Occurrence of Cymbasoma longispinosum Bourne, 1890 (Copepoda: Monstrilloida) in the Curuçá River estuary (Amazon Littoral)

The present work was carried out to verify the occurrence and distribution of Cymbasoma longispinosum Bourne, 1890 in a tropical Amazon estuary from North Brazil. Samplings were performed bimonthly from July/2003 to July/2004 at two different transects (Muriá and Curuçá rivers) situated along the Curuçá estuary (Pará, North Brazil). Samples were collected during neap tides via gentle (1 to 1.5 knots) 200 μ m-mesh net tows from a small boat. Additional subsurface water samples were collected for the determination of environmental parameters. Males and females of Cymbasoma longispinosum were only observed during September and November/2003. The highest number of organisms was found in September/2003 at the Muriá River transect. The presence of C. longispinosum in samples obtained during September and November/2003 could probably be related to the reproductive period of this species in the studied estuary, which is directly related to the dry period in the region. The highest salinity values and the highest number of individuals observed in September/2003 corroborate with the previous assumption, since no C. longispinosum was found during the months comprising the rainy period (January to June).


INTRODUCTION
Monstrilloida constitutes the least known copepod order.Its biology and ecology are poorly known, completely differing from all other Copepoda (Calanoida, Cyclopoida, Harpacticoida, Poecilostomatoida and others) in their peculiar life cycle (Dias 1996).Individuals of this chaetes and molluscs (Suárez-Morales and Gasca The first naupliar and adult planktonic free-swi stages do not present specialized mouth appe (Huys and Boxshall 1991).

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NATÁLIA R. LEITE et al.Dias 1996, Suárez-Morales andGasca 1998).After the first naupliar stage, these organisms experience a gradual transformation inside their host body assuming the definitive appearance of adult copepods (Dias 1996).The presence of a mouth located on an oral papilla linked to a small pharynx and situated, generally, in the center of the cephalic segment is one of the peculiar characteristics for organisms within this order (Davis 1984, Dias 1996).
The purpose of this study, part of the "Milênio Project" (Use and Appropriation of Coastal Zone Resources -RECOS), was to notify the first occurrence of Cymbasoma longispinosum Bourne, 1890 (Copepoda, Monstrilloida), as well as to describe some aspects of its population dynamics, such as density and spatial and temporal distribution in the Curuçá estuary (Pará State -Amazon region, North Brazil).

STUDY AREA
The Northeast littoral of Pará State extends from the mouth of the Pará River to the mouth of Gurupi River, an extension of 600 km (Souza Filho and El-Robrini 1997).The geographic position of Northeast Pará's coast (0-1 • S), together with the coastal embayment and the great width of the Pará/Maranhão continental shelf, propitiates the development of a high energy environment dominated by semidiurnal macrotides with heights ranging from 4 to 6 m ( DHN 2007).
The Atlantic "Paraense" salt coast is represented by long bays with depths oscillating from 5 to 15 m and extensions around 20 km (El-Robrini 1992).The rivers wide mouths present creek channel characteristics and are submitted to coastal marine influences that can be observed up to 45 km inland.In these conditions, mud plains are formed and become mainly colonized by mangrove forests (Mácola and El-Robrini 2004).
According to Prost and El-Robrini (1997), the Northeast "Paraense" coast is located in the center of a large tropical atmospheric circulation system that, to-located in the micro region of "Salgado", in the middle of Northeast Pará, with an area of approximately 673 km 2 .It is limited to the North by the Atlantic Ocean, to the South by Terra Alta County, to the East by Marapanim County and to the West by São Caetano de Odivelas County.
The region's climate is Amazon equatorial according to Köppen classification criteria, and it is characterized by high temperatures with an average value of 27 • C, a small thermal amplitude and abundant rainfall regimen that surpasses 2000 mm.year −1 , with the months of January to June comprising the rainy period and July to December the dry period.
The studied area presents tide heights of 4 m, with higher values (5.5 m) observed during equinoctial spring tides.Salinity in this region ranges from 20 to 22 during the rainy season, and 30 to 35 in the dry season.Vegetation along the margins of the Curuçá estuary is characterized by mangrove forests in which Rhizophora, Avicennia and Laguncularia are the main genera represented.

