Benthic Bacillariophyta of the Paripe River estuary in Pernambuco state , Brazil

The aim of this study was to evaluate the benthic diatom composition from the estuary sediment in the Pernambuco State, based on 32 samples. Samples were collected monthly from September through December 1999 (dry period) and from April through July 2000 (rainy period) during four pre-established sampling stations. Results indicated 19 families and 31 specific and infraspecific taxa. Eight new records were founded for Pernambuco State: Auliscus coelatus, Fallacia nummularia, Navicula algida, Plagiograma pulchellum, Terpsinoe americana, Triceratium antideluvianna and Tryblionella coarctata and one, Auliscus punctatus Bailey, in northeastern Brazil.


Introduction
An estuary is a close contact area between a river and the open sea, mixing freshwater from continental drainage and high levels of salinity seawater (Pritchard, 1967).Plant communities living exclusively in contact with the seabed, such as benthic microalgae, are important primary producers in stream runoff, lakes, periodically inundated areas and estuaries.In estuaries these organisms are abundant when the substrate is rich in nutrients.
The mangrove is a very special environment and living in ecosystems like these implies great physiological adaptation, as observed in phanerogams, cryptogams and animals.Such adaptations are explained by great salinity oscillations due to the influence of the mixing of freshwater and seawater regulated by tide variations.
Diatoms are the most representative algae group in estuarine areas, showing wide distribution, mainly as a result of the euryhaline nature of the majority of this taxa, in addition to requiring a more eutrophic environment (Pritchard, 1967).
There are few studies about diatoms in estuaries and mangrove environments in Brazil.Moreira-Filho and Kutners study (1962) stands out for its identification of 66 planktonic, benthic and epiphytic diatoms in estuary areas in Paraná State, as well as including ecological information, such as their distribution in Brazil and the morphometric measurements of the valves.Silva and Cimardi (1989) tested a method that removes the algae from the sediment and listed 22 taxa of diatoms from the estuary of Ratones, in Florianópolis City, Santa Catarina State.Felício-Fernandes and Souza-Mosimann (1994) studied the diatoms from the sediment of the Tavares River estuary in Santa Catarina State, presenting descriptions and illustrations of all algae material.
In the northeastern region of Brazil there are only studies from Moura et al. (1993) and Azevedo andCutrim (1999, 2001).Moura et al. (1993) studied the periphytic diatoms on natural and artificial substrata in estuaries of Pernambuco State, showing differences according to the substrate where they were attached.Azevedo and Cutrim (1999) carried out a taxonomic study of the periphytic Naviculales and Bacillarialles of Bostrychia radicans and B. tenera in a mangrove in São Luis Island, in Maranhão State and described 14 species and 2 varieties with illustrations.Azevedo and Cutrim (2001) added 27 infraspecific taxa, with descriptions, illustrations and some ecological data from the same location.Felício-Fernandes et al. (2002) recorded individuals of Nitzschia martiana collected in Santa Catarina and Pernambuco States consisting of benthic/periphytic communities in estuaries, presenting taxonomic information about N. martiana and species of associated diatoms.Cyanobacteria from the bottom of the Paripe River estuary, was studied by Branco et al. (2002).
The existence of only a few studies investigating the benthic microalgae of estuarine areas in Brazil presenting measurements and illustrations stimulates this research that intends to contribute to the knowledge of the benthic diatom composition, thereby increasing floristic information about this group in Brazil.
The marine influence is remarkable in throughout almost the whole extension of the estuary, especially during high tides, with the salinity varying between 3.5%o and 37.1%o, with values higher than 20.0%o near the river-head and oxygen around 4.0 mg.L -1 (Silva and Koening, 1993).
The tidal flow in the region shows a semi-diurnal pattern, with two low and two high tides in a period of 24 hours.
Samples were collected monthly along the estuarine area from the Paripe River during low tides from September through December 1999 (dry season) and from April through July 1999 (rainy season), totaling 32.
Four sampling stations were chosen: upstream (Station 1), an intermediate area in the river (Station 2) and two downstream (Stations 3 and 4).Stations 1 and 4 presented sandy sediment and Stations 2 and 3 showed muddy sediment.The sampling of abiotic variables was carried out at one single point just below the surface water in front of Stations 3 and 4. The pH was determined using a Beckman potentiometer zeromatic II, the salinity was determined through a Termo Haake refractometer C-10, B-3, the temperature was measured with a mercury thermometer and the dissolved oxygen by the method described by Winkler (1888).
Samples were collected through scraping the surface of the bottom of the estuarine soil, and were fixed with 4% formaldehyde.All samples collected were rinsed with distilled water using net plankton (22 µm mesh) to wash out the excess sediment.Permanent slides were prepared according to Moreira Filho and Valente Moreira (1981), modified from Simonsen (1974), for a better visualization of the frustule morphology.
The material was analyzed through a Zeiss-Jena light microscope with a coupled photographic apparatus and a micrometer eyepiece.The identification of the species was made using Hustedt (1930Hustedt ( , 1955Hustedt ( , 1959)); Moreno et al. (1996); Silva-Cunha and Eskinazi-Leça (1990) and Round et al. (1990) adopting the classification system from Round et al. (1990).
Considering the presence and absence of the diatoms during the study in the four stations (Table 1), a binary matrix was constructed with the presence signaled by number 1 and absence by number 2. The similarity matrix was calculated by the Jaccard coefficient (Jaccard, 1901) using NTSYS (NTSYS-PC, 2002) software version 2.1 and the UPGMA algorithm (Sneath and Sokal, 1973) to construct the dendrogram.The numbers shown in Table 1, based on the dendrogram, represent the species.
All the studied material is deposited in the Professor Vasconcelos Sobrinho Herbarium (PEUFR) of the Universidade Federal Rural de Pernambuco.

