ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on December 6, 2007
ICES Journal of Marine Science: Journal du Conseil 2008 65(3):351-360; doi:10.1093/icesjms/fsm175
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
This article appears in the following ICES Journal of Marine Science issue: 4th International Zooplankton Production Symposium: Human and Climate Forcing of Zooplankton Populations [View the issue table of contents]
Mesozooplankton grazing in the coastal Gulf of Alaska: Neocalanus spp. vs. other mesozooplankton
1 Department of Biology, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, and Atmospheric, Marine and Coastal Environment (AMCE) Program, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong
2 Louisiana Universities Marine Consortium, Chauvin, LA 70344, USA
3 NOAA Alaska Fisheries Science Center, Seattle, WA, USA
Correspondence to H. Liu: tel: +1 852 23587341; fax: +1 852 23581559; e-mail: liuhb{at}ust.hk
Liu, H., Dagg, J. M., Napp, J. M., and Sato, R. 2008. Mesozooplankton grazing in the coastal Gulf of Alaska: Neocalanus spp. vs. other mesozooplankton. – ICES Journal of Marine Science, 65: 351–360.Three species of large calanoid copepod, Neocalanus flemingeri, Neocalanus plumchrus, and Neocalanus cristatus, dominate the spring biomass of mesozooplankton in the Subarctic Pacific. We compared the grazing impact of Neocalanus species on phytoplankton with grazing by the remainder of the mesozooplankton community in the coastal and shelf waters of the Gulf of Alaska during spring and summer 2003. Neocalanus spp. and other mesozooplankton fed mainly on particles >20 µm, and phytoplankton in the smaller size-fractions (<20 µm) increased in the presence of mesozooplankton, possibly because of a trophic cascade resulting from mesozooplankton consumption of microzooplankton. Neocalanus spp. accounted for most of the mesozooplankton biomass and herbivory in the shelf water of the Gulf of Alaska and in the Prince William Sound (PWS) during April/May. The biomass of other mesozooplankton (mostly small copepods) varied seasonally and spatially; it did not increase in summer after the descent of Neocalanus spp. from the surface layer. On the basis of the clearance rates obtained from our experiments, in spring, grazing by Neocalanus spp. and the remaining mesozooplankton consumed
10% of daily growth of phytoplankton >20 µm in the outer-shelf region, where chlorophyll a concentrations were <0.5 mg m–3, and in PWS. Mesozooplankton consumed a smaller percentage of the >20 µm daily phytoplankton production in the inner- and mid-shelf regions where chlorophyll a concentrations were typically >5 mg m–3 with blooms of large diatoms. In summer, without Neocalanus spp. in the surface layer, mesozooplankton grazing accounted for a very small proportion of phytoplankton production across the whole shelf.
Keywords: grazing, Gulf of Alaska, mesozooplankton, Neocalanus, phytoplankton
Received 22 June 2007; accepted 6 October 2007; advance access publication 6 December 2007.
 |
Introduction |
|---|
 Top Introduction Material and methodsResultsDiscussionConclusionsReferences |
|---|
Three species of large calanoid copepod, Neocalanus flemingeri, Neocalanus plumchrus, and Neocalanus cristatus, commonly dominate the spring biomass of mesozooplankton in the coastal and shelf regions of the Gulf of Alaska (Cooney, 1986; Miller, 1993; Incze et al., 1997; Coyle and Pinchuk, 2003). They have annual life cycles, except for a portion of the N. flemingeri population in the western Pacific and its marginal seas, which is biennial (Miller and Clemons, 1988; Miller and Terazaki, 1989; Mackas and Tsuda, 1999; Tsuda et al., 1999). Each year, Neocalanus nauplii ascend from deep in the water column to the surface water in spring and complete their annual feeding, growth, and development in spring and early summer. Upon completing their growing season and accumulation of lipid stores in the upper ocean, Neocalanus spp. descend from the upper layer to spend late summer, autumn, and winter at 500–2000 m, where they mate, spawn, and die.
The absence of a spring phytoplankton bloom in the Subarctic North Pacific was originally attributed to grazing by Neocalanus spp. (Beklemishev, 1957; Heinrich, 1962; Frost, 1987; Parsons and Lalli, 1988). Egg production by Neocalanus spp. occurs very early in the year at depth, and it was suggested that the early arrival of copepodites at the surface allowed them to control the bloom through grazing. It was later demonstrated that mesozooplankton grazing at ineffective at controlling total phytoplankton production (Dagg, 1993a; Tsuda and Sugisaki, 1994; Boyd et al., 1999). However, mesozooplankton may still play an important role in regulating the abundance of micrograzers (Gifford, 1993) and therefore alter the size structure of the phytoplankton community (Landry and Lehner-Fournier, 1988; Landry et al., 1993a; Shiomoto and Asami, 1999; Liu et al., 2005).
