Taxonomic notes on the species of the genus Micrasterias ( Desmidiaceae , Conjugatophyceae ) from the Metropolitan Region of Salvador , Bahia , Brazil

We present the results of a taxonomic survey of the genus Micrasterias in the Metropolitan Region of Salvador (MRS), Bahia, northeastern Brazil during 2007–2010 and 2014–2015. A total of 275 phytoplanktonic and periphytic samples from 11 municipalities were analyzed. The samples were collected using a plankton net with 20 μm mesh or squeezed from macrophytes. Twenty-nine taxa were identified, which 20 have their geographic distributions expanded. Only M. pinnatifida was considered frequent, occurring in 9 municipalities, while we classified 21 species as rare in the study area. Our results emphasize the importance of the conservation of aquatic bodies in the MRS for the maintenance of biological diversity of desmids and other aquatic organisms.


Introduction
The Metropolitan Region of Salvador (MRS), which is located in the Atlantic Forest biome, has a diversity of natural resources (e.g., hydrographic basins and various plant phytophysiognomies) which are protected by 8 Áreas de Proteção Ambiental (APA; EPA, Environmental Protected Areas): APA Baía de Todos os Santos, APA do Cobre/São Bartolomeu, APA Joanes-Ipitanga, APA Lagoas de Guarajuba, APA Lagoas e Dunas do Abaeté, APA Litoral Norte, APA Plataforma Continental, and APA Rio Capivara (INEMA 2018).Like most Brazilian metropolitan regions, MRS has experienced severe anthropogenic pressure due to increased rates of urbanization and tourism in the region.These activities have exerted strong pressure on the environment, affecting both aquatic and terrestrial ecosystems, which may eventually cause irreparable damage to the biodiversity therein (INEMA 2018).
The genus Micrasterias C.Agardh ex Ralfs comprises approximately 75 currently accepted species (Guiry and Guiry 2018) of unicellular green algae, which exhibit a high level of cellular complexity.The cells are formed by 2 identical halves (semicells) that are differentiated into an apical lobe and a lateral lobe; the latter is subdivided into lobules to the fifth order, which gives these organ-isms a highly branched morphology (Škaloud et al. 2011(Škaloud et al. , Neustupa 2017).According to Škaloud et al. (2011), the genus comprises 8 phylogenetic lines that also include taxa previously placed in other genera of desmids, such as Cosmarium Corda ex Ralfs, Staurodesmus Teiling, and Triploceras Bailey.
The great majority of Micrasterias taxa possess wide geographic distributions, especially in tropical and subtropical regions.Like other members of the Desmidiaceae, they inhabit almost exclusively aquatic environments, and are characteristic of oligotrophic aquatic bodies that are well oxygenated and with a slightly acidic pH, which makes these organisms excellent indicators of water quality as they have high sensitivity to any form of contaminant in the aquatic environment (Brook 1981, Bicudo and Menezes 2017, Coesel 1996, Moresco et al. 2009, Volland et al. 2011).
Herein, we present the results of a taxonomic inventory of the genus Micrasterias in 11 municipalities of the MRS.We provide information on the geographic distribution of taxa, population metrics, illustrations, and taxonomic notes.

Methods
Study area.The MRS occupies an area of 4,375,123 km² and is composed of 13 municipalities (Fig. 1): Camaçari, Candeias, Dias d'Ávila, Itaparica, Lauro de Freitas, Madre de Deus, Mata de São João, Pojuca, Salvador, São Francisco do Conde, São Sebastião do Passé, Simões  , and Vera Cruz (IPEA 2015).Located in the Atlantic Forest biome, the MRS is characterized by a warm and humid climate with little variation (Nunes 1999) and an annual cycle defined by basically 2 seasons, a rainy season from January to July and a dry season from August to December (Grande et al. 2012).According to Braga et al. (1998), mean annual rainfall for the region ranges from about 1200 mm to 1500 mm, and the annual average temperature is approximately 25 °C.

