Botanical Studies (2012) 53: 105-124.
ECOLOGY
Diatom assemblages on Nanaura mudflat, Ariake Sea, Japan: with reference to the biogeography of marine benthic diatoms in Northeast Asia
Jinsoon PARK1 Jong Seong KHIM1*, Taisuke OHTSUKA2, Hiroyuki ARAKI3, Andrzej WITKOWSKI4, and Chul-Hwan KOH5 *
1Division of Environmental Science and Ecological Engineering, Korea University, Seoul 136-713, Republic of Korea
2Lake Biwa Museum, Oroshimo 1091, Kusatsu, Shiga 525-0001, Japan
3Institute of Lowland Technology, Saga University, Saga 840-8502, Japan
4Department of Paleooceanology, Institute of Marine Sciences, University of Szczecin, Waska 13, PL-71-415 Szczecin, Poland
5School of Earth and Environmental Sciences (Oceanography), Seoul National University, Seoul 151-742, Republic of Korea
(Received October 5, 2010; Accepted September 28, 2011)
ABSTRACT. A study was conducted to understand the floral characteristics and diversity of benthic dia­toms (Bacillariophyceae) at Nanaura mudflat (E 130° 10', N 33° 04') on the coast of the Ariake Sea, Japan. A literature review was also performed to better understand the biogeography of the marine benthic diatoms of Northeast Asia. Light microscopic and scanning electron microscopic observations revealed a total of 90 Nanaura taxa. All species were listed along with their dimensions, microstructural densities, and if necessary, their ultrastructures. Dominant species found were Navicula sp. 1 (12.6%), Paralia sulcata (10.3%), Tryblio-nella granulata (8.8%), Navicula flantanica (6.8%), Gyrosigma wansbeckii (5.8%) and Cyclotella striata (5.6%). The abundance of the six species collectively accounted for ca. 50% of the total. As for salinity requirements, marine and brackish-marine forms were dominant, while brackish and freshwater species were also observed. Species composition of diatom flora at the study site showed relatively close similarity with those of mudflat (e.g., Isahaya Bay) and brackish lagoon (Matsukawaura Lagoon) in Japan, but were also similar to those of other localities, e.g. at Songdo mudflat in Korea and Fujian coast in China. Thirteen reports of the benthic diatoms from Northeast Asia were selected for comparison based on diatom habitats and data quality. Twenty-one species of Nanaura diatoms, including Cymatotheca weissflogii and Tryblioptychus cocconeiformis, whose reports are rare in the Western Hemisphere and Europe, occurred across Japan, Korea, and China, and represent common benthic diatoms in Northeast Asia.
Keywords: Biogeography; Diatom flora; Japan; Mudflat; Northeast Asia.
INTRODUCTION
The tidal flats along the Ariake Sea coast of Japan are not only well known for their large surface area (ca. 200 km2, or about 40% of the total area covered by tidal flats in Japan), (Araki et al., 2001), but also for the anti-conservation Isahaya Bay reclamation project. Many studies have been carried out to assess and monitor the Ariake Sea ecosystem as a result of local concern. One of the studies was looking for benthic diatom communities in Isahaya, Ariake Sea (Ohtsuka, 2005), however, the study
*Corresponding author: J.S. Khim & C.H. Koh Correspon­dence and requests for materials during the remaining re­view process would be kindly requested to Prof. J. S. Khim at E-mail: jongseongkhim@korea.ac.kr; Tel: ++82-2-3290-3041; Fax: ++82-2-953-0737.
focused mainly on taxonomic description rather than eco­logical perspectives. While studies of benthic diatoms are of great concern and importance in tidal flat ecosystems, only a few studies in Japan have addressed their ecological implications, such as in benthic-pelagic coupling (Hirose et al., 2004; Koh et al., 2006; Koh et al., 2007).
Apart from Japanese tidal flats, the most typical tidal flats are those of the Yellow Sea in Northeast Asia, which are widely developed along the east coast of China and the west to south coasts of Korea, where studies of marine benthic diatoms are also lacking. Diatom study efforts in Northeast Asia are underestimated, however, due to lack of international exposure, particularly from China. Mean-while, a geographical distribution study of benthic diatoms in Japan, Korea, and China would be of great benefit, and provide a better understanding of the benthic flora bioge­ography of Northeast Asia. Since a limited number of re-
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ports are available on marine benthic diatoms in the three countries listed above, all available literature (n=34) from Northeast Asia encompassing tidal flat or coastal (n=6), as well as other benthic environments, such as estuary (n=5), lake (n=7), river (n=6), and others (n=10), are included for comparison.
The nomenclature and flora established in Europe and North America have long been adopted and applied to flo-ristic and taxonomic studies on benthic diatoms in Asian countries. Using this approach, the taxa identified in the region were considered cosmopolitan. While few endemic forms were reported, their high occurrence in such un­explored habitats was expected. Thus, the correct identi­fication of benthic diatoms in our materials and of other samples from Northeast Asia, is vital for floristic and taxo-nomic studies, especially for comparative studies. Com­parisons based solely on checklists are misleading, and photographic documentation and morphological informa­tion should be addressed as far as possible. In the present study, those species likely misidentified and/or in question among the reviewed literature were carefully reevaluated. Alternative identifications were suggested accordingly and used for regional comparisons before larger comparisons were made.
