Post-bloom grazing byCalanus glacialis, C. finmarchicus andC. hyperboreus in the region of the Polar Front, Barents Sea

Mesozooplankton grazing on phytoplankton, as inferred from gut pigment contents and gut evacuation rates, was studied in relation to primary production and particulate export flux on 6 cruises in the Santa Monica Basin, California, USA. Gut evacuation rates did not vary significantly among different taxa or size classes examined and were consistent with extrapolations of published temperature relationships. Shipboard incubations with cultured phytoplankton and net-collected zooplankton indicated a seasonal difference in the extent to which gut passage converts chlorophyll to non-fluorescent by-products. In autumn experiments, only about 5 % of ingested chlorophyll could not be recovered as phaeopigment. In winter-spring experiments, approximately 70% of ingested chlorophyll (chl) was destroyed. In contrast, other indices of pigment destruction, the ingestion rates of a dominant copepod species and the ratio of water-column phaeopigment:silica fluxes, did not reveal a significant gut passage effect during winter-spring cruises. Mesozooplankton community grazing impact varied from 1.7 to 7.3 mg chl m-' d-l, with higher grazing during the winter-spring period (mean = 5.8 mg chl m-2 d-l) as compared to the autumn (mean = 2.3 mg chl m-2 d-l). On average, mesozooplankton grazing accounted for a loss of 11.7% of chlorophyll standing stock d-' with a 6 cruise range of 6 to 18% d-' Mesozooplankton grazing on phytoplankton accounted for 29 to 4 4 % (mean = 39%) of measured primary production for the winter-spring cruises, but only 16 to 24% (mean = 19%) of production in the autumn. From measured phaeopigment fluxes into sediment traps below the euphotic zone, only 27.5 % (range 23 to 32%) of this grazing on phytoplankton could be accounted for as export flux. Thus, in terms of contribution to particulate flux or remineralization, most mesozooplankton grazing in the Santa Monica Basin was functionally equivalent to that of microzooplankton. Direct grazing on phytoplankton contributed 15 to 38% of carbon flux into sediment traps during winter-spring and 8 to 13 % during autumn. Nonetheless, if feeding on nonpigmented prey is considered from the available information on carbon:phaeopigment ratios of fresh fecal pellets, over 70 % of the carbon flux to traps could have a mesozooplankton grazing origin.

Section: Grazing Rate Estimatessupporting

confidence: 80%

Mesozooplankton grazing in the Southern California Bight. II. Grazing impact and particulate flux

Landry¹,

Lorenzen²,

Peterson³

1994

“…Hansen et al (1990) noted that Calanus spp. displayed no consistent day-night vertical migration patterns during springsummer seasons.…”

Section: Discussionmentioning

confidence: 99%

“…High zooplankton abundance often coincides spatially with high chl a concentration (Hansen et al 1990), and food concentration may stimulate diel migratory behaviour (Conover 1988, and citations therein). Herman (1983) observed that peaks of Calanus glacialis and C. finmarchicus occurrence in north-eastern Baffin Bay were commonly situated 3 to 4 m above the chl a maximum, whereas the distribution pattern of C. hyperboreus coincided with the chl a peak.…”

Section: Discussionmentioning

confidence: 99%

Arctic zooplankton do not perform diel vertical migration (DVM) during periods of midnight sun

Błachowiak‐Samołyk¹,

Kwaśniewski²,

Richardson³

et al. 2006

102

Diel vertical distribution patterns of dominant zooplankton taxa were studied during a period of midnight sun (May 1999) in the Marginal Ice Zone (MIZ) of the Barents Sea along 2 transects across the ice edge. Eight stations were sampled every 6 h over 24 h at 5 depth intervals. Our study confirmed that copepod nauplii (most probably Calanus hyperboreus and C. glacialis) together with Pseudocalanus spp. preferred the surface water layer. The herbivores C. finmarchicus, C. glacialis, and C. hyperboreus concentrated in the upper 50 m depth interval, whereas the omnivores Metridia longa and Microcalanus spp. were generally found in deeper waters. As a result of vertical distribution patterns of the numerically abundant taxa, a bulk of zooplankton was concentrated within the 0-50 m layer. Vertical distribution patterns of all examined taxa/groups varied in time as a result of habitat changes (with respect to water mass distribution and sea depth) as well as random patchiness. Based on our data and on a comprehensive literature survey on Arctic zooplankton diel vertical migration (DVM), we postulate that common zooplankton taxa in the MIZ of the Barents Sea do not perform DVM under the midnight sun. Arctic C. glacialis in May 1999 occupied deeper layers at stations with more ice cover and less melt water. This distribution pattern was probably related to the species' reproduction. At the same time, Atlantic C. finmarchicus was concentrated further away from the ice edge and chlorophyll a maximum, and presumably had not begun its seasonal reproduction. KEY WORDS: Zooplankton · Calanus · Diel vertical migration (DVM) · Marginal Ice Zone · Barents SeaResale or republication not permitted without written consent of the publisher

“…Several studies, however, have shown that high latitude zooplankton can consume a large portion of phytoplankton production (e.g. Hansen et al 1990, Nielsen & Hansen 1995. This variability might reflect seasonal and regional shifts in the ratio between grazers and primary production (Landry et al 1994a).…”

Section: Impact Of the Zooplankton Community On The Bloommentioning

confidence: 99%

Zooplankton response to a phytoplankton bloom near South Georgia, Antarctica

Atkinson¹,

Shreeve²,

Pakhomov³

et al. 1996

A shelf site near the island of South Georgia was sampled during a spring bloom in January 1994. Chlorophyll a (chl a ) values declined from 19 to 6 mg mv3 during the 8 d of sampling. The bloom comprised mainly long pennate diatoms and large colonies of centric diatoms; a 200 pm sieve retained over two-thirds of the chl a. Mesozooplankton biomass was high, 12.3 g dry mass me2 within the top 200 m, and comprised mainly copepods. A series of Longhurst Hardy Plankton Recorder profiles showed that the numerical dominants (Oithona similis, Drepanopus forcipatus and pteropods) resided mainly within the top 20 m, whereas the large, blomass-dominant copepods had secondary maxima rather deeper within the thermocline. D~e l vertical migration was not a feature of this community, being limited to inetridlid and euchaet~id copepods. Gut fluorescence measurements on 7 large copepod species showed that all fed during both day and nlght, although guts tended to be fullest during afternoon and night. About 20% of chl a grazed by these copepods occurred below the mixed layer, thus representing a potentially direct export of carbon from the system via sinking faecal pellets. Algal carbon rations (% body carbon ingested per day) of mixed layer copepods ranged from 3 % (Rhincalanus gigas) to 20% (small copepods). With the exception of R. gigas, these values from gut fluorescence agreed with independent estimates from the site following the d e c l~n e of chl a during incubations in ambient seawater Despite low clearance rates, ingestion rates (per copepodid) were at the upper end of recorded Antarctic values, suggesting food saturation. Calanoides acutus and R gjgas cleared diatoms (including the hlghly elongated 0.5 to 1 mm forms) at maximal rates. Metridla spp., Calanuspropinquus and small copepods, by contrast, cleared dinoflagellates and ciliates faster than diatoms of similar size The total mixed layer zooplankton probably removed < 5 % of daily primary production and < 5 % of protozoan standing stocks per day.