**5. Benthic diatoms composition**

The diatoms community in Peixe Lagoon is composed by 62 taxa distributed in 30 genera composed largely of marine, brackish, and few freshwater species (**Table 2**). Similar results were recorded in an area adjacent to this study [28], where a total of 73 predominantly benthic and brackish taxa were found.

The genera with the greatest number of taxa are *Amphora* Ehrenberg ex Kützing, *Nitzschia* Hassall, and *Diploneis* Ehrenberg ex Cleve. The freshwater species that probably tolerate the wide variation of salinity are *Amphora ectorii*, *Cocconeis neodiminuta*, *C. euglypta*, *Chamaepinnularia truncate*, *Diploneis aestuari*, *D. didyma*, *Nitzschia palea*, *N. scalpelliformis*, *N. frustulum*, *N. vitrea* var. *salinarum*, and *Planothidium delicatulum*. More than 50% of taxa are cosmopolitan, and the remaining are restricted to a large extent to South America. An aspect to be highlighted is


#### **Table 2.**

*Distribution of the diatoms at the North—N, Center—C, and South—S in the four seasons of the year in Peixe Lagoon, from June 2011 to February 2012.*

**197**

*Subtropical Coastal Lagoon from Southern Brazil: Environmental Conditions and Phytobenthic…*

the predominance of birraphid and monoraphid diatoms, which are organisms that have raphe. This structure is a selective characteristic of the epipelic species [59–63] because it promotes the movement of organisms in search for better light and humidity conditions, since it allows the secretion of polymeric substances produced

The community attributes (richness, diversity, and evenness) showed a decreas-

Seasonally, in fall, without connection with the ocean, the community attributes presented the highest values. After the channel opening, the richness was similar in winter and spring, rising in the summer. The values of evenness and diversity increased from winter (0.6–1.7 bits/ind.) to summer (0.8–2.3 bits/ind.) (**Figure 8**). However, these attributes did not differ significantly between the seasons and the

The composition of the diatoms and the physical and chemical variables of the water in the canonical correspondence analysis (**Figure 9**) of the abundant species (25 species with more than 5% abundance) can better demonstrate the community

The sampling units of the South station are grouped on the negative side of axis 1. They were related to the lower values of conductivity and salinity. The species associated with this axis were *Cocconeis sawensis*, *Fragilaria eichhornii*, *Cocconeis euglypta*, *Fallacia florinae*, and *Halamphora coffeaeformis*. In this axis, it is also possible to observe the separation of the sampling units from the North, mainly due to the difference in temperature between hot and cold seasons, in fall and winter months. The related species were *Nitzschia scalpelliformis*, *Luticola simplex*, *Ehrenbergia granulosa*, *Rhopalodia runrichiae*, *Diploneis smithii*, and *D. didyma*. The sampling units of the Center station are grouped on the positive side of axis 2, where higher values of salinity and temperature were observed in the hotter seasons, as well as the lower values of silica and ORP. The species *Opephora pacifica*, *Catenula adhaerens*, and *Opephora* aff. *mutabilis* were related

During the study, we observed periods with higher and lower marine influence, due to the opening of the channel. In fall, the only season in which the channel was closed, the composition of diatom species was distinct in the north and south of the lagoon. The south and south-west quadrant wind might also have been an influence

After the channel opening, it is possible to observe the difference in the composition of the community at the southern portion in relation to the north and center portions of the lagoon. The species highlighted in the south (*Cocconeis sawensis*, *C. euglypta*, *Fallacia florinae*, and *Halamphora coffeaeformis*) are found in brackish and marine waters, with the exception of *C. euglypta*, a characteristic species of freshwater, but it supports high conductivity water [64]. So, the marine influence appeared as one of the main factors

affecting spatial diatom composition and spatial distribution in the lagoon.

ing spatial gradient from the North to the South stations. The specific diversity ranged between 2.3 bits/ind. at North and 0.4 bits/ind. at South and the evenness

**6. Structure of the community** *versus* **environmental conditions**

varied between 74 and 20% at North and South stations.

**6.2 Diatoms composition related to environmental variables**

*DOI: http://dx.doi.org/10.5772/intechopen.87776*

**6.1 Spatial and temporal variation**

by their cells.

station sampling.

dynamics in the system.

to this axis (**Figure 10**).

factor for the distinction of community composition.

*Subtropical Coastal Lagoon from Southern Brazil: Environmental Conditions and Phytobenthic… DOI: http://dx.doi.org/10.5772/intechopen.87776*

the predominance of birraphid and monoraphid diatoms, which are organisms that have raphe. This structure is a selective characteristic of the epipelic species [59–63] because it promotes the movement of organisms in search for better light and humidity conditions, since it allows the secretion of polymeric substances produced by their cells.
