# The DiatomAnorthoneis dulcis Hein from Southern Brazil: Morphology and Ecology

Authors: Garcia Marinês; Talgatti Dávia Marciana
Journal: Research Letters in Ecology
 (2008)

---

## Abstract

A new geographic locality forAnorthoneis dulcis is reported. The paper describes the distribution and relative abundance of A. dulcis in Lagoa dos Patos lagoon (a lagoon in Rio Grande do Sul state, Brazil) from samples collected between 2004 and 2005, and shows that this rare species is present all year round. This study extends the species distribution to South America indicating that the species can thrive on sand grains in lentic estuarine, and freshwater areas. It widens the range of tolerance to environmental parameters. The valve fine structure, morphology, and dimensions are in agreement with the original diagnosis.


---

## Body

## 1. Introduction

The South American diatom flora is
poorly known, and the fine structure issue for South American diatoms has been
rarely addressed. On the other hand, proper taxonomic identifications,
biogeography, patterns of distribution, and frequency of plants are essential
topics for conservation programs.In the Lagoa dos Patos lagoon (30°23′30″ and 32°10′00″ S; 50°30′00″ and 52°15′00″ W), the benthic
diatom flora has revealed several species described for Venezuela and/or
Florida, but rarely recorded elsewhere, such as Amphora tumida Hustedt, Desikaneis
gessneri (Hustedt) Prasad and Desikaneis
howellii Prasad, Fallacia teneroides (Hustedt) D.G. Mann, Fallacia tenera (Hustedt) D.G. Mann, and Staurosira
obtusa (Hustedt) Garcia ([1] and unpublished data).The genusAnorthoneis so far includes nine species, A. dulcis Hein, A. eurystoma Cleve, A. excentrica (Donkin) Grunow, A.
hyalina Hustedt, A. hummii Hustedt, A. minima Foged, A. pulex Sterrenburg, A. tenuis Hustedt, and A. vortex Sterrenburg. Eight
out of these nine species, except  A. dulcis Hein,
are marine and benthic and have been recorded as rare or scarce for several coastal
areas (see [2, 3]) except for Sterrenburg
[4] who found abundant Anorthoneis populations in sediments and on beaches of the North Sea (The Netherlands).Anorthoneis dulcis Hein was described in 1991 from some rivers in Northern
Florida (29°N, USA) as a periphytic species (either adnate or
attached to substrate by mucilage stalks) in subtropical waters in the autumn and winter.Anorthoneis dulcis has
also been found in the Kwang River (South Korea, 36°55′N- 129°25′E)
by LEE et al. [5] on stones at a
depth of 30 cm in areas with slightly brackish water and apparently free from major pollution
sources (their stations 11 and 12) in spring and summer
times. In the stations where A. dulcis occurred, the authors also found Actinocyclus normanii (Greville)
Hustedt and Rhaphoneis surirella Ehrenberg, which are brackish/marine species. Their specimens of A. dulcis were larger in size and had
coarser striae and puncta than specimens in the type material.The
present investigation describes the valve morphology and the fine structure of
specimens studied from Southern Brazil. Data on the frequency, distribution in
this estuarine area and alongside the Western margin of
the Lagoa dos Patos lagoon, and environmental data
are also presented.


