Stewart-Sinclair, P.J., Lam-Gordillo, O., Reeve, G., Bulmer, R., Zabarte-Maeztu, I., and Swales, A. (2027) Standardising tidal position of coastal wetlands across New Zealand estuaries: A national synthesis. Estuarine, Coastal and Shelf Science, 344. 110323.

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Abstract

Coastal wetland distribution in estuaries is strongly controlled by position within the tidal frame, yet comparisons among systems are often confounded by large regional differences. Standardised metrics of tidal position are therefore needed to compare habitat zonation across estuaries with contrasting hydrodynamic settings. Here we apply the Standard Tidal Position Index (STPI) to quantify and compare the tidal position of coastal wetland habitats across Aotearoa New Zealand. Distributions of seagrass, mangroves, and saltmarsh were analysed for 47 estuaries spanning a range of geomorphic types. Habitat elevation was derived from 1-m resolution coastal LiDAR and referenced to estuary-specific tidal ranges from a calibrated TELEMAC-2D hydrodynamic model. Elevation boundaries between habitats were estimated using weighted ordinal regression and normalised within the local tidal frame using STPI.

Across all estuaries, STPI revealed consistent vertical structuring of habitats despite large variation in tidal range, estuary geomorphology, and absolute elevation. National median STPI values placed seagrass below mean tide level (upper boundary ≈ 0.06), mangroves between ≈ 0.06 and 0.37 where present, and saltmarsh above ≈ 0.37. Saltmarsh therefore extended lower in the tidal frame than commonly inferred from neap or spring tidal benchmarks. Standardising elevation within the tidal frame substantially reduced apparent variability in habitat position among estuaries and clarified differences in intertidal zonation between systems with and without mangroves. These results demonstrate that STPI provides a robust and transferable framework for comparing coastal wetland zonation across estuaries with differing tidal regimes, with direct applications for restoration planning and sea-level rise assessment

Item ID:	94424
Item Type:	Article (Research - C1)
ISSN:	1096-0015
Copyright Information:	© 2026 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
Date Deposited:	20 Oct 2026 00:09
FoR Codes:	31 BIOLOGICAL SCIENCES > 3103 Ecology > 310305 Marine and estuarine ecology (incl. marine ichthyology) @ 50% 37 EARTH SCIENCES > 3709 Physical geography and environmental geoscience > 370901 Geomorphology and earth surface processes @ 30% 41 ENVIRONMENTAL SCIENCES > 4104 Environmental management > 410402 Environmental assessment and monitoring @ 20%
SEO Codes:	18 ENVIRONMENTAL MANAGEMENT > 1802 Coastal and estuarine systems and management > 180201 Assessment and management of coastal and estuarine ecosystems @ 60% 18 ENVIRONMENTAL MANAGEMENT > 1802 Coastal and estuarine systems and management > 180203 Coastal or estuarine biodiversity @ 20% 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280111 Expanding knowledge in the environmental sciences @ 20%
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