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Chapter 36. Relationships between ecological models based on ostracods and foraminifers from Sepetiba Bay (Rio de Janeiro, Brazil)
l-Study area and sampled points in Sepetiba Bay.
( m 1
2-Bathymetry in Sepetiba Bay (after Carvalho et ul., 1979).
Ecological Models Based on Ostracods and Foraminifers 469
island (Restinga de Marambaia), a lagoon (Sepetiba Bay), a small delta dominated by fluvial
processes (delta of the Guandu River) and a tidal flat, partially covered with mangroves (Guaratiba area). The system has its present configuration tied to events which occurred after the Wurm
glacial interval; more accurately, it is a post-Flandrian transgression. It fits exactly the microtidal
estuary of Hayes (1976). The climate of this area is the tropical type, hot and humid, rainy in the
summer and dry in the winter, belonging to group A of Koppen's classification. Quaternary coastal
plains and pre-Cambrian rocks of the Serra do Mar constitute the neighbourhood of the complex.
Sepetiba Bay: Abiotic Components
This lagoon, with an area of nearly 305 km2,is semi-isolated from the Atlantic Ocean by an
approximately 40 km-long sand bar, which links the metamorphic Pic0 da Marambaia in the
West to the mangrove area of Guaratiba in the East. A string of metamorphic islands, of which
the largest are Jaguanum in the South and Itacurgi in the North, contributes to the isolation of
The bathymetry is shown on the map (Text-fig. 2). The depth increases gradually from east to
west and is 8-10m in the central portion; there are deep channels between the Jaguanum and
Itacurugl islands reaching down to 27 m. The water temperature ranges from 19.7' to 251°C;
the pH values range from 7.6 to 8.3. Concerning salinity, adopting Boltovskoy's classification
MIXOHALINE 6 EUHALINE BOTTOM SALINITY
BRACKISH TO MlXOHALlNE
1 8 - 5 O/oo
a 26-5O0/0 SAND
SAND 0 7 6 - 1 0 0 % SAND
a 0 . 5 - 1.0 yo
Bottom salinity (mod. from Carvalho et al., 1979). B. Surface salinity (mod. from Carvalho
et a1.r 1979). C . Sediment distribution in Sepetiba Bay. D. Organic matter content.
of currents in Sepetiba Bay based on the distribution of benthic and planktonic micro-
TBXT-FIG.5-Absolute frequency of foraminifers (per 3000 cm' of wet sediment).
a NORMAL MARINE LAGOON
TRANSITIONAL ZONE I
[II]MIXO- EUHALINE B LAGOON
NORMAL MARINE LAGOON
NUMBER OF SPECIMENS
6-Environmental compartments based on specific diversity of foraminifers and specific diversity
in &he environmental compartments (Fisher’s a index).
472 D. DIM-BRITO,
J.A. M o m AND N.WURDIQ
(1976, p. 139), the waters at the bottom are brackish near the mouth of the Guandu River, mixohaline to euhaline in the north-east part as a consequence of the interaction of microtidals (less
than 2 m) and a variable influx of fluvial waters, and euhaline in the main part of the bay. The surface waters are predominantly mixohaline (Text-figs. 3A, B). A salt wedge estuary of Pritchard
(1967) may, thus, be recognized in this area.
The sediments deposited in the lagoon are predominantly fine siliciclastics, with the exception
of the area adjacent to the barrier island and the mouth of the Guandu River, where coarse sediments occur (Text-fig. 3C). The highest content of organic matter, 0.5 to 1.5%, occurs associated
with the most argillaceous sediments (Text-fig. 3D). The CaCO, content in the sediments ranges
from 5 to 25 %, the highest levels being found in the most argillaceous sediments. The granulometry
increases from east to west as a consequence of the progressive, parallel energy increment of the
waters in this direction.
Sepetiba Bay is a relatively calm environment. An ocean stream, however, penetrates the inner
portion of the lagoon, passing between the Jaguanum and Itacurug Islands and heading north;
near the mouth of the Guandu River, the stream suffers a deflection towards the east and proceeds around the bay. Its action causes severe erosion effects in the central portion of the barrier
island. The central area of the bay is calm and, as a consequenceof the main stream, a slow moving
ellipsoidal stream probably exists there (Text-fig. 4).
Cribraetphidium 8ppJA. bemrli
I';y Goudryino ( ? ) exilis
G*inque/ocufina sp. 1
7-Biofacies of foraminffers.
