BENTHIC DIVERSITY OF THE RÍO DE LA PLATA ESTUARY AND
ADJACENT MARINE WATERS
DIEGO A. GIBERTO
SUPERVISOR: CLAUDIA S. BREMEC PNUD Project/Gef RLA/99/G31 2003
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¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ BENTHIC DIVERSITY OF THE RÍO DE LA PLATA ESTUARY AND ADJACENT MARINE WATERS
Report ______
AUTHOR: DIEGO A. GIBERTO SUPERVISOR: CLAUDIA S. BREMEC ______
Summary
The main objectives of this report are to analyze the infralitoral benthic assemblages of the Río de la Plata estuary and adjacent marine zones, and establish broad patterns of species diversity throughout the study area. Species richness was utilized as a measure of diversity. The report was divided in two major approaches: the analysis of an historical background and the EH-09-99 survey. The taxonomical groups that contributed with the major number of species were the mollusks, crustaceans, polychaetes, echinoderms and coelenterates. A classical gradient of increasing species richness from estuarine to marine waters was found. Also, few species were found inhabiting both estuarine and marine waters. The species richness values were high at the continental shelf and the coastal marine environments. The highest number of species was recorded in mussel beds and coarse-sandy bottoms marine assemblages. The irregular pattern of species richness found in marine waters could be due to the presence of different heterogeneous bottom types all over the study area. It is concluded that the available information about benthic communities inhabiting the study area is scarce. In addition, a large portion of the studies were developed mainly on the marine zones < 50 m, while the estuarine zones and the marine zones > 50 m are underestimated. Basic information related with diversity like abundance, biomass, dispersal and temporal variations of macrobenthic species are needed.
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Index
I. Introduction…………………………………………………………………………..1
II. Methodology……………………………………………………………………...... 1
III. Results………………………………………………………………………………..3
IV. Concluding remarks……………………………………………………………...... 5
V. Literature cited……………………………………………………………………….7
VI. Tables……………………………………………………………………………….10
VII. Figures………………………………………………………………………………13
VIII. Appendix…………………………………………………………………………….22
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Introduction
Species diversity is a community attribute influenced by historical events and geographical phenomena; it is also an emergent consequence of local ecosystems-level processes. Changes in diversity reflect changes in ecosystem processes, such as productivity, pathways of energy and material flow, disturbance regime, abiotic stress, and biological interactions (Brown et al., 2001). Species richness, or the number of species, is currently the most widely used diversity measure, together with indexes that also consider the relative species abundance in the community like H’ (Shannon Wiener) o J’ (Pielou’s evenness) (Stirling & Wilsey, 2001). The main objectives of this work are to analyze the infralitoral benthic assemblages of the Río de la Plata estuary and adjacent marine zones, and establish broad patterns of species diversity throughout the study area.
Methodology
Despite the fact that diversity can change without any change in species richness (species richness is not generally the common cause of variation in either H’ o J’) (Stirling & Wilsey, 2001), the species richness was utilized as a measure of diversity in this study, following Gray (2000) who suggested the species richness as a basic estimation of diversity. At the most elementary level, species richness is the total number of species in a given area (Gray, 2000). Following Gray (2000), we calculated for each defined sector the point species richness SRP (number of species in a single sampling unit from a given area) and the sample species richness. The sample species richness can be calculated as the total number of species, SRS, based on a given number of sampling units. Samples species richness is equivalent to the diversity of samples within a habitat, usually called alpha diversity. For the entire study area the SRL or large area species richness was calculated. This is defined as the species richness of a large area which includes a variety of habitats and assemblages. 2
The report was divided in two major approaches, as follows:
Historical background: the prevalent information available in the bibliography of benthic assemblages of the Río de la Plata estuary and adjacent marine zones is the number of species. These studies were done with highly variable sampling methodologies that make unfeasible the building of a detailed species inventory with standardized abundance data (see table I). Systematic publications that focused only on one taxonomical group (see for example Bernasconi & D’Agostino, 1977; Tablado & Maytía, 1988; Boschi et al., 1990) and other ecological ones that do not provide information on the presence of species in every sampling station (Bastida et al., 1989, 1992; Bremec et al. 1998; Bremec and Lasta, 2002; Roux et al., 1993) were not used in the analysis, because it would introduce a bias throughout the species richness pattern of certain taxa at a given area. The study area was divided in four main sectors, as follows: 1) an estuarine zone (mixohaline waters, is equivalent to the sector 1 of EH-09-01 survey), 2) a marine zone in front of the Argentine coast (depth < 50 m, is equivalent to sector 2 of EH-09-01 survey), 3) a marine zone in front of the Uruguayan coast (depth < 50 m, is equivalent to sector 2 of EH-09-01 survey) , and 4) a marine zone with depths > 50 m (is equivalent to sectors 3 and 4 of the EH-09-01 survey) (Fig. 1). These division was made considering oceanographic (salinity, bathymetry) and bottom (sediment composition) features (Urien, 1972; Guerrero et al., 1997, Mianzan et al., 2001), which probably influence the spatial distribution of benthic assemblages. Also, each publication was assigned to the following benthic assemblages: mussel beds (N1, N5 and N7, dominance of Mytilus edulis platensis), scallops beds (N8, dominance of Zygochlamys patagonica), coarse-sandy bottoms (N4, N6, N9 and N10), muddy-bottoms (N6 and N9) and Uruguayan rocky-sandy beaches (N2 and N3) (Table II and Fig. 1).
