Fine-scale biophysical interactions drive prey availability at a migratory stopover site for Phalaropus spp. in the Bay of Fundy, Canada

Estimating the migratory stopover abundance of phalaropes in the outer Bay of Fundy, Canada

“…Brown and Gaskin (1988) characterized the ecology phalaropes in the outer Bay of Fundy as closely tied to the Brier ledges, which act as "tidal pumps" and provide a nexus for phalarope flocks in the region. Quantitative evidence provided by Thorne and Read (2013) substantiates their hypothesis. However, our aerial perspective revealed that large flocks occur in "offledge" areas as well, and that while the ledges provide a focal point for their collective movements, flocks shift widely about them (100s km²) in the span of hours.…”

“…Characterized by strong tidal forcing and irregular bottom topography, both regions contain ledges and shoals that introduce turbulence into the prevailing axis of tidal flow (Aretxabaleta et al 2008). As it collides with ledges (e.g., Northwest Rock 44°19'N, 66°24'W), eddies of cool, upwelled water carrying dense prey form, drift, and degrade locally about the ledges (≤ 1100 m), subject to the agency of semidiurnal ebb-flood cycle (Thorne and Read 2013). Phalaropes exhibit positive spatial association with these patches of vertical mixing in the surrounding marine environment (Brown and Gaskin 1988).…”

Scales and mechanisms of marine hotspot formation

“…Aggregations of mid-trophic species can be important hotspots for top predators that migrate large distances to optimize foraging opportunities (Cotte & Simard 2005, Bailey et al 2010). The mechanisms underlying trophic hotspots can include island/ seamount wake effects (Johnston & Read 2007, Morato et al 2010, up welling shadows (Nur et al 2011, Wingfield et al 2011, Pardo et al 2013, this Theme Section), wind or eddy-driven upwelling (Croll et al 2005, Atwood et al 2010, Thorne & Read 2013, this Theme Section), or bathymetric features (Croll et al 2005, Gende & Sigler 2006. Fundamentally, changes in these hotspots may have indirect consequences on ecosystem functioning that cascade through to top predators.…”

“…Mechanisms of nutrient input into the euphotic zone include freshwater run-off (Chase et al 2007, Planquette et al 2011, aeolian sources (Fan et al 2006), and up welling of deep, nutrient rich water (Mes khidze et al 2007). Up welling (or water column mixing) can be seasonal or episodic when wind driven; however, upwelling-enhanced productivity can also be highly persistent, especially when resulting from relatively static or cyclical processes, such as the interaction of the Equatorial Undercurrent meeting the western Galapagos Islands (Palacios et al 2006) or small scale, tidally driven current interactions with bathymetric features within a bay (Drew et al 2013, Thorne & Read 2013, both in this Theme Section). Likewise, anticyclonic eddies that form in coastal regions and spin-off into or form in the oceanic domain can entrain or upwell macronutrients, leading to 'traveling' open ocean hotspots of productivity (Crawford et al 2007) that are often utilized by upper trophic level predators (Ream et al 2005).…”

“…Due to transport mechanisms and temporal lags, a foraging hotspot may not coincide with a region of enhanced primary productivity. In these cases, spatial discordance can result from downstream transport of prey, such as zooplankton for foraging birds (Hunt et al 1998, Thorne & Read 2013 2012). Top-down hotspots are rare, but facilitated foraging, where pelagic predators such as tuna force forage fish towards the surface and make them more available to seabirds, can result in higher biodiversity at pelagic hotspots (Maxwell & Morgan 2013).…”