Feeding of Copepods on Natural Suspended Particles in Tokyo Bay*

Journal of the Oceanographical Society of Japan Vol.44, pp.217 to 227, 1988

Atsushi Tsudat and Takahisa Nemotot

Abstract: Community grazing rates of copepods were estimated from data taken

during three cruises in Tokyo Bay, based on bottle incubations and a temporal

variation of gut fluorescence. Special attention was paid to the feeding selectivity

in the estimations. Differential grazing was observed in the copepod communities:

Acartia omorii, abundant in February, selectively fed on the particles of dominant

size classes, while Oithona davisae, dominant throughout the year, and Centropages

abdominalis selected large particles (>20ƒÊm). The maximum filtering rates on

certain size classes were several times the average. In addition, a 34-hr investi-

gation of the gut fluorescence of copepods revealed nocturnal feeding in Paracalanus spp., Pseudodiaptomus marinus and Oithona davisae.

Copepod communities collected with a net (95-ƒÊm mesh opening) were esti-

mated to graze, in February 3.0%, in August 3.1-4.5% and in November 4.2-11.9 % of the standing crops of phytoplankton or suspended particlesper day.

1. Introduction O.aruensis(Nishida,1985),is the most domi- Inner Tokyo Bay is a temperate, semi-closed nant species throughout the year, especially bay connected with the offshore waters by Uraga between July and September, while a calanoid. Strait. Eutrophication in the bay began in the copepod Acartia omorii, formerly identified as 1960's and increased until the early 1970's to A. clausi (Ueda, 1986) is abundant from Feb- the level sustained at present (Unoki and Kishi- ruary to June (Anakubo, 1982). Little is known no, 1977; Anonymous, 1984; Han, 1988) with of the impact of zooplankton grazing on phyto- drastic changes in the phytoplankton community plankton communities in Tokyo Bay. Uchima (Marumo and Murano, 1973). Excess of nutri- and Hirano (1986a, b) intensively studied the ents brings a high standing crop and photo- feeding behavior of O. davisae by laboratory synthetic activity of phytoplankton throughout experiments. They presented many interpre- the year (Shibata and Aruga, 1982; Brandini tations of copepod ecology, however, infor- and Aruga, 1983; Han, 1988). Chlorophyll a mation about the in situ grazing rates of domi- concentration rarely falls below 10 mg m-3 even nant herbivorous and omnivorous zooplankton during winter, and often exceeds 100 mg m-3 in is needed to understand the interactions be- summer (Taga and Kobori, 1978: Shibata and tween primary producers and consumers. In Aruga, 1982; Anonymous, 1984). Red tides addition, simultaneous measurements of the were observed for a period of over 100 days in filtering rate,standing stock,and feeding 1982, which consisted of Skeletonema costatum, selectivity of each species are required to obtain Prorocentrum spp., Heterosigma akashiwo and better estimates of the in situ feeding rates of other diatom species (Anonymous, 1984). natural assemblages (Thompson et al., 1982). Copepods are the dominant zooplankton in It should be noted that most studies have ignored the bay. A small cyclopoid copepod Oithona the feeding selectivity in evaluating the in situ davisae, formerly identified as 0. brevicornis or feeding rate of zooplankton assemblages.

*Received 21 Jamary 1988;in revised form 5 The present study estimated the in situ grazing

