Short-term changes in the planktonic community of the western subarctic Pacific during early summer: analysis of sediment trap samples

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1 Bull. Plankton Soc. Japan 58(2): , 2011 The Plankton Society of Japan ) 2) 3) 3) 3) 3) 1) 1) ) ) Short-term changes in the planktonic community of the western subarctic Pacific during early summer: analysis of sediment trap samples R>: O=6H=> 1),K:C-I8=>GD IH=>> 2),T:IHJ>8=> FJ?>@> 3),M>CDGJ K>I6BJG6 3), K6OJ=>@D M6IHJBDID 3),M6@>D C. HDC96 3), 6C9 AIHJH=> Y6B6<J8=> 1) 1) Graduate School of Fisheries Sciences, Hokkaido University, 3 1 1, Minato-cho, Hakodate, Hokkaido, , Japan 2) Graduate School of Agriculture, Kyoto University, Yoshida Hon-machi, Sakyo-ku, Kyoto, , Japan 3) Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2 15, Natsushima-cho, Yokosuka, Kanagawa, , Japan Corresponding author: rie-oh@fish.hokudai.ac.jp Abstract To evaluate short-term changes in the planktonic community, we analysed phytoplankton and zooplankton collected by a sediment trap moored at 150 m depth at St. K2 (47 N, 160 E) in the western subarctic Pacific sampled at two-day intervals during 7 June to 1 July Phytoplankton flux varied from 480 to 372,290 cells m 2 day 1, and had a peak during June. The phytoplankton community was composed of five diatom species and one silicoflagellate species. According to a Bray Curtis cluster analysis, phytoplankton communities were classified into four groups. Zooplankton abundance ranged from 1,137 to 3,385 inds. m 2 day 1 and showed two peaks: June and June. Throughout the study period, large copepod Eucalanus bungii accounted for of the total zooplankton abundance. Gonad maturation of adult females of E. bungii advanced during the study period: immature animals occurred before 15 June, developed during June and newly recruited specimens to the adult female population were observed after 25 June. With regards to the carnivorous zooplankton, the chaetognath community was predominated by Sagitta elegans (99.7 of total abundance). Body length of S. elegans ranged from mm, and the mean body length gradually increased during the study period (0.21 mm per day, r , p 0.01). Gonad maturation was also observed from immature stages in early June to mature stages in late June. As a rule for short-term changes in the planktonic community, phytoplankton abundance fluctuated (max : min 780), while it was stable for zooplankton abundance (max : min 3). Species composition also varied much more for phytoplankton than for zooplankton. For zooplankton, maturation of juveniles and gonad maturation of adults were observed in both herbivores and carnivores. Thus, short-term changes during early summer in the subarctic Pacific were characterized by phytoplankton succession with regards to abundance and species composition and rapid zooplankton growth with regards to development and maturity. Key words: Eucalanus bungii, Sagitta elegans, sediment trap, short-term changes, western subarctic Pacific

2 (2011) 1. (Broecker 1991). (Longhurst 2006). Neocalanus Eucalanus 1991, 1991 Ikeda et al. (2008) (10 20 ) Taniguchi (1999) (Kobari et al. 2003) (Kurita et al. 2004, Sugisaki & Kurita 2004) 1 Shinada et al. 2000, Mochizuki et al. 2002, Tsuda et al. 2004, Shoden et al (Hargrave et al. 1989, Steinberg et al. 1998, Ota et al. 2008, Willis et al. 2008) Seiler & Brandt (1997) Willis et al. (2006) 2003, Onodera et al Okazaki et al. 2003, 2005, 2010 (Kuroyanagi et al. 2002, 2008) 700 4,810 m St. K2 47 N, 160 E, 5,280 m 150 m St. K2 VERTIGO (Buesseler et al. 2008) 0 50 m MR St. K2 (47 N, 160 E) 150 m McLane Mark7G m 2 2 (Fig. 1). 5

3 125 Fig. 1. Location of St. K2 (47 N, 160 E) in the western subarctic Pacific. Arrow and dashed line indicate approximate positions of Oyashio and subarctic boundary, respectively. 1mm 1mm 1/ ml 10 mm Tomas (1997) 1 (PF: phytoplankton flux, cells m 2 day 1 ) PF C V S C (cells), S (ml), V (ml) 10 1/0.5 (0.5 m 2 ) (m 2 ) 1/2 2 (day 1 ) 2 3. Brodskii (1967) Miller (1988) Eucalanus bungii, Metridia pacifica, Neocalanus cristatus, N. flemingeri, Paraeuchaeta elongata E. bungii Miller et al. (1984) I II III IV 1 V 2 VI VII Spent 7 (1997) Sagitta elegans (Body length) Thomson (1947) Terazaki & Miller (1986) Juvenile Stage I Stage II Stage III Stage IV Spent 100 (ZS: zooplankton swimmer, inds. m 2 day 1 ) ZS C C (inds.), 1/0.5 (m 2 ) 1/2 (day 1 ) 2 4. (X: cells m 2 day 1 ) log 10 (X 1) Bray Curtis dissimilarity index (Chiba et al. 2001, Chiba & Saino 2002) BIOSTAT II one-way ANOVA Post hoc (Fisher s PLSD)