EH-09-01 survey: The study area was divided in four main sectors, as follows: 1) an estuarine environment (< 25, mixohaline waters), 2) a coastal environment (> 25, depths < 50 m), 3) a continental shelf environment (depths 50-200 m) and 4) a 3 shelf-break environment (depths > 200 m) (Table II and Fig. 2). This division was made largely following Acha and Lo Nostro (2002).
Results
Historical background
A total of 420 species (SRL) and 14 taxa were recorded in the study area (see list in Appendix 1). Marine waters were characterized by higher number of species than estuarine waters (373 vs. 47 respectively). SRP from the sampling stations of the estuarine waters ranged between 1 and 20, while stations of the marine waters ranged between 1 and 65 (Fig. 3). The taxonomical groups that contributed with the major number of species were the Mollusks (153 species), Crustaceans (88 species), Polychaetes (81 species), Echinoderms (29 species) and Cnidarians (27 species) (Appendix 1).
The estuarine zone was characterized by 6 taxa (SRS= 47), with mollusks, crustaceans and polychaetes contributing with more than 90 % of specific richness (Table III and Fig. 4). The marine waters < 50 m reached the highest number of species and taxa (SRS= 273 and SRS= 138 at Uruguay and Argentine respectively), while deeper stations (> 50 m) displayed the lowest values of specific richness in marine waters (SRS= 51) (Table III and Fig. 4). The contribution of all different taxa recorded at each zone is indicated in Fig. 4. The marine zone > 50 m presented the higher percentages of “exclusive species” (species that were only recorded in the defined area) (84.31%), followed by the marine Uruguayan zone (73.26%) and the marine Argentine zone (54.35%). The lowest value was recorded in the estuarine zone (34.04%). Only ten species were recorded in estuarine and marine waters: Angulus gibber, Corbula patagonica, Mactra isabelleana, Nucula puelcha, Pitaria rostrata, Ancinus depressus, Artemesia longinaris, Pagurus exilis, Pinnixa brevipollex and Encope emarginata.
Benthic assemblages that reached the highest values of SRS were those inhabiting mussel beds (SRS= 213) and coarse-sandy bottoms (SRS= 184) (Table IV). 4
The scallop beds presented the higher values of “exclusive species” (81.58%), followed by the coarse-sandy bottoms (77.17%), mussel beds (76.53%), Uruguayan beaches (53.57%) and the muddy bottoms (34.29%) assemblages. Only two species were recorded at three of the defined assemblages: Mytilus edulis platensis and Pseudoechinus magellanicus (see Appendix 1).
EH-09-01 survey
A total of 145 species (SRL) and 12 taxa were recorded in the study area (see list in Appendix 1 and 2). Mollusks were the dominant group, with 43 species, followed by polychaetes (35 species), crustaceans (32 species) and echinoderms (14 species) (Fig. 5).
The highest value of SRS (sample species richness) was found in the continental shelf environment, while the estuarine environment displayed the lowest SRS value (Fig. 6). The contribution of the different taxa recorded at each environment is indicated in Fig. 4. Mollusks and polychaetes reached the highest richness at the continental shelf environment, while crustaceans richness was highest in the coastal environment (Fig. 7). On the other hand, echinoderms, coelenterates and other less important groups displayed low and similar richness values in all the environments of marine waters analyzed (Fig. 7). The continental shelf environment presented the higher percentages of “exclusive species” (species that were recorded only in the defined area) (51.09%), followed by the coastal (46.25%) and the estuarine (41.67%) environments. The lowest value was recorded in the shelf-break environment (26.09%). Only 5 species were found both in estuarine and coastal waters: Artemesia longinaris, Buccinanops lamarckii, Corbula patagonica, Pagurus criniticornis, and Leptocuma sp.
