Nosy Be Island is the largest (ca. 320 km2) coastal island off Madagascar, located off its NW coast. Along with a number of smaller islands, including Nosy Fanihy, Nosy Sakatia, Nosy Faly, Nosy Ambariobe, Nosy Tanikely, Nosy Komba, Nosy Mamoko and Nosy Tonga, it forms an archipelago, the islands of which originated as volcanoes (Melluso & Morra 2000; Collins & Windley 2002), probably during the Tertiary (Besairie 1968–69–71).
The diatoms of Madagascar are still rather poorly studied. The first studies, containing analyses of materials collected in 1904–2000, were published in 2002. Those surveys concerned only freshwater diatoms and at that time the authors identified 177 new freshwater diatom species (Metzeltin & Lange-Bertalot 2002). The knowledge about marine benthic diatoms from both Madagascar and Nosy Be Island is much more scant. However, there are publications on diatoms from areas close to the Madagascar region, including the analysis of 13 samples collected from Tanzania (Midwest Africa) near the city of Dar-es-Salaam and of one sample from Malindi in Kenia (Foged 1975), as well as a comprehensive study on marine diatoms of the Mascarenhas Archipelago (Mascarene Islands), concerning mainly La Réunion and Rodrigues Islands, where diatoms have been explored in various freshwater environments for many years (Coste & Ricard 1984; Klee et al. 2000), marine diatoms having been addressed since 2005 within the framework of the COSADIM (Coral Sand Diatoms off Mascarenes) project (Riaux-Gobin & Compére 2008; Riaux-Gobin et al. 2010a,b; 2011a,b).
The genus
Species | Source | Region | Comments |
---|---|---|---|
(S.J.C.Zimmermann) Levkov, Metzelti n & A.Pavlov 2013: 208 | Tanzania | Coll. F. Fricke | |
Levkov, Metzeltin & A.Pavlov 2013: 114 | Tanzania | Coll. F. Fricke | |
Levkov, Metzeltin & A.Pavlov 2013: 119 | Tanzania | Coll. F. Fricke | |
Levkov, Metzeltin & A.Pavlov 2013: 131 | Tanzania | Coll. Leg. B. Schröder | |
(Cholnoky) Metzeltin & Lange-Bertalot 1998: 139 | South Africa | Acc. No. MKNDC 6283 | |
(Hustedt) Levkov, Metzelti n & A. Pavlov 2013: 106 | South Africa | Acc. No. MKNDC 6396 | |
Levkov, Metzeltin & A.Pavlov 2013: 241 | South Africa, Indonesia | – | |
(Tempère) Levkov, Metzelti n & A.Pavlov 2013: 177 | New Guinea, Sumatra | Coll. Adams |
The present report describes LM and SEM observations on two
ex O’Meara (1873: 310). Ecology of the two
The analyzed material was collected on 30 June 2014 as an epiphytic sample from mangrove roots at a site designated as NB4a, located near the mouth of a small river on the southern coast of Nosy Be Island (GPS coordinates: 13°24’0.06”S, 48°17’8.58”E; Fig. 1). The authors obtained a permission for sampling from the Ministry of Higher Education and Scientific Research, Antananarivo, Madagascar.
In the laboratory, the sample was treated with 10% hydrochloric acid (HCl) to remove calcium carbonate and, following thorough washing, boiled in 37% hydrogen peroxide (H2O2) to eliminate organic matter. After washing four times with distilled water, the final suspension was pipetted onto coverslips, left for evaporation, and mounted onto glass slides using Naphrax® diatom mountant. The slides were examined under a Zeiss Axio Scope A1 light microscope. Measurements and photographic documentation were performed with the Canon EOS 500D and Canon EOS Utility software. A total of 400 valves were identified to the level of species or variety (or numbered in the case of new species) and counted (Battarbee 1986; Bodén 1991) to assess the relative abundance of all species (including those new to science). Biodiversity indices (i.e. species richness, the Shannon H’ index and the evenness index) were calculated (Shannon 1948; Tuomisto 2012). For scanning electron microscope (SEM) observations, the cleaned material was pipetted onto 25 mm diameter Whatman® Nuclepore 2 µm mesh polycarbonate membrane filters attached to aluminum stubs and sputtered with 20 nm of gold using a Turbo-Pumped Sputter Coater Quorum Q 150OT ES. Diatoms were examined under a Hitachi SU 8010 SEM at the Podkarpackie Innovative Research Center of the Environment (PIRCE), University of Rzeszów.
During sampling, relevant environmental parameters (water pH, temperature, conductivity, salinity, redox potential and dissolved oxygen content) were recorded using the Multiparameter HANNA HI98194 device.
The new species are compared with similar taxa from around the world described in the relevant literature (Metzeltin & Lange-Bertalot 1998, 2002; Moser et al. 1998; Metzeltin et al. 2005; Levkov et al. 2013; Zidarova et al. 2014; Glushchenko & Kulikovskiy 2015; Kohler et al. 2015; Chattová et al. 2017; Glushchenko et al. 2017; Bak et al. 2017; Kociolek et al. 2017; Straube et al. 2017; Wu & Bergey 2017). The adopted terminology follows Round et al. (1990) and Levkov et al. (2013).
Light microscopy (Fig. 2): Valves elliptic-lanceolate in larger specimens to elliptic in smaller specimens, with narrowly rounded apices. Valve length 9–27 μm, width 6.0–10.5 μm. Axial area linear, slightly narrower at the apices and weakly expanded toward the central area. Central area wide, asymmetrical, deltoid or rectangular. Raphe filiform, straight to slightly curved. Proximal raphe endings hooked, finishing T- or L-shaped fissures, barely visible in LM (e.g. Fig. 2d, k, m, q, v, aa, ab). Transapical striae in LM punctate, weakly radiate close to the valve center, becoming strongly radiate toward apices, 20–24 in 10 μm.