4 (2011) (X: inds. m 2 day 1 ) one-way ANOVA Post hoc S. elegans Microsoft Excel Solver ,290 cells m 2 day (Fig. 2A). Thalassiosira 4 1 (Dichtyocha speculum) (Fig. 2B) (Fig. 2C). 4 A B Neodenticula seminae Thalassiosira (Fig. 2D) ,701 cells m 2 day 1 C Thalassionema cf. nitzschioides A B A D N. seminae C Fig. 2. Temporal changes in phytoplankton flux (A) and species composition (B) at 150 m depth at St. K2 during 7 June to 1 July Cluster analysis based on phytoplankton flux identified four groups at the 34 dissimilarity level (C). Mean flux and taxonomic composition of each group are shown in (D). Vertical bars in (D) indicate standard deviations. Table 1. Mean phytoplankton flux of each group (A D) identified from cluster analysis (cf. Fig. 2C). For species that showed significant di#erences in one-way ANOVA, a post-hoc test by Fisher s PLSD was also applied. NS: not significant, : p For Fisher s PLSD, groups not connected with lines are significantly di#erent (p 0.05). Species Abundance (cells m 2 day 1 ) One-way A B C D ANOVA Fisher s PLSD Asteromphalus sp NS Corethron cf. criophilum ,184 0 NS Dictyocha speculum ,157 0 NS Neodenticula seminae 1,360 5,110 25,973 0 D A B C Thalassionema cf. nitzschioides 0 1,762 62,800 0 NS Thalassiosira spp. 1,060 2,472 23, NS

5 127 (Table 1) ,137 3,385 inds. m 2 day (Fig. 3A) E. bungii N. flemingeri (Fig. 3B) 22 3 (Fig. 3C) A B C 6 23 A B, C (Fig. 3D) E. bungii A 80 C 60 N. flemingeri 7 / N. cristatus S. elegans mm A Candacia columbiae, B E. bungii C5 C (Table 2) E. bungii 6 15 C6F (98 ) 6 25 C5F/M 40 (Fig. 4A). M. pacifica C6F (Fig. 4B) P. elongata 6 15 C5M C6F 6 19 C3 C4 C5F (Fig. 4C) N. cristatus C4 C5 (Fig. 4D) N. flemingeri C5 (Fig. 4E) E. bungii Stage I III Stage IV VII (Fig. 4E) 6 11 Stage I Stage III Stage I 50 Fig. 3. Temporal changes in abundance of zooplankton swimmers (A) and their taxonomic composition (B) at 150 m depth at St. K2 during 7 June to 1 July Cluster analysis based on abundance of zooplankton swimmers revealed three groups at the 22 dissimilarity level (C). Mean abundance and taxonomic composition of each group are shown in (D). Vertical bars in (D) indicate standard deviations.

6 (2011) Table 2. Mean abundance of zooplankton swimmer in the three groups (A C) identified from the cluster analysis (cf. Fig. 3C). For species that showed significant di#erences, a post-hoc test by Fisher s PLSD was also applied. NS: not significant, : p 0.05, : p For Fisher s PLSD, groups not connected with lines are significantly di#erent (p 0.05). Species Abundance (inds. m 2 day 1 ) A B C One-way ANOVA Fisher s PLSD Copepoda Calanoida Calanus pacificus NS Candacia columbiae A C B Eucalanus bungii C NS Eucalanus bungii C A B C Eucalanus bungii C6 2, , NS Gaetanus simplex NS Heterorhabdus tanneri NS Metridia pacifica NS Neocalanus cristatus C B A Neocalanus flemingeri NS Paraeuchaeta elongata NS Pleuromamma scutullata NS Pseudocalanus minutus NS Pseudocalanus newmani NS Racovitzanus antarcticus NS Scaphocalanus medius NS Scolecithricella minor NS Scolecithricella ovata NS Cyclopoida Oithona spp NS Chaetognatha Eukrohnia hamata NS Sagitta elegans TL: mm C B A Sagitta elegans TL: mm NS Sagitta elegans TL: 33 mm NS Polychaeta Rhynchonereella angelini NS Tomopteris pacifica NS Tomopteris septentrionalis NS Polychaeta spp A C B Gymnosomata Clione limacina NS Amphipoda NS Appendicularia NS Cephalopoda NS Decapoda NS Euphausiacea A C B Fishes NS Isopoda NS Medusae NS Ostracoda A B C (Fig. 4F) (99.7 ) S. elegans S. elegans mm Stage IV (Fig. 5) mm 6 Stage I II 6 25 Stage III Stage IV (Fig. 5).

