Physico-chemical variables and salinity gradient
Three different groups of ponds were divided in this study in terms of conductivity as an important driver of the diatom communities. The physical-chemical variables of the 15 ponds measured in situ are shown in Table 1. The ponds with the lowest EC (oligosaline) (1.4 and 5.3 mScm− 1) are Taraje, Zoñar, Rincón, Calderón and Pilón. These ponds had a range of pH 7.8–8.6, water temperature between 22 and 31.7 ºC, sea distance 45–95 km and altitude of 80–345 m.a.s.l.
The mesosaline ponds are Verde la Sal, Consuegra, Salada, Montellano and Honda, with EC between 10.9–17.3 mScm− 1, pH 8.2–8.5, water temperature 22-30.6 ºC, sea distance 6-100 km and altitude 33–453 m.a.s.l. (Table 1). The eusaline ponds are (Tíscar, Gosque, Ratosa, Ballestera and Zarracatín) (32.3–51.6 mScm− 1), pH 7.5–9.1, water temperature 23.4–35.2 ºC, sea distance 58–99 km and altitude 40–450 m a.s.l. (Table 1).
Table 1. Site location in ponds and environmental factors measured “in situ”. Sites where Navicula maiorpargemina sp. nov was found are marked with an asterisk *
Diatom community composition
A total of 150 taxa from 55 diatom genera were identified in the 15 samples from the studied ponds. The n-MDS ordination plot of diatom samples showed a stress of 0.14 (Fig. 3). Eusaline ponds were differentiated from the rest of the ponds by the following species Halamphora cf. pertusa, Tryblionella pararostrata, Cocconeis euglypta and Halamphora sp. 1. Halamphora sp. 1 (Figs. 4–8, Appendix 1) was more abundant in Gosque and Ratosa ponds with more than 25% of relative abundance. Cocconeis euglypta (Fig. 13, Appendix 1) with more than 60% of relative abundance in Gosque. Tryblionella pararostrata (Fig. 17, Appendix 1) appeared with the highest percentage (90%) of relative abundance in Ballestera. Halamphora cf.pertusa (Figs. 24–26, Appendix 1) appeared in several ponds with a maximum of 49% of relative abundance in Zarracatín.
In mesosaline ponds, the most representative diatom taxa were Planothidium delicatulum (Figs. 9–12, Appendix 1) that almost reached 60% of relative abundance in Salada pond, Navicula veneta (Fig. 18, Appendix 1) with a maximum of more than 50% in Consuegra and Nitzschia elegantula (Fig. 19, Appendix 1) with a maximum relative abundance in Verde de la Sal with 77%. A clear separation, based on diatom assemblages, between eusaline and oligosaline ponds is visible along axis 1 of the ordination diagram with the mesosaline ponds mediating the other two groups of ponds (Fig. 3).
The PERMANOVA global test showed that the diatom communities present in each type of pond, according to conductivity, are different and statistically significant (Pseudo-F = 1.513. p = 0.012.). Pair-wise tests revealed that significant statistical differences occurred between eusaline and oligosaline as well as between eusaline and mesosaline ponds (Table 2). Nevertheless, the communities were not significantly different between mesosaline and oligosaline ponds (t = 0.952, p = 0.652).
Table 2
Statistical differences between diatom assemblages from ponds with different conductivities based on a permutational multivariate analysis of variance, PERMANOVA. Statistically significant differences (p < 0.05) in bold.
Conductivity class
|
t
|
p(perm)
|
Eusaline - Oligosaline
|
1.4048
|
0.007
|
Eusaline - Mesosaline
|
1.2867
|
0.034
|
Oligosaline-Mesosaline
|
0.95277
|
0.652
|
SIMPER analysis revealed a dissimilarity of 98.37 % within diatom assemblages from eusaline and oligosaline ponds and 94.48 % within diatoms from eusaline and mesosaline ponds (Table 3). Meanwhile the average dissimilarity between mesosaline and oligosaline was lower in SIMPER analysis (87.78%).
One species that characterized oligosaline ponds was Navicula veneta (Fig. 18, Appendix 1) with a relative abundance of 11.0 % and 18.0 % in Taraje and Pilon ponds, respectively. Other species were Nitzschia inconspicua (Figs. 14–16, Appendix 1) with more than 60% in Taraje and Pseudostaurosira brevistriata (Figs. 20–22, Appendix 1) with more that 70% of relative abundance in Zóñar.
