Fecal Pellet Carbon Research Articles

Plankton distribution and vertical flux of biogenic matter during high summer stratification in the Krka estuary (Eastern Adriatic)

The aim of this study was to investigate phytoplankton abundance, composition and vertical export in the highly stratified Krka estuary, Croatia. The estuary is stratified throughout the year, and an interface between fresh- and brackish water plays an important role in production and degradation of biogenic matter. Vertical export of particulate organic carbon (POC), phytoplankton carbon (PPC) and faecal pellet carbon (FPC) was studied by deploying sediment traps in the middle and lower reach of the estuary and in the adjacent coastal zone. Zooplankton faecal pellet (FP) production experiments were conducted to provide additional information on the potential contribution of FP to the total carbon flux. High suspended concentrations of POC, chlorophyll a and phytoplankton was found in the lower reaches of the Krka estuary, adjacent to a source of anthropogenic eutrophication. The fraction of organic detritus to the total POC flux was 61–69% inside the estuary but only 7% at the marine station. This indicates that the primary producers in the surface layer of the Krka estuary are decomposed in and below the interface and then settle as detritus to the bottom. Low sedimentation rates in the coastal zone outside the estuary revealed that the eutrophication does not spread out of the estuary. Mesozooplankton played a modest role in vertical flux regulation, due to their low abundance and dominance of smaller forms as well as low faecal pellet production rates. It is concluded that processes taking place at the freshwater-seawater interface are of major importance for the vertical carbon flux in the investigated area.

Real-time quantification of microbial degradation of copepod fecal pellets monitored by isothermal microcalorimetry

This study introduces isothermal microcalorimetry as a method to describe microbial degradation of copepod fecal pellets through measurements of the metabolic heat-flow produced by the degrading microbial community. We monitored the heat-flow for 20 to 24 h from samples of 300 to 1500 fecal pellets from a laboratory-cultivated calanoid copepod, Acartia tonsa Dana, fed on the chryptophyte Rhodomonas salina in excess. The microbes grew at 0.095 to 0.24 h -1 . Specific degradation rates were calculated using 3 different literature values of the carbon:volume ratio of fecal pellets. The mean ± SD specific degradation rates, Rd, were estimated at 0.023 ± 0.015 h -1 (for carbon:volume ratio of 0.39 pg C μm -3 ) and at 0.047 ± 0.038 h -1 (for carbon:volume ratio of 0.25 pg C μm -3 ), defined as the proportion of fecal pellet carbon completely oxidised to CO2 h -1 . The lowest car- bon:volume ratio (0.085 pg C μm -3 ) resulted in >100% fecal pellet carbon degradation within 20 h. These degradation rates are very high, presumably reflecting a fully active bacterial population. The limiting factor for microbial growth was not inorganic nutrients (N and P), but labile dissolved organic carbon (DOC). We compared heat-flow in situations with and without oxygen, and found it to be 1 order of magnitude lower under anoxic conditions. This indicates the presence of anaerobic or facultative bacteria associated with the fecal pellets. Possible applications of the methodology are discussed.

Fate of sinking particles, especially fecal pellets, within the epipelagic zone in the North Water (NOW) polynya of northern Baffin Bay

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 278:17-25 (2004) - doi:10.3354/meps278017 Fate of sinking particles, especially fecal pellets, within the epipelagic zone in the North Water (NOW) polynya of northern Baffin Bay Makoto Sampei1,*, Hiroshi Sasaki2, Hiroshi Hattori3, Mitsuo Fukuchi1, Barry T. Hargrave4 1National Institute of Polar Research, 9-10, Kaga 1-chome, Itabashiku, Tokyo 173-8515, Japan 2Senshu University of Ishinomaki, Ishinomaki, Miyagi 986-8580, Japan 3Hokkaido Tokai University, Minamisawa, Minamiku Sapporo, Hokkaido 005-8601, Japan 4Department of Fisheries and Oceans, Bedford Institute of Oceanography, Dartmouth, Nova Scotia B2Y 4A2, Canada *Email: sampei@nipr.ac.jp ABSTRACT: Moored time-programmed sediment traps were deployed from late August 1997 through late July 1999 in the North Water (NOW) polynya to determine the fate of sinking particles in the upper 200 m water column (epipelagic zone). The contribution of phytoplankton carbon (PPC), fecal pellet carbon (FPC), and other unidentified particulate carbon (UPC) to total particulate organic carbon (TPOC) collected in sediment traps varied over the 2 yr. UPC fluxes contributed significantly to TPOC fluxes (ca. 37 to 96%) during the sampling period. FPC fluxes (ca. 20 to 33 mgC m-2 d-1) dominated the TPOC fluxes (ca. 45 to 62%) between July and August 1998, when the highest TPOC fluxes occurred. However, during the period of highest primary production (June) more than 99% of the total fecal pellets produced in the epipelagic zone (ca. 74 to 122 mgC m-2 d-1) did not reach 200 m. No marked decreases in fecal pellet production in the upper 50 m and flux at 200 m were observed in July. The changing proportion of FPC flux between June and July suggests that losses of fecal pellets due to fragmentation by coprophagy and/or coprorhexy by zooplankton equivalent to ca. 73-121 mgC m-2 d-1 occurred in the upper mesopelagic layer in June. The fate of sinking particles represented by these fecal pellets can be influenced by the retention processes mediated by coprophagous feeding behavior of zooplankton within the epipelagic layers of the NOW. KEY WORDS: Polynya · Coprophagy · Coprorhexy · Fecal pellet · Retention process · Sediment trap · POC flux · Fragmentation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 278. Online publication date: September 06, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Is sedimentation of copepod faecal pellets determined by cyclopoids? Evidence from enclosed ecosystems