Dominant species in Northeast Asian tidal flats seem to be different from their European and North American counterparts, judging from previous reports as well as per­sonal observations. For example, often missing in Korea and Japan are large motile species representing genera of e.g. Navicula, Nitzschia, Bacillaria, Cylindrotheca, Gy-rosigma, Pleurosigma, and Surirella (Hustedt, 1939, 1955, 1959; Brockmann, 1950; Hendey, 1964; Underwood, 1994; Witkowski et al., 2004), which often dominate European tidal flats. While the predominant species in Northeast Asia, accepting that data is limited, are reported as a large Haslea species (H. nipkowii) from a Japanese mudflat (Othsuka, 2005) and Fogedia and Navicula (per­sonal data) from the Korean sand flat. To better understand their floral characteristics in terms of biogeography, we first tried to extract the typical and common species in Ja­pan (Nanaura), Korea (Songdo), and China (Fujian), then address their global distribution.
In brief, the present study aimed to: 1) report the diatom flora of the Nanaura mudflat, Ariake Sea, along with each species' relative abundance and dimensional and micro-structural information based on light microscopic (LM) and scanning electron microscopic (SEM) observations; 2) examine and compare concurrently occurring species between Nanaura mudflat and Northeast Asia and their biogeographic distribution; and 3) extract and address the global distribution of typical and/or common Northeast Asian species.
MATERIALS AND METHODS
Sampling and observation
The top 0-0.5 cm of surface sediment was collected
Figure 1. Map showing the study area and 11 other benthic habi­tats in Northeast Asia from which diatom flora literature were reviewed. A-D (): coastal and mudflat environments; A: Nan­aura mudflat (this study); B: Gyeonggi Bay (Choi, 1988; Noh et al., 2001); C: Fujian coast (Jin et al., 1985, 1991); D: Isahaya Bay (Ohtsuka, 2005); E-H (): brackish water environments; E: Matsukawaura Lagoon (Nigorikawa and Hasegawa, 1999); F: Kase River Estuary (Yamakawa, 1994); G: Lake Kamo (Hase­gawa and Nigorikawa, 1993); H: Nakdong River Estuary (Cho, 1988); I-L (o): freshwater environments; I: Yungchun Dam Res­ervoir (Lee et al., 1992); J: Hii River (Ohtsuka, 2002); K: Ina-gawa River (Houki, 1986); L: Lake Biwa (Watanabe and Houki, 1988).
from the uppermost tidal flat during ebb tide at Nanaura (E 130。 10', N 33° 04'), Ariake Sea, Japan, on Oct. 2002 (Figure 1). Permanent slide cleaning and preparation in­volved a concentrated HCl and H2O2 treatment to remove calcium carbonate particles in the sediment and organic materials in the cells. Permanent slides were made us­ing pleurax mountant. The specimens were then photo­graphed under the Olympus BX60 LM with x60 Plan Apo objective lens, Zeiss Axioscop LM with x100 Achromat objective lens, and JEOL 6301F SEM (Figure 4). Under the LM observation (Figures 5-8), ca. 1,000 valves were counted and the relative abundance of each taxon was cal­culated.
Literature survey
A literature survey followed by comparative analysis were performed to gain a better understanding of the floral characteristics of Nanaura diatoms. Of major interest here­in was to delineate the regional and habitual distribution of Nanaura diatoms across the various benthic habitats in Northeast Asia.
Diatom taxa identified to the species level only (n=77) were considered for the analysis. First, we collected all
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available literature (n=34) on benthic diatom floristic studies reported in Northeast Asia (Table 1). Reports on benthic diatoms from brackish and freshwaters were also included for analysis, as many species from Nanaura mudflat are not likely typical marine. Literature selec­tions were made, for comparative purposes, based on the following criteria; 1) whether the study dealt with repre­sentative benthic habitats, 2) whether the number of con­currently occurred species (present vs. other studies) was relevant, 3) whether the percentage of species with pho­tographs (relative to total reported) is comparable enough (>33.3%) between studies, and finally 4) whether salinity is clearly given as marine, brackish, or fresh environment. Each criterion was evaluated and scored as good (o = 1.0), acceptable (A = 0.5), or inappropriate (x = 0) and those without an 'x' and with a summed score > 3 were selected for analysis.
Cluster analysis
Of 34 floristic studies for Northeast Asia, a total of 13 (7 in Japan, 4 in Korea, and 2 in China), representing 11 benthic habitats, were finally selected, after which cluster analysis was performed. First, Nanaura species (n=77)
were listed alphabetically as "objectives" in the cluster analysis matrix. Twelve habitats (Nanaura mudflat + 11 selected localities) were then arranged as variables of the matrix shown in Table 3. Secondly, the occurrence of cor­responding species in each habitat was given as '+1 (oc­curred)' and '0 (absent)', respectively. In the meantime, warranting the data quality, a few species of question­able identity in the corresponding literature(s) were re-identified based on original and/or authoritative literature (Table 4). Finally, the meta-data (viz. 12x77 matrix) was computed using Multivariate Statistical Package (MVSP -Kovach Computing Services, 1993). The cluster analysis employed the minimum variance method. Squared Eu­clidian Distance was adopted as dissimilarity index. The resulting dendrogram is presented in Figure 2.
RESULTS
Species composition and abundance of Nan-aura diatoms
In total, 90 diatom taxa from Nanaura mudflat were observed. Table 2 shows the list of species with their di­mensions and microstructural densities. Overall, benthic
Figure 2. Dendrogram by cluster analysis for the 77 Nanaura diatoms, where corresponding taxa are clearly identified to the species level. The value of the dissimilarity index (Squared Euclidian Distance) applied was 12, and Nanaura diatoms are divided into three
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Table 2. List of diatom taxa observed in Nanaura mudflat. Relative abundance, dimensional information and density of microstruc-tures were presented as well.
