Domingo A. Gagliardini

The role of the Rı́o de la Plata bottom salinity front in accumulating debris

The Río de la Plata, one of the most important South American estuarine environments, is characterized by a bottom salinity front that generates an ecotone between the river and the estuary. Based on bottom trawls and costal sampling we describe the distribution, types, and amount of debris found in the bottom and shoreline across this front. Plastics and plastic bags were the main debris types in both areas. Concentrations of total debris upriver the front were always significantly higher than downriver the front showing that the front acts as a barrier accumulating debris. Moreover, a large part of debris end ups accumulated in the coastal area upriver the frontal position. This area is particularly sensitive because the coastline encompasses an UNESCO Man and the Biosphere Reserve and a Ramsar site, and due to the ecological significance of the front for many valuable species.

Inferring Complex Hydrographic Processes Using Remote-Sensed Images: Turbulent Fluxes in the Patagonian Gulfs and Implications for Scallop Metapopulation Dynamics

Abstract San Jose Gulf is a small semienclosed bay connected by a narrow mouth to a much larger basin, the San Matias Gulf. Intriguingly, this comparatively small water body, characterized by high biological productivity, has contributed most of the historical shellfish production in the region. A remote sensing approach allowed us to advance a composite conjecture aimed at explaining that phenomenon. A combination of circulation, strong tidal currents, and coastal topography leads to the formation of a frontal system inside San Jose Gulf and to the development of turbulent fluxes that drive the hydrographic regime. The front divides the San Jose Gulf in two domains (west and east). The origin of water flowing into the west domain was tracked to the Valdes Frontal System, on the continental shelf. The west domain is highly turbulent due to the formation of vortexes and dipoles during the tidal cycle. Detachable dipoles formed at the edge of jets outflowing from San Jose Gulf can reach the central part of San Matias Gulf, constituting a possible larval transport mechanism between the two gulfs. Our results led us to postulate that (1) nutrients from the continental shelf are “trapped in” and larvae are retained in the east domain of San Jose Gulf, resulting in persistently high biomass of secondary producers, and (2) asymmetrical exchange, in the form of vorticial flows, “pumps out” waterborne material from the San Jose Gulf into San Matias Gulf, affecting the connectivity between the two basins.

Evaluation of SeaWiFS and MODIS chlorophyll-a products in the Argentinean Patagonian Continental Shelf (38° S-55° S)

Field measurements of surface chlorophyll‐a concentration were used to evaluate for the first time the performance of the standard Moderate Resolution Imaging Spectroradiometer (MODIS) and both standard and regional Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) ocean colour algorithms in the Patagonian Continental Shelf (PCS) between 38° S and 55° S. The results showed that the regional algorithms did not significantly improve the global algorithm estimates. Moreover, the SeaWiFS OC4v4 algorithm, National Aeronautics and Space Administration (NASA) standard chlorophyll product, showed the best performance among all the algorithms examined. Nonetheless, all the global and local algorithms analysed showed uncertainties dependent on chlorophyll concentration. Low chlorophyll‐a concentration values tended to be overestimated and high values tended to be underestimated. A regional analysis within the PCS showed that higher uncertainties are found in the homogeneous side of the tidal fronts present in the PCS, in areas suggested to be optically complex case 2 waters, while a better result (less bias) was obtained in the southern mid‐shelf region. We discuss the probable reasons and provide possible explanations of the regional differences in the performance of the algorithms.