Vertical flux of faecal pellets was compared in 26 vertically stratified 27 m 3 (diameter 2 m, depth 9.3 m) in situ seawater enclosures deriving from four separate experiments on the Norwegian west wast. Sediment traps were mounted in the non-mixed lower layer at 8 m depth. The zooplankton community composition was natural in three of the experiments, while manipulated to include four concentrations of Calanus finmarchicus in one. Calanoid copepods such as C. finmarchicus, Paracalanus spp., Pseudocalanus spp. and Microcalanus spp. dominated the zooplankton biomass in all mesocosms, except in eight of the enclosures where the cyclopoid copepod Oithona spp. occupied up to 40% of the biomass. Vertical flux of faecal pellet carbon (FPC) showed a significant negative correlation with Oithona biomass. In order to determine the retention potential of Oithona, measured sedimented faecal pellet carbon (FPC sed ) was compared with estimated maximum and minimum egestion rates. FPC sed decreased with increased biomass of Oithona. When the contribution of Oithona to the total copepod biomass was high, FPC sed was reduced to a few per cent of the maximum calanoid egestion rate (E max ) and was significantly less than the expected minimum calanoid egestion rate (E min ) in four of the mesocosms. On the other hand, FPC sed increased towards E max when the fraction of calanoid copepods increased towards 100% of the total copepod biomass. The results were obtained in experiments characterized by an extensive range of physical and biological processes. We suggest that the biomass ratio between pellet-producing (calanoids) and pellet-reworking copepods (Oithona) may be used to predict relative pellet retention and/or sedimentation rates of calanoid faecal pellets in natural plankton.

Seasonal variation in production, retention and export of zooplankton faecal pellets in the marginal ice zone and central Barents Sea

Vertical distribution and sedimentation of faecal pellets (FPs) as well as the production rates of FPs by larger copepods were studied during three cruises to the Barents Sea in March and May 1998, and July 1999. Three to five 24-h stations were selected during each cruise, where at least one main station was located in Arctic water (ArW), one in the polar front region (PF) and one in Atlantic water (AW). A winter scenario was encountered in March with very low concentrations of FPs in the water column, most of the time well below 0.1 mg faecal pellet carbon (FPC) per cubic meter, and with sedimentation rates below 3 mg FPC m −2 day −1 at all depths and stations. Increased concentrations of FPs were observed in May and the maximum biomass of FPs was found in ArW (4.8 mg FPC m −3). This was reflected in high vertical flux of FPs in the ArW, just below the chlorophyll maximum (∼150 mg FPC m −2 day −1). FPC sedimentation explained ∼40% of the total particulate organic carbon (POC) export at 90 m depth at this station. Copepod FP production was moderate to high in May, reflecting favourable feeding conditions. Large spatial variation in the estimated retention potential of FPs was observed, ranging from 96% in AW to ∼40% in the PF region. The July scenario did not differ very much from that observed in May. The lowest suspended concentrations and vertical flux of FPs were again observed in AW, in spite of the high pellet-production rate. FPC explained 34% of the POC export out of the upper layer in ArW, 40% in the PF region, but only 8% in AW. The calculated retention potential of 70% of the produced copepod FPs in AW decreased to 60% and 47% in the PF region and ArW, respectively. Krill FPs comprised a significant fraction of both suspended and sedimented FPC throughout the central Barents Sea. The data show that spatial and temporal variations in the FP “retention filter” are extensive and evidently of importance for the patterns of vertical flux of organic matter and the regulation of pelagic–benthic coupling in the Barents Sea.

