Bahia Blanca Estuary Research Articles

Feeding Interrelationships and Comparative Morphology of Two Young Sciaenids Co-occurring in South-western Atlantic Waters

Diet and morphology of the sciaenids striped weakfish, Cynoscion guatucupa, and whitemouth croaker, Micropogonias furnieri, from Bahia Blanca estuary (South America) were studied and compared between March 2000–February 2001. Significant differences in mouth morphometric parameters between striped weakfish and whitemouth croaker were found. Premaxila + maxila length, dentary length, and mouth gape were always larger in the former than in the latter. However, analyses of variance (ANOVA) indicated no differences in the mean maximum size of prey consumed by both species. Schoener’s dietary overlap was generally moderate between the three ontogenetic trophic groups of striped weakfish and whitemouth croaker. High dietary overlap was observed in winter and summer, when both species prey heavily on Peisos petrunkevitchi and mysid shrimps, respectively. In this study, no evidence of food competition was found between young striped weakfish and whitemouth croaker.

Residual Flow Structure at a Scour-hole in Bahia Blanca Estuary, Argentina

Abstract Two-dimensional data of mean and sediment flow collected at a natural confluence of channels in the inner Bahia Blanca Estuary are presented. We describe the two-dimensional flow field to assess the role of changes in bed morphology occurring during transport-effective events on the structure of flow at a confluence; and to examine how the flow structure varies with changes in the ratio of momentum flux. At each station, vertical profiles of velocity, salinity, temperature and suspended sediment were obtained during the whole tidal cycle and residual fluxes were obtained. Lagrangean flux is higher than possible fresh water input, denoting an extra output of water which is the flux over the tidal flats along the southern and northern coasts of the channel. The effect of the junction produces a distortion of the vertical profile flow and in the suspended sediment transport. The effect of the particular conformation of the system makes necessary for consider the lateral effect of the tidal flats in ...

Novel mechanism of stream formation in coastal wetlands by crab–fish–groundwater interaction

A novel mechanism of stream development in coastal wetlands was observed in the form of interaction between the burrowing crab (Chasmagnathus granulata) and groundwater seepage. This process may eventually be further promoted by the predatory action of the white croaker fish (Micropogon opercularis). These so-called crab streams occur on the banks of major tidal channels in a salt marsh of the Bahia Blanca Estuary (Argentina). As the tide recedes, water is retained in the crab burrows on the marsh surface. The presence of lateral burrows produced by crab recruits promotes subterranean piping flow driven by the hydraulic head in the vertical burrow. Groundwater generally seeps along the tidal channel banks but is particularly prominent and concentrated where crab burrows perforate the banks. Where predatory attacks by the croaker fish enlarge the burrow mouths, the drainage rills become wider and deeper because more seeping water is collected in the shallow crater from where it is funnelled into the developing streams. The crab stream is then produced by water draining from the crab burrow mouth, acting initially by cut-back erosion and followed by forward erosion of the relatively unconsolidated muddy sediments.

On the age and growth of flounder Paralichthys orbignyanus (Jenyns, 1842) in Bahía Blanca Estuary, Argentina

Estimates of age and growth of flounder Paralichthys orbignyanus (Jenyns,1842) were made by analysing fish from commercial catches in Bahia Blanca estuary (39° LS). A total of 823 fish caught by fishing fleets operating in the estuary were collected between February 1997 and January 1998. Age was determined via scale reading and growth estimation parameters using von Bertalanffy’s equation. Annulus formation occurred in August. The age for the total population, which ranged from 7.7 to 87.5 cm TL was 0–7. Age ranged from 0 to 6 years (21.5–71.9 cm TL) in males and from 0 to 7 years (24.9–87.5 cm TL) in females. Length–weight relationships were W(g)=0.0093 L(cm) exp. 3.03 for the total population, W(g)=0.0147 L(cm) exp. 2.91 for females, and W(g)=0.0168 L(cm) exp. 2.87 for males, respectively. As from age three, females were longer and heavier than males. The growth parameters estimated for the total population, for females and for males were L∞=83.29, 79.66, and 46.11 cm, respectively; k values were 0.18, 0.23, and 0.92, respectively, and t0 values were −1.87; −1.54, and −0.62, respectively. Similarly to other flounders,P. orbignyanus is a typical inhabitant of estuaries and coastal regions. Adults stay in the study area mainly during spring and summer, they go outside or offshore during the spawning period and then they return to the estuary for feeding and recovering.