Most studies of mesozooplankton feeding in the Subarctic Pacific have focused on Neocalanus spp., which are only present in surface waters for a few months of each year. Little is known about the grazing impact of other mesozooplankton at other times of the year (Frost, 1993), and almost no grazing studies for the coastal Gulf of Alaska have been published. In the coastal Gulf of Alaska, the abundance of mesozooplankton increases until autumn, although total biomass begins to decline after early summer when Neocalanus spp. descend (Incze et al., 1997; Coyle and Pinchuk, 2003). In this paper, we compare the grazing impact of Neocalanus species and the rest of the mesozooplankton community on phytoplankton in the coastal and shelf waters of the Gulf of Alaska during spring and summer 2003. The purpose of this study was to (i) compare the relative importance of Neocalanus spp. and other components of the mesozooplankton community in consuming phytoplankton during spring, and (ii) to determine whether the biomass and grazing impacts of other mesozooplankton increase in summer after the ontogenetic descent of Neocalanus spp.
|
Material and methods |
|---|
|
TopIntroductionMaterial and methodsResultsDiscussionConclusionsReferences |
|---|
During April/May 2003, grazing experiments were conducted at inner-shelf (IS), mid-shelf (MS), and outer-shelf (OS) stations along the Seward line in the coastal Gulf of Alaska and in the Prince William Sound (PWS) for three Neocalanus species (Figure 1, Table 1). Separate experiments were conducted for the non-Neocalanus mesozooplankton community during both the April/May and July/August cruises (there were no Neocalanus spp. in the surface layer in summer).
|
|
Live Neocalanus spp. were collected with a 202 µm plankton net with a 20-l aquarium codend (Reeve, 1981) from the upper 50 m immediately before the experiments. CVs of Neocalanus spp. in good condition were sorted, and a variable number of each species was placed in 2.3 l polycarbonate bottles filled with seawater (prescreened through 200 µm mesh), taken from the depth at which light levels were 50% that of the surface, and incubated on deck for 24 h. Typically, two N. cristatus and four N. flemingeri or N. plumchrus CV were added to each bottle. All experimental bottles were tightly capped, and one layer of neutral screen was applied to each bottle to decrease light by 50%. Incubation temperature was controlled by running seawater from the ship's seawater system. Bottles with no Neocalanus added were also prepared as controls. Typically, three control and four treatment bottles for each experimental species were prepared in each experiment. Chlorophyll a concentrations in three size-fractions (<5, 5–20, and >20 µm) were measured for each experiment. Initial chlorophyll concentration was obtained from the experimental water before it was added to the bottles, and final concentrations were determined from duplicate subsamples removed from each incubation bottle. Individual CV and CIV Neocalanus spp. were collected, rinsed in distilled water, and dried in a 60°C oven on a precombusted and preweighed glass-fibre filter for dry weight measurements. For other mesozooplankton taxa, the same experimental design was used, except that an aliquot of live mesozooplankton (after removal of Neocalanus spp. CV and CIV, when they were present) mixture was added to each treatment bottle (Liu and Dagg, 2003). Dry weights of mesozooplankton from the same aliquots were measured, and mesozooplankton ingestion per unit dry weight was calculated. In addition, mesozooplankton biomass and abundance were determined at each experimental site.
At each experimental site, large zooplankton were collected with a 1-m2 MOCNESS with 500 µm mesh nets. The net was fished at midnight, and 6–7 oblique samples were collected from 100 or 150 m depth to the surface (0–10 m, 10–20 m, 20–40 m, 40–60 m, 60–80 m, 80–100 m, and 100–150 m). Copepodid stages III–V of the Neocalanus species were identified, staged, and enumerated.
Chlorophyll a was determined by placing the filters in 90% acetone for 24 h at –20°C. Chlorophyll a fluorescence from the resulting extract was measured with a Turner Designs fluorometer (Parsons et al., 1984), which had been calibrated with a purified chlorophyll a extract (Sigma Chemicals).