   Dimension in mm    
     Density of microstructures in 10 mm     
Species
Relative abundance
(%)
Diameter
Length/ Width
Areaolae (A), Costae (C), Fibulae (F), Longitudinal Striae (LS), Marginal Processes (MP), Oblique Striae (oS), Striae (S), Transapical Ribs (TR) and Transapical Striae (TS)
Centric Diatoms
Actinocyclus octonarius
0.1
45-60
A: 10
Actinocyclus octonarius var. tenellus
0.1
39-41
A: 8-9
Actinoptychus senarius
0.7
3-42
Asteromphalus flabellatus
0.1
38-44/29-33
A: 15
Aulacoseira granulata
0.2
5
A: 16 (on valve mantle)
Coscinodiscus oculus-iridis
0.1
153
A: 4-5; MP: 2
Coscinodiscus radiatus
0.2
65-68
A: 4-6
Cyclotella choctawhatcheeana
2.2
8.5-10
S: 18 (at the margin)
Cyclotella litoralis
3.8
13-17
S: 13 (at the margin)
Cyclotella radiosa
0.2
9-19
S: 15 (at the margin)
Cyclotella stelligera
0.1
9
S: 12 (at the margin)
Cyclotella striata
5.6
15-30
S: 8-9 (at the margin)
Cymatotheca weissflogii
2.9
13-17/12-15
A: 11
Ditylum brightwellii
0.1
33
A: ~10
Eucampia zodiacus
0.1
57
A: 13
Paralia sulcata
10.3
9-23
S: 12 (at the margin)
Rhizosolenia imbricata
0.1
25
A: 20 (on valve mantle)
Skeletonema grethae
1.6
7.5-10
A: ~30
Thalassiosira allenii
1.9
8
A: 24; MP: 5
Thalassiosira bramaputrae
1.6
15-25
A: 20
Thalassiosira eccentrica
1.2
17-28
A: 7-8 at the valve center, 9 near the valve margin
Thalassiosira eccentrica var. fasciculata
0.4
29-34
A: 10 at the valve center, 12 near the valve margin; MP: 4
Thalassiosira ferelineata
1.2
18-23
A: 6-7
Thalassiosira lundiana
0.1
20
A: 30; MP: 12
Thalassiosira nordenskioeldii
0.3
22
A: 15-18; MP 2.5
Thalassiosira oestrupii var. ventrickae
1.1
12-17
A: 9-10 at the valve center, 12 near the valve margin
Thalassiosira pacifica
0.3
23
A: 13; MP: 6
Thalassiosira punctigera
0.1
53
A: 15-18; MP: 4
Thalassiosira tenera
1.1
11-20
A: 9; MP: 5
Tryblioptychus cocconeiformis
0.7
19-27/17-25
S: 9
Araphid Diatoms
Delphineis surirella
0.1
13-27/8-14
A: ~9; TS: 8
Neodelphineis pelagica
0.4
15-21/4.5-5
TS: 14
Rhaphoneis rhomboides
0.2
25/14
A: 10; TS: 10
Thalassionema nitzschioides
1.9
30-49/3
A: 12
Raphid Diatoms
Achnanthes longipes
0.2
31-43/9.5-12
TS: 15
PARK et al. ― Mudflat diatoms across Northeast Asia 111
Table 2. (Continued)
   Dimension in mm   
     Density of microstructures in 10 mm     
Species
Relative abundance
(%)
Diameter
Length/Width
Areaolae (A), Costae (C), Fibulae (F), Longitudinal Striae (LS), Marginal Processes (MP), Oblique Striae (OS), Striae (S), Transapical Ribs (TR) and
Transapical Striae (TS)
Achnanthes cf. pseudogroenlandica
0.1
30-35/6
TS: 12 in RV, 9 in RLV
Achnanthes sancti-paulii
0.1
35/19
A: 11; TS: 7
Amphora richardiana
0.1
29-33/7-7.5
A: ~15; S: 12 at the dorsal side, 18 at the ventral side
Cymbella turgidula
0.1
31/11
A: 24; TS: 9
Diploneis aestruarii
0.1
18-21/7.5
TS: 15
Diploneis crabro
0.1
90/29
TS: 5-6
Diploneis cf. smithii
0.1
35/17
TS: 9
Raphid Diatoms (continued)
Diploneis weissflogii
0.1
25-36/11-15
TS: 9-10
Entomoneis alata
1.6
53-67/15
TS: 16
Frustulia interposita
0.1
117/22
LS: 15; TS: 18
Frustulia vulgaris var. elliptica
0.1
42/8.5
TS: ~30
Giffenia cocconeiformis
4.3
37-47/20-23
TS: ~7
Gomphonema biceps
0.1
28/7.5
TS: 12
Gyrosigma diminutum
0.4
100/13
LS: 24; TS: 20
Gyrosigma fasciola var. globifera
0.2
77-97/10-12
LS/TS: 24 (equal in number)
Gyrosigma gibbyi
0.3
105/10
LS: 24; TS: 22
Gyrosigma cf. marcum
0.1
116/10
LS: 27-30; TS: 28
Gyrosigma cf. sterrenburgii
0.5
190-335/22­23
LS: 14; TS: 12
Gyrosigma wansbeckii
5.8
80-101/12­14
LS/TS: 18 (equal in number)
Gyrosigma sp.
2.6
70-74/9-9.5
LS/TS: 24 (equal in number)
Haslea sp.
