Journal of the Oceanographical Society of Japan Vol.42, pp.487 to 489, 1987

Short Note

Rate of Filtering of Fecal Pellets by omorii (Copepoda; )

Tenshi Ayukait

Abstract: Adult females of Acartia omorii were allowed to feed on fecal pellets voided by

its juveniles (copepodite stages I and II) in a mixture with the diatom Thalassiosira decipiens.

The rate of filtering of pellets by adult females was 50.3•}11.5ml indiv-1d-1, being twice as high as the rate of filtering of T. decipiens.

Suspended particulate organic matter in sea- The details of the rearing method have been

water is composed mainly of non-living particles described elsewhere by Ayukai (1986). All

such as so-called organic detritus and organic experiments were carried out at 17•Ž in the

aggregates (ref. Nishizawa, 1966, 1969). The darkness using 100-ml bottles as experimental

concentration of living phytoplankton, in turn, vessels. is generally no more than the level for herbivo- The rate of defecation by juvenile A. omorii rous calanoid to meet the basic food was preliminarily determined. A single juvenile requirements (Mullin and Brooks, 1976). The was placed into bottles containing T. decipiens utilization of non-living particles by copepods at different concentrations between 200-1,400 has been a matter of interest (Poulet, 1976; cells These bottles were set onto a grazing

Heinle et al., 1977; Roman, 1984). wheel rotated at 0.25 rpm. After 14 hr incuba-

Fecal pellets are one typical form of organic tion, 1ml of borax-neutralized formalin was detritus. PaffenhOfer and Strickland (1970) were added to the bottles. Each bottle was allowed first to document "coprophagy" by copepods, to stand and the supernatant was withdrawn

PaffenhOfer and Knowles (1979) reported that with a siphon. Residual water was transferred two species of copepods consumed naupliar fecal to a counting chamber and the size and number pellets as fast as they did phytoplankton the of pellets were measured under an inverted volume of which was similar to that of the microscope. pellets. The defecation rate of juvenile A. omorii was In the present study, adult females of Acartia plotted against the initial concentration of T. omorii (Ueda, 1986) were allowed to feed on decipiens because no significant change in the fecal pellets voided by its juveniles (copepodite concentration was observed (Fig. 1). The stages I and II) in a mixture with the diatom critical concentration for saturation of the de-

Thalassiosira decipiens (13.4 pm ESD,=equiva- fecation rate was about 1,000 cells ml-1 of T. lent spherical diameter; 1270 ƒÊm3V,=volume). decipiens. The pellets observed above the critical

The importance of fecal pellets as a food source concentration had an equivalent spherical dia- was evaluated by asking whether or not adult meter of 25.3 ƒÊm and a volume of 1.62•~104ƒÊm3. female A. omorii selectively fed on pellets rather During 14 hr incubation, about 20% of pellets than the diatom. were partially broken. The partial disintegra-

Juvenile and adult female A. omorii used were tion of pellets little affected the determination reared from eggs on cultured phytoplankton . of the defecation rate, but was liable to be a

* Received 20 June 1986; in revised form 7 No - Source of error in examining the utilization of

vember 1986; accepted 28 November 1986. pellets. Since the continuous stirring of water

† Faculty of Agriculture, Tohoku University, with a grazing wheel might result in an in-

Sendai, 980, Japan. creased percentage of broken pellets, water in 488 Ayukai

Table 1. Average concentration, filtering rate

and ingestion rate of adult female Acartia omorii feeding on fecal pellets voided by its

juveniles (copepodite stages I and II) in a mix- ture with the diatom Thalassiosira decipiens. Data are the mean•} the 95% confidence limits.