Clearance rate, F, (ml animal–1 d–1 for Neocalanus spp. and ml mg dry wt–1 d–1 for mesozooplankton) on each size fraction of chlorophyll a was calculated using the formula of Frost (1972):
|
|
|
|
Ingestion rate (I, ng Chl animal–1 d–1 for Neocalanus spp. and ng Chl mg dry wt–1 d–1 for mesozooplankton) is calculated by
|
|
|
|
Because we only measured feeding rates of Neocalanus CVs during the spring and summer 2003 cruises, we used the clearance rates of N. cristatus and N. flemingeri CIV, measured in 2001 at the same study sites, to estimate the ingestion of Neocalanus spp. CIV (Liu et al., 2005; Dagg et al., 2006). Measurement of the clearance rate for N. cristatus CIV were conducted on 19 and 20 April 2001 at OS and MS, respectively, where chlorophyll a concentrations were 0.31 and 0.37 mg m–3 with 62% and 76% of that in <5 µm fraction, respectively. Average clearance rate was 182.6 ml copepod(s)–1 d–1 (n = 10, s.d. = 125.5). Experiments with N. flemingeri CIV were conducted at the IS station on 25 April 2001 (chlorophyll a concentration = 3.75 mg m–3 with 82% in >20 µm size fraction), with measured average clearance rate of 62.5 ml copepod(s)–1 d–1 (n = 6, s.d. = 13.4).
|
Results |
|---|
|
TopIntroductionMaterial and methodsResultsDiscussionConclusionsReferences |
|---|
During April/May, the shelf-break station (OS) had low total chlorophyll a and a large contribution from the <5 µm size-fraction, in contrast with other stations where spring chlorophyll a concentrations were high and dominated by large cells (Figure 2). During July/August, total chlorophyll a concentrations were <1 mg m–3, and small phytoplankton (<20 µm) dominated at all stations except IS. Neocalanus spp. were abundant at OS and moderately abundant at MS, IS, and PWS during April/May. Virtually no Neocalanus spp. were found in the upper 50 m during July/August. In April/May, other copepods were more abundant in the inshore and PWS waters than in the offshore waters (Table 2). Abundance of other copepods increased at OS and MS in summer after the ontogenetic descent of Neocalanus spp., mainly because of the increase in the abundance of Oithona spp. at OS and Pseudocalanus spp. at MS. In contrast, abundance of other copepods decreased at PWS in summer because of fewer Metridia spp. and Oithona spp. At IS, abundance of Metridia spp. and Oithona spp. also decreased, but the total copepod abundance remained largely unchanged as abundance of Pseudocalanus spp. doubled (Table 2).
|
|
Multidepth sampling by MOCNESS conducted during our cruises reveal that, despite variations between sampling locations, the CV of all three Neocalanus species were concentrated in the upper 20 m (often most abundant between 10 and 20 m, Figure 3), whereas stages CIII and CIV were mostly below 20 m (data not shown). Dry weights of Neocalanus spp. varied substantially, both temporally and spatially (Table 3). Using the dry weight data, the total biomass of Neocalanus spp. CIV and CV during April/May reached 62.6 mg dry wt m–3 at OS. In contrast, the biomass of other mesozooplankton was only 2.5 mg dry wt m–3 (Figure 4a). Neocalanus spp. CIV and CV accounted for more than 96% of total mesozooplankton biomass at this station. The biomass of Neocalanus spp. was lower at MS and IS than at OS, but its contributions to total mesozooplankton biomass were still 93% and 86%, respectively. PWS had the highest biomass of non-Neocalanus mesozooplankton (13.2 mg dry wt m–3, including Neocalanus spp. CI–CIII), but still, Neocalanus spp. accounted for 64% of total zooplankton biomass. In July/August, except for a small number of N. plumchrus at the OS, no Neocalanus spp. CIV and CV occurred in the upper 50 m water column of the study area. The biomass of other mesozooplankton varied largely in accordance to their abundance (Figure 4b, Table 2).
|
|
|
All three species of Neocalanus fed mostly on phytoplankton cells >20 µm; only at the OS stations, where chlorophyll a concentration was low and dominated by small cells, were positive clearance rates on chlorophyll <20 µm occasionally observed (Table 4). Mean clearance rates for N. flemingeri and N. cristatus were low (or undetectable) in the high chlorophyll IS and MS water, higher in PWS, and the highest in the low chlorophyll OS. Neocalanus plumchrus clearance rate was measured only at OS, and its mean rate was similar to that of N. flemingeri (MJD, unpublished data). Therefore, clearance rates obtained from N. flemingeri were applied to N. plumchrus to estimate total ingestion at stations where the clearance of the latter was not measured.