### 1.1. Material and Methods

The Lagoa dos Patos lagoon is the largest
lagoon in Brazil and has a surface area of
9 910 Km2. The lagoon coastline is essentially composed of
unconsolidated Quaternary sediments
forming extensive and continuous sandy beaches and sandy spits. Sands along the
Western side of the lagoon are poorly sorted, with fine-to-coarse sand grains [6].Sediment samples were collected from the Lagoa dos
Patos lagoon between 2004 and 2005
in several sampling sites: Barra do Ribeiro (three
sites), Arambaré (three sites), São Lourenço do Sul (three sites), Feitoria Spit
(one site), Lagoa Pequena mouth (one site), and Laranjal Bay (seven sites). In
all these sites, the two first millimeters of sand or muddy/sandy surface were
collected from the wet areas
next to the splash zone (Figure1). The samples were fixed with Lugol’s solution at 0.3%.
Fixed material was deposited in the Herbarium
of the Department of Botany, Federal University of Pelotas (Rio Grande do Sul,
Brazil) with access number ranging from 22858 to 24073. In total, 163 samples
were studied.Figure 1
Sampling sites at
Lagoa dos Patos lagoon.The
sand and mud (only at Lagoa Pequena mouth) samples were cleaned by the method
described in Simonsen [7]. Aliquots were dried onto on-cover slips and mounted
in Hyrax for permanent slides. For each sample, at least two slides were
mounted. Slides were examined with an Olympus BX 40 light microscope with phase
contrast. For scanning electron microscopy (SEM), cleaned frustules were dried
on a stub, coated with gold at 1 kV for 4 minutes, and examined with Jeol 6060
at an accelerating voltage of 15 or 20 kV.For
samples collected in Laranjal Bay during 2005, 400 valves were counted in permanent slides at 1000× and
the abundant species were determined by their frequency. At least two slides per station were
observed. For all the slides studied, the whole cover-slip surface was observed
under 400× in order to check the occurrence ofAnorthoneis.The conductivity was determined with a Korning CD55 meter,
which measures conductivity between 0 and 2000 μS/cm with 3% error. The
pH was determined with na HI 8314 pH meter (Hanna Instruments, Mich, USA). Terminology follows [8, 9].


## 1.1. Material and Methods

The Lagoa dos Patos lagoon is the largest
lagoon in Brazil and has a surface area of
9 910 Km2. The lagoon coastline is essentially composed of
unconsolidated Quaternary sediments
forming extensive and continuous sandy beaches and sandy spits. Sands along the
Western side of the lagoon are poorly sorted, with fine-to-coarse sand grains [6].Sediment samples were collected from the Lagoa dos
Patos lagoon between 2004 and 2005
in several sampling sites: Barra do Ribeiro (three
sites), Arambaré (three sites), São Lourenço do Sul (three sites), Feitoria Spit
(one site), Lagoa Pequena mouth (one site), and Laranjal Bay (seven sites). In
all these sites, the two first millimeters of sand or muddy/sandy surface were
collected from the wet areas
next to the splash zone (Figure1). The samples were fixed with Lugol’s solution at 0.3%.
Fixed material was deposited in the Herbarium
of the Department of Botany, Federal University of Pelotas (Rio Grande do Sul,
Brazil) with access number ranging from 22858 to 24073. In total, 163 samples
were studied.Figure 1
Sampling sites at
Lagoa dos Patos lagoon.The
sand and mud (only at Lagoa Pequena mouth) samples were cleaned by the method
described in Simonsen [7]. Aliquots were dried onto on-cover slips and mounted
in Hyrax for permanent slides. For each sample, at least two slides were
mounted. Slides were examined with an Olympus BX 40 light microscope with phase
contrast. For scanning electron microscopy (SEM), cleaned frustules were dried
on a stub, coated with gold at 1 kV for 4 minutes, and examined with Jeol 6060
at an accelerating voltage of 15 or 20 kV.For
samples collected in Laranjal Bay during 2005, 400 valves were counted in permanent slides at 1000× and
the abundant species were determined by their frequency. At least two slides per station were
observed. For all the slides studied, the whole cover-slip surface was observed
under 400× in order to check the occurrence ofAnorthoneis.The conductivity was determined with a Korning CD55 meter,
which measures conductivity between 0 and 2000 μS/cm with 3% error. The
pH was determined with na HI 8314 pH meter (Hanna Instruments, Mich, USA). Terminology follows [8, 9].


