**6.3 Diatoms related to sediment**

Another important factor regarding diatom distribution is the sediment characteristic [66, 67]. In the Center and South stations, the surface of the Peixe Lagoon is essentially covered by sandy sediments, in which we find *Campylosira cymbelliformis*, *Catenula adhaerens*, *Dimeregramma minus*, and *Staurophora soodensis* species usually associated with sand grains.

In deeper sites of the lagoon, such as near the North, the sediments are thinner, with addition of silt and clay [49]. In this station, where muddy sand is present, we observed more clearly the seasonal variation of the diatom community. This site also showed highest diversity (1.7–2.4 bits/ind.) and richness (16–26 táxons) and the presence of more exclusive epipelic species; among these are the following: *Caloneis permagna*, *Luticola simplex*, *Nitzschia dissipatoides*, *N. scapelliformis*,

#### **Figure 10.**

*I. A. maracaiboensis. II. Amphora sp. 2. III. A. ectorii. IV. Halamphora coffeaeformis. V. Rhopalodia runrichiae. VI. Opephora pacifica. VII. O. aff. mutabilis. VIII,IX. Erhembergia granulosa. X. Fallacia subforcipata. XI. F. florinae. XII. Placoneis elegantula. XIII. Navicula phylleptosomaformis. XIV. Seminavis strigosa. XV. Nitzschia frustulum. XVI. N. palea. XVII. N. scalpelliformis. XVIII,XIX. Cocconeis euglypta. XX,XXI. C. sawensis. XXII. Luticola simplex. XXIII. Catenula adhaerens. XXIV-XXVII. Fragilaria eichhornii. XXVIII. Diploneis didyma. XXIX. D. litoralis var. clathrata. XXX. D. interrupta. XXXI. D. smithii. Scale bar = 10 µm.*

*N. vitrea* var. *salinarum*, *Rhopalodia runrichiae*, and *Terpsinöe americana* (**Table 2**). In agreement with other studies, the epipsammic fraction appeared to be much more stable than epipelic assemblage [9, 67].

**201**

**8. Conclusions**

**Acknowledgements**

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

We expected to find planktonic forms in the sediment due to the low depth of the lagoon and because of the fact that the sediment usually integrates planktonic and periphytic taxa [3]. The absence of planktonic forms could be explained by the hydrographic processes that tend to transport nonliving, unattached forms out of the system, similar to estuaries [67]. Furthermore, the location of the sampling stations, since the material was collected on the lagoon margin, was outside the water surface. However, it is known that in periods with decreasing wind intensity, water tend to return flooding areas that had been exposed [50]. A few planktonic species in the sediment were also recorded in a study of microphytobenthos in the Gulf of Trieste, Europe, although the collections were made in submerged sediment [65]. Comparing with an earlier study about phytoplankton at Peixe Lagoon, with sampling performed during the same period, *Asterionellopsis glacialis* (Castracane) Round, *Chaetoceros gracillis* Pantocsek, and *Skeletonema potamos* (Weber) Hasle were found in abundance in plankton samples. In this study, however, these species were not found in the sediment; whereas *Diploneis didyma*, a highlighted species found in benthos, was also present in the plankton. The species *Cocconeis sawensis* was recorded at the southern benthos of the lagoon, and it was also observed in the plankton and epiphyton in association with the macroalgae *Cladophora* sp. in the fall and winter seasons [33, 46]. This suggests that in shallow environments, the plankton receives a greater contribution of benthic species than the opposite. Similar

results were found in shallow estuarine zone of Patos Lagoon [19].

and tidal inducing waves and currents are the causes of this process.

salinity and temperature in subtropical coastal systems.

Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001.

Estuary and shallow coastal waters develop the process of resuspension whereby sediment particles with diatoms enter the water column. Examination of diatoms in the water revealed that 75% of frustules belonged to pennate forms and we concluded that flooding tides were responsible for a net transport of epipelic diatoms from the mudflat to a salt marsh. The resuspension of the diatoms can be the source of the chl *a* peak in the plankton [68]. So, this organism may greatly augment the primary production in water [69, 70]. Other investigations have showed large number of benthic diatoms in the water column [71, 72]. The wind, flooding tides,

In the Peixe Lagoon, the benthic diatoms were present in high diversity. Among the attributes of the community, the taxonomic composition best responded to the environmental variables. The quantitative attributes did not show significant relationships. The connection with the ocean, salinity, rainfall, wind action, and temperature were strongly related to the spatial and seasonal variation of the composition of the diatom community in this lagoon system. These organisms substantiate their use as indicators of environmental variations, mainly regarding

We thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico-Programa de Capacitação em Taxonomia (CNPq-PROTAX) for the financial support and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for a doctoral grant to the first author and to CNPq for Productivity Grant to the second author. This study was financed in part by the Coordenação de Aperfeiçoamento de

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

**7. Sediment and water interaction**

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