0.1
35-41/13-14
LS: 24; TS: 13
Navicula acutirostris
0.1
23/6
TS: 18
Navicula flantanica
6.8
41-61/9-12
A: ~20; TS: 9-10
Navicula mannii
0.8
18.5-21/7.5­8.5
TS: 9-10
Navicula pavillardii
0.6
48/9-12
A: ~30; TS: 12
Navicula sp. 1
12.6
34-51/7.5
TS: 11
Navicula sp. 2
2.3
28-38/6-6.5
TS: 12-13
Neidium affine
0.1
46/11
TS: 22
Nitzschia amphibia
0.1
21/4
F: 7; TS: 18
Nitzschia gyrosigma
0.2
300-530/9­9.5
F: 5-6; LS: 21; TS: 24
Nitzschia ligowskii
0.1
25-28/8
F: 9; TS: 27-30
Nitzschia pellucida
2.2
64-65/15
F: 10-11
Nitzschia sigma
0.3
83-87/6.5-7
F: 8-11; TS: 27
Nitzschia sp.
1.8
32.5-57.5
/6.5-7
F: 10-12; TS: 25-27
Pinnularia cf. parvulissima
0.1
59/11
TS: 10
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Table 2. (Continued)
  Dimension in mm  
   Density of microstructures in 10 mm   
Species
Relative abundance
(%)
Diameter
Length/Width
Areaolae (A), Costae (C), Fibulae (F), Longitudinal Striae (LS), Marginal Processes (MP), Oblique Striae (OS), Striae (S), Transapical Ribs (TR) and
Transapical Striae (TS)
Plagiotropis pusilla
0.1
88-105
TS: 16-18
Pleurosigma diverse-striatum
0.1
48-50/14
OS: 20-21; TS: 18
Pleurosigma normanii
0.1
94.5-159 /16.5-24
LS/TS: 18 in the middle, 21 at the apices (equal in number)
Pleurosigma sterrenbergii
0.1
210-215/42­48
LS/TS: ~13 (equal in number)
Psammodictyon panduriforme var. continua
0.1
23/9
F: 15; TS: 21
Psammodictyon roridum
0.1
23/9
F: 12; TS: 27
Rhoicosphenia abbreviata
0.1
50/8
TS: 13
Staurophora salina
0.1
49/8
TS: 16
Surirella recedens
0.1
30-53/18.5­35
C: ~2
Surirella sp.
3.2
28-54.5/17­25
C: ~3; TS: ~18
Trachyneis aspera
0.5
70-76/15-17
TS: 9-10
Trachyneis cf. formosa
0.3
90/17
TS: 11-12
Tryblionella adducta
0.7
23-24.5/8
TS: 15
Tryblionella coarctata
0.1
52/13
TS: 10
Tryblionella cf. debilis
0.1
39/10
F: 8; TR: 11
Tryblionella granulata
8.8
24.5-34
/11.5-13
F: 6.5; TS: 7
Tryblionella hyalina
1.3
18.5-29/9.5­12
F: 9-10; TS: 8.5-10.5
Tryblionella marginulata
0.1
53/10
F: 11; TS: 24
Tryblionella punctata
0.5
34-46.5/ 16.5-20.5
F: 8; TS: 8
Tryblionella salinarum
0.1
28/11
F: 10; TR: 18
and tychoplanktonic species dominated the benthic diatom assemblages at Nanaura mudflat. Among 90 Nanura dai-toms, 30 taxa were centric and 60 were pinnate, with four being araphid and fifty-six raphid. Tychoplanktonic spe­cies such as Paralia sulcata, Cylotella striata, and C. lito-ralis dominated centric diatoms, whereas true planktonic ones, such as Thalassiosira species, were rare.
Meanwhile, typical brackish (Aulacoseira granulata, Nitzschia sigma, Rhoicosphenia abbreviata, and Thalassi-osira bramaputrae) and fresh species (Cycotella stelligera, Cymbella turgidula, Frustulia vulgaris var. elliptica, Gom-phonema biceps, Neidium affine, and Nitzschia amphibia) were also found, collectively accounting for <3% of the diatom assemblages at Nanaura mudflat. The freshwater discharge from the nearby Kase River may have brought
and redeposited the six freshwater diatom species into the Nanaura mudflat, especially since only one valve was found and one photo taken for each of them.
Dominant species showing >5% relative abundance were Navicula sp. 1 (12.6%) followed by Paralia sulcata (10.3%), Tryblionella granulata (8.8%), Navicula flan-tanica (6.8%), Gyrosigma wansbeckii (5.8%), and Cyclo-tella striata (5.6%). The six species, all of them marine, accounted for about half of the entire diatom assemblages.
Co-occurrence of Nanaura diatoms in Northeast Asia
We selected and compared data from 13 different stud­ies, on 11 benthic habitats (Figure 1), with our results (Table 3). Five out of the six studies on marine benthic
PARK et al. — Mudflat diatoms across Northeast Asia
113
Table 3. List of 77 diatom taxa clearly identified in Nanaura mudflat and their co-occurrence among 11 other benthic habitats from Northeast Asia, based on literature survey of 13 floristic reports of benthic diatoms (see Table 1). Environments of 12 areas (Nanaura plus 11 other habitats) were categorized, according to the salinity information provided by authors, into three groups viz. Marine, Brackish water, and Freshwater. Diatom taxa were listed in three groups (Group I; rarely reported taxa, Group II; mudflat taxa, Group III; brackish & fresh taxa) as the result of cluster anaylsis (+ indicates occurrence of corresponding taxa in a given area).