## 2. Results

### 2.1. Observations on the Morphology

Anorthoneis dulcis Hein (see [9, Figures 2–21, Figures
2–9])Dimensions: lenght: 16–18 μm; width: 10–12 μm; striae in 10 μm: 18–20
(22); areolae in 10 μm: 20–23.Observations in SEM.Raphe valve: in SEM, the undulation of the valve face is more
noticeable than in LM (see Figure 2). The slightly radiate striae are formed by
a single row of round areolae with almost the same size next to the raphe and
valve margins.
Around the margin, every single stria is composed of two areolae. These areolae
vary in shape from circular to elliptical. Around the valve, there is a costa-like
thickening at the angle between the valve face and the mantle. This thickening
separates the biseriate striae from the small and elongated areolae present
along the valve margin (see Figures 3 and 4). The raphe is short, straight, and
filiform. The proximal and distal external raphe ends are small and are droplet
shaped (see Figures 3 and 4). Internally, the proximal raphe ends in opposite
directions and the distal raphe ends have helictoglossae (see Figures 4, 5, 6, and 7). Rapheless valve: the striae are
radiate and composed of coarse and round areolae (Figure 9). Next to the valve margin, the
areolae are variable in shape (see Figure 8) and occasionally biseriate striae
are found.Figure 2
LM. Raphe and rapheless valve.Figure 3
External general view of the raphe valve.Figure 4
Another raphe valve in external view.Figure 5
Internal general view of valve.Figure 6
Detail of a valve in internal view showing the proximal raphe endings in
opposite directions.Figure 7
Detail of Figure5, showing
the distal raphe
end in helictoglossa.Figure 8
External view of the rapheless valve.Figure 9
Internal view of the rapheless
valve.


### 2.2. Distribution and Environmetal Data

Anorthoneis dulcis was a rare species in Lagoa dos
Patos lagoon occurring in a few sites (Table 1) and in very low number. In
general, only one or two frustules/valves were observed in each permanent slide
analyzed. It is
interesting to notice that Barra do Ribeiro and Arambaré are located under
strong freshwater water influence.Table 1
Samples whereA. dulcis was
recorded alongside Lagoa dos Patos lagoon Western margin with its respective
collecting date, electric conductivity, and pH.
Location nameDateConductivity (μS/cm)pHBarra do Ribeiro (30°18′11″S–51°17′07″W)August 20046006.7Arambaré (30°55′52″S–51°30′14″W)August 20042206.5São Lourenço do Sul (31°21′48″S–51°57′40″W)March 200415008.0São Lourenço do Sul (31°21′48″S–51°57′40″W)August 20042206.5Spit of Feitoria/Lagoa Pequena mouth
(31°40′36″S–52°01′52″W)April 2004——São Lourenço do Sul (31°21′48″S–51°57′40″W)March 200510906.2In
Laranjal Bay, from the seven sites studied,A.
dulcis was observed only in São Gonçalo Spit during 2004 (Table 2), but in
2005 it was found in São Gonçalo Canal, São Gonçalo Spit, and Promenade. The quantitative study of A. dulcis at Laranjal Bay revealed that the highest
values of the relative frequency observed were between 1.3–1.5% (see Figure 10),
although it is a rare species in this Bay.Table 2
Electric conductivity (μS/cm), pH, and air temperature (°C) of
samples collected in 2004 at São Gonçalo Spit.
MonthConductivity (μS/cm)pHAir temperature (°C)January1797.127May>20007.417July>20006.321.4August>20006.7—September18156.821.5Figure 10
Relative frequency ofA. dulcis at Laranjal Bay  in 2005.No seasonal pattern forA. dulcis was
observed (Table 3). Therefore, it was present throughout the year.Table 3
Conductivity (μS/cm),(pH) and
air temperature (°C) of samples collected in 2005 when A. dulcis was present at Laranjal Bay.
São Gonçalo SpitSão Gonçalo CanalPromenade(31º46′50″S–52º13′18″W)(31º47′10″S–52º13′23″W)(31º46′28″S–52º13′35″W)January>2000(6.4) 31Not observedNot observedMarch—(7.5)-Not observedNot observedJuly128(6.5) 14Not observedNot observedAugust134(7.0) 15105(7.7) 15774(7.0) 16September>2000(6.0) 18.51246(7.0) 18.5Not observedOctober466(6.4) 20Not observed466(6.4) 19November100(7.2) 23.5Not observedNot observedDecember>2000(6.7) 22Not observedNot observedAt Lagoa dos Patos lagoon,A. dulcis was found at electric conductivity values varying from 100 to 2000 μS/cm areas
with freshwater and brackish water influence. The pH
during the study period ranged from 6.0 to 8.0 and the temperature ranged from
14ºC to 31ºC.


