, Portugal.
authors.forename: Iván F
authors.initials: IF
authors.lastname: Rodil
mesh_terms: D000818:Animals; D017753:Ecosystem; D004777:Environment; D006801:Humans; D009520:New Zealand