Filho
Sampling and taxonomic analyses.We analyzed 275 samples from 11 of the 13 municipalities of the MRS (taxa of Micrasterias were not recorded in both Madre de Deus and Simões Filho); 133 samples were collected during 2007-2010 and 142 from 2014-2015.Periphytic material was obtained through the squeezing of macrophytes, while plankton were collected using a plankton net with 20 µm mesh.We examined our material under an Olympus LX35 Optical Microscope and photographed using a MicroPublisher -QImaging MP5.0-RTV-CLR-10-C digital camera.The samples were preserved in Transeau's solution, following Bicudo and Menezes (2017), and incorporated into the liquid collection of the State University of Feira de Santana Herbarium (HUEFS) after analysis.
Frequencies of occurrence for each species of Micrasterias identified were calculated for the MRS and for each of the 11 municipalities, by considering the number of samples in which each taxon occurred in relation to the total number of samples collected (n = 275).Frequency categories followed Matteucci and Colma (1982), as follows: > 70% (very frequent, VF); ≤ 70% and > 40% (frequent, F); ≤ 40% and > 10% (occasional, O); and ≤ 10% (rare, R).
A Venn diagram was prepared showing the distribution of Micrasterias taxa richness among the 5 largest APAs within the MRS (Baía de Todos os Santos, Joanes-Ipitanga, Lagoas de Guarajuba, Litoral Norte, and Rio Capivara) using software available at the Bioinformatics and Evolutionary Genomics (2018) website.

Results
Analysis of the 275 samples from 11 municipalities of the MRS revealed the occurrence of 29 taxa corresponding to 19 species, 12 typical varieties, and 14 non-typical varieties of their respective species, as well as 2 taxonomic forms (Table 1).Notes.Although this species is easy to recognize, according to Bicudo and Sormus (1981) the morphology of the polar lobe may vary.Among the MRS samples the polar lobe was either rectilinear or slightly convex, with 2-denticulate or only 1-denticulate extremities.The taxon generally occurs in oligotrophic to mesotrophic, slightly acidic (pH < 7.4) environments, where they make up the metaphyton or periphyton (Felisberto and Rodrigues 2005, Sophia et al. 2005, Silva and Felisberto 2015).Despite being recorded in more than half of the municipalities studied, we consider it rare in the MRS, occurring in only 17 of the 275 samples analyzed (Table 2).Notes.According Ribeiro et al. (2015), the presence of 3-lobulate, wing-like basal lobes confer M. alata var.alata a characteristic morphology that distinguishes it from other members of the genus.This species was found in the municipalities of Camaçari, Lauro de Freitas, Mata de São João, Salvador, and Vera Cruz.We classify it as occasional in the MRS (Table 2).Notes.Micrasterias americana var.bahiensis was newly described by Oliveira et al. (2009) from material collected in the municipality of Camaçari, and through the reanalysis of the type material, we note that it is morphologically close to Micrasterias americana (Ehrenb.)Ralfs var.boldtii Gutw.These 2 varieties differ by the morphology of the polar lobe, which is narrower in the former, with sharper ends and rectilinear or slightly concave inferior margins, while in the latter it is wider with more inflated extremities and slightly convex inferior margins.Micrasterias americana var.bahiensis occurred only in Camaçari, where it had a frequency of occurrence of < 10% (Table 2).Notes.Micrasterias arcuata var.arcuata is similar to M. arcuata Bailey var.subpinnatifida Nordstedt, although the 2 varieties can be distinguished by the curvature of the basal lobes, which are parallel to the polar lobe in var.subpinnatifida and curved towards the apical lobe in the typical variety.In Bahia, it has been cited for Chapada Diamantina (Fӧrster 1964) and for the municipalities of Conde, Esplanada, and Entre Rios (Oliveira 2011).Micrasterias arcuata var.arcuata is rare in the MRS, having been found in only 1 sample unit.Ours is the first record of M. arcuata var.arcuata from the MRS (Table 2).Notes.Micrasterias arcuata Bailey var.expansa differs from the typical variety because it has subcunate apical lobe that is always smaller than the set of basal lobes, an apical margin that always has a slight median depression and