Group
Diatom taxa
Marine
Brackish
Fresh
Aa(Jb) B(K) C(C) D(J)
E(J) F(J) G(J) H(K)
I(K) J(J) K(J) L(J)
Group I
Amphora richardiana
+
+
Asteromphalus flabellatus
+
Cyclotella choctawhatcheeana
+
+
Diploneis aestruarii
+
+
Ditylum brightwellii
+
Eucampia zodiacus
+
Gyrosigma diminutum
+
Gyrosigma wansbeckii
+
Navicula acutirostris
+
Navicula flantanica
+
+
Navicula pavillardii
+
Neodelphineis pelagica
+
Nitzschia gyrosigma
+
+
Nitzschia ligowskii
+
Plagiotropis pusilla
+
Psammodictyon roridum
+
Rhizosolenia imbricata
+
Skeletonema grethae
+
Thalassiosira allenii
+
Thalassiosira ferelineata
+
Thalassiosira lundiana
+
Thalassiosira oestrupii var. ventrickae
+
+
Thalassiosira pacifica
+
+
Thalassiosira tenera
+
+
Tryblionella adducta
+
+
Group II
Achnanthes longipes
+
+
+ +
Achnanthes sancti-paulii
+
+
+
Actinocyclus octonarius
+
+
Actinocyclus octonarius var. tenellus
+
+ +
+
Actinoptychus senarius
+
+ + +
+ +
Coscinodiscus oculus-iridis
+
+
+
Coscinodiscus radiatus
+
+ +
+
Cyclotella litoralis
+
+ + +
+
Cyclotella radiosa
+
+
Cyclotella striata
+
+ +
Cymatothwca weissflogii
+
+ + +
Delphineis surirella
+
+ + +
+ +
Diploneis crabro
+
+
Diploneis weissflogii
+
+ +
+
Entomoneis alata
+
+ + +
+
Frustulia interposita
+
+ +
+
Giffenia cocconeiformis
+
+ + +
+
Gyrosigma fasciola var. globifera
+
+
Gyrosigma gibbyi
+
+
Navicula mannii
+
+ +
+
Nitzschia pellucida
+
+
+
Paralia sulcata (sensu lato)
+
+ + +
+ +
Pleurosigma diverse-striatum
+
+ +
+
Pleurosigma normanii
+
+ +
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Botanical Studies, Vol. 53, 2012
Table 3. (Continued)
Group
Diatom taxa
                                      
Mari
ne
                         
Brac
kish
                               
Fresh
Aa(Jb) B(K)
c(c)
D(J)
E(J)
F(J)
G(J) H(K)
I(K)
J(J) K(J)
L(J)
 Group I
Pleurosigma sterrenbergii
+
+
+
Psammodictyon panduriforme var. continua
+
+
+
Rhaphoneis rhomboides
+
+
+
+
Staurophora salina
+
+
+
Surirella recedens
+
+
+
+
Thalassionema nitzschioides
+
+
+
+
Thalassiosira eccentrica
+
+
+
+
Thalassiosira nordenskioeldii
+
+
Thalassiosira punctigera
+
+
Thalassiosira subeccentrica
+
+
Trachyneis aspera
+
+
+
+
Tryblionella coarctata
+
+
+
+
Tryblionella granulata
+
+
+
+
+
+
Tryblionella hyalina
+
+
+
+
Tryblionella marginulata
+
+
Tryblionella punctata
+
+
+
+
+
Tryblionella salinarum
+
+
+
Tryblioptychus cocconeiformis
+
+
+
+
+
Group III-1
Aulacoseira granulata
+
+
+
+
+
+
+
Nitzschia sigma
+
+
+
+
+
+
Rhoicosphenia abbreviata
+
+
+
+
+
+
+
+
+
Thalassiosira bramaputrae
+
+
+
+
+
+
Group III-2
Cyclotella stelligera
+
+
+
+
+
Cymbella turgidula
+
+
+
+
+
+
+
Frustulia vulgaris var. elliptica
+
+
+
Gomphonema biceps
+
+
+
+
Neidium affine
+
+
+
Nitzschia amphibia
+
+
+
+
+
+
No. of occur
red taxa
90
34
31
26
20
16
11
8
7
5
5
5
aA: Nanaura mudflat (this study), B: Gyeonggi Bay (Choi, 1988; Noh et al., 2001), C: Fujian coast (Jin et al., 1985; Jin et al., 1991), D: Isahaya Bay (Ohtsuka, 2005), E: Matsukawaura Lagoon (Nigorikawa and Hasegawa, 1999), F: Kase River Estuary (Yamakawa, 1994), G: Lake Kamo (Hasegawa and Nigorikawa, 1993), H: Nakdong River Estuary (Cho, 1988), I: Yungchun Dam Reservoir (Lee et al., 1992), J: Ina-gawa River (Houki, 1986), K: Hii River (Ohtsuka, 2002), L: Lake Biwa (Watanabe and Houki, 1988). bA country code to which a given area belongs was given in parenthesis, viz. (C): China, (J): Japan, and (K): Korea.
diatoms were selected, while four of the 13 brackish and four of 15 the freshwater studies were found suitable for comparison purposes. Co-occurrences of Nanaura diatoms across Northeast Asia were provided in salinity groups (viz. in the order of marine, brackish, and fresh) and fur­ther arranged according to the number of concurrently oc­curred species in each group.