August 1988;accepted 9 August 1988. rates of herbivorous and omnivorous copepod

†Ocean Research hstitute,University of Tokyo communities by bottle incubations on cruises 1-15-1 Minamidai,Nakano,Tokyo 164,Japan in the inner part of Tokyo Bay. Special 218 Tsuda and Nemoto attention was paid to their size selectivity model 111 fluorometer (Lorenzen, 1966). The in the estimation of community grazing rates. area with the highest concentration was selected Furthermore, the community grazing rate was as the sampling station. The vessel was anchored also evaluated based on a temporal variation of over 14 to 34 hr for sampling and experiments. the gut fluorescence. 2.1. Ingestion rate Copepods were collected with a Norpac net 2. Materials and methods (45 cm mouth diameter : 95-pm mesh opening) Sampling and experiments were carried out hauled vertically from near bottom to the surface, on three cruises of the R/V Tansei Maru, of the and then transferred to 5-1 containers filled with Ocean Research Institute, University of Tokyo surface seawater and kept at ambient tempera- in the northern part of Tokyo Bay (Fig. 1). tures. Food media were prepared by passing During the KT-83-13 cruise, in vivo chlorophyll surface seawater through a 63-pm mesh to re- fluorescence at the surface was monitored with move large particles and zooplankton. Numeri- a continuous water-sampler attached to a Turner cally abundant copepods were sorted into filtered seawater under a dissecting microscope, and after determining species, sex and developmental stages, active and undamaged individuals were injected into glass bottles (140-650 ml) filled with the food medium. Only adult females were used in experiments on Acartia omorii, whereas for other copepods species copepodites were sorted in each species from the samples regardless of developmental stages and sex. Duplicate bottles of each species were placed on a cell roller to prevent the particles from settling (2 rpm). The incubation lasted for about 6 hr during the night, in darkness at ambient temperatures (Table 1). Size distributions of the suspended particles in the bottles were measured at the beginning and end of the incubations with a Coulter Counter model TAII attached to a 140-pm aperture which covered particles between 2.52 and 64.0 pm. Two bottles without copepods were used as controls. Copepod density during Fig. 1. Sampling stations in Tokyo Bay. Station the incubations and other experimental conditions T3: KT-83-1 cruise, 18-19 February 1983. are summarized in Table 1. Ingestion rates and Stations 2 and 9: KT-83-13 cruise, 1-9 August filtering rates on each size class of particles were 1983. Station 1: KT--85-16 cruise, 6-8 No- vember 1985. calculated using the equations of Frost (1972).

Table 1. Experimental conditions of the two cruises in Tokyo Bay.

a Adult females . b Copepodites and adults . Copepod Feeding in Tokyo Bay 219

For estimating the standing stock, copepods the gut clearance time for Pseudodiaptomus were collected with the same net equipped with marinus and smaller copepods (Oithona davisae a flowmeter, hauled from nearbottom to the and Paracalanus spp.), respectively, based on surface. They were preserved in 5% (v/v) buf- the body size and ambient temperature (Dagg fered formalin seawater soon after the collection. and Grill, 1980; Kiorboe et al., 1982; Tsuda. Copepods were identified and counted under a and Nemoto, 1987). Since some residual chloro- microscope for an appropriate aliquot (1/32-1/64). phyll a was present, gut pigment content was The estimated abundances of the copepod were shown as chlorophyll a+phaeopigment. The combined with the filtering rates of the copepod pigment content and the estimated ingestion rate on each size class of food particles to obtain a were expressed as chlorophyll-a-equivalent community grazing rate (Thompson et al., 1982). weight. Measured pigment was considered to originate from only phytoplankton cells, since 2.2. Gut fluorescence no other pigment fluorescing was detected at the Sampling was sustained for 34 hr at a hourly wavelength of chlorophyll a and its derivatives interval, between 6 and '8 November 1985 at in the starved copepods (Baars and Helling, 1985). Station 1 (Fig. 1). A collection of copepods was The gut fluorescence method is useful to accomplished by vertical hauls with the Norpac investigate the natural feeding rates of herbivo- net from near bottom (17-m depth) to the rous copepods since short-term ingestion rates can surface. Soon after sampling, the copepods were be estimated without artificial effects. Wang narcotized with a drop of chloroform (Gannon and Conover (1986) pointed out that grazing rates and Gannon, 1975) and collected on a glass estimated by the gut fluorescence method were fiber filter(45-mm diameter,GF/C).The filters underestimated due to pigment loss caused by were frozen at -20•Ž in darkness within 20 destruction and assimilation of pigment through min after sampling, and used for pigment analy- the gut passage. Usually, gut passage time has sis ashore. been estimated from the exponential decrease of Gut fluorescence of the copepods was measured the gut fluorescence of previously satiated cope- within two months after the sampling the pods. Although Wang and Conover (1986) procedure of Mackas and Bohrer (1976). The assumed that the estimated gut passage time samples were re-suspended into cold (5•Ž), consisted only of the defecation of fecal pellets, filtered seawater.The copepods were sorted the decrease of copepod gut fluorescence in under a dissecting microscope with a dim filtered seawater should include the defecation light and rinsed twice with filtered seawater. of and also the destruction of pigment. More- For each species, duplicate subsamples of over, the assimilation of pigment should be 10 to 100 individuals each were put in screw- accompanied by its destruction, since the fluo- capped vials with 90% (v/v) acetone, and rescence in starved copepods was very small. were allowed to extract a day and night Thus, gut passage times, which have been in a dark freezer. Over 95% of the extraction estimated actually included not only the yield was obtained by the same procedure, with defecation but also the destruction and 90% acetone for small copepods (Pleuromamma assimilation of pigment. A more appropriate gracilis, Paracalanus spp.) and over 85% for term is "fluorescence residence time". Further- large copepods (Calanus sinicus, Scolecithrix more, linearities are present between the gut danae and Pleuromamma xiphias) in a study in pigment content and the ingestion rate esti- Sagami Bay (Tsuda, unpublished). Simard et al. mated from bottle incubations (Tsuda and Ne- (1985) found no difference between samples moto, 1987; Wang and Conover, 1986). There- ground and unground with 100% methanol fore, we concluded that the gut fluorescence extraction. Therefore, the grinding step was method is still valid for the estimation of natural eliminated. Chlorophyll a and phaeopigment feeding rates of copepods. were measured with a Turner model 111 fluoro- Water samples for chlorophyll a and phaeo- meter. pigment were taken from three depths (0,5,10m) Grazing rates were estimated from the gut with a Van Dorn sampler, and analyzed fluoro- pigment content assuming a 1.0 and 0.5 hr as metrically after Strickland and Parsons (1972). 220 Tsuda and Nemoto

