Blinded by the light? Nearshore energy pathway coupling and relative predator biomass increase with reduced water transparency across lakes

Abstract

Habitat coupling is a concept that refers to consumer integration of resources derived from different habitats. This coupling unites fundamental food web pathways (e.g., cross-habitat trophic linkages) that mediate key ecological processes such as biomass flows, nutrient cycling, and stability. We consider the influence of water transparency, an important environmental driver in aquatic ecosystems, on habitat coupling by a light-sensitive predator, walleye (Sander vitreus), and its prey in 33 Canadian lakes. Our large-scale, across-lake study shows that the contribution of nearshore carbon (δC) relative to offshore carbon (δC) to walleye is higher in less transparent lakes. To a lesser degree, the contribution of nearshore carbon increased with a greater proportion of prey in nearshore compared to offshore habitats. Interestingly, water transparency and habitat coupling predict among-lake variation in walleye relative biomass. These findings support the idea that predator responses to changing conditions (e.g., water transparency) can fundamentally alter carbon pathways, and predator biomass, in aquatic ecosystems. Identifying environmental factors that influence habitat coupling is an important step toward understanding spatial food web structure in a changing world.

Water clarity and temperature effects on walleye safe harvest: an empirical test of the safe operating space concept

“…, Tunney et al. ), although changes in TOHA over time have rarely been quantified or linked directly to walleye abundance (but see Chu et al. , Jones et al.…”

“…Recent research has also demonstrated that walleye populations in lakes with low water clarity can access multiple prey sources and achieve higher biomass compared to lakes with high water clarity (Tunney et al. ). As water clarity increases and TOHA decreases, walleye may be restricted to offshore and deepwater habitats throughout most daylight hours.…”

“…Still, other lakes with more complex bathymetries and different trophic status may respond differently to changing conditions. Lakes with more TOHA support higher walleye biomass and harvest (Christie and Regier 1988, Lester et al 2004, Tunney et al 2018, although changes in TOHA over time have rarely been quantified or linked directly to walleye abundance (but see Chu et al 2004, Jones et al 2006. Water clarity and TOHA affect walleye populations through a number of pathways.…”

“…, Tunney et al. ). Increasing water clarity and warming temperatures are associated with declining walleye and increasing Centrarchid (sunfishes and black bass) populations in lakes throughout North America (Robillard and Fox , Hansen et al.…”

“…A lake's clarity, temperature, and bathymetry determine its thermaloptical habitat area (TOHA), that is, the area of a lake in which optical and thermal conditions for walleye overlap. A lake's TOHA is positively related to walleye production and catch rates at broad spatial scales (Lester et al 2004, Tunney et al 2018. Increasing water clarity and warming temperatures are associated with declining walleye and increasing Centrarchid (sunfishes and black bass) populations in lakes throughout North America (Robillard and Fox 2006, Hansen et al 2015.…”