The occurrence of faecal material in relation to different pelagic systems in the Southern Ocean and its importance for vertical flux

Abstract:During the SO-JGOFS-Polarstern-cruise in Oct/Nov 1992, faecal pellet abundance and distribution were determined in order to assess the impact of zooplankton grazing and defecation within the following three typical Antarctic plankton regimes in the Atlantic sector: the Marginal Ice Zone (MIZ), the southern Antarctic Circumpolar Current (ACC) and the Polar Frontal region (PFr). In contrast to the more southern regions, the PFr was characterised by the occurrence of relatively dense phyto-plankton blooms and high copepod concentrations. Faecal pellets were relatively abundant in the MIZ reaching up to > 105 µg faecal pellet carbon (FPC) m-3, whereas the values in the more northern regions were about one to two orders of magnitude lower: about 6 µg FPC m-3 in the southern ACC and less than 1 µm FPC m-3 in the PFr. Thus, the region with the highest phyto- and zooplankton concentrations showed by far the lowest faecal pellet standing stock concentrations. These results were compared to other regions in the Southern Ocean and to other regions in the world oceans and possible reasons for this situation and the potential ecological impact are discussed. Our investigations show, that not only the biomass of phytoplankton and zooplankton, but also mainly the structures of the plankton communities are decisive for sedimentation potentials of carbon and silica via faecal pellets in the different regions of the ocean.

Eutrophication and vertical flux: a critical evaluation of silicate addition

Availability of dissolved silicate (DSi) can affect phytoplankton species composition and the pelagic-benthic coupling. Further, consumption of DSi is assumed to be proportional to export production and sedimentation. The effect of DSi on the vertical flux of biogenic matter was investi- gated in 4 mesocosm experiments, where all enclosures were fertilised with nitrate and phosphate (NP), while half of the enclosures were given DSi as well (NPS). Sedimentation rates were expected to increase with consumption of DSi according to the 'silicate-sedimentation' hypothesis, as a result of diatom aggregate formation and/or increased faecal pellet production form diatom-grazing cope- pods. Diatoms and faecal pellet carbon did contribute significantly more to the vertical flux in the NPS than in the NP enclosures. However, sedimentation of particulate organic carbon (POC) was still not significantly different between the NP and NPS treatments. This was due to high sedimentation rates of Phaeocystis pouchetii in the NP enclosures. The results of these experiments indicate that the relationship between DSi and daily carbon export is not necessarily as simple as suggested by the silicate-sedimentation hypothesis. Much of the uncertainties concerning the hypothesis are related to the sedimentation of P. pouchetii, as they contribute not only cell carbon but also mucilagenous matter.

Biological components of Ross Sea short-term particle fluxes in the austral summer of 1995–1996

The Ross Sea, a region of high seasonal production in the Southern Ocean, is characterized by blooms of the haptophyte Phaeocystis antarctica and of diatoms. The different morphology, structural composition and consumption of these two phytoplankton by grazing zooplankton may result in different carbon cycling dynamics and carbon flux from the euphotic zone. We sampled short-term (∼2 days) particle flux at 5 sites from 177.6°W to 165°E along a transect at 76.5°S with traps placed below the euphotic zone at 200 m during December 1995–January 1996. We estimated carbon flux of as many eucaryotic organisms and fecal pellets as possible using microscopy for counts and measurements and applying volume:carbon conversions from the literature. Eucaryotic organisms contributed about 20–40% of the total organic carbon flux in both the central Ross Sea polynya and in the western polynya, and groups of organisms differed in contribution to the carbon flux at the different sites. Algal carbon flux ranged from 4.5 to 21.1 mg C m −2 day −1 and consisted primarily of P. antarctica (cell plus mucus) and diatom carbon at all sites. Different diatom species dominated the diatom flux at different sites. Carbon fluxes of small pennate diatoms may have been enhanced by scavenging, by sinking senescent P. antarctica colonies. Heterotrophic carbon flux ranged from 9.2 to 37.6 mg C m −2 day −1 and was dominated by athecate heterotrophic dinoflagellate carbon in general and by carbon flux of a particular large athecate dinoflagellate at two sites. Fecal pellet carbon flux ranged from 4.6 to 54.5 mg C m −2 day −1 and was dominated by carbon from ovoid/angular pellets at most sites. Analysis of fecal pellet contents suggested that large protozoans identified by light microscopy contributed to ovoid/angular fecal pellet fluxes. Carbon flux as a percentage of daily primary production was lowest at sites where P. antarctica predominated in the water column and was highest at sites where fecal pellet flux was highest. This indicates the importance of grazers in carbon export.