3. Results dantly in February 1983, and Pseudodiaptomus 3.1. Plankton composition marinus and Paracalanus spp. in November Copepod fauna was dominated by only a few 1985. species through the three cruises (Table 2). The size spectrum of the suspended particles Oithona davisae was dominant throughout the had three peaks in February (Fig. 2). Ac- samplings and comprised 99% of the total cording to the microscopic observations, the number of copepods in summer. Acartia omorii peak at the smallest size was comprised mainly and Centropages abdominalis occurred abun- of Prorocentrum minimum, that for the middle

Table 2. Numerical abundance of copepods (inds 1-1) collected with a Norpac net

(95-ƒÊm mesh opening) in Tokyo Bay. nc: not counted

a Paracalanus spp . and Acartia omorii are included.

A B C

Fig. 2. Particle concentration, ingestion rate and filtering rate of Acartia omorii females feeding on natural suspended particles in Tokyo Bay on 18 February 1983.A:50 inds 1-1, B: 100 inds 1-1, C: 200 inds 1-1. Copepod Feeding in Tokyo Bay 221 size consisted of Thalassiosira rotula, and ingestion rate at the peak of the largest size

Ditylum brightwellii and tintinnids made up the (Fig. 4). The filtering rate increased rapidly in largest peak. Two peaks were observed in the the size range of 20 to 64 ƒÊm.

August size spectrum (Fig. 5), the smaller peak Similar results were obtained for Oithona being comprised of Cryptophyceae and larger one of diatoms T. rotula, Leptocylindrus danicus A B and Cerataulina pelagica. In November, Chryptomonas/Chroomonas, Prorocentrum tries- tinum, Gymnodinium sp. and L. danicus were abundant in the water column as also reported in Han (1988). 3.2. Grazing of copepods Acartia omorii in February showed high ingestion rates at the peaks of the size distribution of suspended particles (Fig. 2). High filtering rates were also found at the size forming peaks or slightly larger sizes, although selective feeding was not clearly observed at the peak of the middle size. Since the filtering spectrum was depressed at the highest copepod density, the filtering spectra of the lower density

(<100 copepods 1-1) was used to estimate the community filtering rate. A positive correlation Fig. 4. Particle concentration, ingestion rate and (r= 0.74) was found between the ingestion rate and particle concentration (Fig. 3). filteringrate of Centropages abdominalis feeding on natural suspended particles in Tokyo Bay. Centropages abdominalis in February A: 18 February, B: 19 February 1983. scarcely fed on particles smaller than 20 ƒÊm in diameter, including the smaller peaks (P. minimum and Th. rotula), and showed a high A B

