Production of DOC by Calanus finmarchicus, C. glacialis and C. hyperboreus through sloppy feeding and leakage from fecal pellets (original) (raw)
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Marine Ecology Progress Series, 2012
Copepod faecal pellets (FP) are considered important contributors to vertical carbon flux, but investigations comparing FP production with FP export using sediment traps conclude that vertical export is not their only fate. FP are degraded to a large extent in the upper 60 m, and even among large, fast-sinking FP, only a fraction reaches sediment traps deeper than 200 m. Retention mechanisms for copepod FP are still not well understood. In order to investigate the relative importance of the small (<180 µm) compartment of the plankton community versus larger filter-feeding copepods for degradation of large, fast-sinking FP, we incubated FP produced by Calanus finmarchicus (Gunnerus) in 180 µm-filtered water from the chlorophyll a maximum. From a series of experiments, we found that the degradation of large FP is time-dependent, as no degradation was apparent after 20 or 48 h of incubation, but after 72 h FP volume was reduced by 32%. We also found that large filter-feeding copepods may facilitate the degradation process, since FP degradation increased from 0 to 75% after 48 h of incubation in the presence of 5 C. finmarchicus. We conclude that ciliates and dinoflagellates are able to degrade large copepod FP, but that this process is too slow to explain observed retention of large FP in the upper 200 m of the water column due to fast sinking of large particles. Rather than looking for single-factor explanations for flux-regulating processes, we stress the importance of investigating combined effects in relevant time frames to understand the complexity of carbon flux regulation in natural systems.
Marine Ecology Progress Series, 1987
The chemlcal composihon was analyzed of faecal pellets produced by copepods from Bedford Basin (Nova Scotia, Canada), mainly Pseudocalanus spp. and Temora longicornis, fed dfferent concentrations of the diatom Thalassiosira weissflogii. The feeding response of copepods to day-to-day changes in food concentration involved adjustments of ingestion rate in < 24 h; die1 differences in ingestion rate were found In copepods acclimated to high food concentration but not in those acclimated to low food concentration. Carbon and nitrogen content of faecal pellets (percentage of dry weight) was independent of food concentration, acclimation period to a given food concentration, and ingestion rates. Mean pellet composition was 25 % C and 3 % N; a higher C:N ratio in faecal pellets (7 to 9) as compared with that of the food (5.5) suggested that N was assimilated more efficiently than C. These results suggest that single values of the chemical composition of pellets might be used to estimate vertical flux of carbon and nitrogen via zooplankton faecal pellets. However, a comparison with literature data suggests that differences in carbon and nitrogen content of copepod faecal pellets might result from differences in food quality.
Small copepods (<2 mm) are the most abundant metazoans in the world’s oceans, a keystone in pelagic food webs. Small copepods are considered to be omnivorous, feeding on unicellular protists and phytoplankton, with carnivorous feeding –i.e. preying on zooplankton- restricted to larger copepods and cyclopoid copepods. We developed a PCR based technique that detected a diverse range of zooplankton species (eight families of decapods, bivalves, fish, and also other copepods) within the digestive tract of copepods traditionally considered to be “herbivorous”. This finding provides evidences that a significant component of copepod diets has been overlooked owed to the methodologies traditionally been carried out –visual inspection and pigments analysis. Such predatory behaviour extends the trophic role of small copepods in upwelling food webs, affecting the mesozooplankton communities through intraguild predation. Furthermore, this study helps to explain the discrepancies found between quantified phyto/microzooplankton ingestion and metabolic demands of copepods. In order to infer the consequences of this overlooked predatory behaviour to the flux of Carbon in the whole pelagic ecosystem, we screened the literature to obtain an estimate of weight specific ingestion rates (WSIR) based on their averaged weight for adult calanoid (n=121) and cyclopoid copepods (n=41), in the field (n=125) and under laboratory conditions (n=37). By multiplying the estimated WSIR by the standing stock of adult copepods in the upper 100 m of the ocean -assuming that i) copepods are approximately 80% of the total zooplankton biomass ii) only 50% are adults and iii) calanoids comprise between 30 to 40% of total copepods (the rest being cyclopoid copepods) - our carbon budget estimates show that on a global scale, copepods process, between 3.41 - 3.70 up to 20.75 - 21.87 gigaton (Gt) C yr-1 through zooplankton predation based on field and laboratory measured WSIR, respectively. This conservative field estimate reveals that copepods are channeling 31.28 - 33.95% more carbon towards upper trophic levels than previous estimates focused on phytoplankton and microzooplankton consumption (10.9 Gt C yr-1). Hence, copepod intrigued predation should definitely be considered in oceanic biogeochemical cycles and ecosystem models.