Seston effects on faecal pellet carbon concentrations from a mixed community of copepods in Balsfjord, Norway, and the Antarctic Polar Front

The effects of phytoplankton community composition on faecal pellet carbon concentrations from a mixed community of large (>500 m) copepods were examined in studies in two areas: Balsfjord, Norway, and the Pacific sector of the Antarctic Polar Front. The Balsfjord study was conducted during the spring bloom of 1994. Faecal pellet production rates, dry weights and total amino acid carbon concentrations were positively correlated with chlorophyll concentrations. However, faecal pellet carbon concentrations were not correlated to chlorophyll levels but rather appeared related to the phytoplankton community composition. Lower faecal pellet carbon concentrations were consistently found when diatoms constituted >50% of the available plankton. Similar results were found in the Antarctic Polar Front study, which was conducted during the austral spring and summer of 1997–1998. Over spring and summer, faecal pellet carbon concentrations were negatively correlated with particulate biogenic silica concentrations. Results from both of these field studies suggest that, on a community level, the diet of copepods affects the carbon concentration of the pellets and thus the potential flux of carbon via faecal pellets. 2001 International Council for the Exploration of the Sea

Estimates of oceanic mesozooplankton production: a comparison using the Bermuda and Hawaii time-series data

Abstract Mesozooplankton growth rates were estimated for the Hawaiian (HOT) and Bermuda (BATS) ocean time-series stations using the empirical model of Hirst and Lampitt (Marine Biology 132 (1998) 247), which predicts copepod growth rate from temperature and body size. Using this approach we derived seasonal and annual estimates of mesozooplankton production as well as rates of mesozooplankton ingestion and egestion using assumed growth and assimilation efficiencies for the period 1994–1997. Annual mesozooplankton production estimates at HOT (average 0.79 mol C m −2 yr −1 ) were higher than production estimates at BATS (average 0.33 mol C m −2 yr −1 ) due to both higher mesozooplankton biomass and higher estimated mesozooplankton individual growth rates. Annual primary production at the two sites was similar (average 14.92 mol C m −2 yr −1 at HOT and 13.43 mol C m −2 yr −1 at BATS). Thus, mesozooplankton production was a greater fraction of primary production at HOT (0.05) as compared to BATS (0.02). Mesozooplankton potentially contributed more to the gravitational flux of carbon at HOT, where the ratio of the average annual estimate of mesozooplankton fecal pellet carbon production/annual estimate of carbon flux at the base of the euphotic zone was 1.03 compared to the same ratio of 0.39 at BATS. Mortality estimates were similar to estimates of mesozooplankton production when compared over the entire study period. The higher mesozooplankton biomass and derived rate parameters at HOT compared to BATS may be due to the more episodic nature of nutrient inputs at BATS, which could result in mis-matches between increases in phytoplankton production and the grazing/production response by mesozooplankton. In addition, there is evidence to suggest that there are periodic blooms of gelatinous macrozooplankton (salps) at BATS that may not be captured sufficiently by the monthly sampling program. Thus the gelatinous zooplankton would add to the overall grazing impact on the phytoplankton at BATS as well as the contribution of zooplankton to the gravitational flux of biogenic material via fecal pellet production.

Comparison of the springtime vertical export of biogenic matter in three northern Norwegian fjords