Fig. 3. Relationships between the particle concentration and the ingestion rate of Acartia Fig. 5. Particle concentration, ingestigation rate omorii (February; solid circle), Centropages and filtering rate of Oithona davisae feeding abdominalis (February; open circle) and Oithona on natural suspended particles in Tokyo Bay. davisae (August; solid triangle). A: 1 August, B: 8 August 1983. 222 Tsuda and Nemoto

davisae as for C. abdominalis. They had high to 64ƒÊm. Especially with sizes greater than ingestion rates, not on particles smaller than 40 ƒÊm, a filtering rate as high as 40 ml 1-1 hr-1

10ƒÊm, but on larger particles (Fig. 5). The was observed, which indicated that the com- filtering rate increased rapidly with particle munity filtered about the half of the water size in the size range from 20 to 64 ƒÊm. Sig- column between dusk and dawn at the above nificant positive correlations were not observed particle size range with the maximum filtering between the particle concentration and the in- rate (Fig. 7). The community was estimated gestion rate for either O. davisae or C. abdominalis (Fig. 3).

3.3. Community grazing

In February the filtering spectra of Acartia omorii and Centropages abdominalis were used to estimate a community grazing rate, and in August only those of Oithona davisae were used since their numerical abundance accounted for 99% of the total copepods. In

February the filtering spectrum of the copepod community largely reflected that of A. omorii

(Fig. 6). The copepods did not feed on particles smaller than 5 ƒÊm and increased their filtering rate at about 10 and 50 pm, which cor- Fig. 7. Estimated community filtering spectrum respond to the dominant size classes of phyto- of Oithona davisae in Tokyo Bay on 1 August plankton. The copepod community was estimat- (solid circle) and 8 August (open circle) 1983. ed to consume 2.4% and 10.3% of the standing stock of suspended particles per day at the peaks of 10 and 50 ƒÊm, respectively, assuming that their feeding continued from dawn to dusk.

With the same assumption, 3.0% of the total suspended particles measured (2.52-64.0 ƒÊm) were estimated to be grazed by the copepod community.

In August the community filtering rate increased rapidly in the particle size-range of 20

Fig. 8. Temporal variation of tidal height (upper), Fig. 6. Estimated community filtering spectrum chlorophyll a (middle) and phaeopigment (lower) of copepods (dotted area: Acartia omorii, open in the water column at Station 1 during a area: Centropages abdominalis) in Tokyo Bay 34-hr sampling period between 6 and 8 No- on 18 February 1983. vember 1985. Copepod Feeding in Tokyo Bay 223 to graze 4.5 and 3.1% of the total suspended after dusk increased to 0.8 ml copepod-1 hr-1 just particles measured (2.52-64.0 ƒÊm) per day on 1 before dawn. The gut fluorescence and filtering and 8 August, respectively. rate of copepodites IV and V of P. marinus

3.4. Feeding rhythms showed parallel fluctuations to those of the adult

Chlorophyll a concentration at Station 1 varied females (Fig. 9). with time and depth, but neither a diel rhythm Nocturnal feeding was also observed in Oithona

nor tidal effect was observed (Fig. 8). The davisae and Paracalanus spp. (Fig. 10). The

maximum concentration appeared at the upper gut fluorescence of O. davisae was high at night,

5-m depth. Integrated chlorophyll a concen- although the peak appeared at different times

tration throughout the water column (0-10 m) during the two nights. The gut fluorescence of

was higher on the first night than on the Paracalanus spp. increased after dusk and

second. Phaeopigment concentration was less remained relatively constant until before dawn.