|
As with Neocalanus spp., we measured positive filtration rates for other mesozooplankton, mainly on cells >20 µm (Table 5). The clearance rates of Neocalanus spp. and other mesozooplankton on >20 µm phytoplankton revealed a negative relationship with chlorophyll a concentration in both spring and summer (Figure 5).
|
|
Neocalanus spp. accounted for most zooplankton herbivory in the shelf-break region in April/May, although low total ingestion was caused by low chlorophyll concentration (Figure 6). The Neocalanus spp. contribution to total mesozooplankton herbivory was lower in the IS region and PWS than in the OS, although high total ingestion was the result of high chlorophyll concentrations. Mesozooplankton ingestion of chlorophyll a was extremely low during July/August.
|
Overall, only a small fraction of total chlorophyll a was consumed by mesozooplankton during both seasons. On the basis of zooplankton biomass derived from net tows of the upper 50 m (upper 40 m for Neocalanus spp. CIV and CV), mesozooplankton consumed
7% of the >20 µm chlorophyll a during 24 h in the OS station, with Neocalanus spp. CIV and CV responsible for >96% of this ingestion (Figure 7a). Mesozooplankton ingested 2–3% d–1 of >20 µm chlorophyll a at the MS and IS stations and in PWS. During summer when Neocalanus spp. were absent, mesozooplankton (mostly small copepods) consumed less than 1% d–1 of phytoplankton standing stock throughout the coastal and shelf regions. Using phytoplankton growth rates measured by the dilution method on the same cruises (data provided by S. Strom), the percentage of the daily growth (i.e. production) of phytoplankton in >20 µm size class that was consumed by mesozooplankton in spring was highest (12.4%) in PWS, followed by OS (9.7%), IS (4.2%), and MS (3.3%; Figure 7b). Mesozooplankton daily consumption of large phytoplankton production in summer was below 1% at all sites, ranging from 0.1% to 0.7%.
|
|
Discussion |
|---|
|
TopIntroductionMaterial and methodsResultsDiscussionConclusionsReferences |
|---|
It has been demonstrated that grazing by the copepod community is not able to control phytoplankton production in the Subarctic Pacific Ocean (Dagg, 1993a). It is also well demonstrated that microzooplankton is capable of consuming all phytoplankton production in the <20 µm fraction and about half the production of >20 µm phytoplankton in the coastal water of the Gulf of Alaska (Strom et al., 2007). We know that Neocalanus spp. and other copepods do not feed on small cells (Frost et al., 1983; Landry and Lehner-Fournier, 1988; Liu et al., 2005). One objective of this study was to determine if mesozooplankton dominated by Neocalanus spp. are able to consume most large phytoplankton that escape microzooplankton grazing in the Subarctic Pacific. On the basis of our results, mesozooplankton grazing is largely ineffective at controlling phytoplankton biomass, because mesozooplankton removed at most 12% of the >20 µm phytoplankton production (Figure 7b). Estimating mesozooplankton removal of phytoplankton using Neocalanus spp. abundance in the upper 20 m instead of 40 m yielded estimates that do not change our conclusions; consumption of daily phytoplankton growth at OS increased to
16% from 10%. However, our estimates of the impact of mesozooplankton grazing on phytoplankton biomass are likely an underestimate for two reasons. First, ingestion rates of Neocalanus spp. and the remaining mesozooplankton were probably underestimated, mainly because the abundance of large particles in the incubation bottles was greatly reduced before the end of the 24 h incubation. Clearance rates obtained for Neocalanus spp. CV in this study were somewhat lower than those observed in a similar study conducted in the same area in 2001, in which the clearance rate of N. cristatus CV was estimated to be as high as >1 l copepod(s)–1 d–1 in low chlorophyll OS waters (Liu et al., 2005). Because we typically added two N. cristatus CV in a 2.3 l bottle, the water inside the bottle would be completely filtered once during the incubation period, thus severely reducing the concentration of large prey particles and underestimating the in situ clearance rates. Second, our calculation used average mesozooplankton abundance in the upper 50 m (upper 40 m for Neocalanus spp. CIV and CV) and chlorophyll concentration in the surface (50% surface irradiance) layer. Because the euphotic layer was much shallower than 50 m at all study sites, except at OS which was close to 50 m, average chlorophyll concentrations in the upper 50 m would be much lower, which could translate to a greater mesozooplankton grazing impact. On the other hand, Neocalanus spp. were concentrated in the upper 20 m or between 10 and 20 m (Figure 3; Mackas et al., 1993; Goldblatt et al., 1999), resulting in a much higher grazing impact on phytoplankton in that particular layer. Grazing by gelatinous mesozooplankton was largely excluded in our estimate because our experimental design was not able to handle their fragile bodies. Appendicularians were the most abundant gelatinous mesozooplankton in the study area with average abundance in the upper 50 m of more than 100 ind. m–3 at all sites except OS in spring, and 10–40 ind. m–3 during summer at all stations. In contrast to copepods, appendicularians have very high ingestion rates (up to 100–1000% of body carbon per day; e.g. Deibel, 1988; Vargas and González, 2004) and feed mostly on cells <20 µm (Alldredge and Madin, 1982; Bedo et al., 1993). Separate experiments conducted during the summer cruise revealed that appendicularians consumed up to 8% of total chlorophyll a in the water layer above the thermocline in the IS and MS regions (RS, unpublished data).