Waterbird Response to Changes in Habitat Area and Diversity Generated by Rainfall in a SW Atlantic Coastal Lagoon

Abstract The rainfall regime of the Pampas region of Argentina shows a long-term cyclic behavior that has increased in intensity over the historical mean during the last four decades. In this paper we explored the effects of changes in monthly cumulative rainfall on lagoon and riparian habitat, and, in turn on the wetland waterbird community. We also explored the responses of waterbird morphofunctional groups to fluctuation in water level and habitat diversity caused by the change in rainfall at the Mar Chiquita Coastal Lagoon, Argentina (37°32’ to 37°45’S, 57°19’ to 57°26’W). Analysis of satellite images shows that increases in rainfall increased wetland water surface, but reduced riparian habitat area and habitat diversity. Increases in water surface negatively affected the abundances and species richness of waterbirds; habitat diversity did not explain a significant portion of total waterbird variability. Shorebirds (i.e., yellowlegs, plover, sandpiper) were the most affected by reduction in mudflats and habitat diversity. Other waterbirds (i.e., long-legged wading birds, waterfowls) were affected by increases in water surface (ducks, swans, long-legged waterbirds and gulls), decrease in mudflat availability (long-legged waterbirds and gulls), and decrease in habitat diversity (ducks). Our results show that the inter-annual variability in the rainfall pattern influenced the presence and abundance of most waterbirds, and species richness and composition. Fluctuation in water depth per se is known to be a key factor for habitat use of many waterbirds, but habitat diversity also needs to be considered.

Comparison of AVHRR and SeaWiFS imagery with fishing activity and in situ data in San Matías Gulf, Argentina

Seven years (January 2000 to December 2006) of AVHRR and SeaWiFS data were used to estimate monthly climatological means and to present SST and chlorophyll-a seasonal evolution in San Matías Gulf, located between 40° 47′ S and 42° 13′ S on the Argentine coast. SST and chlorophyll-a satellite maps corresponding to spring–summer showed two well differentiable sectors: the southern zone presented colder waters and higher chlorophyll-a concentration while the northern one showed warm water and lower chlorophyll-a. Hake (Merluccius hubbsi) is the most important resource in terms of landings and economic revenues of the San Matías Gulf. Fishing activity data gathered by a Vessel Monitoring System (2004–2006) were linked with SST and chlorophyll-a maps showing that the fishing vessels operated on the thermal front from November to March and had the maximum hake yields. In addition, AVHRR-SST and SeaWiFS-chlorophyll-a data were compared with temperature and chlorophyll-a measured in oceanographic surveys carried out in 2007.

Dusky dolphin: modeling habitat selection

Abstract The use of habitat selection models to predict the likely occurrence of wild populations is an important tool in conservation planning and wildlife management. The goal of our study was to build habitat selection models for the dusky dolphin (Lagenorhynchus obscurus) in Golfo Nuevo, Argentina. Random transects were surveyed by boat in 2002–2007. A grid of 1.5 × 1.5-km squares (cells) was constructed for the study area. We characterized each cell by depth, slope, distance from shore, sea-surface temperature, concentration of chlorophyll a, presence–absence of dolphins, and a coefficient of use by dusky dolphins. Models were developed for warm and cold seasons and for all data combined. Data collected during 2002–2005 were pooled to develop the model, and data collected during 2006–2007 were used for cross-validation. Logistic regression with a binomial error structure and a logit-link function were used to relate the presence of dolphins to habitat variables. Models with gamma structure and log-li...

Spatial patterns of the Argentine hake Merluccius hubbsi and oceanographic processes in a semi-enclosed Patagonian ecosystem

Abstract Time-series of fishing position, landings, satellite-derived sea-surface temperature and chlorophyll a concentrations were used to relate the spatial–temporal distribution of the Argentine hake Merluccius hubbsi with seasonal oceanographic processes in San Matías Gulf. Also, the seasonal effect of fishing on the hake population structure was analysed. During summer the fleet was concentrated over the area of the frontal system, obtaining the best catch-per-unit-effort (CPUE) of hake in relatively deep waters. In autumn, the dispersion of the fleet due to a reduction in CPUE coincided with the dissipation of the front, suggesting that the distribution and shoaling of the Argentine hake is associated with seasonal thermal structures. In spring, the thermal structure of the waters and the chlorophyll a blooms seem to modulate the timing of spawning of hake, which occurs mainly in October–November. In addition, the fleet captured a higher proportion of females in the gonadal recovery stage during warm months (November–April). While winter catches (May–October) consisted mainly of males, the intense summer fishing may result in a high impact on the female population. This information is relevant to design of spatial management tools intended to provide biological sustainability to the hake fishery.