ZOOPLANKTON COLLECTION AND ANALYSIS
Zooplankton samples were collected bimonthly from July/2003 to July/2004 by means of a 3-minute horizontal plankton hauls accomplished with a 200 μm mesh size plankton net, 2 m long and with a 0.60 m mouth diameter equipped with a mechanical flowmeter (Hydrobios-Kiel, Model 438 110) to estimate filtered water volume.
Samples were taken in the Muriá Creek, located along the margins of Abade village, and in the Curuçá River, which is located in the vicinity of Curuçá County.Each sampling area was comprised by 4 stations: M1, M2 M3 and M4, and C1, C2, C3 and C4, respectively (Fig. 1).Single diurnal hauls were performed during ebb neap tides, totaling 8 samples in each expedition.
Additional in situ measurements of temperature, pH and salinity were taken with a multianalyser equipment (Orion 105).Water transparency was determined using a Secchi disc.In order to determine concentrations After collection, samples were conditioned in 500 mL plastic flasks containing buffered formalin solution (sodium tetraborate) at 4%. Density was determined calculating the number of sample individuals divided by the filtered seawater volume.
Collected organisms were sorted and identified using a Zeiss stereoscopic microscope (Stemi 2000), a light Zeiss microscope (Axioskop 40) and specialized literature (Rose 1933, Trégouboff andRose 1957).Males and females were identified, dissected and illustrated through schematic drawings for a better species identification.
Total body length measurements (abdomen and cephalothorax) were taken using a micrometric scaled rule adjusted to the ocular of the microscope.different copepod species (Figs. 2 and 3).In the female, the presence of two urosomal somites, with only one free somite located between the genital double somite and the caudal rami, confirms genus identification (Isaac 1975).On the samples collected in September/2003, 156 individuals (89 males and 67 females) were observed.The Muriá sample stations showed a higher number of individuals (145) than those obtained at stations located in the Curuçá River (11).At station M1, 22 individuals comprised of 10 females and 12 males (0.77 org.m −3 ) were observed.Male measured body lengths (cephalotorax and abdomen) ranged from 1.23 mm to 1.50 mm  station M1 (Muriá), with a total density of 0.29 org.m −3 .Samples from this month were comprised of 8 individuals, being 5 females and 3 males.Male body lengths ranged from 1.13 mm to 1.50 mm (1.21 ± 0.11 mm), and females from 1.88 mm to 2.78 mm (2.40 ± 0.16 mm). Figure 4 shows the average body length variations for the different months and stations.

DISCUSSION
There is currently no available information on hydrological characteristics of the Curuçá estuary in the scientific literature.However, recorded salinity values for the Curuçá estuary were higher than those reported by Barletta-Bergan (1999) and Krumme and Liang (2004) in the Caeté estuary, and D.S. Santana, unpublished data, for the Marapanim estuary, both located in Northeast Pará (Amazon littoral).These estuaries, like others located in Northern Brazil, are submitted to a semidiurnal macrotide regimen and present high hydrodynamics characterized basically by the strong influence of rainfall and tidal current circulation (Barletta-Bergan 1999, Krumme and Liang 2004, Magalhães et al. 2006), which could explain the transport and, consequently, the wide species in the studied estuary, which is directly to the dry period in the region.The highest salin ues and the highest number of individuals obser September/2003 corroborate with the previous as tion, since no C. longispinosum was found dur months comprising the rainy period (January to The presence of this copepod species in the inn tions of the Muriá creek could be related to the influence near the sampling stations, where the ex of other creeks could be verified connecting the creek to the Atlantic Ocean, as well as the creek's c structure, which is wider than the Curuçá River.results are in accordance with those reported b (1996) and Duarte (1999), who recorded the prese this species in high salinity ecosystems from the tiba Bay (Rio de Janeiro) and the Espírito Sant both in Southeast Brazil.
According to the literature, C. longispino a typical species in marine environments, occur tropical waters of the northeast Atlantic (Suárez-M 1994) and presenting an irregular distribution, could be attributed to scant Monstrilloida in pl collections worldwide and the reduced effort of about this copepod group (Isaac 1975).

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NATÁLIA R. LEITE et al.Dias (1996) in the Sepetiba Bay (Rio de Janeiro, Brazil) presented body lengths ranging from 2.01 to 2.55 mm, and 1.33 to 1.57 mm, respectively.Duarte (1999), in the Espírito Santo Bay (Southeast Brazil) also reported female and male body lengths (1.98-2.54mm, and 1.10 and 1.46 mm, respectively) that were higher than the ones observed in this study.It was possible to note that individuals from Northern Brazil (Curuçá estuary) presented shorter body lengths than those recorded by Dias (1996) and Duarte (1999), except for males collected at station M1, which were much larger than those reported by the latter.Palavras-chave: Região Amazônica, Monstrilloida, nova ocorrência, estuário tropical.
Fig. 1 -Map of Curuçá County (Amazon Region) showing the sampling stations in the Muriá Creek (M1 to M4) and Curuçá River (C1 metric methodology adapted from Strickland and Parsons (1972).
The entire collection has been deposited in the Laboratory of Plankton and Microalgae Culture/Federal University of RESULTS Temperature ranged from 20.6 • C in January/2 the station M1 to 31 • C in July/2003 at stations C C2. Salinity showed a minimum value of 6.1 at C1 and a maximum of 40.8 at station C4 in Ma and November/2003, respectively.Hydrogenion tential (pH) oscillated from 6.87 (March/2004) tion C1 to 8.12 (November/2003) at station C4 dissolved oxygen concentrations ranged from 3 station C1 in January/2004 to 8.42 in July/2003 tion C2.Minimum and maximum water transp and suspended particulate matter values were 0 (May/2004) at station M1, 5.00 m (November/2 station C3, 13 mg.L −1 (July/2003) at station C 98.6 mg.L −1 (January/2004) at station M1, respe Males and females of Cymbasoma longispi were registered only in samples collected in S ber and November/2003 (dry period).Females w ways larger than males as reported for different co species (Mauchline 1998)."main"-2010/8/6 -16:21 -page 580 -#4 580 NATÁLIA R. LEITE et al.

Fig. 4 -
Fig. 4 -Average male and female body length variations (mean ± SD) in the different months and sampling stations in the Curuçá River estuary (Curuçá County, Amazon Region).