Diel vertical migration of copepod species was not considered in this study. No significant diel vertical migration has been observed for all three Neocalanus species in the open Subarctic Pacific (Mackas et al., 1993) or in the coastal Gulf of Alaska (Napp et al., 1996), but many other copepods are known to migrate to the surface during the night and stay at depth during the day. Goldblatt et al. (1999) reported significant diel difference in biomass in summer in the oceanic Gulf of Alaska, probably because of diel vertical migration by copepods such as Metridia pacifica and C. pacificus. Our experiments were all conducted during daylight from net tows conducted in the morning. Net tows conducted at noon and midnight during the spring cruise at IS (50–0 m) and PWS (100–0 m) did not reveal any difference in zooplankton abundance and composition (data not shown). However, this does not completely rule out diel vertical migration as an important phenomenon to be included in estimating mesozooplankton herbivory.
Our results also indicate that some of the small copepods increased in the offshore waters in summer after the descent of Neocalanus spp. from the surface layer, but the total grazing impact was still small. Previous studies of the annual cycle of mesozooplankton biomass in the coastal Gulf of Alaska demonstrate the same pattern with a spring peak coinciding with the occurrence of Neocalanus spp. (Coyle and Pinchuk, 2003, 2005). Monthly sampling conducted along the Seward Line and in PWS, 1997–2000 (Coyle and Pinchuk, 2003), revealed a sharp decrease in the abundance of large calanoid copepods from May to July, because of the absence of Neocalanus spp. from shelf waters. At the same time, the total abundance of copepods was greater in July, mostly as a result of greater abundances of small species such as Pseudocalanus spp. and Oithona similis. Nevertheless, biomass was lower in July because populations are dominated by smaller calanoids and cyclopoids. Our few data are in general agreement with these patterns (Table 2, Figure 4). In our study, the abundance of total mesozooplankton (including Neocalanus spp.) in the oceanic OS region decreased slightly during summer (Table 2), but biomass decreased 20-fold from 62.6 to 3.2 mg dry wt m–3 (Figure 4). In the shelf waters, where Neocalanus spp. biomass was not as high during spring, the summer decrease in biomass was not great (Figure 4). One reason we did not observe a significant increase in total copepod abundance in summer is probably that the mesh size (202 µm) of the net we used to collect mesozooplankton was not adequate to retain smaller organisms such as Oithona and Oncaea (Gallienne and Robins, 2001).
Neocalanus spp. are suspension-feeders that rely on the establishment of a feeding current to collect food particles. They are efficient at taking in particles >5 µm (Frost et al., 1983) or >2 µm (Landry and Lehner-Fournier, 1988) and have been reported feeding on phytoplankton, microzooplankton, and detrital particles (Greene and Landry, 1988; Dagg, 1993b; Gifford, 1993; Liu et al., 2005). Because microheterotrophs are the major grazers of phytoplankton in the Subarctic Pacific (Landry et al., 1993b; Rivkin et al., 1999; Liu et al., 2002; Strom et al., 2007), mesozooplankton may exert an indirect effect on phytoplankton production as predators of microzooplankton (Landry et al., 1993a; Liu et al., 2005). The overall effect of mesozooplankton grazing is to shift phytoplankton community structure towards dominance by small cells, a mechanism that counterbalances the microzooplankton grazing pressure, which usually causes greater mortality in pico- and nanophytoplankton than in microphytoplankton (Strom et al., 2007).