Feeding habits of the juvenile striped weakfish, Cynoscion guatucupa Cuvier 1830, in Bahía Blanca estuary (Argentina): seasonal and ontogenetic changes

The aim of this study was to analyze the feeding habits of the juvenile striped weakfish, Cynoscion guatucupa Cuvier, from Bahia Blanca estuary, Argentina. C. guatucupa is one of the most important regional fishing resources although in the last 10 years landings have greatly decreased. The year class strength of fish as well as stock size and yield are determined during the early life stages. Knowledge about the diet of young C. guatucupa may therefore contribute to our better understanding of the influence that the changes occurring in the biota of the estuary exert on the abundance fluctuations of this species. To this end, we investigated the ontogenetic and seasonal dietary changes of C. guatucupa between 1.00 and 12.99 cm total length (age 0+), and we related them to changes in habitat use and prey selection. Two dietary shifts were found during ontogeny. The first shift, at approximately 4 cm total length, involved a change from demersal-pelagic prey (mysid shrimps) to demersal-benthic prey (Peisos petrunkevitchi Burkenroad). The second shift, at approximately 8 cm total length, involved a progressive increase in ichthyophagy (mainly an increase consumption of the Argentine anchovy Engraulis anchoita Hubbs & Marini). Seasonal dietary changes were also found. They evidenced the changes in the availability of organisms. In autumn, the chaetognath Sagitta friderici Ritter-Zahoni, P. petrunkevitchi, and E. anchoita were the dominant prey items; in winter, the copepod Labidocera fluviatilis Dahl along with S. friderici, mysids, and P. petrunkevitchi constituted the majority of the diet; and, in summer, mysids were the most important prey item consumed. Selectivity data showed that whereas some prey items, such as the copepods Acartia tonsa Dana and Paracalanus parvus (Claus) and S. friderici, were consistently negatively selected by all size classes throughout the year, other prey items, such as fish larvae, mysids, and P. petrunkevitchi,were selected in one season and avoided in another. Additional dietary seasonal differences observed in our research indicate that the limited food supply and the low water temperatures are limiting factors for winter juveniles in BahOa Blanca estuary. These factors may also directly influence the more-than-10 cm total length seaward migration of large numbers of C. guatucupa that is registered at the end of every autumn.

Small- and large-scale effect of the SW Atlantic burrowing crab Chasmagnathus granulatus on habitat use by migratory shorebirds

Here we address the question of whether the presence of the burrowing crabs Chasmagnathus granulatus affects small- and large-scale habitat use by migrant shorebirds. This crab is the dominant species in soft bare sediments and vegetated intertidal areas along the SW Atlantic estuaries (southern Brazil 28°S to the northern Argentinean Patagonia 42°S). They generate very extensive burrow beds in soft bottom intertidal areas. Our information shows that this burrowing crab affects the small-scale habitat use by shorebirds, given that shorebirds never walk through the funnel-shaped entrances of burrows. Given that crab burrow entrances occupy up to 40% of the intertidal area, there is a large decrease of available shorebird habitat in crab beds, restricting their activity to the spaces between the burrows. The southern migratory shorebird Charadrius falklandicus maximize the use of these areas by foraging closer to the burrows than the other bird species. Neotropical migrants, such as Calidris fuscicollis, Pluvialis squatarola and Tringa melanoleuca, used foraging paths that tended to maximize the distance from burrows, especially the distance to larger burrows. A field experiment showed that this was not necessarily due to a decrease in the availability of polychaetes near the crab burrows. A combination of landscape measurements and satellite images showed that crab beds covered up to 40% of the intertidal area of the Mar Chiquita coastal lagoon (37°40′S, Argentina), and nearly 100% of the intertidal area of the Bahia Blanca estuary (38°48′–39°25′S, Argentina). These two estuaries are located along the migratory flyway of Neotropical migratory shorebirds, but the Bahia Blanca estuary (area∼110,000 ha) shows a much lower shorebird diversity than Mar Chiquita (area∼4500 ha). The most common species in Bahia Blanca is the two-banded plover C. falklandicus, the species least affected by crabs at Mar Chiquita and which prefers to use high-density crab areas as foraging sites. The oystercatcher Haematopus palliatus was also most abundant in high-density crab areas, but they used these areas for resting. The abundances of preys varied during the study period and between the crab density areas, indicating that the use of these areas by birds is independent of crab density. However, burrowing crabs affect the depth distribution of polychaete and thus their availability to shorebirds. We suggest that this shorebirds–burrowing organism interaction could be generalized for other intertidal estuarine habitats.