As for co-occurrence between Nanaura and other ben-thic habitats, as expected, relatively larger numbers of spe­cies co-occurred as the corresponding salinity increased (viz. <8 in fresh, between 8-20 in brackish, and >21 in marine habits, respectively), Interestingly, the greatest number of co-occurred species were not found in Japan, where selected sites, such as Isahaya mudflat (n=26) and Kase River Estuary (n=16), are geographically close to Nanaura mudflat, but in Songdo mudflat, Korea (n=34) followed by the Fujian coast, China (n=31). All together, physical environment (viz. salinity) seemed to prevail over
geographical distance (viz. locality) when determining oc­currence similarity (or species composition). Meanwhile, certain species found in Nanaura mudflat also co-occurred in freshwater habitats across Japan and Korea (Table 3), but since this was most often a single specimen among all of the corresponding species (n=10), they should not be considered typical mudflat diatoms.
Floral characteristics of Nanaura diatoms
To further find out the floral characteristics in Nanaura mudflat, 77 Nanaura species identified to the species were cluster-analyzed in terms of co-occurrence in Northeast Asia (Figure 2). Cluster analysis clearly exhibited three groups, described below in greater detail.
Group I (n=25) included 'rarely reported taxa' through­out the benthic habitats of Northeast Asia. The group included some planktonic species such as Cyclotella choc-tawhatceeana, Ditylum brightwellii, Eucampia zodiacus,
PARK et al. — Mudflat diatoms across Northeast Asia
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Figure 3. Co-occurrence of Nan-aura diatoms in Songdo mudflat (Korea) and Fujian coast (China). Relative abundance (%) and diatom classification (centric, araphid, and raphid) are also provided.
Rhizosolenia imbricata, and Thalassiosira spp., not con­sidered typical benthic taxa. Included in our material was the planktonic Skeletonema grethae, recently described as "new to science" (Sarno et al., 2005). Nitzschia gyrosigma, which is similar to N. sigmoidea, was also newly described from Northeast Asia (Ohtsuka, 2005).
Group II (n=42) consisted of mostly marine and brackish-marine taxa, thus designated 'coastal and mudflat taxa'. Many of them occurred concurrently not only in marine environments such as Songdo mudflat, Korea and Fujian coast, China, but also in brackish water environ­ments e.g., Matsukawaura Lagoon, Japan (Nigorikawa and Hasegawa, 1999). Most of the centric diatoms in the group, i.e., Coscinodiscus spp., Cyclotella spp., Paralia sulcata, and Thalassiosira eccentrica are often found in coastal sediments and are thought to be neritic species (Witkowski et al., 2000). Pennate diatoms in the group (e.g., Diploneis spp., Gyrosigma spp., Pleurosigma spp., and Tryblonella spp. etc.) are mostly mudflat taxa.
Group III (n=10) was rather small in number but could be further divided into two sub-groups. Group III-1 consisted of 4 species of Aulacoseira granulata, Nitzs-chia sigma, Rhoicosphenia abbreviata, and Thalssiosira bramaputrae. They were found throughout Northeast Asia across a wide range of salinities but particularly in brackish environments. Group III-2 consisted of typical freshwater species Cycotella stelligera, Cymbella tur-gidula, Frustulia vulgaris var. elliptica, Gomphonema bi­ceps, Neidium affine, and Nitzschia amphibia. Altogether, Group III was designated 'brackish and freshwater taxa'.
Figure 4. SEM photos of Paralia sulcata (A, B) and Skeletone­ma grethae (C). Scale bar = 1 (im in A, B, 5 (im in C.
PARK et al. — Mudflat diatoms across Northeast Asia
117
DISCUSSION
Regional distribution of the Nanaura diatoms in Northeast Asia
As for Japanese marine habitats, the diatom flora of Isahaya Bay in the western Ariake Sea was found most comparable to that of Nanarua mudflat, with 26 taxa in common. The number seems rather low considering 1)
their relative closeness within the Ariake ecosystem (ca. 50 km apart) and 2) their similar substratum of fine mud. The dominant Isahaya mudflat species apparently differed from those found in Nanaura mudflat; Haslea nipkowii was the most dominant (ca. 20% abundance) followed by Paralia sulcata (ca. 11%), Cyclotella litoralis (ca. 9%), and Nitzs-chia gyrosigma (ca. 8%) in Isahaya Bay (Ohtsuka, 2005). One possible cause would be the influence of freshwater
Figure 5. LM photos of Nanaura diatoms. A, Actinocyclus octonarius; B, A. octonarius var. tenellus; C, Actinoptychus senarius; D, As­teromphalus flabellatus; E, Aulacoseira granulata; F, Coscinodiscus ocmlus-iridis; G, C. radiatus; H, Cyclotella choctawhatcheeana; I, C. litoralis; J, C. radiosa; K, C. stelligera; L, C. striata; M, Cymatotheca weissflogii; N, Ditylum brightwellii; O, Eucampia zodiacus; P, Paralia sulcata; Q, Rhizosolenia imbricate; R, Skeletonema grethae; S, Thalassiosira allenii; T, T. bramaputrae; U, T. eccentric; V, T. eccentrica var. fasciculata; W, T. ferelineata. Scale bar = 10 (im in C-E, H-N, P, R-W, 15 (im in A, B, F, G, O, Q.
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discharge from several rivers including the Kase River on the Nanaura assemblages, which is supported by the fact that none of the freshwater species (viz. Group III-2) were reported in the Isahaya Bay (Table 3). Although 'Honmyo River' flows into Isahaya Bay, it may not be comparable to the Kase River, due to its small scale. Seasonality could be another reason for the different species composition,
considering the different sampling time in Isahaya (May) and Nanaura (October). Among brackish water habitats in Japan, the diatom flora in Matsukawaura Lagoon was the most similar to that of Nanaura mudflat, showing 20 spe­cies in common. The rather high number of concurrently occurred species found in Matsukawaura Lagoon could be attributed to the comparably high salinity (ca. 30%o).