Besides Neocalanus spp., Metridia spp., Pseudocalanus spp., and Oithona spp. are the predominant mesozooplankton taxa in both seasons. Metridia pacifica is carnivorous in summer in the Alaskan gyre, feeding on dinoflagellates and heterotrophic flagellates >25 µm, but the abundance of Metridia is low enough that only 1% of daily production and standing stock of their prey is ingested (Goldblatt et al., 1999). Goldblatt et al. (1999) suggest that predation by small mesozooplankton may be an important source of phytoplankton mortality. Copepods <1 mm total length (e.g. Oithona spp.) are always the most abundant type of mesozooplankton in the Gulf of Alaska, and their weight-specific ingestion rate is higher than that of the large copepods (Peters, 1983; Moloney and Field, 1991). In our study, Pseudocalanus spp. and Oithona spp. are the most abundant copepods (Table 2), and the weight-specific clearance rate for mesozooplankton other than Neocalanus was higher than those measured for Neocalanus spp. CV (Figure 8). However, despite their great abundance, the overall grazing impact of mesozooplankton other than Neocalanus spp. remained insignificant in both spring and summer (Figure 7).
|
In our study, Neocalanus spp. CI–CIII stages were mixed within other mesozooplankton. On the basis of the abundance of these copepodites and the dry weight data reported by Kobari et al. (2003), they accounted for a maximum of 28.5% of the other mesozooplankton dry weight biomass in OS, but were virtually non-existent in IS. Therefore, their contribution of both biomass and ingestion (assuming they have the same dry-weight-specific ingestion rate as the other mesozooplankton) is very small compared with that of Neocalanus spp. CIV and CV.
|
Conclusions |
|---|
|
TopIntroductionMaterial and methodsResultsDiscussionConclusionsReferences |
|---|
Neocalanus spp. CIV and CV accounted for most mesozooplankton biomass and herbivory throughout the Gulf of Alaska and in PWS during April/May. Composition of other mesozooplankton (mostly small copepods) varied between spring and summer, although the net effect was that total mesozooplankton biomass did not increase in summer after the descent of Neocalanus spp. from the surface layer.
In spring, grazing by Neocalanus spp. and other crustacean mesozooplankton consumed a minimum of 10% of daily growth of phytoplankton >20 µm in the OS region of the Gulf of Alaska and in PWS, and less than that in the MS and IS region. As these rates are most likely underestimated, the real impact of mesozooplankton on phytoplankton biomass in spring could be higher. In contrast, because of the disappearance of Neocalanus spp. in the surface layer and the constant low biomass, copepod herbivory has very little impact on phytoplankton during summer. Gelatinous mesozooplankton, such as appendicularians, which have a dry-weight-specific clearance rate more than one order of magnitude higher than copepods, may be responsible for significant grazing on phytoplankton in both seasons.
|
Acknowledgements |
|---|
We thank the captain and crew of RV "Alpha Helix", chief scientist Suzanne Strom, and the technicians and students aboard the cruise for their assistance, and Jean Rabalais for zooplankton identification and counting. This project is supported by NSF Grant #OCE-0102381.
|
References |
|---|
|
TopIntroductionMaterial and methodsResultsDiscussionConclusionsReferences |
|---|
-
Alldredge A. L., Madin L. P. Pelagic tunicates: unique herbivores in the marine plankton. BioScience (1982) 32:655–663.[CrossRef][Web of Science]
Bedo A. W., Acuna J. L., Robins D., Harris R. P. Grazing in the micron and sub-micron particle size range: the case of Oikopleura dioica (Appendicularia). Bulletin of Marine Science (1993) 53:2–14.[Web of Science]
Beklemishev K. V. The spatial relationships of marine zoo- and phytoplankton. Trudy Instituta Okeanologii, Akademiya Nauk SSSR (1957) 10:253–378.
