Feeding on dispersed vs. aggregated particles: The effect of zooplankton feeding behavior on vertical flux

Abstract

Zooplankton feeding activity is hypothesized to attenuate the downward flux of elements in the ocean. We investigated whether the zooplankton community composition could influence the flux attenuation, due to the differences of feeding modes (feeding on dispersed vs. aggregated particles) and of metabolic rates. We fed 5 copepod species—three calanoid, one harpacticoid and one poecilamastoid–microplankton food, in either dispersed or aggregated form and measured rates of respiration, fecal pellet production and egg production. Calanoid copepods were able to feed only on dispersed food; when their food was introduced as aggregates, their pellet production and respiration rates decreased to rates observed for starved individuals. In contrast, harpacticoids and the poecilamastoid copepod Oncaea spp. were able to feed only when the food was in the form of aggregates. The sum of copepod respiration, pellet production and egg production rates was equivalent to a daily minimum carbon demand of ca. 10% body weight-1 for all non-feeding copepods; the carbon demand of calanoids feeding on dispersed food was 2–3 times greater, and the carbon demand of harpacticoids and Oncaea spp. feeding on aggregates was >7 times greater, than the resting rates. The zooplankton species composition combined with the type of available food strongly influences the calculated carbon demand of a copepod community, and thus also the attenuation of vertical carbon flux.

Copepod Grazing Influences Diatom Aggregation and Particle Dynamics

“…However, no changes in the S. marinoi and C. neogracile aggregate size or abundance have been observed with E. acutifrons (Table 7 and Figures 3, 4, 7, 8). Cruise feeders detritivores (such as E. acutifrons) feeding on marine snow has already been demonstrated (Koski et al, 2005(Koski et al, , 2007(Koski et al, , 2017 and is often associated to particle flux attenuation. However in our study, E. acutifrons with prey to predator size ratios ranging from 7 to 20 did not significantly change the particle spectra neither in size nor in abundance or sinking rates (Figure 8).…”

“…Swimming of large Euphausiids was demonstrated to fragment marine aggregates into small particles that sink more slowly, become accessible to small grazers and microbial organisms, thus enhancing remineralization and carbon cycling (Dilling and Alldredge, 2000;Goldthwait et al, 2004Goldthwait et al, , 2005. Sinking organic materials such as marine snow aggregates and fecal pellets could also constitute alternative food sources for mesozooplankton (Dagg, 1993;Lampitt et al, 1993;Steinberg, 1995;Dilling et al, 1998;Kiørboe, 2000;Dilling and Brzezinski, 2004;Koski et al, 2017). Ostracods, cladocerans, ascidian larvae, and copepods are aggregate colonizers, and can feed either on prokaryotic community located inside or at the surface of the aggregates, or directly on the aggregate matrix (Green and Dagg, 1997;Shanks and Walters, 1997).…”

“…From 20 to 70% of the aggregate carbon biomass may be degraded by these colonizers during their sinking under the euphotic zone (Kiørboe, 2000). In a recent study investigating copepod grazing behavior on aggregated particles, Koski et al (2017) demonstrated that both harpacticoida and poecilostomatoida copepods were able to feed on aggregates and could thus attenuate the particle carbon flux. Aggregation processes and dynamics are increasingly understood via the combination of laboratory experiments and models (Beauvais et al, 2006;Passow and De La Rocha, 2006;Gärdes et al, 2011;Jackson, 2015;Prairie et al, 2019), mesocosm experiments (Alldredge et al, 1995;Passow and Alldredge, 1995b;Svensen et al, 2001Svensen et al, , 2002Moriceau et al, 2018;Cisternas-Novoa et al, 2019), and in situ observations (Lampitt et al, 2010;Laurenceau-Cornec et al, 2015;Nowald et al, 2015;Giering et al, 2017;Cavan et al, 2018;Bach et al, 2019).…”

“…Swimming activity being intrinsically linked to feeding, copepod flexible diet may also modulate particle fluxes through differential grazing between free diatoms and aggregated diatoms (Bochdansky and Herndl, 1992;Bochdansky et al, 1995) or by changing the composition of the phytoplankton community (Bach et al, 2019). Their distinct functional feeding traits as filter feeders or ambush feeders (Kiørboe, 2011;Lombard et al, 2013b;Koski et al, 2017) make them organisms of particular interest to study particle dynamics. Recognizing that only very few studies have dealt with the interactions between large particles and grazers under laboratory conditions, we propose here to study the effects of both copepod grazing and swimming activities on diatom aggregate dynamics (i.e., changes in size, sinking velocity, and elemental composition) using rolling tank experiments (Shanks and Edmondson, 1989).…”

Effect of anthropogenic warming on microbial respiration and particulate organic carbon export rates in the sub-Antarctic Southern Ocean

“…Another advantage of a short incubation is that it reduces the time available for wall or bottle effects to influence our results. We also used 20 ml sized vials, which were 5× larger than similar previous studies (Cavan et al 2017b, Koski et al 2017, to further reduce bottle and wall effects. However, the vials were still small enough to allow us to concentrate particles into a small volume and measure a decline in oxygen concentration.…”