Rofshouaenio rofshouseni / Cribroefphidium8 pp
Textulorio r p . l / Texfulorio rp. 2
Ecological Models Based on Ostracods and Foraminvers 473
Sepetiba Bay: Biotic Components
The major microbiological elements present in the Sepetiba Bay include, in addition to Foraminifera and Ostracoda, micromollusca, diatoms, Radiolaria (not common), Archeomonadidae
and sponge spicules (not common). Maps showing their distribution were presented by Moura
et al. (1982). The biotic data, as well as the abiotic, were obtained from 176 sample stations. The
field work was carried out between May and August, 1978.
Essentially benthic Foraminifera occurred in the area researched. The contents include eury-
Mine and stenohaline species, distributed in specific areas :mixed Lagoon (mixohaline to euhaline
&Foraminifera1 frequency/diversity in the 4 environmental divisions (including the biofacies).
TEXC-FIG.0-Absolute frequency of ostracods (per 3000 cm3 of wet sediment).
474 D. DIAS-BRITO,
J.A. M o m AND N. WURDIG
waters), marine Lagoon (euhaline waters) and marine environment (euhaline waters with good
circulation). No distinction between live and dead specimens was made at the time of collection.
Thus, the work was based on total populations existing in the surface sediments collected. Considering that the sedimentation rate in this area is significant and utilizing the results obtained by
Walton (1955), it may be assumed that the maps represent primarily the distribution of live foraminifera.
The foraminifers are distributed throughout the lagoon. The highest frequencies occur in the
most unstable environments, where stresses are high and there is a large availability of nutrients.
Rotalids largely predominate and miliolids are rare (Text-fig. 5). Maps showing the distribution
of the three suborders have been published by Bronnimann, Moura and Dias-Brito (1981b).
. . , .O
of ostracods in Sepetiba Bay.
TEXT-FIG.11-Ostracod biofacies: specific distribution. Remarks concerning the biofacies 9 and 10. In Biofacies 9,
several species that occur in the north, as well as in the south, are not present in the deeper central part (27 m).
This is characteristic of Kangarina sp., Orionina sp., Keijia sp., Morkhovenia sp., Xestoleberis sp. and Bairdidae
(Text-fig. 13). This phenomenon should be related to the presence of the marine current that enters the bay this
way. This is in agreement with the interpretations of Bronnimann, Moura and Dias-Brito (1981). However,
Perissocytheridea sp. 1, Coquimba spp. and Pistocythereis spp. occur in this central area. On the other hand,
Mutilus spp., Callistocythere sp. 3(?), Paracypris sp., Hemicytherura sp. and Padenborchella sp. only occur in the
south of Biofacies 9. This assemblage characterizes a sub-facies under the influence of a more marine water
mass, here called the Mutilus*spp. subfacies after the most common genus in the area. The remarkable
difference between Biofacies 9 and 10 is the insignificant occurrence of Perissocytheridea sp. 1 in Biofacies 10.
ffinuythere C L lhinii
Perisoeytheridw sp. 1
21 -10 Eost port
6-10 west port
Pcrissocythwideo rp 1
TOM110 Sp 1
Collistocythen rp. 1
Tondlo r p . 1
Perissocytherideo rp. 1
ffinicythere cL beinii
R cf. Rrommelbeini
Loaoconcho r p . 2
Perisscrytheridw r p . 1
T h r n staths
P e r i m y t h e r i d w rp. 1
Pistcrythereis rp .
Collistocythwe ap. 2
Tonello so. 1
81 - m Widespread
Collistocythere 0 . 1
Tonello rp. 1
Collistocythwe r p . 2
Parissocytlhridw rp. 1
38-50 Fort port
Tonefio rp. 1
Pistmythereis r p .
c o llirtocythue spp.
Collistocythere r p . 1
- - - - - - - - __ - -
Pellucistuno r p
Porocmris o. &ememis rp.
aeijia rp. Orionino rp.
Mutilus 4. Coudites sp.
Coquimbo r p p
Collistocythsr# rp. 3 ?
Perisscrytheridw rp. 1
- - -- - - - - - - _ _ _ - - - - - ap.
-.9-8.4 9 - 8.4
0 --8.3kO 0
!I - 25 25-23
BATHliMETRY ( m )
M I XOH.