variable in time and space. These fluctuations correspond with those of the filterillg rates estimated with the same assump- Female Pscudodiaptomus marinus were collect-

ed by vertical hauls frcm the near bottom to tions as in P. marinas (Fig. 10). the surface between dusk and just before dawn 3.5. Estimate of community grazing rate but not during the daylight. The gut fluores- from gut fluorescence cence of P. marinus increased with time after The chlorophyll consumption by Oithona dusk, andthe maximum value was observed at davisae, the numerically dominant copepod in midnight (Fig. 9). Since the gut fluorescence is November 1985, was estimated to be 3.60 mg considered to be partly affected by the variation Chl. m-2 day-1, accounting for 74% of the total at food environments, we estimated the filtering consumption by the copepod community (Table rate of P. marinus as an index of feeding activity, 3). The chlorophyll consumption by the copepod assuming that they grazed at the depth of the community during night was 4.81 mg Chl. m-2 maximum chlorophyll concentration and their day-1 on the first day and 3.03 for the second, if

gut clearance time was 1 hr. The filtering rate it was assumed that Paracalanus spp. would had a similar fluctuation on each night (Fig. 9). graze the same amount of phytoplankton in the The filtering rate of 0.3 ml copepod-1 hr-1 just first night as ill the second.The average daily consumption by the copepod community was

Fig. 9. Temporal variations of gut pigment content (solid circle) and estimated filtering rate Fig. 10. Temporal variations of gut pigment (open circle) of l'seudodiaptomus marinus content (solid circle) and estimated filtering rate female (A) and CIV-CV (B) in Tokyo Bay. (open circle) of Paracalanus spp. (A) and The night period is indicated by shaded bars Oithona davisac (B) in Tokyo Bay. The night on time axis. period is indicated by shaded bars on time axis. 224 Tsuda and Nemoto

Table 3. Chlorophyll consumption by copepods (>20 ƒÊm). Uchima and Hirano (1986a) demon- (Paracalanus spp., Pseudodiaptomus marinus strated by laboratory experiments that O. davisae

and Oithona davisae) in Tokyo Bay, 7-9 No- never fed on diatoms regardless of their size,

vember 1985. nd: not determined but on dinoflagellates, ciliates and other motile

