Zooplanktivore fish body growth responses to browning‐induced light limitation vary over ontogeny, but not with fish density

Renee M Van Dorst,Magnus Huss,Richard Svanbäck,Anna Gårdmark

doi:10.1111/eff.12605

Abstract

AbstractOngoing climate change is leading to browning of many lakes and coastal areas, which can impair fish body growth and biomass production. However, whether and how effects of light limitation caused by browning on fish body growth vary over early ontogeny is unknown. In this study, we set up a mesocosm experiment to test whether roach (Rutilus rutilus) body growth responses to browning depend on body size, and if findings are robust over roach densities. We also studied a potential mechanism for size‐specific responses by conducting an aquaria experiment to test if size‐specific prey selectivity in roach changes with browning. We found that roach body growth responses to browning‐induced light limitation vary over ontogeny (independent of roach density), negatively affecting body growth of young‐of‐the‐year (YOY) but not of 1‐year‐old individuals. We also show that this difference in growth response is likely a consequence of browning‐induced alterations in zooplankton community composition and variation in prey selectivity between YOY and 1‐year‐old fish. This suggests that we should account for the diverse effects of browning over fish ontogeny, mediated via altered prey composition and ontogenetic changes in prey preference, when assessing overall impacts of browning on aquatic ecosystems.

Highlights

Climate change, changes in land use and recovery from acidification are leading to “browning” of many temperate lakes and coastal areas, due to increased concentrations of dissolved organic carbon (DOC) and iron (Creed et al, 2018; Larsen et al, 2011; Roulet & Moore, 2006; Weyhenmeyer et al, 2016)
We set up a mesocosm experiment to test whether roach (Rutilus rutilus) body growth responses to browning depend on body size, and if findings are robust over roach densities
We found that roach body growth responses to browning-induced light limitation vary over ontogeny, negatively affecting body growth of young-of-the-year (YOY) but not of 1-year-old individuals

Summary

| INTRODUCTION

Changes in land use and recovery from acidification are leading to “browning” of many temperate lakes and coastal areas, due to increased concentrations of dissolved organic carbon (DOC) and iron (Creed et al, 2018; Larsen et al, 2011; Roulet & Moore, 2006; Weyhenmeyer et al, 2016) This browning reduces light availability in the water, negatively affecting feeding rates (Jönsson et al, 2013; Ranåker et al, 2012), body growth (van Dorst et al, 2019, 2020) and biomass production (van Dorst et al, 2019). The only observations suggesting that browning responses may vary with body size were made in a species with distinct ontogenetic shifts in diet (European perch, Perca fluviatilis; van Dorst et al (2019); van Dorst et al (2020)) In these studies, small fish feeding on pelagic resources were less negatively affected by browning than larger fish feeding on benthic invertebrates and fish. To test whether responses to browning-induced light limitation vary over early ontogeny (and body size), we conducted (1) a pelagic mesocosm experiment to study growth responses of young-of-the-year (YOY) and 1-year-old roach to browning under different roach densities and (2) an aquaria experiment to test whether there are size-specific differences in prey selectivity of roach in clear and brown waters

| METHODS

| RESULTS

Findings

| DISCUSSION