Papers by Ana Martínez Goicoechea
Vertical and horizontal distributions of chlorophyll were analyzed during six cruises (three in a... more Vertical and horizontal distributions of chlorophyll were analyzed during six cruises (three in autumn and three in spring), from 1991 to 1998, over the Uruguayan shelf. Differences in biomass were found between and within seasons, displaying great variability. Phytoplankton biomass was high even during the spring (max: 19:25 mg m À3 ; mean AE SD: 2.82 AE mg m À3); autumn values were also relatively high (max: 7:62 mg m À3 ; mean AE SD: 1.69 AE 1:45 mg m À3) compared with other frontal regions. Maximum values were associated with Coastal Water (CW), Subtropical Water (STW) and the result of them mixing together in autumn. Maximum values were also observed in CW, Subantartic Water (SAW) and their mixing together during the spring. These features highlight the role of CW in fertilization of oligotrophic water masses (i.e. tropical water) and its action in adding stability to unstable SAW, thereby enhancing productivity. The highest values in both seasons were recorded in 1995 (ENSO cold year), emphasizing the high influence of SAW and defining it as a major nutrient source. Two well-defined zones with high chlorophyll concentration were observed in both seasons; one in the southern extreme of the study area and the other in the northern coastal region. Both zones were associated with frontal zones. This shelf convergence system is similar to the Brazil–Malvinas Confluence Zone, but with the CW as another important component, responsible for the surface density fronts and the main source of silicates.
to volume ratio (S/V). Phytoplankton weighted average S/V increased with turbidity along the grad... more to volume ratio (S/V). Phytoplankton weighted average S/V increased with turbidity along the gradient, while individual size did so with salinity. High S/V and low morphological variability supported higher PP, appearing as responses to cope with light limitation in this environment. Multiple linear regressions indicated that morphological variability alone explained 72 % of PP, reinforcing the utility of traitbased approaches when targeting relations between phytoplankton communities and ecosystem functioning.
Stable isotopes (d 13 C and d 15 N) together with chlorophyll a and densities of surf diatoms wer... more Stable isotopes (d 13 C and d 15 N) together with chlorophyll a and densities of surf diatoms were used to analyze changes in trophic niches of species in two sandy beaches of Uruguay with contrasting mor-phodynamics (i.e. dissipative vs. reflective). Consumers and food sources were collected over four seasons , including sediment organic matter (SOM), suspended particulate organic matter (POM) and the surf zone diatom Asterionellopsis guyunusae. Circular statistics and a Bayesian isotope mixing model were used to quantify food web differences between beaches. Consumers changed their trophic niche between beaches in the same direction of the food web space towards higher reliance on surf diatoms in the dissipative beach. Mixing models indicated that A. guyunusae was the primary nutrition source for suspension feeders in the dissipative beach, explaining their change in dietary niche compared to the reflective beach where the proportional contribution of surf diatoms was low. The high C/N ratios in A. guyunusae indicated its high nutritional value and N content, and may help to explain the high assimilation by suspension feeders at the dissipative beach. Furthermore, density of A. guyunusae was higher in the dissipative than in the reflective beach, and cell density was positively correlated with chlorophyll a only in the dissipative beach. Therefore, surf diatoms are important drivers in the dynamics of sandy beach food webs, determining the trophic niche space and productivity. Our study provides valuable insights on shifting foraging behavior by beach fauna in response to changes in resource availability.
ORTEGA, L. and MARTI´NEZ, A., 2007. Multiannual and seasonal variability of water masses and fron... more ORTEGA, L. and MARTI´NEZ, A., 2007. Multiannual and seasonal variability of water masses and fronts over the) variability in the composition of water masses on the Uruguayan shelf were analyzed. The main difference between seasons was the presence of Tropical Water (TW) and a relative dominance of Subtropical Water (STW) over Subantartic Water (SAW) in autumn, whereas spring was characterized by a dominance of SAW and the absence of TW. Changes in the composition of water masses, surface temperature distributions, and front positions and strengths are discussed in regards to biological implications. Our results reveal seasonal changes in the frontal zone position and suggest an enhaced migration during El Niñ o Southern Oscillation (ENSO) warm and cold episodes, reaching higher latitudes during the former (e.g., autumn of 1998). During cold episodes, the position of the frontal zone reached lower latitudes, with prevailing cold waters over the shelf. Higher frontal strength was observed during ENSO episodes, mainly because of the haline component of CW at the surface. The combination of highly variable freshwater inputs and the occurrence of shelf convergences produced a distinctive hydrographic system with a high degree of seasonal and interannual variation and an evident impact on ecological processes. ADDITIONAL INDEX WORDS: Río de la Plata, thermohaline fronts, shelf convergence.
Revista de biología marina y oceanografía, 2006
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Papers by Ana Martínez Goicoechea