Characteristics of Tidal Channels in a Mesotidal Estuary of Argentina

Abstract Bahia Blanca Estuary is a complex network of tidal channels, extensive tidal flats, low marshes areas and islands. The lack of a large source of sediments either from river or the shelf results in that the tidal channels of this estuary controlling the dispersal of sediment into the system. A 3-year study of morphodynamic equilibrium has been carried out in the tidal channels of Bahia Blanca Estuary with the aim to investigate the evolution of the system. Detailed changes in the spatial bathymetry linked to the observed flow and sediment processes give a clearer indication of the tidal circulation in the channels. This paper discusses morphologic variability and processes of the erosion, deposition and transport of sediment, which determines the morphological evolution of the system. Current measurements showed that channels appeared to be ebb-dominated with peak speeds of up to 1.2 m/s. Examination of current durations suggests that flood-time dominance is about 7 hr, while ebb period is 5 hr. T...

Decadal change in zooplankton seasonal succession in the Bahia Blanca estuary, Argentina, following introduction of two zooplankton species

Seasonal zooplankton succession (mainly of the mesozooplankton) in the inner zone of Bahia Blanca estuary during the period 1990-1991 was compared to that from the period 1979-1980 in order to detect changes having taken place in 10 years. Taxonomic composition, zooplankton abundance, species occurrence and temperature-salinity conditions were studied within the two annual cycles. This estuarine ecosystem has been deeply affected by a population increase and by the rapid growth of industrial activity and maritime traffic over the last two decades. Several changes in the zooplankton assemblage composition and structure were detected, probably due to temperature- salinity gradient patterns, which showed discernible differences. Dominance, during winter-spring, of two new invading species, namely, the cirriped Balanus glandula and the copepod Eurytemora americana, causing a decrease in the autochthonous key copepod Acartia tonsa, was one of the principal features of the period 1990-1991. Seasonal changes in diversity and species richness, as well as differences in the multivariate general pattern of the zooplankton community structure with a consequent decrease in the community stability during the second period, were also observed.

Industrial Impact on Marsh Soils at the Bahia Blanca Ria, Argentina

The Bahia Blanca Estuary is located in southern Buenos Aires province, Argentina. The area is linked to a petrochemical industrial complex, whose raw materials and final products contaminate the surrounding areas via atmospheric pollution and effluents, which are dumped in the estuary waters. To establish the effects of the industrial waste disposal on the nearest coastal soils, 17 samples were taken at different distances from the loading dock and the outfall pipes of the industrial complex. Later, the physicochemical characteristics of the soil samples, their hydrocarbon contents, sulfides, sulfates, Zn, Cu, and Pb were analyzed and a comparison was made to control samples, which were not affected by the industrial outfall. Hydrocarbons, Zn, Cu, and Pb contents were found at levels that modified the physical and chemical characteristics of the soils. The resistance to penetration shows that the thinner the film of water that surrounds the particles or aggregates, the smaller the migration of organic micelle, which settle on the surface of the contact material. This is demonstrated by the degree of cohesion reached by the particles and the strong influence on the index of hydrophobicity. The high porosity shows that the continuity of the porous space of the soil matrix is impeded by the presence of pollutants, which generate areas that are highly limiting to water flow. The oxidation-reduction potential and the low concentrations of soluble forms of Cu and Pb compared with their concentrations precipitated as sulfides confirm the action of the pollutants.

Mercury distribution in estuarine environments from Argentina: the detoxification and recovery of salt marshes after 15 years

Fil: Marcovecchio, Jorge Eduardo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Instituto Argentino de Oceanografia. Universidad Nacional del Sur. Instituto Argentino de Oceanografia; Argentina. Universidad Nacional de Mar del Plata; Argentina

Variabilidad en la abundancia y retención de larvas de crustáceos decápodos en el estuario de Bahía Blanca, Provincia de Buenos Aires, Argentina

Distribution of larvae of decapod crustacean was studied in the Bahia Blanca estuary with the objective of testing the hypothesis that some species can be retained in the estuary and other can be dispersal offshore waters and can be reinvaded. Larvae of 30 species were identificated, the most abundance corresponding to Chasmagnathus granulata (84%) and Cyrtograpsus altimanus (60%) respectively. A high number of stages of these species were found between 120 km and 80 km in the inner zone of the estuary with 6000 ind/100 m 3 . The maximum density was

Morphometric variables and individual volume of Eurytemora americana and Acartia tonsa females (Copepoda, Calanoida) from the Bahía Blanca estuary, Argentina