extremities with divergent spines (Sormus 1980, Oliveira 2017).This variety has a restricted distribution in Brazil, with records only for 3 states: Bahia (Oliveira et al. 2017), Minas Gerais (Nordstedt 1877), and São Paulo (Borge 1918).It is rare in the MRS but is occasional in the municipalities of Lauro de Freitas and Mata de São João (Table 2).Notes.Micrasterias arcuata Bailey var.robusta is very similar to M. arcuata var.expansa from which it differs by having shorter cell lobes and inflated basal lobes.We observed no significant morphological variation, but compared to the material from São Paulo described by Bicudo and Sormus (1982), the specimens from MRS have a slightly narrower polar lobe.The variety had a frequency of occurrence of < 10% in the MRS, and we classified it as rare (Table 2).Notes.The variety is easily recognizable by its 3-lobed semicells and "T"-shaped apical lobe with acuminate extremities.It resembles and may even be mistaken for Micrasterias arcuata Bailey var.subcornuta Förster, from which it differs only in the ornamentation of the zygosporum cell wall, which in var.subcornuta has papillae (Bicudo and Sormus 1982).Although we did not observe the zygospore, we chose to identify our material as M. arcuata var.subpinnatifida because it has measurements consistent with that variety; that is, twice the size recorded for M. arcuata var.subcornuta.In addition, it has the "T"-shaped apical lobe and semicells with basal lobes parallel to each possessed by M. arcuata var.subpinnatifida.This variety was recorded in about 23% of the samples analyzed in the MRS, and we consider it to be occasional in the MRS (Table 2).Notes.Micrasterias denticulata var.denticulata is easily identified by the presence of similar lateral and basal lobes, linear and closed cell incisions, and lobules of the last order with rectilinear extremities possessing small denticles.According to Šťastný (2010), the species is usually found composing the periphyton of mesotrophic and acidic (pH < 6.5) environments in European lakes.In Brazil, however, it has been reported occurring in both periphyton and phytoplankton (Aquino et al. 2014).We consider it rare in the study area, because it was found in only 2 of our 275 samples (Table 2).united in pseudofilaments, which makes it easy to recognize (Ribeiro et al. 2015).In the MRS, we recorded it in the municipalities of Camaçari, Mata de São João, and Vera Cruz.No morphological variation was observed in these populations.This taxon occurred in approximately 10% of our samples, and thus we classified it as rare in the MRS (Table 2).Notes.This taxon is widely distributed in Brazil, with records for all regions of the country (Araújo et al. 2015).In Brazil, there are reports of its occurrence in phytoplankton (Bortolini et al. 2010) and periphyton (Camargo et al. 2009) of rivers, and in bromeliad phytotelmata environments (Ramos et al. 2011).In the MRS, we found it occasionally in approximately 17% of our samples ( Notes.The species is known to be polymorphic, varying mainly in the width and curvature of the polar lobe and opening of the interlobular incisions (Santos et al. 2016, Moresco et al. 2009).It has a wide occurrence in Brazil (Araújo et al. 2015), being reported for both phytoplankton and periphyton (Felisberto andRodrigues 2005, Melo et al. 2005).In the MRS, it was the most represented taxon, recorded from 10 of the 11 municipalities sampled.We classify it as rare only in the municipality of Camaçari ( Notes.Micrasterias laticeps var.acuminata differs from the typical variety of the species because it possesses acuminate instead of 2-denticulate basal lobes.In the literature, the main morphological variation described for M. laticeps var.acuminata is with the interlobular incisions, which may be shallow or deep and with an acutangular or rounded vertex; however, in the studied populations such variation was not observed.Micrasterias laticeps var.acuminata has a wide geographic distribution, occurring in all regions of Brazil, both in plankton and periphyton from oligotrophic to acidic (pH < 5.9) mesotrophic environments (Camargo et al. 2009, Aquino et al. 2014, Araújo et al. 2015, Silva and Felisberto 2015).Although we recorded this variety in most of the municipalities of the MRS, it