Results
The occurrence of species in the estuary during the sampling periods is presented in Table 1.Thirty three species were identified, and distributed in 16 orders and 20 families.

THALASSIOPHYSALES Catenulaceae
Amphora angusta Gregory var.ventricosa (Gregory) Cleve (Figure 35) Dimensions: 40.0-56.0µm apical axis; 9.0-10.0µm transapical axis; 15 striae on the dorsal margin and 16 on the ventral one, in 10.0 µm.The average of the hydrological traits of the estuary analyzed during the period of this study is given in Table 2.

Diploneis bombus
The presence of species (Table 1) during two seasonal periods distinguished three groups of diatoms (Figure 36).Group A was constituted by twenty eight The clusters showed a similarity between them (A = 0.23, B = 0.37 and C = 0.57) (Figure 36), however, in spite of the above mentioned grouping, the similarity values in the constituting of these groups are low.

Discussion
During the period of this study the temperature was constant throughout the year, pH was always alkaline, no anoxia was observed even though low oxygen rates and high levels of salinity were determined during the whole period of this study (Table 2).All results corroborated those of Silva and Koening (1993) and Lacerda et al. (1998).From 33 species identified, eight (Auliscus coelatus, Fallacia nummularia, Navicula algida, Plagiograma pulchellum, Terpsinoe americana, Triceratium antidelu-vianna and Tryblionella coarctata) were first mentioned in the State of Pernambuco, and Auliscus punctatus was also first mentioned in northeastern Brazil.This was confirmed after consulting a checklist of marine microalgae of the State of Pernambuco (Eskinazi-Leça et al., 2002).Significant differences in the species composition during the dry and rain seasons were not found (Table 1, Figure 36).The small dimensions of the Paripe River estuary, associated to the elevated influence of the semi-diurnal tidal regime, with two high tides and two low tides in 24 hours, promotes uniform environmental conditions and small variations in salinity which corroborates with the similarity analyses of the species composition.
Benthic diatoms can grow adhered to diverse natural or artificial substrata (Moura et al., 1993 , 1999, 2001).According to Watherbee et al. (1998), diatoms present a true raphe with a high fixing capacity in many substrata, as a result of excreting mucilaginous substances through the raphe, facilitating the cell adhesion.When it does not possess a raphe or it is only founded in only one valve, adhesion should be possible through extracellular mucilaginous substances excreted by other sites of the frustule (rimoportula), consisting of characteristic fixing structures, such as peduncles and gelatinous masses.Around 76.5% from the order show raphe and mucilage extrusion strategies (Moura et al., 1993;Felício-Fernandes and Souza-Mosimann, 1994and Azevedo and Cutrim, 1999, 2000).We conclude from this analysis that the presence of algae throughout the year, with small remarkable variations, may be a consequence of reduced environmental variations in this ecosystem.

Table 2 .
Clustering dendrogram of diatoms by UPGMA analysis of similarity matrix data using 33 OTUs (operational taxonomic units) and Jaccard's coefficient.The numerical scale indicates the level of similarity at which clusters are formed, according to Jaccard's coefficient (A = 0.23, B = 0.37 and C = 0.57).Mean of environmental variables from the four stations during the study in the Paripe River-PE.