Table 3
Most representative taxa of the three groups of ponds according to conductivity (oligosaline, mesosaline and eusaline) obtained by SIMPER analysis. (Average dissimilarity: Eusaline/Oligosaline: 98.37 %; Eusaline/Mesosaline: 94.48 %; Oligosaline/Mesosaline: 87.78 %).
|
|
Average abundance
|
|
|
Ponds
|
Taxa
|
Code
|
Eusaline
|
Mesosaline
|
Oligosaline
|
Tryblionella pararostrata (Lange-Bertalot) Clavero and Hernández-Marin Clavero
|
TRPA
|
22.18
|
1.24
|
0.07
|
Halamphora sp1
|
HALA
|
17.78
|
2.18
|
0.00
|
Cocconeis euglypta Ehrenberg
|
COCO
|
15.37
|
0.14
|
0.29
|
Navicula veneta Kutzing
|
NVEN
|
0.15
|
16.41
|
14.41
|
Pseudostaurosira brevistriata (Grunow in Van Heurck) Williams and Round
|
PBRE
|
0.00
|
0.00
|
14.18
|
Planothidium delicatulum (Kütz.) Round et Bukht
|
PDEL
|
0.00
|
11.76
|
0.00
|
Nitzschia elegantula Grunow in Van Heurck
|
NELE
|
0.09
|
15.83
|
0.47
|
Nitzschia inconspicua Grunow
|
NINC
|
0.97
|
5.90
|
12.40
|
Halamphora cf.pertusa J.G.Stepanek & J.P.Kociole
|
HPER
|
11.83
|
1.09
|
0.06
|
Nitzschia solita Hustedt
|
NSOL
|
0.00
|
0.68
|
5.79
|
Parlibellus cruciculoides (Brockmann)Witkowski. Lange-Bertalot and Metzeltin
|
PCRL
|
5.77
|
1.93
|
0.00
|
Tryblionella apiculata Gregory
|
TAPI
|
1.01
|
5.67
|
4.34
|
Taxonomic section
Phylum Ochrophyta Caval.-Sm. (Cavalier-Smith 1995)
Class Bacillariophyceae Haeckel emend. Medlin and Kaczmarska (Medlin and Kaczmarska 2004)
Subclass Bacillariophycidae Round (Round et al. 1990)
Order Naviculales (Bessey 1907 sensu emend)
Family Naviculaceae (Kützing 1844)
Genus Navicula (J.B.M. Bory de Saint-Vincent 1822)
Navicula maiorpargemina D. Fernández-Moreno, P. Sánchez-Castillo, C. Delgado, S.F.P. Almeida sp. nov
Figures 30–48: LM. Figures 49–54: SEM
Type material
Holotype: Phycotheque GDA-algae slide number 3285 prepared with material from the sample collected in Zarracatín and housed in the Herbarium. University of Granada (Spain).
Isotype: Slide BM 101 920, prepared with material from the sample collected in Zarracatín, housed in the Natural History Museum. London (UK).
Type locality: Zarracatín wetland, Endorreic Complex of Utrera, province of Seville, Andalusia, south of Spain. Geographical coordinates: 37° 2'2.85" N. 5°48'8.30" W: coll. Pedro M. Sánchez Castillo and David Fernández Moreno; coll date 17 June 2006.
Etymology: Refers to the biggest dimensions when it is compared with the most similar species Navicula pargemina.
Description
Microscopy observations (LM and SEM)
Valves narrowly lanceolate to rhombic-lanceolate, gradually tapering towards the apices, length 21.3–30 µm, width 4–5 µm in n = 30. Raphe straight, central pores both deflected in the same direction (Fig. 50, 52). Axial area unilaterally widened specially at the central area which is asymmetrical with a shorter stria on one side (Figs. 30–31, 33, 50–52). Transapical striae slightly radiate near the valve centre (Figs. 34–35), changing to convergent towards the apices (Fig. 32) and 15–17 striae in 10 µm. Each stria is uniseriate composed of linear areolae (Figs. 49–52) and the number of lineolae are 60–70 in 10 µm. Internal view of the raphe shows no intermission in the sternum near the central nodule (Figs. 49, 51). The internal view of the valvar poles shows the distal raphe endings terminating in small helictoglossae (Fig. 53). Externally the raphe at the poles is hooked (Fig. 54).
Comparison of the new species with type material of Navicula pargemina and other similar species
Morphological features of Navicula maiorpargemina sp. nov. and comparison with five species of Navicula which appear in high conductivity waters are presented in Table 4.
N. maiorpargemina appears in this study in water with high electric conductivity as some other small Navicula, nevertheless, these have morphological and morphometrical clear differences which makes it easy to distinguish between them if present in the same samples.
N. maiorpargemina may overlap in terms of length (Table 4) with N. dilucida and N. groschopfii, however, N. maiorpargemina is wider (4–5 µm vs 2–4 µm) than N. dilucida but not wider than N. groschopfii (4–5 µm) (Table 4). The number of striae in 10 µm is lower in N. maiorpargemina (15–17 in 10 µm) compared with N. dilucida (18–24 in 10 µm) and N. groschopfii (20 in 10 µm) (Table 4). According to the outline, N. dilucida and N. groschopfii are more rhombical shaped compared to N. maiorpargemina which has a more parallel valve outline. In comparison with the estuarine species N. abscondita (Batte et al. 2013), N. maiorpargemina is bigger in length (21.3–30 µm vs. 18–40 µm). On the other hand N. consentanea is smaller than N. maiorpargemina (12–20 µm vs. 21.6–30.5 µm) and with higher striae density in 10 µm (20–24 vs. 15–17) respectively. Another important difference between N. maiorpargemina and the four Navicula species previously mentioned is the absence of valves always appearing in pairs after the oxidation process; and which is visible in the SEM micrographs (Figs. 32–36, 38–39).