occurred in only 12% of our samples, and thus, we considered it to be occasional ( Notes.Micrasterias laticeps var.ampliata, unlike the typical variety of the species, has the face of the semicell inflated, apical lobe wider than the set of basal lobes, and ends of the polar lobe with single spines, which always face upwards.In Bahia, this taxon has been recorded for Chapada Diamantina (Förster 1964) and for Mata de São João (Oliveira 2011).Micrasterias laticeps var.ampliata was found in only 3 of our 275 samples, which reflects its low frequency of occurrence in the MRS (Table 2).Notes.This species can exhibit variation in the projection of the lateral and basal lobes, concavity of the polar lobe, and the presence or absence of supraisthmal facial decoration (Růžička 1981, Ribeiro et al. 2015, Silva and Felisberto 2015).In the samples from the MRS, the most varied character in the study specimens was the projection of the lateral and basal lobes, which were mostly projected horizontally rather than diagonally.Although this species is commonly recorded in periphyton (Felisberto and Rodrigues 2005, 2008, Camargo et al. 2009), there are also reports of its occurrence in plankton (Melo et al. 2005).In the MRS we consider it to be rare (Table 2).Notes.The literature reveals that M. pinnatifida var.pinnatifida is a common taxon in floristic inventories in Brazil.Although it is easy to identify, studies report that it is highly polymorphic, including one study dedicated to the observation of its polymorphism (Sormus and Bicudo 1974).Micrasterias pinnatfida var.pinnatifida resembles M. arcuata var.subpinnatifida, but differs in possessing 2-denticulate lobes instead of 1-denticulate lobes.We observed morphological variation in the apical lobe (width and concavity of the apical margin) and lateral lobes (presence or absence of a spine in the upper margin of the lobes) in the MRS.In European lakes, Šťastný (2010) reported this species in the periphyton of mesotrophic and acidic (pH < 6.5) environments, but in Brazil it has also been recorded in phytoplankton (Melo and Souza 2009).We found M. pinnatifida var.pinnatifida in 9 of the 11 municipalities studied and consider it to be frequent in the MRS (Table 2).
Notes.Micrasterias quadridentata is similar to M. rotata var.rotata but differs in possessesing a larger cell size, linear and closed cellular incisions, and lobules with the extremities possessing short denticles.The morphology of the lobules can vary, with their ends being rectilinear, or 4-denticulate or, more commonly, 2-denticulate (Bicudo and Sormus 1982, Moresco et al. 2009, Menezes et al. 2013).However, no variation was observed in our study.In Paraná, Menezes et al. (2011) recorded M. quadridentata in both the metaphyton and the periphyton of an urban artificial lake.Ours is the first record of this species from the MRS, where we consider it to be rare (Table 2).Notes.Micrasterias radians is morphologically close to M. furcata var.furcata; however, it is distinct because it possesses a more robust cell, shorter and wider polar lobe, rectilinear to concave apical margin, and extremities terminating in short processes.Although Ramos et al. (2018) observed this species to be fairly polymorphic, we observed no variation in our specimens.This species occurred in 12% of our samples, and thus, we consider it to be occasional (Table 2).and Sormus (1982), some specimens may have denticles close to the apical notch of the polar lobe, but we did not observe such variation in our specimens.Although we consider it to be rare in the MRS, it was one of the most represented taxa, occurring in 9 of the 11 municipalities studied (Table 2).Notes.Micrasterias radiosa var.elegantior is easily recognized by its narrow lobules and its deep and open incisions.However, identification of this variety requires some care as, according to the literature (Prescott et al. 1977, Bicudo andSormus 1982) and with our observations, some individuals may possess small spines on the margins of the polar lobe and the median sinus.This brings them closer to M. radiosa var.ornata f. ornata, but this taxon differs by always having a row of spines along the deepest incisions.We found M. radiosa var.elegantior in 5 municipalities and consider it to be occasional (Table 2).