Figure 6. LM photos of Nanaura diatoms. A, Thalassiosira lundiana; B, T. nordenskioeldii; C, T. oestrupii var. venrickae; D, T. paci­fica; E, T. punctigera; F, T. tenera; G, Tryblioptychus cocconeiformis; H, Delphineis surirella; I, Neodelphineis pelagic; J, Rhaphoneis rhomboids; K, Thalassionema nitzschioides; L, M, N, Achnanthes longipes; O, P, A. cf. pseudogroenlandica; Q, A. sancti-paulii; R, Amphora richardiana; S, Cymbella turgidula; T, Diploneis aestuarii; U, D. cmbro; V, D. cf. smithii; W, D. weissflogii; X, Entomoneis alata; Y, Frustulia interposita; Z, F. vulgaris var. elliptica. Scale bar = 10 (im in A-D, F, G, H-T, V, W, Z, 15 (im in E, U, X, Y.
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Meanwhile, only a few species (n = 10), mostly of Group III, were reported from benthic habitats in freshwater envi­ronments.
Nanaura diatoms also concurrently occurred in Songdo mudflat, Korea (n = 34) and Fujian coast, China (n = 31) (Figure 3). Twenty one species, namely Actinocyclus
octonarius var. tenellus, Actinoptychus senarius, Coscino-discus radiatus, Cyclotella litoralis, C. striata, Cymatoth­eca weissflogii, Delphineis surirella, Diploneis weissflogii, Entomoneis alata, Frustulia interposita, Giffenia cocco-neiformis, Paralia sulcata, Pleurosigma diverse-striatum, P. normanii, Surirella recedens, Thalassiosira eccentrica,
Figure 7. LM photos of Nanaura diatoms. A, Giffenia cocconeiformis; B, Gomphonema biceps'; C, Gyrosigma faciola var. globifera; D, G. diminutum; E, G. gibbyi; F, G. cf. macrum; G, G. cf. sterrenburgii; H, G. wansbeckii; I, G. sp.; J, Haslea sp.; K, Navicula acutiro-stris; L, N. flantanica; M, N. mannii; N, N. pavillardii; O, N. sp. 1.; P, N. sp. 2.; Q, Neidium affine; R, Nitzschia amphibia; S, N. gyro­sigma; T, N. ligowskii; U, N. pellucida; V, N. sigma; W, N. sp.; X, Pinnularia cf. parvulissima; Y, Plagiotropispusilla. Scale bar = 10 um in A, B, J-R, T. W-Y, 15 um in C-I, S, U, V.
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Trachyneis aspera, Tryblionella granulata, T. hyalina, T. punctata, and Trybiloptychus cocconeifromis were com­mon across Nanaura, Songdo, and Fujian, representing typical diatom taxa for Northeast Asia and accounting for
43.3% of the total. Among the above species, the dominant species (>5%) are Paralia sulcata (10.3%), Tryblionella granulata (8.8%), and Cyclotella striata (5.6%), collec­tively accounting for ca. 60% of total common species.
Figure 8. LM photos of Nanaura diatoms. A, Pleurosigma diverse-striatum; B, P. normanii; C, P. sterrenburgii; D, Psammodictyon panduriforme var. continua; E., P. roridum; F, Rhoicosphenia abbreviata; G, Staurophora salina; H, Surirella recedens; I, S. sp.; J, Trachyneis aspera; K, T. cf. formosa; L, Tryblinonella adducta; M, T. coarctata; N, T. cf. debilis; O, T. granulata; P, T. hyalina; Q, T. marginulata; R, T. punctata; S, T. salinarum. Scale bar = 10 (im in D, E-G, L-S, 15 (im in A, B, H-K, and 20 (im in C.
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Overall, the above species comprised a relatively great proportion of Nanaura mudflat both individually and col­lectively and are thus likely abundant and widespread across Northeast Asia.
Worldwide occurrence of Nanaura diatoms
Certain species among the Nanaura assemblages were distributing worldwide. Species such as Actinocyclus oc-tonarius, Actinoptychus senarius, Coscinodiscus oculus-iridis, Entomoneis alata, Nitzschia pellucida, Paralia sulcata, Pleurosigma normanii, Thalassionema nitzs-chioides, Thalassiosira eccentrica, Tryblionella granulata, and T. salinarum have been reported as cosmopolitan species in the coastal areas (Hasle and Syvertsen, 1997; Witkowski et al., 2000). Previous reports of P. sulcata, however, may be of one of three Paralia spp., viz. P. capi-tata, P. fenestrata, and P. sulcata (Sawai et al., 2005), thus further study is needed to verify the worldwide distribution of P. sulacata, sensu stricto. Nitzschia ligowskii, recently described as new to science, has also been reported as dis­tributing worldwide (Witkowski et al., 2004).