Boyd P. W., Goldblatt R. H., Harrison P. J. Mesozooplankton grazing manipulations during in vitro iron enrichment studies in the NE Subarctic Pacific. Deep-Sea Research II (1999) 46:2645–2668.[CrossRef]
Cooney R. T. The seasonal occurrence of Neocalanus cristatus, Neocalanus plumchrus and Eucalanus bungii over the northern Gulf of Alaska. Continental Shelf Research (1986) 5:541–553.[CrossRef][Web of Science]
Coyle K. O., Pinchuk A. I. Annual cycle of zooplankton abundance, biomass and production on the northern Gulf of Alaska Shelf, October 1997 through October 2000. Fisheries Oceanography (2003) 12:327–338.[CrossRef][Web of Science]
Coyle K. O., Pinchuk A. I. Seasonal cross-shelf distribution of major zooplankton taxa on the northern Gulf of Alaska shelf relative to water mass properties, species depth preferences and vertical migration behavior. Deep-Sea Research II (2005) 52:217–245.[CrossRef]
Dagg M. J. Grazing by the copepod community does not control phytoplankton production in the Subarctic Pacific Ocean. Progress in Oceanography (1993) a 32:163–183.[CrossRef][Web of Science]
Dagg M. J. Sinking particles as a possible source of nutrition for the large calanoid copepod Neocalanus cristatus in the Subarctic Pacific Ocean. Deep-Sea Research I (1993) b 40:1431–1445.[CrossRef]
Dagg M., Liu H., Thomas A. Effects of mesoscale phytoplankton variability on the copepods Neocalanus flemingeri and N. plumchrus in the coastal Gulf of Alaska. Deep-Sea Research I (2006) 53:321–332.[CrossRef]
Deibel D. Filter feeding by Oikopleura vanhoeffeni: grazing impact on suspended particles in cold ocean waters. Marine Biology (1988) 99:177–186.[CrossRef]
Frost B. W. Effects of size and concentration of food particles on the feeding behavior of the marine planktonic copepod Calanus pacificus. Limnology and Oceanography (1972) 17:805–815.[Web of Science]
Frost B. W. Grazing control of phytoplankton stock in the open Subarctic Pacific Ocean: a model assessing the role of mesozooplankton, particularly the large calanoid copepods Neocalanus spp. Marine Ecology Progress Series (1987) 39:49–68.[CrossRef][Web of Science]
Frost B. W. A modeling study of processes regulating plankton standing stock and production in the open Subarctic Pacific Ocean. Progress in Oceanography (1993) 32:17–56.[CrossRef][Web of Science]
Frost B. W., Landry M. R., Hassett R. P. Feeding behavior of large calanoid copepods Neocalanus cristatus and N. plumchrus from the Subarctic Pacific Ocean. Deep-Sea Research (1983) 30:1–13.
Gallienne G. P., Robins D. B. Is Oithona the most important copepod in the world's oceans? Journal of Plankton Research (2001) 12:1421–1432.
Gifford D. J. Protozoa in the diets of Neocalanus spp. in the oceanic Subarctic Pacific Ocean. Progress in Oceanography (1993) 32:223–237.[CrossRef][Web of Science]
Goldblatt R. H., Mackas D. L., Lewis A. G. Mesozooplankton community characteristics in the NE Subarctic Pacific. Deep-Sea Research II (1999) 46:2619–2644.[CrossRef]
Greene C. H., Landry M. R. Carnivorous suspension feeding by the Subarctic calanoid copepod Neocalanus cristatus. Canadian Journal of Fisheries and Aquatic Sciences (1988) 45:1069–1074.
Heinrich A. K. The life histories of plankton animals and seasonal cycles of plankton communities in the oceans. Journal du Conseil Permanent International pour l'Exploration de la Mer (1962) 27:15–24.
Incze L. S., Siefert D. W., Napp J. M. Mesozooplankton of Shelikof Strait, Alaska: abundance and community composition. Continental Shelf Research (1997) 17:287–305.[CrossRef][Web of Science]
Kobari T., Shinada A., Tsuda A. Functional roles of interzonal migrating mesozooplankton in the western Subarctic Pacific. Progress in Oceanography (2003) 57:279–298.[CrossRef][Web of Science]
Landry M. R., Gifford D. J., Kirchman D. L., Wheeler P. A., Monger B. C. Direct and indirect effects of grazing by Neocalanus plumchrus on plankton community dynamics in the Subarctic Pacific. Progress in Oceanography (1993) a 32:239–258.[CrossRef][Web of Science]
Landry M. R., Lehner-Fournier J. M. Grazing rates and behaviors of Neocalanus plumchrus: implications for phytoplankton control in the Subarctic Pacific. Hydrobiologia (1988) 167/168:9–19.
