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.
Highlights
North American avifauna have suffered a net loss approaching 3 billion birds, or ∼29% relative to 1970 abundance estimates, including steep declines in migratory shorebird species (Rosenberg et al, 2019)
The five most abundant fatty acids found in biofilm during spring/summer sampling included 16:0, 16:1n–7 20:5n–3 (EPA), 22:3n–3, and 22:6n–3 (DHA) (Table 2)
This same pattern of an approximate doubling in measures of fatty acid content from values observed in early spring to late April and May, followed by a decline to summer and early fall period (August/September), was apparent in all the summed measures of fatty acids, including saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), PUFA, n–3, and n–6 fatty acids (Figure 2)
Summary
North American avifauna have suffered a net loss approaching 3 billion birds, or ∼29% relative to 1970 abundance estimates, including steep declines in migratory shorebird species (Rosenberg et al, 2019). The authors attributed this collapse to the “loss of ecosystem integrity, function and services.”. Fatty Acids, Biofilm and Shorebirds of the stopover locations that are so vital to the success of their annual migrations Often these stopover sites are hotspots of biological diversity and productivity and, more often than not, occur in estuarine ecosystems (Butler et al, 2001). We seek to achieve this goal by linking the temporal and spatial dynamics of essential fatty acids, as available in the microphytobenthos, to the needs of migrating shorebirds
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