(mg Chl. m-2 day') organisms. By contrast, in the present study,

the peaks at the large size (>20ƒÊm) were

composed mainly of diatoms and accounted for

the major portion of food eaten by O. davisae

and other copepods. Since the experiments using

a particle counter as well as gut content fluo-

rescence did not reveal whether copepods fed on

diatoms or not, further study is needed to de-

a Copepodites and adults . termine the composition of the food of the natural population of Oithona davisae and other estimated to be 5.36 mg Chl. m-2 day-1. Integ- copepods. rated chlorophyll a concentration varied from Abundant copepods in Tokyo Bay were classi- 45.2 to 141.1 mg m-2, and consequently the fied as omnivores except for Paracalanus spp. copepod community was estimated to graze 3.5 These copepods showed high filtering rates on to 4.8% of the phytoplankton standing crop large particles (>20ƒÊpm). Consequently, the com- during a night and 4.2 to 11.9% during a night munity filtering spectra were also high in the and day. larger size range of particles. This size range corresponds with where the phytoplankton domi- 4. Discussion nates in the biomass as well as the productivity Nival and Nival (1976) showed that size selec- in neritic waters (Malone, 1971). The maximum tion of particles by Acartia clausi depended on filtering rates of copepod communities,observed the mesh size of their filtering basket. Active at dominant size classes or large particles, were selection of abundant particle sizes, which could several times that of the average rate. This not be explained by a passive selection model, result emphasizes the importance of estimating have been reported in the Acartia species the food selectivity by copepods. Differential (Wilson, 1973; Poulet and Marsot, 1978; grazing observed in the copepod communities Donaghay and Small, 1979) and other copepods probably affects on the species composition (Richman et al., 1977; Poulet, 1978). In the of phytoplankton in nature, which has been present study, Acartia omorii showed selective reported for experimental conditions (Sonntag feeding on abundant particles, although it was and Parsons, 1979; Ryther and Sanders, 1980). not clear on the peak at the middle size. Break- The feeding impact of copepod communities on age of larger particles was considered to occur small particles was lower than that on large during the feeding experiments since many cells particles for every season, especially in the of Thalassiosira rotula which the peak at middle summer. Since the dominant copepod (Oithona size consisted of, were detected in the fecal davisae) preferred large particles, microzooplank- pellets of A. omorii (Tsuda, unpublished). More- ton such as ciliates and heterotrophic flagellates over, on the same cruise, peak tracking feedings are presumably important as grazers on nanno- were observed by A. omorii on cultured red- plankton and also as food for omnivorous cope- tide phytoplankton, Prorocentrum minimum and pods. Heterosigma akashiwo (Tsuda and Nemoto, Nocturnal feeding by herbivorous copepods is 1984). These selective feedings on abundant a commonly observed phenomenon (Mackas and particles, presumably active growing cells, are Bohrer, 1976; Kicbrboe et al., 1982; Simard et considered to be advantageous for copepod al., 1985). A classical explanation for nocturnal nutrition and also have effects on the compo- feeding is that copepods migrate daily through sition of the phytoplankton assemblages. Oithona the water column between phytoplankton-rich davisae and Centropages abdominalis scarcely and poor layers with a constant filtering rate fed on small particles but preferred large particles (Gauld, 1953). This explanation partly fits the Copepod Feeding in Tokyo Bay 225 results for Pseudodiaptomus marinus which Malone and Chervin, 1979; Sonntag and Parsons, showed a clear diel vertical migration between 1979; Dagg et al., 1982; Joris et al., 1982; the near-benthic layer and the upper water Dagg and Turner, 1982; Nicolajsen et al., 1983; column. However, a constant filtering rate was Tsuda et al., 1985). Although we did not mea- not observed during the night in the present sure the primary production, high photosynthetic study. Although the diel vertical migration of activity has been reported in Tokyo Bay (Funa- Oithona davisae has not been studied in Tokyo koshi et al., 1974; Shibata and Aruga, 1982; Bay, a high biomass was observed in the day- Brandini and Aruga, 1983). If we assumed that time in shallow waters where the chlorophyll a the primary productivity in Tokyo Bay is 2gC concentration was high (Anakubo, 1982). There- m-2day-1(Funakoshi et al.,1974,Yamaguchi fore, other explicable models (e.g., the hunger- and Shibata, 1979), the copepod community will satiation model of Pearre, 1973) are needed to graze, at most, about 10% of the primary explain the feeding rhythm of non-migrating production. copepods. Daily community grazing rates were calculated Acknowledgements from the results of bottle incubations, assuming We wish to thank Drs. S. Nishida and K. that the feeding period lasted from dusk to dawn, Furuya for their helpful suggestions through- based on the time series observations of gut out this work. We are also grateful to Dr. fluorescence.However,weak Huorescence was M. Terazaki for his continuous encourage- observed even in the daytime for O. davisae and ment and Prof. C. B. Miller, Oregon State Paracalanus spp. This result suggested that a University, for his critical reading of the manu- part of the population continued to graze during script. Thanks are extended to the captain, the daytime, and/or different types of functional officers and crew members of the R/V Tansei response to food concentration existed in copepods Maru for their cooperation in collecting samples. between night and day as in cladocerans (Haney, This study was partly supported by the Nissan 1985). The community grazing rate estimated Science Foundation. by the bottle incubation method might be some- what low, since daytime feeding was ignored. References On the other hand, the gut fluorescence method Anakubo, T. (1982): Dynamics of zooplankton com- disregarded feeding selectivity and could not munities in Tokyo Bay. M.S. thesis, Tokyo evaluate the ingestion rate on microzooplankton Univ. Fish.. 100 pp. (in Japanese) and pigment-free particles but only on phyto- Anonymous (1984): Report of the investigations on the biological pollutions in Tokyo Bay. Bureau plankton cells. Accordingly, ingestion rates of omnivorous copepods are underestimated. How- of environmental protection of the Tokyo Metro- ever, it would be advantageous to understand politan Government, 149 pp. (in Japanese) Baars, M.A. and G.R. Helling (1985) : Methodical the interactions between primary producers and problems in the measurement of phytoplankton copepods as primary consumers. ingestion rate by gut fluorescence. Hydrobiol. From bottle incubations the copepod communi- Bull., 19, 81-88. ties were estimated to graze 3.0% and 3.1-4.5% Brandini, F.P. and Y. Aruga (1983): Phytoplankton of the standing crops of suspended particles per biomass and photosynthesis in relation to the day in February and August, respectively. environmental conditions in Tokyo Bay. Jap. J. In November the gut fluorescence method Phycol., 31, 129-147. estimated that the copepod community grazed Dagg, M.J. and D.W. Grill (1980) : Natural feeding rates of Centropages typicus females in the New 4.2-11.9% per day. The estimate in February York Bight. Limnol. Oceanogr., 25, 597-609. by bottle incubations might be considerably Dagg, M.J. and J.T. Turner (1982) : The impact of low, since the ingestion rate of the numerically copepod grazing on the phytoplankton of the abundant copepod Oithona davisae was not Georges Bank and the New York Bight. Can. J. measured. The reported part of the primary Fish. Aquat. Sci., 39, 979-990. production consumed by zooplankton grazing Dagg, M.J., J. Vidal, T.E. Whiteledge, R.L. Iverson ranged from less than 1% to over 100% (Menzel and J.J. Goering (1982) : The feeding, respiration and Ryther, 1961; Taguchi and Fukuchi, 1975; and excretion of zooplankton in the Bering Sea 226 Tsuda and Nemoto