Low SRP values were found at the stations of the estuarine environment (Fig. 8).
On the other hand, stations of marine waters displayed unevenly SRP values, ranging from stations with one (i. e. station 805, with sandy bottoms and only one species, the sand dollar Encope emarginata) to 39 species (station 802). The relation between species richness and salinity and depth is displayed in Fig. 9. 5
Opposite to species richness, both environmental variables displayed a constant pattern from marine to estuarine waters, lacking of a strong relationship with the curve of SRP (Significant correlation only between species and salinity at p < 0.05, r = 0.47).
Concluding remarks
1) The benthic assemblages of the estuarine environment were characterized by low diversity values, while adjacent marine zones reached the highest values. This pattern is in coincidence with the early predictions for mixohaline waters of Remane and Schlieper (1971). The species richness values were high at the continental shelf and the coastal environments. However, species richness in the shelf-break environment was lower than the other marine environments. 2) Higher number of species was recorded at mussel beds and coarse-sandy bottoms assemblages. These are characterized by a higher structural complexity than the homogenous muddy bottoms; this heterogeneity is associated with higher number of possible niches that allows the coexistence of an elevated number of species. Also, a general pattern of “widespread to exclusive” species from the estuarine to the marine zone respectively were found. This was also reflected in the composition of the muddy bottoms (mainly widespread species) to the scallop beds (mainly exclusive species). 3) Few species were found inhabiting both estuarine and marine waters (less than 3% of 420 species recorded in the historical analysis and less than 5% of 145 species in the EH-09-01 survey). 4) The irregular pattern of species richness found in marine waters could be due to the presence of different heterogeneous bottom types all over the study area. Except for the channel zone, the marine environment is characterized by sandy bottoms, with a transitional zone, and a coarse sedimentary texture in the inner shelf (Urien, 1972). The influence of bottom type had an important effect in the spatial distribution and diversity of the fauna (see Platell and Potter, 1996; Brown et al., 2001). 6
5) Available information about benthic communities inhabiting the study area is scarce. In addition, a large portion of the studies were developed mainly on the marine zones < 50 m, while the estuarine zones and the marine zones > 50 m are underestimated. Basic information related with diversity like abundance, biomass, dispersal, and temporal variations of macrobenthic species are needed.
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Literature cited
Acha, M. & Lo Nostro, S. 2002. Biology of the populations. Technical report. PNUD Proyect/GEF RLA/99/G31: 52 pp. Bernasconi, I & D’Agostino, M. M. 1977. Ofiuroideos del Mar Epicontinental Argentino. Revista del Museo Argentino de Ciencias Naturales”Bernardino Rivadavia” e Instituto Nacional de Investigación de las Ciencias Naturales 5(5): 65-125. Bastida, R., Roux, A. & Bremec, C. 1998. Investigaciones sobre las comunidades bentónicas en la zona común de pesca Argentino-Uruguaya. Frente Marítimo 5:115-129. Bastida, R., Roux, A. & Martínez, D. E. 1992. Benthic communities of the Argentine continental shelf. Oceanologica Acta 15: 687-698. Boschi, E. E., Fischbach, C. E., & Iorio, M. I. (1992). Catálogo ilustrado de los crustáceos estomatópodos y decápodos marinos de Argentina. Frente Marítimo 10: 7-94. Brankevich, G., Roux, A. & Bastida, R. Relevamiento de un banco de pesca del besugo (Sparus pagrus) en la plataforma bonaerense. Características fisiográficas generales y aspectos ecológicos preliminares. Frente Marítimo 7(A); 75-86. Bremec, C. & Roux, A. 1997. Resultados del análisis de una campaña de investigación pesquera, sobre comunidades bentónicas asociadas a bancos de mejillón (Mytilus edulis platensesis D’Orb.) en costas de Buenos Aires, Argentina. Revista de Investigación y Desarrollo Pesquero 11: 153-166. Bremec, C. S. & Lasta, M. L. 2002. Epibenthic assemblage associated with scallop (Zygochlamys patagonica) beds in the Argentinean shelf. Bulletin of Marine Science 70: 89-102. Bremec, C., Lasta, M. L., Lucifora, L. & Valero, J. 1998. Análisis de la captura incidental asociada a la pesquería de viera patagónica (Zygochlamys patagonica King and Broderip, 1832). INIDEP Informe Técnico N° 22:1-18 pp. 8
