Seven ecological and technical attributes for biofilm-based recovery of shorebird populations in intertidal flat ecosystems

Abstract

Soft-bottomed intertidal flats are essential foraging areas for shorebirds but are severely impacted by threats such as coastal development and climate change. Notwithstanding the urgency for humanintervention (conservation, restoration and creation) of tidal flats, few ecologically based technical guidelines exist for the artificial (clearly intended human intervention) intertidal flats, and none explicitly consider the unique properties of intertidal biofilm as a critical food source for small-bodied shorebirds. We propose that effective human intervention in intertidal flat ecosystems can be developed through mirroring the needs of small-bodied shorebirds. Scientific evidence from intertidal flat recovery projects in Japan is summarized, and foraging requirements of shorebirds are reviewed with a focus on intertidal biofilm as a critical food source. These findings are used to propose the primary goal of intervention, that is maximizing total energy intake for population recovery of small-bodied shorebirds through biofilm. Three sub-goals are presented for creating environmental conditions in which (1) a broad spectrum of food sources is available, but particularly intertidal biofilm; (2) maximizing energy intake rate per individual; and (3) maximizing foraging activity. We then describe seven key ecologically based technical attributes for artificial intertidal flats that promote use by small-bodied shorebirds: depositional environment, complex shoreline, gentle slope, gradient of grain sizes from muddy to sandy, maximum water depth at the lowest tide 5 cm or less, freshwater inflow and unobstructed sight-lines. Critical questions remain for effective intervention in intertidal flat ecosystems, including food web dynamics, variation in the quality and quantity of food sources, especially biofilm, optimal sedimentary environment systems (interaction between grain size, bed slope and elevation), monitoring involving comparisons with appropriate benchmark (control) habitats, quantifying foraging behaviour and the synergy and trade-offs among ecosystem services.