0 STR A C O D S
f a n e l l o sp. 1
C y p r i d e i s salebroso
Perissocyth.c f. kromelbeini
Loxoconcho sp, 2
Argilloecio s p .
X e s t o l e b e r i s spp.
P e l l u c i s t m o sp.
P o r o c y p r i s sp.
K e i j i o sp.
Urocy th e r d s s p.
124stracod biofacies: specific distribution.
& Collistotytherc sp. 3(? 1
B2 Mutilus p.
8 Porocypris sp 1
Coguimbo s p ~
- Minicythere c f
Collistocvthere SD 1
e Collistocithere s p 2
Tm-na 13-Distribution of ostracod species in Sepetiba Bay.
Pistocythere ts spp.
478 D. DIAS-BRITO,
A high dispersion in the specific diversity (Fisher’s a index) was recorded in Sepetiba Bay. Once
this fact was verified, four station groups were recognized where the index varied, respectively, from
1 to 3, 2 to 5, 5 to 10, and > 10. It was then possible to define four environmental divisions, with
two transitional zones: MIXEDLAGOON A, MIXEDLAGOON B, MARINELAGOON and MARINE
ENVIRONMENT (Text-fig. 6). Stations with less than 300 specimens were not taken into account
in the calculations of the index.
In addition to having been divided into four environmental divisions, the lagoon was subdivided
into seven biofacies, the names of which originated from the predominant taxon or taxa (Text-fig.
Text-fig. 8 summarizes the frequency and diversity patterns recognized for Sepetiba Bay. This
is the synthetic, fundamental graph for the distribution of foraminifers in the area studied. The
distribution of the species in the biofacies as well as the parameters controlling such distribution
are shown by Bronnimann, Moura and Dias-Brito (1981b, Text-figs. 4 and 5, p. 1866). The
distribution of the major species, among the 180 found in the bay, is also discussed in this paper.
The study of Ostracoda includes a preliminary taxonomic study, which will form the basis of a
more detailed one in the future. Specific differentiation was usually informal, the various species
being given numbers. Such a classification, however, provided good support for the research into
the ecological model of Ostracoda in Sepetiba Bay.
The Ostracoda are distributed throughout the area researched. The largest area of the lagoon
contains between 30 and 130 ostracods per 3,000 cm3of wet sediment collected from the lagoon
floor. Some areas are almost destitute of ostracods; there are areas, however, with richer faunal
contents (Text-fig. 9).
No diversity index was calculated for Ostracoda in the bay. Nevertheless, the number of species
which occurs in each defined biofacies was recognized based on Ostracoda.
1. Perissocytheridea sp!l, station BS 4, Biofacies 4. 2. Perissocytheridea sp. 2, station BS 1, Biofacies
3. 3. Perissocytheridea sp. 3(?), station BS 175, Biofaces 9. 4.Perissocytheridea cf. P. Kroemmelbein Pinto
and Ornellas. station BS 22, Biofacies 5. 5. Cyprideis riograndensis Pinto and Ornellas ( q ) ,station BS 37,
Biofacies 4. 6. Cyprideis riograndensis ($), station BS 37,Biofacies 4. 7. Minicythere cf. M . heinii Ornellas,
station BS 5, Biofacies 4. 8. Cytherura sp. 1, station BS 1,Biofacies 3. 9. Cytherura sp. 2 (?), station BS 37,
Biofacies4. 10. Cytherura sp. 3(?), station BS 155, Biofacies 5. 11. Callistocythere sp. 1, station BS 1,
Biofacies 3. 12. Calfistocythere sp. 2, Biofacies 8 (slide 153). 13. Tanella sp. 1, station BS 5,Biofacies 4. 14.
Cyprideis salebrosa Van den Bold ( q ) ,station BS 8,Biofacies 3. 15. Cyprideis salebrosa Van den Bold (8).
station BS 8, Biofacies 3. 16. Loxoconcha sp. 1, station BS 147, Biofacies 9. 17. Loxoconcha sp. 2, station
BS 1, Biofacies 3. 18. Pistocythereis sp. 1, station BS 164, Biofacies 9. 19. Pistocythereis sp. 2, station BS
138, Biofacies 6. 20. Neornonoceratina sp. 1, station BS 150,Biofacies 8. 21. Neomonoceratina sp., station
BS 149, Biofacies 8. 22. ArgTIloecia sp. 1, station BS 157, Biofacies 5.