Large Vertical Migrations ofPyrosoma atlanticumPlay an Important Role in Active Carbon Transport

Abstract

Pyrosomes are efficient grazers that can form dense aggregations. Their clearance rates are among the highest of any zooplankton grazer, and they can rapidly repackage what they consume into thousands of fecal pellets per hour. In recent years, pyrosome swarms have been found outside of their natural geographical range; however, environmental drivers that promote these swarms are still unknown. During the austral spring of 2017 a Pyrosoma atlanticum swarm was sampled in the Tasman Sea. Depth‐stratified sampling during the day and night was used to examine the spatial and vertical distribution of P. atlanticum across three eddies. Respiration rate experiments were performed onboard to determine minimum feeding requirements for the pyrosome population. P. atlanticum was 2 orders of magnitude more abundant in the cold core eddy (CCE) compared to both warm core eddies, with maximum biomass of 360 mg WW·m−3, most likely driven by high chlorophyll a concentrations. P. atlanticum exhibited diel vertical migration and migrated to a maximum depth strata of 800–1,000 m. Active carbon transport in the CCE was 4 orders of magnitude higher than the warm core eddies. Fecal pellet production contributed to the majority (91%) of transport, and total downward carbon flux below the mixed layer was estimated at 11 mg C·m−2·d−1. When abundant, P. atlanticum swarms have the potential to play a major role in active carbon transport, comparable to fluxes for zooplankton and micronekton communities.

Mesozooplankton and Micronekton Active Carbon Transport in Contrasting Eddies

“…This productive eddy formed adjacent to the continental shelf a week prior to sampling, entraining shelf water, before moving off the shelf into the warmer EAC (Roughan et al, 2017). In September 2017, three eddies were sampled ( Figures 1D,E): an ∼150 km cold-core eddy off Brisbane (∼27.5 • S; "B-CCE"), a large (∼200 km) warm-core eddy (WCE) that formed from the retroflection of the EAC (∼33 • S; R-WCE), and an ∼150 km WCE sampled south of the Tasman Front (∼35 • S) that was also formed from EAC water (Henschke et al, 2019).…”

“…In the southwestern Pacific Ocean, there are no studies that look at active carbon transport of both mesozooplankton and micronekton within or across eddies, but one study assessed the contribution of pelagic tunicates (Henschke et al, 2019). Some mesozooplankton and micronekton studies have focused on the subtropical convergence off eastern Tasmania (Young and Blaber, 1986;Young et al, 1987Young et al, , 1988, while the mesozooplankton and micronekton communities in the temperate Tasman Sea are comparatively understudied.…”

Sinking of Gelatinous Zooplankton Biomass Increases Deep Carbon Transfer Efficiency Globally

“…Jelly‐C fecal pellets are rich in carbon and nitrogen, are slowly degraded by microbes (Caron et al, ; Iversen et al, ), and sink fast, in some cases faster than 2,000 m day −1 (doliolids and salps; Turner, ). Jelly‐C fecal pellets contribute greatly to the total organic carbon flux at various depth intervals (100 to 2,000 m), between 30% and 60% on average, depending on the location (Pakhomov et al, ; reviewed by Gleiber et al, ; Henschke et al, ; Turner, ). Although jelly‐C fecal pellets and biomass transfer contribute significantly to the vertical flux of organic carbon, both pathways are highly intermittent, restricted to jelly bloom events and subsequent collapses.…”

“…Jelly-C fecal pellets are rich in carbon and nitrogen, are slowly degraded by microbes (Caron et al, 1989;Iversen et al, 2016), and sink fast, in some cases faster than 2,000 m day −1 (doliolids and salps; Turner, 2002). Jelly-C fecal pellets contribute greatly to the total organic carbon flux at various depth intervals (100 to 2,000 m), between 30% and 60% on average, depending on the location (Pakhomov et al, 2002;reviewed by Gleiber et al, 2012;Henschke et al, 2019;Turner, 2002).…”

“…A jelly-C dominated zooplankton community, which often occurs at the local and regional scale, not only increases the transfer efficiency via sinking (dead) jelly-C biomass, but also via active jelly-C fecal pellets production during bloom events (Bruland & Silver, 1981;Caron et al, 1989;Henschke et al, 2019;Iversen et al, 2016;Perissinotto & Pakhomov, 1998). Jelly-C fecal pellets are rich in carbon and nitrogen, are slowly degraded by microbes (Caron et al, 1989;Iversen et al, 2016), and sink fast, in some cases faster than 2,000 m day −1 (doliolids and salps; Turner, 2002).…”