Eurytemora americana and Acartia tonsa are the two most important copepods from the Bahia Blanca estuary plankton. For this study, 30 females were selected from recently preserved samples. Prosome length (PL), width (PW) and height (PH), urosome length (UL) and width (UW) measured in each female and subsequently the following ratios PL/PW, PL/PH, PW/PH and PL/UL were determined. Individual volumes for E. americana and A. tonsa females were estimated following the morphometric method in order to obtain individual biomass values. Regression tests were conducted for both species between individual volume and prosome length or width as independent variables, fitting data to a power model. Regression lines were compared through covariance analysis and single pair comparisons in order to evaluate the temporal behavior of the relationships. PL/UL was the best ratio for separating one species from the other. Average individual volume and std. error estimated for E. americana and A. tonsa were 0.0749 (±0.0097) mm3 and 0.0399 (±0.0049) mm3, respectively. Strong differences between both copepods morphometric variable and rate values were observed. A size and volume decrease was detected associated with higher temperatures and less phytoplankton available for food. According to R2 values of regression lines prosome width and prosome length were good volume predictors on different dates for E. americana, however, prosome width was the best predictor on the majority of dates for A. tonsa. Differences in slopes and mean variances found between regression lines demonstrated seasonal variability. General regression equations between volume and PL or PW for each species could be derived.

<i>Eurytemora americana</i> Williams, 1906, not <i>Eurytemora affinis</i> (Poppe, 1880), inhabits the Bahía Blanca estuary, Argentina

SUMMARY: The aim of this report is to clarify the taxonomical identity of the species of Eurytemora (Copepoda, Calanoida) present in the Bahia Blanca estuary, Argentina. Observations of taxonomical details were performed and the results led us to conclude that this species is Eurytemora americana Williams, 1906 and not Eurytemora affinis (Poppe, 1880), as previously identified. E. americana is a recent invader in this estuary and could have been accidentally introduced with ballast water of ships.

Deep-scour holes at tidal channel junctions, Bahia Blanca Estuary, Argentina

Deep-scour holes are common features at the junction of tidal channels in the Bahı́a Blanca Estuary (Argentina), where both channels have similar morphodynamic characteristics. In order to study their possible origin and evolution pattern, the two largest known holes in the estuary were investigated. These holes are located in the Tres Brazas Channel and La Lista Channel, respectively, and have depths of 12–27 m (2–17 m relative relief with respect to the channels' bottoms). Their borders have a steep scour side (3.5°) at the mouth of each confluent channel and a gentle side (1.5°), corresponding to a depositional zone at the opposite downstream side. Geomorphologic characteristics, the nature of the tidal circulation associated to the Tres Brazas Channel, and estimates of the net sediment transport suggest that the evolution of the holes is related to flood dominance acting on the steep side (inner face) and ebb dominance over the gentle (outer) side. Holes migrate headward in a pattern opposite to similar holes formed in fluvial reaches.

Effect of irradiance and temperature on the growth rate of Thalassiosira curviseriata Takano (Bacillariophyceae), a bloom diatom in Bahia Blanca estuary (Argentina)

Long-term phytoplankton studies in the Bahia Blanca estuary showed a seasonal pattern characterized by a winter-early spring bloom of diatoms dominated by Thalassiosira curviseriata. Laboratory experiments were carried out to elucidate the influence of irradiance, temperature and salinity on the growth rate of T.curviseriata. The maximum daily growth rate was 1.93 divisions at 20°C. The compensation point (Ic) varied from approaching zero to 3.08 µmol m-2 s-1, a values were ~0.020-0.070 divisions µmol-1, and the calculated Ik (the irradiance at which initial slope line reaches the maximum rate of growth) varied between 32 and 36 µmol m-2 s-1. Growth became light saturated (when µ = µmax) between 70 and 80 µmol m-2 s-1, and was inhibited at ~150 µmol m-2 s-1 at all tempera- tures (5-20oC). The range of temperatures at which T.curviseriata can grow (5-20°C) coincides with the temperature range over which it is found in the field. In contrast, the thermal optimum for growth, 20°C, was higher than the range of temperatures (between 5 and 10°C) characteristic of the winter-early spring bloom in Bahia Blanca estuary. The mean specific growth rate of T.curviseriata was not affected by salinity over the tested range between 25 and 40 p.p.t. Field observations and experimental data support the characterization of T.curviseriata as a eurythermal and euryhaline species adapted to growth at relatively low light intensity. These characteristics may explain the ability of T.curviseriata to flourish seasonally when light conditions are apparently limiting and its presence almost year round under variable conditions of temperature and salinity.