A comparison of vertical flux of biogenic matter, phytoplankton and faecal pellets was carried out in April 1997 in 3 fjords, Ullsfjord, Balsfjord and Malangen, which exhibit different hydro- graphic conditions in the inner northern Norwegian coastal zone. Vertical export of biogenic matter was high (200 to 850 mg particulate organoc carbon (POC) m -2 d -1 ) compared to previous years, par- ticularly that of chlorophyll a (0.9 to 22 mg m -2 d -1 ). Some differences in the timing and composition between the fjords were detected, but on average, vertical export in the upper 100 m was similar in all three. Average phytoplankton carbon (PPC) sedimentation was 136 mg C m -2 d -1 , and it con- tributed 35 ± 12% to the vertical export of POC. The diatoms Thalassiosira angulata, T. norden- skioeldii, Chaetoceros socialis and C. furcellatus were by far the most important taxa, contributing on average 68% to the PPC export. Another dominant spring bloom species in northern Norwegian fjords, the colony-forming prymnesiophyte Phaeocystis pouchetii, contributed on average only 12% to the vertical PPC flux, and it was of minor importance in Balsfjord. In contradiction to previous find- ings in the area, vertical POC export was not dominated by faecal pellet carbon (FPC) (125 mg C m -2 d -1 ). While a significant export of FPC and retention of PPC was observed during the vernal blooms in 1982, 1992 and 1996 (PPC/FPC = 0.23 ± 0.02), a mismatch scenario was encountered in 1997 (PPC/ FPC = 1.32 ± 0.31), resulting in large-scale vertical export of diatoms. The differences in vertical export of biogenic matter between fjords were much smaller than interannual differences. It is sug- gested that interannual differences in oceanic-coastal coupling, crucial for the advection of meso- and macrozooplankton from the shelf adjacent to the fjords and for grazing, are the cause for the recurrent match and infrequent mismatch scenarios.

Contribution by mezooplankton focal pellets to the carbon flux on Nordvestkbanken, north Norwegian shelf in 1994

Abstract Fecal pellet production rates for mesozooplankton (> 500 µm) were measured monthly at a shelf edge and inshore station in northern Nonvegian coastal waters during Nlarch-September as part of the Ocean Margin Exchange (OMEX) stLrdy. The total potential fecal pellet carbon flux was higher at the inshore station except in May when Calanus finmarchicus (Gunnerus) was more abundant at the shelf edge. Mesozooplankton fecal pellets had the potential to contribute 2.5 % (April & September) to> 100% (May-August) of the POC flux found in sediment traps. This compared with only 5-35 %, when fecal pellet carbon flux was measured from trap pellets suggests that a significant amount of fecal pellet remineralization or coprophagy was occurring in the surface waters. Calanus finmarchicus apparently plays a pivotal role in moderating pellet carbon flux on Nordvestbanken both through its potential fecal pellet production and possibly through coprophagy. Carbon ingestion by the lccrge mesozooplankton at the shelf e...

Release of dissolved organic carbon from copepod fecal pellets in the Greenland Sea

The particulate and dissolved carbon pools within fecal pellets as well as their release of dissolved organic carbon (DOC) were traced with 14C-labeled fecal pellets produced by large calanoid copepods collected in the Greenland Sea. Two experimental designs were used to examine DOC within and released from copepod fecal pellets. In the first experiment, in which 14C-labeled fecal pellets were incubated in rotating bottles, there was a continual and dynamic interaction between the particulate organic carbon (PO 14C) and DO 14C pools within the fecal pellets. Initially the fecal pellets contained 50% of their total 14C-labeled carbon as DO 14C. Of the initial DO 14C pool, 86% was utilized or leached from the fecal pellets within 6 h, after which DO 14C concentrations in the pellets remained low. In contrast, PO 14C concentrations remained constant through the first 6 h and then slowly declined such that particulate fecal pellet carbon was lost at a rate of 0.007±0.003/h. The estimated half-life of the 14C-labeled carbon in the fecal pellets was 2.4 days. In order to investigate the effects of sinking on DOC release from pellets, fecal pellets were suspended in water columns for 5.5 days through which successively deeper water (max depth 300 m) was pumped each day. Dissolved organic carbon was released from the fecal pellets sinking through this simulated water column under both biotic and abiotic conditions. After 5.5 days, 39% of the fecal pellet 14C was found in the DO 14C pool of the surrounding water under biotic conditions. The majority of this DO 14C was released during the first 48 h at an estimated rate of 0.04–0.22 ng DO 14C/pellet/h based on fecal pellets with a total organic carbon (TOC) concentration of 10 ng C/pellet. Eighty four percent of the TO 14C within the fecal pellets was lost during the 5.5 days which gives an estimated carbon half-life of 3.3 days. With an average pellet sinking velocity of 50 m/day, this results in most of the carbon being lost from the pellets in the first 48–72 h which corresponded in this experiment to the upper 100–150 m. This result suggests that fecal pellet carbon may be primarily recycled in the upper water column in polar waters. Estimating the amount of DOC released from calanoid copepod fecal pellets over the 3.5 month grazing season in the central Greenland Sea gives an average value of 6 g DOC/m 2 which is comparable to the estimated annual production of DOC from new production.