Bremec, C. S., Schejter, L. & Giberto, D. A. 2001. Vieira patagónica. Unidad norte de manejo-CTMFM. Evaluación de biomasa fauna acompañante año 2001. INIDEP n° 14, 12 pp. Brown, J. H.; Morgan Ernest, S. K.; Parody, J. M. & Haskell, and J. P. 2001. Regulation of diversity: maintenance of species richness in changing environments. Oecologia 126: 321-332. Demicheli, M. A. 1984. Estudios exploratorios del infralitoral de las playas arenosas uruguayas. I. Playa Portezuelo. . Comunicaciones de la Sociedad Malacológica del Uruguay 6(47): 235-249. Giberto, D. A. 2001. Fondos de alimentación de la corvina rubia (Micropogonias furnieri) en el estuario del Río de la Plata, Argentina-Uruguay. Facultad de Ciencias Exactas y Naturales. Universidad Nacional de Mar del Plata. 83 pp. Gray, J. S. 2000. The measurement of marine species diversity, with an application to the benthic fauna of the Norwegian continental shelf. Journal of Experimental Marine Biology and Ecology 250: 23-49. Guerrero, R. A.; Acha, E. M.; Framiñan, M. B. and Lasta, C. A. 1997. Physical oceanography of the Río de la Plata Estuary, Argentina. Cont. Shelf Res. 17 (7): 727-742. Hill, J. S. 2000. The measurement of marine species diversity, with an application to the benthic fauna of the Norwegian continental shelf. Journal of Experimental Marine Biology and Ecology 250: 23-49. Juanicó, M. & Rodriguez Moyano, M. 1975. Composición faunística de la comunidad de Mytilus edulis platensesis D’Orbigny, 1846 ubicada a unas 55 millas al SE de la Paloma. Comunicaciones de la Sociedad Malacológica del Uruguay 4(29): 113-116. Mianzan, H., C. Lasta, E. Acha, R. Guerrero, G. Macchi, and C. Bremec. 2001. The Río de la Plata estuary, Argentina-Uruguay, p. 185-204. In Seeliger U., L. D. de Lacerda and B. Kjerve (eds.), Coastal Marine Ecosystems of Latin America. Springer-Verlag, Berlin. 9
Obenat, S., Ferrero, L. & Spivak, E. 2001. Macrofauna associated with Phyllochaetopterus socialis aggregations in the southwestern Atlantic. Vie et Milieu 51(3): 131-139. Plattell, M. and I. Potter. 1996. Influence of water depth, season, habitat and estuary location on the macrobenthic fauna of a seasonally closed estuary. Journal of the Marine Biological Association of the United Kingdom 76: 1-21. Remane, A. and C. Schlieper, 1971. Biology of Brackish Water. John Wiley and Sons, New York, 372 pp. Riestra, G., Giménez, J. L. & Scarabino, V. 1992. Análisis de la comunidad macrobentónica infralitoral de fondo rocoso en Isla Gorriti e Isla de los Lobos (Maldonado, Uruguay). Frente Marítimo 11(A): 123-127. Roux, A. & Bremec, C. 1996. Comunidades bentónicas relevadas en las transecciones realizadas frente al Río de la Plata (35°15’S), Mar del Plata (38°10’S) y Península Valdes (42°35’S), Argentina. INIDEP Informe Técnico 11: 1-13. Roux, A., Bastida, R., & Bremec, C. 1993. Comunidades bentónicas de la plataforma continental argentina. Campañas transección BIP “Oca Balda” 1987/88/89. Bolm. Inst. oceanogr. S. Paulo 41: 81-94. Scarabino, V., Maytía, S. & Cachés, M. 1975. Carta binómico del departamento de Montevideo. I. Niveles superiors del sistema litoral. Comunicaciones de la Sociedad Malacológica del Uruguay 4(29): 117-130. Stirling, G. and Wilsey, B. 2001. Empirical relationships between species richness, evenness, and proportional diversity. The American Naturalist 158 (3): 286- 299. Tablado, A & Maytia, S. 1988. Presencia de Perissasterias polyacantha H. L.
