Carbon sequestration and zooplankton lunar cycles: Could we be missing a major component of the biological pump?

Abstract

The plankton outburst during the so-called late winter bloom in subtropical waters was studied in relation to lunar illumination in the Canary Island waters. Nutrient enrichment by mixing and dust deposition promoted a bloom of phyto-and zooplankton. Mesozooplankton biomass increased as the winter mixing progressed but peaked in every full moon and decreased thereafter because of the effect of predation by interzonal diel vertical migrants (DVMs). The pattern was similar to the one described in lakes due to predation by fishes and confirms that this phenomenon is important in the sea. The estimated consumption and subsequent transport of epipelagic zooplankton biomass by DVMs after every full moon is on the order of the mean gravitational export and is an unaccounted flux of carbon to the mesopelagic zone that may play a pivotal role in the efficiency of the biological pump.Most of the research about the downward flux of carbon in the ocean has centered on the so-called gravitational flux, the transport due to the sedimentation of the particulate organic carbon production from the euphotic layer to the mesopelagic zone. In tropical and subtropical regions this flux is a low number, normally less than 10% of primary production (Karl et al. 1996). Another component of the biological pump is the so-called active flux due to the transport of carbon by vertical migrants. These organisms feed on the shallower layers of the ocean at night and return to their daytime residence at depth where they metabolize carbon or simply are eaten by other organisms. The role of these rather large organisms (mesozooplankton and micronekton) in the ocean carbon sequestration has been almost neglected. Active flux is a rather complex mechanism that involves the gut flux (Angel 1989) (the transport due to the release of feces below the mixed layer), carbon dioxide respiration (Longhurst et al. 1990), dissolved organic carbon excretion (Steinberg et al. 2000), and mortality (Zhang and Dam 1997) at depth. The few values available at present mainly based on respiration at depth indicate that the active downward carbon flux is highly variable, ranging from 4% to 70% of the gravitational flux (Herná ndez-Leó n and Ikeda 2005a). However, diel vertical migrants (DVMs) account for the control of 5-10% of the daily epipelagic zooplankton production (Hopkins et al. 1996), and this ingested food is efficiently transported downward (Pearre 2003). The consumption of epipelagic zooplankton by these organisms and their role in the fate of a bloom are at present poorly known.A way to study the biological pump in subtropical waters is to understand the development of the bloom during winter, when nutrients are present in the euphotic zone. The late winter bloom in subtropical waters is produced by cooling of the shallower layers of the ocean, eroding the thermocline and allowing a small flux of nutrients to the euphotic zone. This process promotes the increase in primary production and the growth of micro-and mesozooplankton. Atmospheric Saharan...

Trophic Diversity of Plankton in the Epipelagic and Mesopelagic Layers of the Tropical and Equatorial Atlantic Determined with Stable Isotopes

“…Additional environmental variability is provided by the influence of diazotrophy (atmospheric nitrogen fixation) in the subtropical region, generally more important in the western waters but occasionally affecting also waters near Canary Islands [26][27][28][29][30]. Zooplankton composition and biomass in this region reflect the productivity of the surface waters (for example, References [21,25]) and previous studies on the vertical migrations of zooplankton [12,25] and mesopelagic fish [31] showed a measurable impact of these movements on carbon fluxes and export to deep ocean layers. Stable isotopes revealed that some of the most abundant mesopelagic fish (as myctophids) greatly depend on zooplankton [32], while copepods (one of the most abundant zooplankton taxa) showed a marked increase in heavy nitrogen isotopes with depth [21].…”

“…Migrating organisms include phyto-and zooplankton [7,8], fish [9,10], cephalopods, seabirds, mammals, and even reptiles [11]. Most migrations have been related to the daily light cycle but also to the lunar [12] and seasonal periods [13]. One of the major drivers of these migrations is food [9].…”

Efficient trawl avoidance by mesopelagic fishes causes large underestimation of their biomass

“…Mesopelagic (200 to 1000 m depth) fishes are important planktivores and prominent prey for higher trophic levels in all the world's oceans (Gjøsaeter & Kawaguchi 1980, Lam & Pauly 2005 and, because of pronounced diel vertical migrations (DVM), contribute to the biological pump whereby organic material is transported from upper layers down to the waters at depth (Hidaka et al 2001, Hernández-León et al 2010. The current global biomass estimate of mesopelagic fishes, primarily based on catches by micronekton sampling gears prior to 1980, amounts to approximately 1 gigatonne (10 9 t wet weight) (Gjøsaeter & Kawaguchi 1980, Lam & Pauly 2005.…”

Factors affecting the fatty acid composition of mesopelagic fish of the continental slope in the South China Sea

“…Because of their diel vertical migration (DVM), mesopelagic fish link primary consumers including copepods and zooplankton to higher predators including large pelagic fish, benthic fish, and marine mammals (Choy et al, 2012;Collins et al, 2012;Olivar et al, 2012). They play an important role in ocean food webs (Cherel et al, 2010;Kaartvedt et al, 2012), and their DVM behavior makes a significant contribution to the transfer of organic matter from the upper productive layer to deeper layers (Radchenko 2007; Hernández- León et al, 2010;Dypvik et al, 2012). However, the huge biomass of these fish is underutilized.…”