Table 4
Comparison between Navicula maiorpargemina sp. nov. and the morphologically and ecologically similar taxa (all data from the literature with the exception of N. pargemina Yallop and Underwood)
(References)
|
N. maiorpargemina Fernandez Moreno, Sanchez Castillo, Delgado, Almeida sp. nov.
|
N. pargemina Underwood and Yallop 1994
|
N. abscondita Hustedt 1939
|
N. dilucida Hustedt 1939
|
N. consentanea Hustedt 1939
|
Navicula groschopfii Hustedt 1939
|
Valve Length (µm)
|
21.3–30
|
12–18 (Underwwod and Yallop 1994); 15.0-19.3 (this study)
|
18.0–40.0
|
15.0–29.0
|
12.0–20.0
|
15.0–30.0
|
Valve Width (µm)
|
4.0–5.0
|
3.0–4.0
|
4.0–6.0
|
2.0–4.0
|
4.0–5.0
|
4.0–5.0
|
Valve outline
|
Narrowly lanceolate to rhombic–lanceolate
|
Linear-lanceolate to lanceolate
|
Lanceolate
|
Narrowly lanceolate
|
Lanceloate
|
Rhombic-lanceolate
|
Valve apices
|
Acute apices
|
Acute apices
|
Fairly acute apices
|
Acutely rounded
|
Acutely rounded
|
Acutely rounded
|
Central area
|
Slightly asymmetrical and on one side developed as a narrow transversely rectangular fascia
|
Asymmetrical and on one side developed as a narrow transversely rectangular fascia
|
Small and circular
|
Narrow
|
Absent
|
Rhombic
|
Axial area
|
Unilaterally widened
|
Unilaterally widened
|
Very narrow
|
Very narrow. Linear barely widened
|
Absent
|
Narrow
|
Number of striae in 10 µm
|
15–17
|
22–25
|
15
|
18–24
|
20–24
|
20
|
Striae patterns
|
slightly radiate at the centre to slightly convergent towards the apices
|
Very slightly radiate to parallel
|
Very slightly radiate in the middle
|
Slightly radiate in the middle thoroughly
|
Slightly radiate in the middle
|
Slightly radiate in the middle. Parallel close to apices
|
Raphe
|
Straight. external central endings close
|
Straight
|
Straight. external central endings approximateclose
|
Straight. external central endings close
|
Straight. external central endings close
|
Straight. External central endings moderately distant
|
Ecology
|
Endorheic saline water
|
Brackish-marine water
|
Silty sediments
|
Marine
|
Marine
|
Marine
|
Navicula maiorpargemina sp. nov. (Figs. 29–37; 48–53) was compared with the light micrographs of type material of Navicula pargemina (Figs. 38–47) which is the most similar species because the valves remain together even after the oxidizing treatment. The specimens measured from the type material of N. pargemina (n = 20), showed a small range in valve length (15.0-19.3 µm); its width was 3–4µm and 22–25 striae in 10 µm. The measurements in the original description of Underwood and Yallop (1994) are slightly different (12–18 µm in length; 2.0–4.0 µm in width; 20–29 striae in 10 µm; Table 4) but does not overlap with the new taxon described in the present study.
The most similar species with N. maiorpargemina is N. pargemina which is smaller than the population of this study. The length of N. maiorpargemina varies between 21.3 to about 30 µm; its width varies between 4 and 5 µm while N pargemina showed a length of 12–18 µm (15-19.3 in this study) and a width of 3–4 µm. Both possess linear to lanceolate valve shape. Although sometimes N. maiorpargemina appears slightly lanceolate to rhombic shape (Figs. 30, 33). The valve apices are cuneiform and never rounded like N. pargemina. In N. maiorpargemina the striae are coarser (15–17 in 10µm) when compared to N. pargemina (20–29 in 10µm).
Despite the differences between N. pargemina and N. maiorpargemina now described we verified some similarities between the two taxa. Namely valves found in pairs even after the oxidation process with one valve in valvar view and the other in girdle view (i.e. Figures 30–31, 34 for N. maiorpargemina and Figs. 44, 46 for N. pargemina); asymmetrical axial central area but smaller in N. maiorpargemina.
In SEM micrographs valves are commonly found in pairs, one in face view and the other obliquely/connective view (Fig. 50). According to Underwood and Yallop (1994) in Figs. 11–12, the central area is wider in N. pargemina than in N. maiorpargemina sp. nov. (Fig. 49–52). Hymens were not found in N. maiorpargemina sp. nov. as described in N. pargemina and the number of lineolae is 60–70 instead of 100 for N. pargemina.