7 129 Fig. 4. Temporal changes in abundance and copepodid stage composition of zooplankton swimmers: Eucalanus bungii (A), Metridia pacifica (B), Paraeuchaeta elongata (C), Neocalanus cristatus (D) and N. flemingeri (E) at 150 m depth at St. K2 during 7 June to 1 July For E. bungii C6F, abundance and gonad maturation composition (Stage I III) during the same period are shown in (F). Fig. 5. Temporal changes in body length and gonad stage frequency of the chaetognath Sagitta elegans at 150 m depth at St. K2 during 7 June to 1 July Triangles indicate mean body length in each sampling period. Numbers in parentheses show the number of examined specimens (Underwater profiling buoy system: Fujiki et al. 2008) a Fig. 6 JAMSTEC MR06 03 ( jp/msv2 DATA/23/MR pdf)

130 58 2 (2011) Fig. 6. Temporal changes in chlorophyll a (A) and primary productivity (B) measured by the Underwater Profiling Buoy System (Fujiki et al. 2008) moored at St.

8 (2011) Fig. 6. Temporal changes in chlorophyll a (A) and primary productivity (B) measured by the Underwater Profiling Buoy System (Fujiki et al. 2008) moored at St. K2 during 7 June to 15 July Triangles in chl. a panel (A) indicate three sampling periods for water column phytoplankton abundance (cf. Fig. 7). Redawn and modified from cruise report of MR06 03 ( DATA/23/MR pdf). Fig. 7. Results of cluster analysis based on water-column (0 50 m) diatom cell density at St. K2 on 12, 21, 29 June 2006 (A). Three groups were identified at 66 dissimilarity (A). Cell density and species composition of each group (B). Vertical bars in (B) indicate standard deviations. Vertical and temporal distribution of each group is shown in (C).

9 131 a m (1.4 mg m 3 ), a 40 m (Fig. 6A) m (Fig. 6B) a 6 20 a 1 MR , m (cells L 1 ) Fig A C (Fig. 7A) A Fragilariopsis spp., B Cylindrotheca closterium C Coscinodiscus spp., Neodenticula seminae, Pseudo-nitzchia seriata complex (Fig. 7B) A B m, C m (Fig. 7C) a A 6 29 C (Fig. 6A). (0 50 m) ( 13,440 cells m 2 day 1 ) (Fig. 2A), m a (Fig. 6A), (Fig. 7B, C) (Fig. 2A), a (Fig. 6A), (Fig. 7B, C). (0 50 m) (Figs. 2, 7) m 150 m 10 mm Tomas m Fragilariopsis spp. 3 mm, Tomas m (Fig. 3A) (Fig. 3B) (Miller et al. 1984)

10 (2011) (Table 2) (Ikeda et al. 2008) 150 m E. bungii (Fig. 3B) C6F 6 25 C5F C5M C5 (Fig. 4A) Stage I Stage III 6 27 Stage I (Fig. 4F) E. bungii C5 C6F E. bungii (Miller et al. 1984, Shoden et al. 2005) E. bungii C3 C5 3 4 (Miller et al. 1984) 1 2 (Tsuda et al. 2004, Shoden et al. 2005) 6 11 a (Fig. 6A) (Fig. 7B, C) 6 25 C5 (Fig. 4A, F). C3 C C5 C6 E. bungii C3 C4 C5 C6 (Yamaguchi et al. 2010a, 2010b). E. bungii 4 (Fig. 4B E) M. pacifica, N. cristatus, N. flemingeri P. elongata E. bungii Neocalanus 2 C5 (Miller et al. 1984) (150 m) C4 C5 (N. cristatus) C5 (N. flemingeri) M. pacifica (Batchelder 1985, Padmavati et al. 2004) 1mm P. elongata C C6F C5F (p 0.05, U-test) S. elegans Fig. 8. Temporal changes in mean body length of Sagitta elegans during 7 June to 1 July Regression analysis between mean body length (Y) and julian day from 1 June 2006 (X) is shown. Vertical bars indicate standard deviations. For details of data, see Fig. 5.

11 mm (Fig. 8) 6 Stage I II 6 25 Stage III Stage IV (Fig. 5) S. elegans (Terazaki 1998) S. elegans mm (Fig. 5) 1 48 mm (Terazaki and Miller, 1986) S. elegans S. elegans m (Terazaki & Marumo 1979) 4 3. Fig (Figs. 2, 7) 3 (Fig. 3) (Fig. 4) (Fig. 8), (Fig. 5) (Fig. 6A) (Figs. 4, 5) E. bungii Fig. 4A, Fig. 4F (Calanus finmarchicus) (Nieho# et al. 1999) (Hirche et al. 2001) Fig. 9. Schematic diagram showing temporal changes in planktonic community at St. K2 during June 2006.

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Body length, weight and chemical composition of the ontogenetically migrating copepods in the Western Subarctic Gyre of North Pacific Ocean

Body length, weight and chemical composition of the ontogenetically migrating copepods in the Western Subarctic Gyre of North Pacific Ocean Bull. Plankton Soc. Japan 55(2): 0000, 2008 The Plankton Society of Japan 2008 1) 1) Deborah K. Steinberg 2) 1) 8900056 45020 2) Verginia Institute of Marine Science, College of William and Mary, P.O.