Micrasterias radiosa
Micrasterias radiosa Ralfs var.ornata Nordstedt f. ornata, 1869 Figure  Notes.Micrasterias radiosa var.ornata f. ornata is very similar to, and can be mistaken with, M. radiosa Ralfs var.ornata Nordstedt f. aculeata (W.Krieger) Croasdale, but it is distinguished by the presence of small spines arranged along the median sinus and the deeper lobular incisions (Bittencourt-Oliveira and Mecenas 1994).Although not so common in floristic surveys, this form occurred in 8 of the 11 municipalities sampled, although we classify it as rare in the MRS (Table 2).Notes.Micrasterias radiosa var.ornata f. aculeata stands out among all other subspecific taxa of M. radiosa recorded in this study in having robust spines along the median sinus margins, deeper cellular incisions, and 2-5 denticles on the apical margin of the polar lobe.Among the other taxa of M. radiosa recorded in the MRS, this one that had the most restricted distribution, occurring in only 5 municipalities (Table 2).Notes.Bicudo and Sormus (1982) reported variation in the shape and projection of the polar lobe, opening of the cellular incisions, and lobulation of the basal lobes of M. rotata var.rotata.However, in the MRS, this taxon was morphologically very homogeneous, showing little or no variation.According to Šťastný (2010), in European lakes the species usually occurs in mesotrophic and acidic (pH < 6.5) environments, where it makes up the periphyton.However, in Brazil this species is reported occurring in both the periphyton and phytoplankton of oligotrophic environments (Melo et al. 2005, Felisberto andRodrigues 2008).In the MRS, we found M. rotata var.rotata in fewer than 10% of our samples, and thus, we consider it rare (Table 2).Notes.Micrasterias thomasiana var.notata is characterized by cells with a subcircular contour, elongate apical lobe, presence of 2 convergent denticles located at the margin of the apical notch of the polar lobe, and the presence of 3 intumescences located at the base of each semicell, although this last character is variable and may or may not be present, as observed by Santos et al. (2016) and Moresco et al. (2009).In European lakes, Šťastný (2010) reported its occurrence in oligotrophic or mesotrophic, acidic (pH < 6.5) environments, where it was most of the time on underwater substrates or associated with submerged aquatic plants.In the MRS, we classified this variety as rare because it was only recorded in the municipalities of Mata de São João and Vera Cruz (Table 2).Notes.Micrasterias torreyi var.nordstedtiana differs from the typical variety of the species because it possesses cells that are longer than wide, has 2-denticulate lobes, and the lobes have inflated inner margins partially covering each other.Oliveira (2011) reported variation in the morphology of the polar lobe of material from the municipalities of Esplanada and Conde, but we found no variation in our MRS specimens; in the MRS, populations were small and very homogeneous.This is the first record of this variety from the MRS, where we consider it rare (Table 2).Notes.Micrasterias truncata var.pusilla is a common and widely distributed taxon in Brazil (Araújo et al. 2015).According to Oliveira et al. (2009) and Ribeiro et al. (2015), this variety it is quite polymorphic, but our specimens from the MRS, presented variation only in the morphology of the polar lobe.Some individuals presented apical lobe typical of var.pusilla, with a convex apical margin and acuminate extremities.Other specimens presented apical lobe similar to that of M. abrupta var.abrupta, with rectilinear apical margin and bifurcated extremities.Nemjová et al. (2011), who studied the morphological and molecular differentiation of the species complex of M. truncata, observed that Australian strains of M. truncata var.pusilla were closely related to M. zeylanica F.E. Fritsch.Thus, they believed that Australian strains assigned to var.pusilla probably are a separate species, and they suggested the need for a future review of the M. zeylanica/M.truncata var.pussila complex originating in Australia.In Brazil, the variety is referred to phytoplankton and the periphyton of oligotrophic and mesotrophic environments (Felisberto and Rodrigues 2005, 2008, Aquino et al. 2014, Silva and Felisberto 2015).Although we found M. truncata var.pusilla at a low frequency in the MRS, it was one of the most represented, occurring in 8 of the 11 municipalities studied (Table 2).

Discussion
Based on our 275 samples, the richest municipalities in terms of the number of taxa were Mata de São João (24), Camaçari (18), and Vera Cruz (16), while Dias d'Ávila and Itaparica were the least rich, with only 2 and 3 taxa recorded, respectively.The large number of taxa recorded from Mata de São João and Camaçari may be related to the great diversity of aquatic bodies in these municipalities, which happen to be the largest in the MRS, which is reflected in our greater sampling effort in these 2 areas.According to Magurran (1988), the greater the heterogeneity of habitats, the greater the diversity of niches and, consequently, the greater the richness of species.