during a spring bloom. Deep-Sea Res., 29, 45-63. Menzel, D. W. and J. H. Ryther (1961): Zooplankton Donaghay, P.L. and L.F. Small (1979) : Food selection in the Sargasso Sea off Bermuda and its relation capabilities of the estuarine copepod Acartia to organic production. J. cons. perm. in Explor. clausi. Mar. Biol., 52, 137-146. Mer., 26, 250-258. Frost, B.W. (1972) : Effects of size and concentration Nicolajsen, H., F. Mohlenberg and T. Kiorboe (1983): of food particles on the feeding behavior of the Algal grazing by the planktonic copepods Centro- marine planktonic copepod Calanus paczficus. pages hamatus and Pseudocalanus sp. during the Limnol. Oceanogr., 17, 805-815. spring phytoplankton bloom in the Oresund. Funakoshi, M., N. Nakamoto and K. Hogetsu (1974): Ophelia, 22, 15-31. Primary production and the roll of red tide in Nishida, S.(1985): Taxonomy and distribution of Tokyo Bay. Ann. Rep. Special Project Res. the family Oithonidae (Copepoda, Cyclopoida) in Environment & Human Survival, Ministry Educ., the Pacific and Indian Oceans. Bull. Ocean Res. 115-128. (in Japanese) Inst., Univ. Tokyo, 20, 1-167. Gannon, J. E. and S. A. Gannon (1975): Observations Nival, P. and S. Nival (1976): Particle retention on the narcotization of crustacean zooplankton. efficiencies of an herbivorous copepod, Acartia Crustaceana, 28, 220-224. clausi (Adult and copepodite stages): Effects on Gauld, D. T.(1953): Diurnal variations in the grazing grazing. Limnol. Oceanogr., 21, 24-38. of planktonic copepods. J. mar. biol. Ass. U. K., Pearre, S. Jr. (1973): Vertical migration and feeding 31, 461-474. in Sagitta elegans Verrill. Ecology, 54, 300-314. Han, M.-S.(1988): Studies on the population dynam- Poulet, S. A. (1978): Comparison between five co- ics and photosynthesis of phytoplankton in Tokyo existing species of marine copepods feeding on Bay. Ph. D. thesis, Univ. Tokyo, 172 pp. naturally occurring particulate matter. Limnol. Haney, J. F.(1985): Regulation of cladoceran filtering Oceanogr., 23, 1126-1143. rates in nature by body size, food concentration Poulet, S. A. and P. Marsot (1978): Chemosensory and diel feeding patterns. Lirnnol. Oceanogr., 30, grazing by marine calanoid copepods (Arthropoda: 397-411. Crustacea). Science, 200, 1403-1405. Joris, C., G. Billen, G. Lancelot, M. H. Daro, J. P. Richman, S., D. R. Heinle and R. Huff (1977): Grazing Mommaerts, A. Bertels, M. Bossicart, J. Nijs by adult estuarine calanoid copepods of the and J. H. Hecq (1982): A budget of carbon cycling Chesapeake Bay. Mar, Biol., 42, 69-84. in the Bergian coastal zone: Relative roles of Ryther, J. H. and J. G. Sanders (1980): Experimental zooplankton, bacterioplankton and benthos in the evidence of zooplankton control of the species utilization of primary production. Netherlands composition and size distribution of marine J. Sea Res., 16, 260-275. phytoplankton. Mar. Ecol. Prog. Ser., 3,279-283. Kiorboe, T., F. Mohlenberg and H. Nicolajsen (1982): Shibata, Y. and Y. Aruga (1982): Variation of chloro- Ingestion rate and gut clearance in the planktonic phyll a concentration and photosynthetic activity copepod Centropages hamatus (Lilljeborg) in of phytoplankton in Tokyo Bay. La mer, 20, relation to food concentration and temperature. 75-92. Ophelia, 21, 181-194. Simard, Y., G. Lacroix and L. Legendre (1985): In Lorenzen, C. J. (1966): A method for the continuous situ twilight grazing rhythm during diel vertical measurement of in vivo chlorophyll concentration. migrations of a scattering layer of Calanus Dee-Sea Res., 13, 223-227. finmarchious. Limnol. Oceanogr., 30, 598-606. Mackas, D. and R. Bohrer (1976): Fluorescence Sonntag, N. C. and T. R. Parsons (1979): Mixing an analysis of zooplankton gut contents and an enclosed, 1300 m3 water column: Effects on the investigation of diel feeding patterns. J. Exp. planktonic food web. J. Plankton Res., 1, 85-102. Mar. Biol. Ecol., 25, 77-85. Strickland, J. D. H. and T. R. Parsons (1972): A Malone, T. C. (1971): The relative importance of practical handbook of seawater analysis. 2nd ed. nanoplankton and netplankton as primary pro- Bull. Fish. Res. Bd. Canada, 167, 310 pp. ducers in tropical oceanic and neritic phytoplankton Taga, N. and H. Kobori (1978): Phosphatase activity communities. Limnol. Oceanogr., 16, 633-639. in eutrophic Tokyo Bay. Mar. Biol., 49, 223-229. Malone, T. C. and M. B. Chervin (1979): The pro- Taguchi, S. and M. Fukuchi (1975): Filtration rate duction and fate of phytoplankton size fractions of zooplankton community during spring bloom in the plume of the Hudson River, New York in Akkeshi Bay. J. Exp. Mar. Biol. Ecol., 19, Bight. Limnol. Oceanogr., 24, 683-696. 145-164. Marumo, R. and M. Murano (1973): Succession of Thompson, J. M., A. J. D. Ferguson and C. S. Reynolds plankton diatoms in Tokyo Bay. La mer, 11, (1982): Natural filtration rates of zooplankton 70-82. (in Japanese) in a closed system: the derivation of a community Copepod Feeding in Tokyo Bay 227

