Retention, breakdown, and biological utilisation of deciduous tree leaves in an estuarine tidal flat of southwestern British Columbia, Canada

In an estuarine mudflat connected to a mountainous stream, coarse leaf material from deciduous trees was examined for its utilisation by invertebrates, retention, and breakdown rate. Leaves from the stream were deposited in the upper intertidal parts near the stream mouth. Their standing stocks were high in fall (∼23.8 g AFDM·m^-2) and mostly disappeared by spring. Breakdown rates of red alder leaf packs were higher at subtidal and lower intertidal stations (k = 0.013-0.027·day^-1) than at stream channel and upper intertidal stations (k = 0.006-0.009·day^-1). Longer contact of leaves with relatively warmer seawater may have enhanced leaf breakdown by microbial activities. In the upper intertidal stations, the decrease in the amount of deposited leaves from fall to spring (k = 0.023-0.039·day^-1) was faster than leaf breakdown in the leaf packs, thus physical export was probably significant in the decrease in deposited leaves. Meanwhile, amphipods dominated the invertebrates colonising leaf packs. The invertebrate densities did not significantly differ between natural and polyester leaf packs, suggesting contribution of leaves as a microhabitat rather than a food source. The carbon and nitrogen stable isotope signatures of amphipods indicated that benthic microalgae were their primary food source regardless of natural or artificial leaf packs.