We found that only M. pinnatifida var.pinnatifida was considered frequent, whereas 24% of the taxa were classified as occasional and 72% were rare (Table 2).The rarity of species may be due to intrinsic (biological or ecological characteristics that are characteristic of the species) or extrinsic (anthropogenic causes) factors and is generally expressed by species with low relative abundances and restricted geographic distributions (Gaston 1994, Partel et al. 2005, Resh et al. 2005).Urbanization is usually the primary cause of biodiversity loss because it promotes changes in natural environments (McKinney 2006), which increases the risk of species extinction (McKinney 1997, Partel et al. 2005).Thus, the high number of rare taxa in the MRS is possibly closely related to the high rates of urbanization of the region, which in 2010 already reached approximately 98% of urbanized area (Fernandes and Guimarães 2014).Among the municipalities of the MRS, Fernandes and Guimarães (2014) found that Mata de São João, besides having the largest area, had the least urbanization among the municipalities; in our study, this might have influenced the higher number of taxa observed here compared to the entire MRS.
A minimum of 100 samples is required for good sampling effort and a reliable estimate of the distribution pattern of a species (Matteucci and Colma 1982).According to these authors, populations with a regular (uniform) spatial distribution pattern tend to have a high frequency of occurrence, whereas for aggregated (grouped) populations the frequency of occurrence tends to be lower.Thus, our results suggest that in the MRS most of the Micrasterias taxa possess aggregate distribution patterns, as more than 70% of them had low frequencies of occurrence (recorded from < 10% of the 275 samples; Table 2).This is true for the MRS as a whole but not for the municipalities individually, as the number of samples collected in each of them was fewer 100, which, according to Matteucci and Colma (1982), does not allow us to make safe inferences about the distribution pattern of Micrasterias within each of these areas.
From the data obtained, a Venn diagram (Fig. 33) was generated with the purpose of evaluating the distribution of Micrasterias taxa in the 5 largest APAs of the MRS, APA Bahia de Todos os Santos, APA Joanes-Ipitanga, APA Lagoas de Guarajuba, APA Litoral Norte, and APA Rio Capivara.We found that of the 29 taxa inventoried, only 5 were common in the APAs listed above: M. alata var.alata, M. borgei var.borgei, M. furcata var.furcata, M. laticeps var.laticeps and M. pinnatifida var.pinnatifida (Table 3).The APAs Baía de Todos os Santos (which in addition to the islands belonging to Candeias, Simões Filho, São Francisco do Conde, and Salvador, encompasses the islands of Madre de Deus and Itaparica) and Lagoas de Guarajuba (municipality of Camaçari) had 16 and 13 taxa, respectively, of which Micrasterias furcata var.dichotoma occurred exclusively in the first, and M. amer-icana var.bahiensis exclusively in the second (Table 3).On the other hand, the APA Rio Capivara (Camaçari) did not possess any exclusive taxa.
According to data from INEMA (2018), the APAs of the MRS are subject to various environmental conflicts, such as the release of domestic and industrial effluents into aquatic ecosystems, deforestation, fires, unplanned real estate occupation, inadequate disposal of solid waste, and illegal extraction of sand, among others.Such activities have compromised the preservation of these areas and directly or indirectly the availability and quality of the aquatic habitats contained therein, causing serious problems such as siltation, heavy metal contamination, increases of water temperature and turbidity, and eutrophication, among others, which interfere in the balance of the ecosystem and consequently its biodiversity (Mota 2003, Agostinho et al. 2005, INEMA 2018).
When comparing our data (Table 1) with previous inventories in the MRS by Oliveira et al. (2009Oliveira et al. ( , 2017) ) and Santos et al. (2016), it is evident that our study contributes the most to the knowledge of the diversity and geographic distribution of Micrasterias because it surveyed a greater number of municipalities ( 11) and recorded a greater number of taxa (29).
The diversity of Micrasterias found in Mata de São João was similar to that found by Oliveira et al. (2017), who reported 28 taxa occurring in APA Litoral Norte, of which 23 occurred in the aforementioned municipality; 3 taxa listed by the authors were not found in the present study: M. prescottiana C. Bicudo and Sormus, M. truncata (Corda) Bréb.ex Ralfs var.truncata f. gibbosa Thomasson and M. arcuata var.Thus, we increase the number of Micrasterias present in Mata de São João, from 23 to 27, of which M. quadridentata, M. radians, M. rotata var.rotata and M. thomasiana var.notata are new occurrences for the area.Comparing our data with those obtained by Oliveira et al. (2009) for the APAs Lagoas de Guarajuba and Rio Capivara (both in the municipality of Camaçari), there was an increase in the number of taxa from 14 to 18, with M. abrupta, M. radians, M. radiosa var.radiosa and M. radiosa var.ornata f. ornata being new occurrences for the area.Finally, considering the study by Santos et al. (2016) for Itaparica Island, with the exception of M. furcata var.dichotoma, which was cited as an addition to the desmid flora of Brazil, all of the other taxa also occur in other municipalities of the MRS.