A few diatoms that appeared among Nanaura assem­blages have rarely been reported worldwide. Gyrosigma gibbyi was first described in New Zealand in 2003 and our study is the second report of this species in the world and the first in the northern hemisphere. Gyrosigma gibbyi was also recorded in the Korean mudflat as Gyrosigma sp. (Noh et al., 2001) thus possibly widespread in Northeast Asia. Nitzschia gyrosigma, first described in Isahaya Bay (Ohtsuka, 2005), was also observed in the present study. So far the locality of N. gyrosigma is limited to the Ari-ake Sea, Japan, however, the corresponding species was observed in the Korean mudflat (personal observation). Thus it is possible that N. gyrosigma is widespread across Northeast Asia yet reported as N. sigmoidea, which is very similar (Ohtsuka, 2005) under LM observation. The first report of three for Pleurosigma sterrenburgii is from New Zealand (Stidolph, 1993) followed by two more from the German Wadden Sea (Sterrenburg, 2003; 2005). Thus our study is the first report of the species in Asia, second in the Northern Hemisphere, and fourth worldwide. Pleu-rosigma sterrenburgii was also recorded in the Korean mudflat as P. angulatum (Noh et al., 2001) supporting the possible endemism of the taxon in the marine littoral as suggested by Sterrenburg (2003). Skeletonema grethae, first described in 2005, is another species with few re­ports worldwide. Kooistra et al. (2008) stated that "it is clear that most Skeletonema species are widely distributed throughout either temperate or tropical coastal regions" and "S. grethae is apparently the only exception to the widespread distribution of the species with its distribution only along the Atlantic side of the USA". However, pro­vided that our identification is correct, the distribution of S. grethae should be greater, and include the Pacific Ocean. There was also a record of S. grethae from the Pacific coast of Canada (Sarno et al., 2005), which was somehow not counted by Kooistra et al. (2008). Thus, distribution of S. grethae may not be restricted to Atlantic Ocean.
Furthermore, there seemed to be some rarely reported species in the Western Hemisphere and Europe that are common in Northeast Asia. Cymatotheca weissflogii, which was first described on the western coast of Africa (Hendey, 1958), has not seemingly been reported from USA and Europe. The only record of its location in the Western Hemisphere is in Brazil (Priscila et al., 2008), with a couple of reports of it in Northeast Asia (Jin et al., 1985; Choi, 1988; Ohtsuka, 2005). Rarely reported from the Western Hemisphere is also Tryblioptychus cocconei-formis, which was first reported in 1883 by Cleve from Labuan near Borneo (Prasad et al., 2002). Its distributions are somehow global, however, there are only two records from the Western Hemisphere, viz. one from Florida, USA (North America) and the other from Georgetown, Guyana (South America), with no record from Europe. On the con­trary, there were many reports of the taxon from the East Asia (Prasad et al., 2002). All together, C. weissflogii and T. cocconeiformis, which co-occurred among the mudflats of Japan, Korea and China (Figure 3), are considered char­acteristic of the Northeast Asian mudflats. Overall, the benthic diatom species found in Nanaura mudflat showed a wide spectrum of biogeographical distribution; some were cosmopolitan, some were typical of the mudflats of Northeast Asia, and some were rare worldwide (Figure 3).
Acknowledgment. This work was supported by the Na­tional Research Foundation of Korea Grant funded by the Korean Government (KRF-2006-312-C00446). This work was also supported, in part, by the NRF grant funded by MEST (NRF-2010-0010500/2011-0004261) awarded to JSK. Sampling was conducted during a guest professor­ship by C.H. Koh at the Institute of Lowland Technology (ILT), Saga University, Japan, from April 2002 to March 2003. We thank Prof. Shigenori Hayashi, director of ILT, who arranged the guest professor program including finan­cial support. We also thank Prof. Xiaowei Zhang, Nanjing University, for translating the English abstract into Chi­nese. We also wish to express our gratitude to Ms. Misako Hanada, who strongly supported the SEM photography at Lake Biwa Museum.
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Botanical Studies, Vol. 53, 2012
日本明海七浦灘塗的硅藻：遠東地區硅藻的分類與區域分布
朴鎮淳1 金宗聲1 大塚泰介2 荒木宏之3 Andrzej WITKOWSKI4 高哲煥5
1韓國高麗大學環境生態工學部
2曰本琵琶湖博物館
3日本佐贺大學低地和海洋研究所
4波蘭什切青大學海洋科学研究所古海洋部
5韓國國立首爾大學地球環境科學部
本文硏究了日本明海沿岸七浦灘塗（E 130° 10', N 33° 04')底栖硅藻（Bacillariophyceae)的植物區系
特徵和多樣性。同時開展了文獻檢索以更好地瞭解東北亞地區海洋底棲矽藻的地理分佈。通過光學顯微
鏡和掃描電鏡觀察發現七浦矽藻共有90種。本文列出了這些矽藻物種的名稱並提供了相應的立體資訊
和顯微結構密度'必要時給出了超微結構。優勢種依次爲Navicula sp. 1 (12.6%), Paralia sulcata (10.3%),
Tryblionella granulata (8.8%), Navicula flantanica (6.8%), Gyrosigma wansbeckii (5.8%)和Cyclotella striata
(5.6%)。這6種矽藻大約占了豐度總量的50% 。而按照對鹽度的需求劃分，海水和苦咸水種是優勢
種，但也發現了微咸水和淡水種。被硏究地點的矽藻植物區系組成與日本灘塗（例如諫早灣）和微咸
水潟湖（松川浦）以及韓國的松島灘塗和中國的福建沿海等地的情況比較相似。考慮到矽藻的棲息地
和資料品質，我們選擇了來自東北亞的13份報告進行比較。結果發現包括Cymatotheca weissflogii和
Tryblioptychus cocconeiformis在內的21種七浦矽藻似乎在日本、韓國和中國都有分佈，而西半球和歐洲
的相關報導卻很少，因此這些底棲矽藻被認爲是東北亞地區普遍存在的種。
關鍵詞：生物地理學；硅藻植物區系；日本；灘塗；東北亞。