Seasonal Succession Patterns of Phytoplankton in the Bahía Blanca Estuary (Argentina)

The Bahía Blanca estuary is a shallow, well mixed and highly turbid ecosystem. The phytoplankton is dominated by diatoms with Thalassiosira the major genus in number of species and numerical abundance. A longterm investigation was conducted from 1978 to 1991 including measurements of phytoplankton composition and abundance and environmental factors. Principal Components Analysis (PCA), applied to two periods of four years (1978–1981 and 1988–1991) corroborated the pattern of seasonal distribution in Bahia Blanca estuary; a winter-early spring bloom as the most important event in the annual cycle. This bloom was initiated usually in late-June and extended through September. Seasonal patterns of nutrient concentrations showed a decline coinciding with the diatom bloom and peaks of high concentrations in late summer and autumn. According to the long term observations on phytoplankton and the PCA results, the most important phytoplankton taxa in Bahía Blanca estuary exhibited one of three types of seasonal patterns: very recurrent, winter-early spring blooming species, which included Thalassiosira curviseriata, T. anguste-lineata, T. pacifica, Chaetoceros spp., Skeletonema costatum; species present year-round, e. g. non-blooming species Thalassiosira hendeyi and Paralia sulcata; species with peaks of abundance in late-spring or summer, and presenting more seasonal and interannual variability including phytoflagellates, and the diatoms Cerataulina pelagica and Guinardia delicatula.

Long-term phytoplankton studies in the Bahía Blanca estuary, Argentina

Phytoplankton composition and abundance in the Bahia Blanca estuary, Argentina, have been studied from 1978 to 1993; also water temperature, salinity, transparency, and nutrient concentrations. The pattern of seasonal distribution showed a winter/early spring bloom of diatoms, dominated by Thalassiosira spp., as the most important event in the annual cycle. Annual means of temperature and salinity showed relatively minor variations. Nutrient concentrations (nitrate, silicate, and phosphate) exhibited a positive trend with time. Chlorophyll a showed marked seasonal variations, with maximum values (up to 42 μg l −1 ) during the winter-early spring diatom bloom. The relationship between phytoplankton and environmental factors was investigated using multiple regression analysis. Chl a concentrations and total phytoplankton cell abundance were significantly negatively correlated with temperature, suggesting that temperature was the major source of temporal variability in phytoplankton in the area. Among the nutrients, the highest coefficient was for phosphate concentrations, indicating that this nutrient was more affected by phytoplankton uptake than were silicate and nitrate concentrations.

Importance of Grid-Cell Area in the Estimation of Estuarine Residual Fluxes

Estimation of residual fluxes in estuarine cross sections is a very important procedure to establish, among others aspects, residence time of contaminants, circulation pattern, and sediment transport dynamics. However, the analytical procedure to obtain such values is not trivial and is presented in detail, demonstrating the importance of the grid-cell area as a weighting element in the calculation of spatial averages. The procedure is tested with four different grid designs and it is shown that grids with proportional columns and rows are the only ones that do not introduce statistical noise in the estimation of the residual fluxes. The four designs are also tested with data from a cross section of the Bahia Blanca Estuary (Argentina), results again show that the proportional columns and rows grid provide the best approach in calculating residual fluxes.

Integumental Structures in the Oral Field of Eurytemora Affinis and Acartia Tonsa (Copepoda, Calanoida) in Relation To Their Trophic Habits

[Scanning electron microscopy (SEM) was used to study the morphology of the integumental structures in the oral field of the copepods Eurytemora affinis and Acartia tonsa. Structures observed in these two copepods were different in type, number, and location. E. affinis presented only structures of a filiform type, distributed all over the oral field, whereas in A. tonsa three different types of structures were observed: filiform, papilliform, and conical, distributed according to a complex pattern. The results obtained on the chaetotaxy of the oral field demonstrate a strong morphological adaptation of each copepod to its trophic habits. The ecological implications of these results on the coexistence of populations of both species in the Bahia Blanca estuary are discussed., Scanning electron microscopy (SEM) was used to study the morphology of the integumental structures in the oral field of the copepods Eurytemora affinis and Acartia tonsa. Structures observed in these two copepods were different in type, number, and location. E. affinis presented only structures of a filiform type, distributed all over the oral field, whereas in A. tonsa three different types of structures were observed: filiform, papilliform, and conical, distributed according to a complex pattern. The results obtained on the chaetotaxy of the oral field demonstrate a strong morphological adaptation of each copepod to its trophic habits. The ecological implications of these results on the coexistence of populations of both species in the Bahia Blanca estuary are discussed.]

Biodegradation of crude oil by a marine bacterium isolated from Bahia Blanca Estuary, Argentina

Biodegradation of crude oil by a marine bacterium isolated from Bahia Blanca Estuary, Argentina