Scanning electron microscopy: External view (Fig. 3) – valve mantle with a single row of large elliptic areolae. Few slit-like or elliptic surface depressions (“ghost areolae”) present within the central area (Fig. 3e, arrow). Single isolated pore present in the central area, external, round opening located close to the valve margin (Fig. 3b, arrow). Central area on both valve margins bordered by shortened striae composed of 1–2(3) round or elongated areolae. Proximal raphe ends close to each other, hooked to the side opposite the isolated pore, continuing with irregular, shallow grooves, insect-antennae-like (L-shaped, Fig. 3c) or butterfly-like (T-shaped, Fig. 3e). Transapical striae composed of 4–5 round to elliptic areolae. Distal raphe fissures hooked (question mark form) to the same side (but opposite the proximal raphe endings), not extending onto the valve mantle (Fig. 3f).
Internal view (Fig. 4) – the inner valve surface flat, the central area and the central nodule thickened, forming a stauros. The isolated pore with small, round opening covered by a large, triangular structure, located halfway between valve center and margin (Fig. 4f, arrow). Proximal raphe branches slightly deflected toward the isolated pore (Fig. 4f). Distal raphe branches straight, each terminated as a small helictoglossa (Fig. 4c, arrow). Areolae occluded by hymenes, forming a continuous strip across the striae (Fig. 4e, arrow). Marginal channel narrow, located on the valve face/mantle junction (Fig. 4e, arrowhead).
Type: MADAGASCAR. Nosy Be Island, near Andoany Bay, 13°24’0.06”S, 48°17’8.58”E, July 2014, holotype (assigned here): Slide no. 22010 in Coll. of Andrzej Witkowski at the University of Szczecin (SZCZ), represented by Fig. 2p.
Type locality: Andoany Bay, southern coast, Nosy Be Island, Madagascar
Type habitat: Mangrove roots.
Etymology: The specific epithet refers to the type location, Nosy Be.
Distribution: Known only from the type locality.
Light microscopy (Fig. 5): Valves elliptic-lanceolate in larger specimens to elliptic in smaller specimens, with narrowly rounded apices. Valve length 13.0–22.5 μm, width 6.0–7.5 μm. Axial area linear, slightly narrower at the apices and weakly expending toward the central area. Central area wide, symmetrical, bow-tie-shaped on both valve margins bordered by shortened striae composed of one round or elliptical areola. Raphe filiform, straight to slightly curved. Single isolated pore present in the central area, located halfway between the valve center and margin. Proximal raphe endings close to each other, hooked to the opposite side of the isolated pore, continuing with irregular, shallow, elongated, L-shaped grooves, barely visible in smaller valves, but visible in larger valves in LM (e.g. Fig. 5b, d, e). Transapical striae in LM punctate, weakly radiate close to the valve center, becoming strongly radiate toward the apices, 20–24 in 10 μm.
Scanning electron microscopy: External view (Fig. 6) – Valve mantle with a single row of large elliptic areolae. Single isolated pore distinct, present in the central area, with external, slit-like opening located in a surface depression, halfway between the valve
center and valve margin (Fig. 6a, arrow). Few small, round surface depressions (“ghost areolae”) present around the isolated pore (Fig. 6a, arrowhead). Proximal raphe ends elongated, deflected at 90° (Fig. 6e, arrow). Transapical striae composed of 3–4 round to elliptic or slit-like areolae. Distal raphe fissures hooked on the same side (but opposite the proximal raphe endings), extending to the valve mantle.
An internal valve view is not available due to the limited number of specimens.
Type: MADAGASCAR. Nosy Be Island, near Andoany Bay, 13°24’0.06”S, 48°17’8.58”E, July 2014, holotype (assigned here): Slide no. 22010 in Coll. of Andrzej Witkowski at the University of Szczecin (SZCZ), represented by Fig. 5f.
Type locality: Andoany Bay, southern coast, Nosy Be Island, Madagascar.
Type habitat: Mangrove roots.
Etymology: The specific epithet refers to the type location, Madagascar.
Distribution: The species has been found so far only in the type locality.
During sampling (at low tide), the water temperature and salinity were 32.4°C and slightly above 15 PSU, respectively. Based on the salinity value, the environment is considered brackish.
The oxygen saturation and dissolved oxygen content were 76% and 6.6 mg l−1, respectively. The remaining physicochemical measurements are summarized in Table 2.
Physicochemical parameters of water recorded at the study site on Nosy Be Island during sampling
Temp. °C | pH | ORP mV | DO mg l−1 | 0% | TDS mg l−1 | Salinity PSU | Atm. pressure mbar |
---|---|---|---|---|---|---|---|
32.4 | 6.9 | −104 | 6.6 | 76 | 44 | 15.3 | 1016.5 |
The sample examined was found to contain a total of 48 diatom taxa. The genera identified included
The valve outlines and the shape of the central area in specimens of
The valve shape and striae arrangement in
Metzeltin & Levkov in Levkov, Metzeltin & A.Pavlov (2013: 140); however, these can be distinguished from
The valve outlines in the specimens of
With regard to the valve outline, the shape of the valve apices and striation,
In
The genus
Finally, the species of
The study involved materials collected from mangrove roots at the coast of Nosy Be, a virtually unexplored tropical island off NW Madagascar. The materials contained numerous unidentified taxa from exposed habitats, including