PLANKTONIC CILIATES CHOREOTRICHIDA AND STROMBIDIIDA FROM THE INNER ZONE OF BAHÍA BLANCA ESTUARY , ARGENTINA

Seven species of aloricate planktonic ciliates were identified using protargol staining. Choreotrichida: Strombidinopsidae, Strombidinopsis elongata Song & Bradbury, 1998; Strobiliidae, Strobilidium epacrum Lynn & Montagnes, 1988 and Strombidiida: Strombidiidae, Strombidium capitatum (Leegaard, 1915) Kahl, 1932; S. emergens (Leegaard, 1915) Kahl, 1932; S. acutum Leegaard, 1915; S. dalum Lynn, Montagnes & Small, 1988 and Cyrtostrombidium longisomum Lynn & Gilron, 1993; they were collected from the inner zone of the Bahía Blanca estuary in the southern region of the Buenos Aires province, Argentina. These species represent new records to South America (Argentina).


INTRODUCTION
In last decades the importance of ecological function of micro-organisms in pelagic food webs has been recognized and many studies have been carried out, principally in Europe and North America.Planktonic ciliates constitute a diverse group in a trophic and taxonomic point of view.They are often the dominants of the heterotrophic planktonic protists, representing a link between phytoplankton and higher trophic levels.Investigations show that aloricate ciliates occur in high numbers and consume significant quantities of autotrophic and heterotrophic microbial production (AZAM et al., 1983;FENCHEL, 1987;MONTAGNES & LYNN, 1991).They are eaten in turn by other protozoans, many metazoans and fish larvae (JONSSON, 1986;PIERCE & TURNER, 1992;LONSDALE et al., 1996;PETZ, 1999).The taxonomic composition and ecological characteristics of the aloricated planktonic ciliates from South Atlantic Ocean and coastal zone of Argentina are poorly known.
The aim is to report the assessment of the composition of the aloricate ciliates community in the inner zone from Bahía Blanca estuary, Argentina.

MATERIAL AND METHODS
Bahía Blanca estuary is located on the Atlantic coast at 38°42'-39°25'S, 61°50'-62°22'W.It has a total length of 68 km, being 200 m and 3 to 4 km wide near its head and mouth, respectively.It is a semienclosed body of water characterized as shallow, well mixed and with high turbidity due to a great amount of organic and inorganic suspended material.Strong winds and tidal waves dominate the general circulation (PICCOLO & PERILLO, 1990).
Sampling was done in Puerto Cuatreros located in the inner part of the estuary, near its head (fig.1), from February 1 st , 1994 to February 22 nd , 1995.This part has variable temperature and salinity.The Sauce Chico River, the Napostá Grande stream and other minor creeks, that discharge in the estuary only during rainfall periods, carry most of the freshwater inflow and in dry summers it becomes hypersaline (FREIJE et al., 1981).Water samples were taken out at weekly intervals during daylight hours and high tide from the subsurface (0.50-1 m), using a 3 L Van Dorn bottle.Data of temperature and salinity were also registered.Protargol staining, according to TUFFRAU (1967);LEE et al. (1985) and FOISSNER (1991) was used to estimate the taxonomic composition.Protargol stained species were deposited in the collection of the Laboratorio de Ecología General, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina.

RESULTS AND DISCUSSION
The seven species reported in Puerto Cuatreros belong to the orders Choreotrichida and Strombidiida.They are commonly found in other coastal areas of the world (LYNN et al., 1988;MONTAGNES et al., 1988;LYNN & GILRON, 1993;LEAKEY et al., 1994;PETZ et al., 1995;SONG & BRADBURY, 1998).Some differences in cell size and in numbers of several structures from Puerto Cuatreros populations were observed.MONTAGNES et al. (1988) have demonstrated that spirotrichs show marked size variation in response to environmental influences and regulate numbers of structures in proportion to cell size.
Free-living phagotrophic protozoans are usually believed to have a cosmopolitan distribution and it seems that in environments with similar characteristics the same species could be present (FENCHEL, 1987).The taxonomy and ecology of marine aloricate planktonic ciliates have only recently been described with some frequency using modern cytological techniques thus, little is known about their global distribution and it is difficult to know which species have truly restricted geographic ranges (PIERCE & TURNER, 1992;PETZ, 1999).
Temperature and salinity values registered in Puerto Cuatreros during the study were similar to those encountered in other parts of the world where the same species of aloricate ciliates were also found.These observations would confirm the hypothesis that protozoan species in coastal areas are widely distributed (FENCHEL, 1987).However, Strombidium emergens was recorded at geographically different sites (Weddell Sea; Gulf of Maine, USA and Puerto Cuatreros) and in water temperature quite different.Thus, it is possible that species from different geographical regions have different temperature tolerances (LYNN et al., 1991).Description.Large cell, 97.5-128.7 length, 74-82 width (n =13).Cylindrical body shape with a pointed posterior end; 14-18 longitudinal somatic kineties evenly distributed around the cell.Two spherical to ovoid macronucleus 12-17.6 length to 12-15.6 width positioned in centre of the cell (fig.2).Diameter of adoral zone 39-51.External oral polykinetid zone composed of 17-20 polikinetids.Inner oral polykinetid zone with 4-6 polikinetids, which three of them are independent and located in an oral depression (fig.3).Micronucleus not observed.
Occurrence.The species was present in Puerto Cuatreros mainly in winter months when the diatom bloom occurs; salinity 29.6-35.7 ‰, temperature 8.8-11°C.
Taxonomical remarks.Puerto Cuatreros population of Strombidium emergens is similar to the population described by LYNN et al. (1988) as Strombidium sulcatum.This population was later determined as Strombidium emergens by MONTAGNES et al. (1990).
Environmental parameters.Salinity 26-36 ‰, temperature 5-20°C.Taxonomical remarks.The population of Puerto Cuatreros is similar in size to those of the Gulf of Maine and Jamaican coast described by LYNN et al. (1988) and LYNN & GILRON (1993).It has a similar number of anterior and ventral oral polykinetids and it has a similar macronucleous spherical to conical shape.The specimens of S. dalum recorded in Puerto Cuatreros do not show either the ventral kinety, present only in the Jamaican one (LYNN & GILRON, 1993) nor the "torch-like" shape of the cilia of the anterior polikinetid zone present only in the Gulf of Maine population (LYNN et al., 1988).Ventral kinety was a characteristic apparently overlooked in the Gulf of Maine population and the torch-like shape of the cilia was considered an artefact of fixing and staining in the Jamaican population.Occurrence.In Puerto Cuatreros was recorded in spring; salinity 29-35.5 ‰, temperature 11-22°C.
Environmental parameters.Salinity 34.8 ‰, temperature 14.4°C.Taxonomical remarks.Cyrtostrombidium longisomum from Puerto Cuatreros is similar to the Jamaican population (LYNN & GILRON, 1993) in the body shape, by the presence of a protuberance, a ventral kinety and in the shape and size of the macronucleous.The cell of the Puerto Cuatreros population is larger and shows polysaccharid plates not reported for the Jamaican population.This last feature could be considered a characteristic of the environment.