## 2.1. Observations on the Morphology

Anorthoneis dulcis Hein (see [9, Figures 2–21, Figures
2–9])Dimensions: lenght: 16–18 μm; width: 10–12 μm; striae in 10 μm: 18–20
(22); areolae in 10 μm: 20–23.Observations in SEM.Raphe valve: in SEM, the undulation of the valve face is more
noticeable than in LM (see Figure 2). The slightly radiate striae are formed by
a single row of round areolae with almost the same size next to the raphe and
valve margins.
Around the margin, every single stria is composed of two areolae. These areolae
vary in shape from circular to elliptical. Around the valve, there is a costa-like
thickening at the angle between the valve face and the mantle. This thickening
separates the biseriate striae from the small and elongated areolae present
along the valve margin (see Figures 3 and 4). The raphe is short, straight, and
filiform. The proximal and distal external raphe ends are small and are droplet
shaped (see Figures 3 and 4). Internally, the proximal raphe ends in opposite
directions and the distal raphe ends have helictoglossae (see Figures 4, 5, 6, and 7). Rapheless valve: the striae are
radiate and composed of coarse and round areolae (Figure 9). Next to the valve margin, the
areolae are variable in shape (see Figure 8) and occasionally biseriate striae
are found.Figure 2
LM. Raphe and rapheless valve.Figure 3
External general view of the raphe valve.Figure 4
Another raphe valve in external view.Figure 5
Internal general view of valve.Figure 6
Detail of a valve in internal view showing the proximal raphe endings in
opposite directions.Figure 7
Detail of Figure5, showing
the distal raphe
end in helictoglossa.Figure 8
External view of the rapheless valve.Figure 9
Internal view of the rapheless
valve.