Seasonal patterns and depth-specific trends of zooplankton fecal pellet fluxes in the Northwestern Mediterranean Sea

Because zooplankton feces represent a potentially important transport pathway of surface-derived organic carbon in the ocean, we must understand the patterns of fecal pellet abundance and carbon mobilization over a variety of spatial and temporal scales. To assess depth-specific water column variations of fecal pellets on a seasonal scale, vertical fluxes of zooplankton fecal pellets were quantified and their contribution to mass and particulate carbon were computed during 1990 at 200, 500, 1000, and 2000 m depths in the open northwestern Mediterranean Sea as part of the French-JGOFS DYFAMED Program. Depth-averaged daily fecal pellet flux was temporally variable, ranging from 3.04×10 4 pellets m 2 d -1 in May to a low of 6.98×10 2 pellets m 2 d -1 in September. The peak flux accounted for 50% of the integrated annual flux of fecal pellets and 62% of pellet carbon during only two months in mid-spring (April and May). Highest numerical fluxes were encountered at 1000 m, suggesting fecal pellet generation well below the euphotic zone. However, there was a trend toward lower pellet carbon with in- creasing depth, suggesting bacterial degradation or in situ repackaging as pellets sink through the water column. At 500 m, both the lowest pellet numerical abundance and carbon flux were evident during the spring peak. Combined with data indicating that numerical and carbon fluxes are dominated at 500 m by a distinct type of pellet found uniquely at this depth, these trends suggest the presence of an undescribed mid-water macro-zooplankton or micro-nekton community. Fecal pellet carbon flux was highest at 200 m and varied with depth independently of overall particulate carbon, which was greatest at 500 m. Morphologically distinct types of pellets dominated the numerical and carbon fluxes. Small elliptical and spherical pellets accounted for 88% of the numerical flux, while larger cylindrical pellets, although relatively rare (<10%), accounted for almost 40% of the overall pellet carbon flux. Cylindrical pellets dominated the pellet carbon flux at all depths except 500 m, where a large subtype of elliptical pellet, found only at that depth, was responsible for the majority of pellet carbon flux. Overall during 1990, fecal pellets were responsible for a depth-integrated annual average flux of 1.03 mgC m 2 d -1, representing 18% of the total carbon flux. The proportion of vertical carbon flux attributed to fecal pellets varied from 3 to 35%, with higher values occurring during periods when the water column was vertically mixed. Especially during these times, fecal pellets are a critical conveyor of carbon to the deep sea in this region.

Analysis of copepod fecal pellet carbon using a high temperature combustion method

Analysis of copepod fecal pellet carbon using a high temperature combustion method

The role of sinking fecal pellets in stratified euphotic zones

The euphotic zone at the VERTEX II oligotrophic sediment trap station (18°N, 108°W) can be viewed for simplicity a as two-layered system with (1) an upper mixed layer (0–40 m) of relatively high primary production, low chlorophyll concentration, and low zooplankton biomass, and (2) a lower layer (40–100 m) containing the chlorophyll and particulate organic carbon maxima, higher zooplankton biomass, and relatively low primary production. Particle traps at 30 m yielded no particulate carbon flux, while traps at 120 m registered 38 mg C m −2 d −1, with many visible fecal pellets. Zooplankton in the upper layer apparently produced small pellets which were recycled in situ. Fecal pellet carbon production by 200–2000 μm zooplankton in the lower layer, however, was 30% of trap-measured C flux. Tiny pellets produced by 53–200 μm zooplankton were mostly recycled within the euphotic zone, regardless of which euphotic layer the animals were inhabiting when collected. Comparisons are made between the relative contributions of sinking fecal pellets when the VERTEX II euphotic zone is considered as a single uniform layer rather than as a two-layered system. In addition, comparison of the VERTEX II data with data from the eutrophi VERTEX Vc site (35°50′N, 122°30′W) suggests that zooplankton can be more significantly coupled to carbon flux out of the bottom layers of oligotrophic euphotic zones than to carbon flux out of unlayered eutrophic euphotic zones.

Dissolved and fecal pellet carbon and nitrogen release by zooplankton in tropical waters

Abstract Carbon (C) and nitrogen (N) release by tropical zooplankton (mostly copepods) and micronekton (euphausiids, pelagic red crabs, and salps) was investigated near VERTEX particle traps at 18°N, 108°W (in 1981) and 15°40′N, 107°30′W (in 1982). The objective was to assess the significance of fecal pellet release relative to respiratory and dissolved excretory release of C and N and relative to primary production in the same waters. For small ( Daily fecal pellet C egestion represented only 2 to 3% of both large and small zooplankton body C content, and daily fecal pellet N egestion was