Fig. 1. Relationship between the concentration the average. As shown in Fig. 1, the defeca- of the diatom Thalassiosira decipiens and the defecation rate of juvenile Acartia omorii tion rate of juvenile A. omorii became saturated (copepodite stages I and II). The curve is above 1,000 cells ml-1 of T. decipiens. The drawn freehand. defecation rate of juvenile A. omorii, therefore, is assumed to be constant throughout 20 hr in- the bottles was periodically stirred in the follow- cubation. ing experiment. As a result, the percentage of The rates of filtering and ingestion by adult broken pellets in the control bottles was reduced female A. omorii on cells and pellets are sum- to half. marized in Table 1. Injured juveniles were The rates of filtering and ingestion by adult found in 2 out of 35 experimental bottles, and female A. omorii on cells and pellets were de- results from these bottles were discarded. In termined. First, ten juveniles were placed into addition, the final concentration of T. decipiens each of 45 bottles and allowed to feed on T. in 4 out of the remaining 33 bottles was higher decipiens at the initial concentration of 1,360 than the average concentration in the control cells Water in these bottles was stirred bottles, and their results were also excluded every 2 hr. After 12 hr incubation, 1ml of borax- from the calculation of the filtering rate. neutralized formalin was added to five bottles The filtering rate of adult female A. omorii for counts of cells and pellets. on pellets was 50.3•}11.5ml indiv-1d-1, being Second, a single female was pipetted into each twice as high as that on T. decipiens of small of 35 bottles. These bottles together with five size (Table 1). This result agrees with a well control bottles were further incubated for 8 hr. known trend that copepods selectively ingest The bottle used was 8cm in height and juvenile large particles over small ones (e. g. Frost, 1972). fecal pellets had theoretical sinking rates of 15- and suggests that adult female A. omorii in 20cm hr-1, which were calculated according to nature prefer to utilize large sinking pellets Stokes' equation modified by Komar et al.(1981). rather than small phytoplankton. Thus water in the bottles was stirred every Cowey and Corner (1966) reported that amino 20min in order to suspend pellets. acid composition of fecal pellets voided by the Juvenile fecal pellets were easily distinguished Calanus finmarchicus resembled that of from those of females by their size. The numbers its algal diet. Paffenhofer and Knowles (1979) of T. decipiens and intact pellets were counted successfully reared the copepod Calanus helgol- under an inverted microscope. The rates of andicus from copepodite stage III to adult stage, ingestion and filtering by adult female A. omorii offering fecal pellets as the sole diet. Although on cells and pellets were calculated from the more studies on the nutritive value of pellets difference between initial and final concentrations, are required, the active utilization of pellets according to Frost's equations (1972). seems important for copepods to survive in After 20 hr incubation, the concentration of food-limited environments. T. decipiens was reduced to 980 cells ml-1 on Rate of filtering of fecal pellets by Acartia omorii 489

Acknowledgement natural copepod and euphausiid fecal pellets. I wish to express my sincere thanks to Pro- Limnol. Oceanogr., 26, 172-180. fessor S. Nishizawa, Tohoku University, for Mullin, M. M. and E. R. Brooks (1976): Some con- continuing guidance and encouragement through sequences of distributional heterogeneity of phyto- out the present study. plankton and zooplankton. Limnol. Oceanogr., 21, 784-796. Nishizawa, S.(1966): Suspended material in the sea. References Inf. Bull. Planktl. Japan, 13, 1-33. Ayukai, T.(1986): Feeding elasticity of a planktonic Nishizawa, S.(1969): Suspended material in the sea. marine copepod Acaria clausi (Copepoda: Cala- 2. Reevaluation of the hypothesis. Bull. Plankton noida). Ph. D. thesis, Tohoku University, Japan, Soc. Japan, 16, 1-42. 121 pp. PaffenhOfer, G. -A. and J. D. H. Strickland (1970): A Cowey, C. B. and E. D. S. Corner (1966): The amino- note on the feeding of Calanus helgolandicus on acid composition of certain unicellular algae, and detritus. Mar. Biol., 5, 97-99. of the faecal pellets produced by Calanus fin- PaffenhOfer, G.-A. and S. C. Knowles (1979): Ecologi- marchicus when feeding on them. p.225-231. In: cal implications of fecal pellet size, production Some Contemporary Studies in Marine Science, and consumption by copepods. J. Mar. Res., 37, ed. by H. Barnes, George Allen and Unwin Ltd. 35-49. London. Poulet, S. A.(1976): Feeding of Pseudocalanus minu- Frost, B. W.(1972): Effects of size and concentration tus on living and non-living particles. Mar. Biol., of food particles on the feeding behavior of the 34, 117-125. marine planktonic copepod Calanus pacificus. Roman, M. R.(1984): Utilization of detritus by the Limnol. Oceanogr., 17, 805-815. copepod, Acartia tonsa. Limnol. Oceanogr., 29, Heinle, D. R., R. P. Harris, J. F. Ustach, and D. A. 949-959. Flemer (1977): Detritus as food for estuarine Ueda, H.(1986): Taxonomic reexamination and copepods. Mar. Biol., 40, 341-353. geographical distribution of copepods known as Komar, P. D., A. P. Morse, L. F. Small and S. W. in Japanese coastal waters. J. Fowler (1981): An analysis of sinking rates of Oceanogr. Soc. Japan, 42, 134-138.

Aoartia omorii (Copepoda: Calanoida) の 糞 粒 に 対 す る 濾 水 速 度

鮎 貝 天 志*

要 旨:室 内 実 験 系 に お い て,榛 脚 類 の 一 種Acartia して 与 え,雌 成 体 の 両者 に 対 す る摂 食 に つ い て 調 べ た. omoriiの 雌 成 体 に,そ の 幼 体(copepodite stages I-II) 雌 成 体 の 糞 粒 に 対 す る炉 水 速 度 は50.3±11.5 ml indiv-1

の 糞 粒 及 び 硅 藻 の 一 種Thalassiosira decipiensを 混 合 d-1で,T.decipiensに 対 す る濾 水 速度 の 約2倍 に 相 当

*東 北 大 学 農 学 部 〒980仙 台 市 堤 通 雨 宮 町1-1 す る高 い 値 で あ った.