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東京湾における橈脚類群集の天然懸濁態粒子に対する摂餌

津田敦*・根本敬久*

東京湾内湾部における3回の航海で,橈脚類群集の摂的に摂餌した.この結果,橈脚類群集の特定の餌料サイ餅速度をパーティクルカウンターを用いた飼育実験およズに対する濾水速度は全餌料サイズでの平均濾水速度のび消化管内色素量の時間変動から求めた.橈脚類群集に数倍に達した.また,Paracalanus spp.,Pseudodiapto- は餌料サイズによる選択性の違いが認められた.すなわ mus marinusおよびOithona davisaeについては消化

ち2月に卓越したAcartia omoriiは懸濁粒子サイズス管内色素量の時間変動から夜間に摂餌速度が高いことがペクトルで卓越した粒子を選択的に摂餌し,周年卓越し明らかになった. たOithona davisae,および2月に出現したCentro- 現場橈脚類現存量および実験結果から僥脚類群集のEl pages abdominalisは20μm以上の大型の粒子を選択間摂餌速度を求めた結果,2月には懸濁態粒子現存量の 3.0%,8月には3.1-4.5%,また11月には4.2-11.9% *東京大学海洋研究所プランクトン部門が橈脚類群集に摂餌されると見積られた.可〒164東京都中野区南台1-15-1