Porewater methane transport within the gas vesicles of diurnally migrating Chaoborus spp.: An energetic advantage

Abstract

Diurnally-migrating Chaoborus spp. reach populations of up to 130,000 individuals m−2 in lakes up to 70 meters deep on all continents except Antarctica. Linked to eutrophication, migrating Chaoborus spp. dwell in the anoxic sediment during daytime and feed in the oxic surface layer at night. Our experiments show that by burrowing into the sediment, Chaoborus spp. utilize the high dissolved gas partial pressure of sediment methane to inflate their tracheal sacs. This mechanism provides a significant energetic advantage that allows the larvae to migrate via passive buoyancy rather than more energy-costly swimming. The Chaoborus spp. larvae, in addition to potentially releasing sediment methane bubbles twice a day by entering and leaving the sediment, also transport porewater methane within their gas vesicles into the water column, resulting in a flux of 0.01–2 mol m−2 yr−1 depending on population density and water depth. Chaoborus spp. emerging annually as flies also result in 0.1–6 mol m−2 yr−1 of carbon export from the system. Finding the tipping point in lake eutrophication enabling this methane-powered migration mechanism is crucial for ultimately reconstructing the geographical expansion of Chaoborus spp., and the corresponding shifts in the lake’s biogeochemistry, carbon cycling and food web structure.

The effects of hypolimnetic anoxia on the diel vertical migration of freshwater crustacean zooplankton

“…Consequently, Chaoborus may be expected to increase in waterbodies experiencing increasing durations of anoxia (as suggested by McGinnis et al. ).…”

Influence of water column stratification and mixing patterns on the fate of methane produced in deep sediments of a small eutrophic lake

“…To reach the atmosphere, sediment‐produced CH 4 must be transported through the water column, where it can be consumed by methanotrophs (Rudd and Hamilton ; Utsumi et al ; Kankaala et al ; Bastviken et al ). Sediment‐produced CH 4 is transported in the water column by turbulent diffusion (Adams ), bubble‐mediated transport (McGinnis et al ), plant‐mediated transport (Juutinen ; Carmichael et al ), or migrating zooplankton (McGinnis et al ; Carey et al ). Although considerable efforts have been invested in quantifying the surface aquatic CH 4 fluxes and the relative contribution of the different emissions pathways (Bastviken et al ; Rinta et al ), the in‐lake mechanisms regulating rates of CH 4 production, transport, and oxidation in stratified systems are still poorly understood.…”

Chaoborus spp. Transport CH4 from the Sediments to the Surface Waters of a Eutrophic Reservoir, But Their Contribution to Water Column CH4 Concentrations and Diffusive Efflux Is Minor

“…It has recently been proposed that Chaoborus spp. (midge larvae; order Diptera) may increase CH 4 concentrations in the epilimnion Figure ).…”

“…Chaoborus may transport CH 4 from the sediments to the epilimnia of lakes and reservoirs by taking up CH 4 in their tracheal gas sacs, using this buoyancy to reach surface waters, and then releasing the CH 4 near the surface (Figure ). Gas sac inflation may allow Chaoborus to control their position in the water column, , and may be initiated by a decrease in light intensity . This translocation of CH 4 may occur daily as part of Chaoborus ’ diel vertical migration (DVM), in which Chaoborus remain in the lower hypolimnion and sediments during the day to avoid visual predation from fish and ascend to the surface waters in the evening to feed on migrating zooplankton prey.…”

“…Direct observations are needed to quantify the contribution of the Chaoborus CH 4 pump to lake and reservoir carbon (C) cycling and efflux. While an earlier laboratory study provides an important proof of concept of Chaoborus ’ ability to absorb and release CH 4 , additional measurements of CH 4 release using Chaoborus collected from the natural environment are needed to determine the magnitude of their CH 4 transport. Further studies incorporating both diel variation and depth through the water column will provide valuable insight beyond the single time and depth sampling by McGinnis et al, as many Chaoborus only migrate to the metalimnion, not epilimnion, and the timing of their DVM may vary throughout a diel period. − …”