Peak Abundance of Fatty Acids From Intertidal Biofilm in Relation to the Breeding Migration of Shorebirds

Abstract

Intertidal biofilm is a thin layer of microbes and meiofauna enmeshed in an extracellular polymeric matrix within and on top of mudflat sediment. This medium provides a dynamic resource for a variety of consumers in estuarine habitats, and is rich in essential fatty acids that birds require for long-distance migration. We measured seasonal changes in biofilm fatty acid content from spring to summer on the Fraser River Estuary, one of the richest and most important ecosystems for migrant and wintering waterbirds in Canada. Fatty acid content in biofilm showed a strong seasonal pattern with a peak in the spring that is associated with the northward migration of Western Sandpipers (Calidris mauri) to their breeding grounds. This peak is linked to the abundance and physiological state, and hence nutritional condition, of epipelic diatoms, which, in turn, depend on a combination of mudflat topography, salinity, temperature, and nutrients that can fluctuate widely with the freshwater inputs from the Fraser River. Specifically, areas with higher elevation (i.e., ∼1 m) had longer periods of exposure to ambient conditions (i.e., light, warm temperatures, gas exchange into/out of biofilms) that facilitated more biofilm growth and higher fatty acid content. Moreover, springtime changes in water chemistry (i.e., salinity/osmotic stresses and nutrients) and temperature facilitated the production of higher overall total lipid/fatty acid contents in the mudflat biofilms compared to summer. Effective conservation of migrating shorebirds depends on the protection of underlying processes at important stopover sites that promote biofilm communities to escalate their production of lipids, including essential fatty acids, during key times of the year.

Age‐ and sex‐related dietary specialization facilitate seasonal resource partitioning in a migratory shorebird

“…Several studies have documented the importance of n‐3 polyunsaturated fatty acids in exercise performance (Maillet & Weber, 2006, 2007). Although biofilm contains low concentrations of these fatty acids, their concentrations peak in spring, and sandpipers could consume a sufficient quantity of biofilm to enhance their migratory performance (Quinn et al., 2017; Schnurr et al., 2019, 2020).…”

“…The western sandpiper is considered a generalist with a diverse diet that includes benthic invertebrates and biofilm—a thin layer of microphytobenthos, bacteria, and detritus encased in a polysaccharide‐rich matrix of extracellular polymeric substances that forms on the surface of mudflats (Stal, 2003; Underwood & Paterson, 2003). Biofilm is an important food for migrating western sandpipers during spring, but little is known about biofilm consumption during mid‐winter or whether biofilm consumption differs among sexes and age classes (Kuwae et al., 2012; Schnurr et al., 2019, 2020).…”

“…We also hypothesized that juveniles would consume more biofilm and microphytobenthos than adults because juveniles are expected to have less prey handling experience than adults (Durell, 2000, 2003). In addition, we hypothesized that biofilm and microphytobenthos consumption would be greater in spring at the onset of migration than during mid‐winter based on the expectation that sandpipers consume biofilm and microphytobenthos to help fuel their migration and reduce competition during periods when high densities of birds occupy foraging sites (Kuwae et al., 2012; Schnurr et al., 2019, 2020).…”

Book Reviews

“…Conservation planning needs to include protection of underlying processes shaping biofilm communities, and future work on shorebirds should focus on identifying and modelling the links between food web complexity and ecosystem resilience. Note that the authors take up their own challenge; they show for instance in a recent publication that the timing of migration of Western Sandpipers Calidris mauri coincides with a peak in biofilm (Schnurr et al 2020).…”

Sandpipers go with the flow: Correlations between estuarine conditions and shorebird abundance at an important stopover on the Pacific Flyway

“…Freshwater input to estuarine mudflats increases during the spring freshet, a period of high discharge following snowmelt, which begins in spring and peaks in early summer. Freshwater released onto mudflats may induce sudden environmental changes, creating conditions favorable to some diatom species within the estuarine community, and triggering enhanced diatom lipid production, which increases the energy available for uptake by foraging shorebirds (Schnurr et al, 2019(Schnurr et al, , 2020.…”