Marine Ecology Progress Series 262:185
Using 14 C-labeled phytoplankton as tracer, we investigated 2 mechanisms of immediate dissolved organic carbon (DOC) release during grazing activity of Calanus spp. -sloppy feeding and leakage from newly expelled fecal pellets. Half of the carbon cleared by Calanus spp. was released as DOC through sloppy feeding. Freshly expelled fecal pellets lost more than 20% of their carbon content within the first hour, corresponding to 6% of the carbon cleared. Thus, copepods should not only be considered as an essential link to higher trophic levels, but also as a feedback link to the microbial food web.
Marine Ecology Progress Series, 2005
Only a minor fraction of copepod defecation appears to leave the upper water column as fast-sinking fecal pellets in coastal waters. This study suggests that most egested matter from copepods is retained in the water column because (1) > 50% of fecal matter is released as small, slowsinking particles that are not surrounded by a peritrophic membrane and (2) small fecal pellets sink slowly and are degraded rapidly. The production, appearance and fate of fecal material from the calanoid copepod Acartia tonsa (fed on 2 different phytoplankton species, the cryptophyte Rhodomonas salina and the diatom Skeletonema costatum) was followed in association with the grazing activity of the copepod in a laboratory experiment. For both diets, > 50% of the defecation was released as dispersed small (<10 µm) non-pellet-bound particles. The diatom was less suitable as a food item than the flagellate and led to a 3 times higher rate of grazing and egestion. Nevertheless, specific assimilation and egg production per female were 2 times higher for the Rhodomonas diet versus the Skeletonema diet. As a result, the total egestion comprised 18% of the ingestion of Rhodomonas and 27% of the Skeletonema ingestion. In terms of vertical loss, sinking rates for both types of fecal pellets were ca. 5 m d-1 and, in terms of degradation, ca. 0.5 d-1 (18°C) in the absence of copepods. Transferring these findings to similar neritic conditions suggests that 60% of the fecal pellets from copepods will be recycled within a 15 m deep mixed layer and that > 80% of the total fecal matter can be expected to be retained when the unbound fecal material is also included.
Advances in Marine Biology, 2004
We compare the nature of copepod outfluxes of nonliving matter, the factors controlling their rate and their fate, and finally their role, particularly their relative importance in the carbon and nitrogen cycle. Copepods release dissolved matter through excretion and respiration and particulate matter through production of faecal pellets, carcasses, moults, and dead eggs. Excretion liberates several organic C, N, and P compounds and inorganic N and P compounds, with inorganic compounds constituting the larger part. The faecal pellets of copepods are covered by a peritrophic membrane and have a highly variable size and content. There is less information on the nature of other copepod particulate products. The weight-specific rates of posthatch mortality, respiration, excretion, and faecal pellet production have similar C or N levels and are higher than those of moulting and egg mortality. In general, most important factors controlling these rates are temperature, body mass, food concentration, food quality, and faunistic composition. Physical and biological factors govern the vertical fate of copepod products by aVecting their sedimentation speed and concentration gradient. The physical factors are sinking speed, advection, stratification, turbulent diVusion, and molecular diVusion. They influence the sedimentation speed and degradation of the copepod products. The biological factors are production, biodegradation (by zooplankton, nekton, and microorganisms) and vertical migration of copepods (diel or seasonal). Physical degradation and biodegradation by zooplankton and nekton are faster than biodegradation by microorganisms. The most important copepod outfluxes are excretion and faecal pellet production. Excretion oVers inorganic nutrients that can be directly used by primary producers. Faecal pellets have a more important role in the vertical transport of elements than the other particulate products. Most investigation has focused on carbon burial in the form of copepod faecal pellets, measured by sediment traps, and on the role of ammonia excretion in nutrient recycling. Full evaluation of the role of copepod products in the transport and recycling of elements and compounds requires a quantification of all copepod products and their diVerent fates, particularly detritiphagy, remineralization, and integration as marine snow. 254 C. FRANGOULIS ET AL. closely linked, as nutrient and light availability drive the biogenic components of the carbon cycle. The oceans are likely to be a major sink for released anthropogenic carbon on a long-term basis (Wollast, 1991). Marine flora incorporate inorganic carbon into organic molecules, constituting 40% of the total organic carbon production of the earth, and 95% of this production is by phytoplankton (Duarte and Cebrian, 1996). The carbon entering the upper ocean can be transferred to deep waters via three pathways; a physical one (the solubility pump; i.e., the transport of inorganic and organic carbon by deep