## 2.2. Distribution and Environmetal Data

Anorthoneis dulcis was a rare species in Lagoa dos
Patos lagoon occurring in a few sites (Table 1) and in very low number. In
general, only one or two frustules/valves were observed in each permanent slide
analyzed. It is
interesting to notice that Barra do Ribeiro and Arambaré are located under
strong freshwater water influence.Table 1
Samples whereA. dulcis was
recorded alongside Lagoa dos Patos lagoon Western margin with its respective
collecting date, electric conductivity, and pH.
Location nameDateConductivity (μS/cm)pHBarra do Ribeiro (30°18′11″S–51°17′07″W)August 20046006.7Arambaré (30°55′52″S–51°30′14″W)August 20042206.5São Lourenço do Sul (31°21′48″S–51°57′40″W)March 200415008.0São Lourenço do Sul (31°21′48″S–51°57′40″W)August 20042206.5Spit of Feitoria/Lagoa Pequena mouth
(31°40′36″S–52°01′52″W)April 2004——São Lourenço do Sul (31°21′48″S–51°57′40″W)March 200510906.2In
Laranjal Bay, from the seven sites studied,A.
dulcis was observed only in São Gonçalo Spit during 2004 (Table 2), but in
2005 it was found in São Gonçalo Canal, São Gonçalo Spit, and Promenade. The quantitative study of A. dulcis at Laranjal Bay revealed that the highest
values of the relative frequency observed were between 1.3–1.5% (see Figure 10),
although it is a rare species in this Bay.Table 2
Electric conductivity (μS/cm), pH, and air temperature (°C) of
samples collected in 2004 at São Gonçalo Spit.
MonthConductivity (μS/cm)pHAir temperature (°C)January1797.127May>20007.417July>20006.321.4August>20006.7—September18156.821.5Figure 10
Relative frequency ofA. dulcis at Laranjal Bay  in 2005.No seasonal pattern forA. dulcis was
observed (Table 3). Therefore, it was present throughout the year.Table 3
Conductivity (μS/cm),(pH) and
air temperature (°C) of samples collected in 2005 when A. dulcis was present at Laranjal Bay.
São Gonçalo SpitSão Gonçalo CanalPromenade(31º46′50″S–52º13′18″W)(31º47′10″S–52º13′23″W)(31º46′28″S–52º13′35″W)January>2000(6.4) 31Not observedNot observedMarch—(7.5)-Not observedNot observedJuly128(6.5) 14Not observedNot observedAugust134(7.0) 15105(7.7) 15774(7.0) 16September>2000(6.0) 18.51246(7.0) 18.5Not observedOctober466(6.4) 20Not observed466(6.4) 19November100(7.2) 23.5Not observedNot observedDecember>2000(6.7) 22Not observedNot observedAt Lagoa dos Patos lagoon,A. dulcis was found at electric conductivity values varying from 100 to 2000 μS/cm areas
with freshwater and brackish water influence. The pH
during the study period ranged from 6.0 to 8.0 and the temperature ranged from
14ºC to 31ºC.


## 3. Discussion

Regarding the occurrence, no noticeably
seasonality was detected but the previous authors foundA. dulcis in fall and winter times in Northern Florida. In South
Korea, it was present in spring and summer.Table4 lists some water characteristics from Florida by Hein [9], from South
Korea by Lee et al.
[5], and this study in Laranjal Bay. These
measurements show that A. dulcis can
thrive over a wider range than originally described. The range of pH in the
sampling area in Lagoa dos Patos lagoon is slightly more acid than in Northern Florida
and South Korea.Table 4
Range of water characteristics in
some rivers in Northern Florida and Laranjal Bay.
WaterFlorida  (EUA)South KoreaLaranjal BaycharacteristicsTemperature
(ºC)15–27(water)21.2–23.8(water)14–31(air)pH7.5–8.17.8–8.16.0–8.0Electric conductivity318–497432–480100–2000(μs/cm)Regarding the dimensions measured, Leeet al. [5] found larger specimens than Hein [9], which allows us to extend
the dimensions of A. dulcis to 21.5 μm (apical apex) and to 16.5 μm (transapical apex).In the estuary
of the Lagoa dos Patos lagoon,A. dulcis seems to present the pattern of occurrence
of most other Anorthoneis species, that is, it is being observed in low
density, is being registered as scarce and/or seldom, and it lives attached or next to sand grains in marine/estuarine
habitats. This pattern was described by Sterrenburg [4], with the notable exception that in his
study abundant populations of Anorthoneis (A. vortex and A. pulex) were recorded.The analysis of
more than 55 valves during the period of 2 years of sampling revealed that more
than 99% of the valves were not broken or eroded, a phenomenon characteristic
of allochthonous diatoms. In addition to this, whole frustules were found in
the permanent slides.In conclusion,A.
dulcis has a wide global distribution in world occurring in North and South
Americas as well as
in Asia. It
occurs in freshwater (lentic and lotic) habitats as a periphytic diatom in
Florida and in Southern Brazil as an epipsammic diatom. On the other hand, in
estuarine areas, it occurs in lentic (Brazil) and lotic (South Korea) habitats as
an epipsammic and epilithic diatom, respectively.



---

*Source: 140245-2008-02-14.xml*