Final remarks.The identification of species, especially rare species, are extremely important for understanding the structure and dynamics of biological communities.This knowledge makes it possible to identify priority areas for conservation, as well as to develop actions aimed at protecting biodiversity (Lyons et al. 2005, McCreadie andAdler 2008).In our study, we highlight the importance of the MRS in understanding the biodiversity and geographic distribution of Micrasterias.We also emphasize the importance of the conservation of aquatic bodies in the MRS for the maintenance of biological diversity, which is seriously threatened as a result of increasing urbanization in the MRS.
The APA Litoral Norte, which was represented in our study only by the municipality of Mata de São João, was the most species-rich, with 24 taxa found and with 4 taxa found in no other areas: Micrasterias denticulata, M. laticeps var.ampliata, M. papillifera var.glabra, and M. quadridentata.The APA Joanes-Ipitanga, although it is large (ca 65,500 ha) and includes part of the municipalities of Camaçari, Candeias, Dias d'Ávila, Lauro de Freitas, São Francisco do Conde, São Sebastião do Passé, and Salvador (INEMA 2018), had only 18 taxa, of which only M. torreyi var.nordestedtiana and M. arcuata var.arcuata were exclusive.

Figure 33 .
Figure 33.Venn diagram showing the distribution of Micrasterias among the most representative Environmental Protection Areas (APA Baía de Todos os Santos (TSB), APA Joanes-Ipitanga, APA Lagoas de Guarajuba, APA Litoral Norte, APA Rio Capivara) of the Metropolitan Region of Salvador, Bahia, Brazil.

W.Krieger var. borgei, 1939
Santos et al. (2016)rature revealed that this species can vary with regard to the projection of the polar lobe, morphology of the lateral and basal lobes, and quantity and arrangement of the spines on the cellular wall.Micrasterias borgei var.borgei and M. rotata var.rotata may be visually similar; however, the separation between them is made through the ornamentation of the cell wall, as M. borgei presents robust spines distributed all over the face of the cell, different from M. rotata, which has a smooth cell wall.M. borgei var.borgei can also present some resemblance to the varieties of M. radiosa studied, but unlike M. borgei var.borgei, all varieties of M. radiosa here identified have lateral and basal lobes of sizes same, broadly deep cell incisions, and polar lobe with 2 or more spines.As withSantos et al. (2016), who observed specimens from Itaparica Island, the populations analyzed here from other municipalities of the MRS exhibited variation only in the morphology of the lateral and basal lobes, which were sometimes similar to each other or sometimes unequal, but the lateral lobes were always larger than the basal lobes.In Brazil, M. borgei var.borgei occurs in both phytoplankton and periphyton and has been recorded in environments with low pH val- near to BA-093, 1, Menezes et al. 2011s and G.J.P. Ramos, a/no.(HUEFS219816);SãoSebastiãodoPassé,Canabrava,08/IX/2014, M.A. Santos et al. s/n.(HUEFS 219794); Vera Cruz, Lagoon near to BA-532, 23/VII/2015, M.A. Santos and C.A. Ribeiro s/n.(HUEFS 219233).Notes.ues(Meloetal.2009,Menezesetal. 2011).Although M. borgei var.borgei is widely distributed in the MRS, occurring in seven of the 11 municipalities studied, it presented a low frequency of occurrence (Table2).Micrasterias denticulataBrébisson ex Ralfs var.denticulata, 1848 Figure 9 Material examined.Brazil, Bahia, Mata de São João, Praia do Forte, 26/VII/2009, I.B.Oliveira and J.T. Farias, s/n.(HUEFS 155787).

Table 3 .
Distribution of Micrasterias among the most representative Environmental Protection Areas in RMS, highlighting the common taxa between APAs and those that occurred exclusively in each of them.