DETECTION OF SMALL-SCALE COASTAL OCEANOGRAPHIC PROCESSES THROUGH LANDSAT-TM/ETM+ IMAGES: IMPLICATIONS FOR THE STUDY OF BIOLOGICAL PROCESSES ALONG THE PATAGONIAN COASTS OF ARGENTINA

The Argentine coastal zone, with its highly productive coastal waters, allows the existence of important seabird and marine mammal breeding assemblages, fish and crustacean spawning and nursery areas, and extensive macroalgae and mollusk beds. Knowledge of factors determining the dynamics of coastal waters is urgently needed to help understand their influence on biological processes and marine biodiversity. Available information in the region is currently scarce due to the low number of oceanographic cruises and oceanographic modeling studies. We evaluate the capacity of high-resolution satellite information for the identification and analysis of coastal processes such as fronts, upwellings, and small scale eddies. Using two case studies, we show how the analyses of temporal sequences of LANDSAT-TM and ETM+ images allow refining the formulation of biological

OCEAN FEATURE DETECTION USING MICROWAVE BACKSCATTER AND SUN GLINT OBSERVATIONS

Synthetic Aperture Radar (SAR) satellite sensors have demonstrated their ability to observe ocean features related to dynamical processes including internal waves, currents, eddies, fronts, and the presence of bathymetric features. Because of the high resolution of available SAR sensors, circulation details and small-scale processes can be detected that are not observable by other sensors more frequently used for ocean research such as the NOAA AVHRR and the ORBVIEW2 SeaWiFS. In contrast to these, LANDSAT-TM thermal and optical channels can be used to observe sea surface temperatures, surface layer ocean color (upwelled radiance) as well as sun glint (reflected radiance) patterns of surface roughness at a spatial resolution comparable to that of SAR. Several examples of TM images obtained in 1997-2002 over the Argentine coastal ocean region where selected from an extensive data set. These images were analyzed and compared with a series of SAR images acquired over the same region by the ERS satellites and in some cases near coincident with the TM data. A close inspection of these data demonstrates that over a sun glint region, a high-resolution optical sensor can provide observations of sea surface patterns related to ocean dynamic processes very similar to those captured by SAR. The ability of TM to detect such ocean features can extend and complement the use of SAR data for ocean research

Identification of Bed Forms Through ERS SAR Images in San Matías Gulf, Argentina

Abstract The European Space Agency (ESA) funded two projects in 1991 and 1994 concerning the observation of the Argentine coastal environment with synthetic aperture radar (SAR). Studies were carried out for the periods 1992–1994 and 1994–1997. Several ERS-1/2 satellite SAR images were acquired over the San Matías Gulf in the Patagonian coast during these two periods. SAR is a side-looking imaging radar that operates from either a satellite or an aircraft. The instrument emits a series microwave pulses toward the earth in a direction perpendicular to the flight path. Imagery is constructed from the strength and time delay of the returned signals, which depend primarily on the roughness and dielectric properties of the surface under observation and the distance from the radar. Ocean surface roughness wave-like patterns, imaged as a series of bright and dark linear features by SAR, are persistently observed over the San Matías Gulf mouth region. A total of thirty-three (33) ERS-1/2 SAR images (100 km × 100 km) from 15 different orbits from 1992 to 2000 were analyzed. This series of observations has allowed for a detailed examination of the location, persistence, and the conditions involved in the imaging of the observed wave-like patterns. Very strong tidal currents of the order of 2 m/s characterize the gulf region. The characteristics of recurrent surface patterns in the SAR images indicate that they are caused by the interaction of the tidal currents with bed forms in the bottom topography of the gulf. The location of these bed forms is poorly documented in the available bathymetric charts of the region. The SAR images show the significant potential that satellite radar observations have as a tool for detecting unmapped coastal ocean bottom features, particularly, where bathymetric mapping activities can be extremely difficult, dangerous, or costly.