Landry M. R., Monger B. C., Selph K. E. Time dependency of microzooplankton grazing and phytoplankton growth in the Subarctic Pacific. Progress in Oceanography (1993) b 32:205–222.[CrossRef][Web of Science]
Liu H., Dagg M. J. Interactions between nutrients, phytoplankton growth, and micro- and mesozooplankton grazing in the plume of the Mississippi River. Marine Ecology Progress Series (2003) 258:31–42.[CrossRef][Web of Science]
Liu H., Dagg M. J., Strom S. Grazing by the calanoid copepod Neocalanus cristatus on the microbial foodweb in the coastal Gulf of Alaska. Journal of Plankton Research (2005) 27:647–662.
Liu H., Suzuki K., Saino T. Phytoplankton growth and microzooplankton grazing in the Subarctic North Pacific Ocean and Bering Sea during summer 1999. Deep-Sea Research I (2002) 49:363–375.[CrossRef]
Mackas D. L., Sefton H., Miller C. B., Raich A. Vertical habitat partitioning by large calanoid copepods in the oceanic Subarctic Pacific during spring. Progress in Oceanography (1993) 32:259–294.[CrossRef][Web of Science]
Mackas D. L., Tsuda A. Mesozooplankton in the eastern and western Subarctic Pacific: community structure, seasonal life histories, and interannual variability. Progress in Oceanography (1999) 43:335–363.[CrossRef][Web of Science]
Miller C. B. Development of large copepods during spring in the Gulf of Alaska. Progress in Oceanography (1993) 32:295–317.[CrossRef][Web of Science]
Miller C. B., Clemons M. Revised life history analysis for large grazing copepods in the Subarctic Pacific Ocean. Progress in Oceanography (1988) 20:293–313.[CrossRef][Web of Science]
Miller C. B., Terazaki M. The life histories of Neocalanus flemingeri and Neocalanus plumchrus in the Sea of Japan. Bulletin of the Plankton Society of Japan (1989) 36:27–41.
Moloney C. L., Field J. G. The size-based dynamics of plankton food webs. I. A simulation model of carbon and nitrogen flows. Journal of Plankton Research (1991) 13:1003–1038.
Napp J. M., Incze L. S., Ortner P. B., Siefert D. L. W., Britt L. The plankton of Shelikof Strait, Alaska: standing stock, production, mesoscale variability and their relevance to larval fish survival. Fisheries Oceanography (1996) 5:19–38.[CrossRef][Web of Science]
Parsons T. R., Lalli C. M. Comparative oceanic ecology of the plankton communities of the Subarctic Atlantic and Pacific Oceans. Oceanography and Marine Biology Annual Review (1988) 26:317–359.
Parsons T. R., Maita Y., Lalli C. M. A Manual of Chemical and Biological Methods for Seawater Analysis. (1984) Oxford: Pergamon Press. 173.
Peters R. H. The Ecological Implications of Body Size. (1983) Cambridge: Cambridge University Press.
Reeve M. R. Large cod-end reservoirs as an aid to the live collection of delicate zooplankton. Limnology and Oceanography (1981) 26:577–580.[Web of Science]
Rivkin R. B., Putland J. N., Anderson M. R., Deibel D. Microzooplankton bacterivory and herbivory in the NE Subarctic Pacific. Deep-Sea Research II (1999) 46:2579–2618.[CrossRef]
Shiomoto A., Asami H. High-west and low-east distribution patterns of chlorophyll a, primary productivity and diatoms in the Subarctic North Pacific surface waters, midwinter 1996. Journal of Oceanography (1999) 55:493–503.[CrossRef]
Strom S. L., Macri E. L., Olson M. B. Microzooplankton grazing in the coastal Gulf of Alaska: variations in top-down control of phytoplankton. Limnology and Oceanography (2007) 52:1480–1494.[Web of Science]
Tsuda A., Saito H., Kasai H. Life history of Neocalanus flemingeri and Neocalanus plumchrus (Calanoida: Copepoda) in the western Subarctic Pacific. Marine Biology (1999) 135:533–544.[CrossRef]
Tsuda A., Sugisaki H. In situ grazing rate of the copepod population in the western Subarctic North Pacific during spring. Marine Biology (1994) 120:203–210.[CrossRef]
Vargas C. A., González H. E. Plankton community structure and carbon cycling in a coastal upwelling system. I. Bacteria, microprotozoans and phytoplankton in the diet of copepods and appendicularians. Aquatic Microbial Ecology (2004) 34:151–161.[CrossRef][Web of Science]
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||