Clark, 1923 (Echinodermata, Asteroidea) en el Océano Atlántico
Sudoccidental. Comunicaciones Zoológicas del Museo de Historia Natural de
Montevideo 12(169): 1-11.
Urien, C. M. 1972. Río de la plata estuary environments. The Geological Society of America, Memoir, 133: 213-233. 10
TABLES
Table I. Bibliographic sources used in the historical analysis.
Number Authors- Year Information Sampling Area Type methods Juanicó & Rodriguez Commercial Marine N1 Presence data Moyano, 1975 dredges waters Scarabino et al., Subtidal N2 Presence data Visual Census 1975 beaches Subtidal N3 Demicheli, 1984 Presence data Scuba beaches Brankevich et al., Abundance Marine N4 Dredge 1990 data* waters Abundance Subtidal N5 Riestra et al., 1992 Scuba data beaches Marine and Roux & Bremec, N6 Presence data Dredge estuarine 1996 waters Bremec & Roux, Abundance Marine N7 Dredge 1997 data waters Abundance & Marine N8 Bremec et al., 2001 Dredge biomass data waters Marine and Abundance & N9 Giberto, 2001 Dredge estuarine biomass data waters Marine N10 Obenat et al., 2001 Presence data Trawl waters * Indicated only for mollusks.
Table II. Sampling design of the EH-09-01 survey. Zone Sampling stations Bottom type Sampling gear Estuarine 4 mud grab Coastal 9 sand, shell debris dredge Continental Shelf 5 sand, shell debris dredge Shelf-break 2 sand, shell debris dredge
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Table III. Taxonomic groups (SRL= 420) at the study area. Contribution to each area is indicated in percentage of sample richness (SRS).
Taxa Estuarine Marine U < 50 m Marine A < 50 m Marine > 50 m
Annelida - 0.37 - - (Olygochaeta)
Annelida 21.28 22.71 8.70 11.76 (Polychaeta)
Brachiopoda - - - 3.92
Briozoa - 2.93 3.62 -
Chaelicerata - 0.73 - -
Cnidaria 4.26 7.33 2.90 5.88
Crustacea 31.91 24.54 15.22 11.76
Echinodermata 2.13 5.13 5.07 31.37
Mollusca 38.30 31.50 60.14 19.61
Nemertea - 1.10 - -
Platelminta - 0.37 - -
Porifera 2.13 2.20 2.90 5.88
Sipunculida - 0.37 - -
Tunicata - 0.73 1.45 9.80
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Table IV. SRS (Sample species richness) recorded at each benthic assemblage defined at the study area.
Taxa Mussel Muddy Coarse- Uruguayan rocky Scallops beds bottoms sandy and sandy beds bottoms beaches
Annelida - - 1 - - (Olygochaeta) Annelida 17 9 55 6 2 (Polychaeta) Brachiopoda - - - - 2 Briozoa 7 - 6 - - Chaelicerata 1 - 1 - - Cnidaria 9 2 13 - 3 Crustacea 36 8 47 13 4 Echinodermata 13 1 14 - 16 Mollusca 120 14 37 8 5 Nemertina 1 - 1 1 - Platelminta 1 - 0 - - Porifera 6 1 4 - 3 Sipunculida - - 1 - - Tunicata 2 - 4 - 3
SRS = 213 35 184 28 38
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FIGURES
Fig. 1. Benthic sampling locations analyzed in the study area. Estuarine (1), marine Argentinean < 50m (2), marine Uruguayan < 50m (3) and marine > 50m (4) zones are also indicated. Benthic assemblages as follows (see text for details): Coarse-sandy bottoms. Mussel beds. Uruguayan rocky-sandy beaches. Scallops beds. Muddy bottoms. 14
Fig. 2. The Río de la Plata estuary and adjacent marine waters, with location of sampling sites (n= 21) (•) and isobaths (m) (EH-09-01). 1 = estuarine environment (< 25, mixohaline waters), 2 = coastal environment (> 25, depths < 50 m), 3 = continental shelf environment (depths 50-200 m), 4 = shelf-break environment (depths > 200 m).
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Fig. 3. Point species richness (SRP) recorded at the study area.
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Fig. 4. Contribution in number of species (in brackets) to the sample species richness (n= SRS) at each defined area.
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