convection) and two biological ones (the carbonate pump and the biological CO 2 pump; i.e., active and passive vertical transport of biogenic particles; Sundquist, 1993). The biological CO 2 pump largely relies on zooplankton. Despite the small size of zooplankton organisms (mm to mm size scale), their total biomass is estimated to be greater than that of other marine consumers such as zoobenthos and zoonekton (Conover, 1978). Herbivorous zooplankters consume more than 40% of the phytoplankton production (Duarte and Cebrian, 1996, and references therein) and release into the surrounding water a variety of liquid and solid materials that contribute to the dissolved matter (DM) and particulate matter (PM), respectively. DM and PM can accelerate the vertical transport of carbon and nutrients to deep water. An important process accelerating vertical fluxes of phytoplankton organic matter is the compaction and packing of this matter into faecal pellets by herbivorous zooplankton (e.g., Smayda, 1971; Turner, 2002). The intensity of this process varies according to the faecal pellet and zooplankton characteristics as well as environmental factors, so that carbon and nutrients will either be rapidly transported out of the eutrophic zone or be recycled in their production zone (Turner, 2002). These diVerent fates of carbon and nutrients transported through zooplankton products highlight the ''switching'' role of zooplankton in the cycle of these elements. The fact that zooplankton can drive the carbon and nutrient cycles by recycling or export of their products makes study of the fates of these products necessary. Furthermore, zooplankton outfluxes give information on the fates of pollutants, as zooplankters can transport elements and unassimilated organisms (even still living) through the sinking of their products (Fowler and Fisher, 1983). Pollutants can be concentrated in these products and transferred by ingestion to other organisms (Fowler, 1977). Reviews already exist on zooplankton-dissolved products (Corner and
Planktonic grazers are a potentially important source of marine dissolved organic carbon
Limnology and Oceanography, 1997
A series of laboratory experiments was performed to measure dissolved organic carbon (DOC) production during herbivorous grazing by heterotrophic protists (ciliate Strombidinopsis acuminatum, dinoflagellate Oxyrrhis marina) and copepods (Calanus pacificus). DOC production by phytoplankton was 31~0 measured. Experiments were performed in artificial seawater to provide a low DOC background against which changes in DOC concentration could be measured directly. We found that DOC production during grazing was high, i.e. 16-37% of algal C content was released as DOC during an ingestion event. Bacterial growth rates were stimulated by grazer activity, most likely due to increased availability of labile DOC; breakage of fecal pellets by copepods may also have yielded DOC. In contrast, DOC production by phytoplankton was low, ranging from 3 to 7% of algal C content per day. Generalizing from these rates, a simple budget shows that grazer DOC production should ba: 4-6 times greater than phytoplankton DOC production in any region of the ocean where grazing is the dominant phytoplankton loss process. Both phytoplankton and grazer species influenced the carbohydrate composition of the DOC produced. Dissolved carbohydrates averaged 30 and 22% of total DOC in phytoplankton-only and grazer-containing treatments, respectively, and most variability in carbohydrate content was due to variations in polysaccharide levels. We conclude that planktonic grazers are potentially a major source of DOC in the marine envronment.
Aquatic Microbial Ecology, 2004
Copepod and appendicularian grazing experiments using naturally occurring planktonic assemblages from a coastal embayment (Mejillones Bay, northern Chile upwelling system at 23º S) were conducted between October 2000 and October 2001. Total carbon ingestion rates based on sizefractioned chlorophyll data showed that dominant copepods (Acartia tonsa, Centropages brachiatus, Oithona similis and Paracalanus parvus) ingested between 2 and 8 µg C ind. -1 d -1 , while appendicularians (Oikopleura dioica and O. longicauda) ingested ~3 to 4 µg C ind. -1 d -1 . Even when most copepods were feeding on larger cells (> 23 µm) at high rates, the smaller copepods also grazed at similar rates on nanoplankton (5 to 23 µm) and picoplankton (< 5 µm). In contrast, chain-forming diatoms were cleared at very low rates by copepods. Bacteria were cleared only by appendicularians (~170 tõ 400 ml ind. -1 d -1 ) but not by any copepod, while heterotrophic protists constituted a substantial proportion in the diet of both copepods and appendicularians (~10 to 100% body carbon d -1 ), particularly during austral spring. Occasionally, copepod C-specific ingestion on heterotrophs was similar to that on autotrophic cells. Large ciliates and dinoflagellates were cleared but not ingested by the appendicularian O. dioica, suggesting a mechanism of trapping large cells in their houses and implying a rapid export of fresh material. Since heterotrophs are a common component in the diet of these 2 groups (omnivory by copepods and bacterophagy by appendicularians), they can potentially affect microbial food webs in this upwelling system and thus carbon export.