A zooplankton d13C and d15N isoscape of San Jorge Gulf, Argentina: the potential for tracking movement and habitat use of top predators over

GALVÁN, DAVID EDGARDO; FUNES, MANUELA; PAPARAZZO FLAVIO; SETH NEWSOME

Conferencia; 11th International Conference on the Applications of Stable Isotope Techniques to Ecological Studies (IsoEcol 2018); 2018

Universidad Catolica Andres Bello

Isoscapes of (baseline) d13C and d15N values at the base of food webs provide useful gradients to track animal movements, especially for highly mobile marine top predators. In pelagic marine ecosystems, a variety of physico-chemical factors influence the d13C and d15N of phytoplankton at the base of the food web. Here we reconstruct a d13C and d15N zooplankton isoscape for the San Jorge Gulf (40,000 km2) off the southern Patagonia coast of Argentina, a unique ecological hotspot for seabirds and marine mammals that also supports a lucrative prawn fishery (50,000 tons/year). In this region, high productivity depends in two oceanographic fronts at the southern and northern margins of the gulf. Isoscapes were reconstructed using zooplankton (sizes between: 200?300μm) collected from a regular grid of stations in November of 2016; while a series of physical (temperature, salinity, density) and chemical (nitrate, phosphate, silicic acid, pH) variables were also measured at each station. Models were constructed to study the variables that better explain isotopic values of zooplankton. Models that did not include random effects presented better fit that full mixed effects models. Subsequent models were constructed using general least square function (gls), and backward method selection (progressive systematic elimination of variables) based on minimum AIC values. Zooplankton d13C values varied between -24.7? and -17.5?. Lower d13C values were observed in the center of the gulf where waters are more strongly stratified, while the northern and the southern margins of the gulf where greater mixing occurs had higher d13C values waters. d15N values varied between 5.6? and 13.5? and generally increased from south to north, which closely correlates with the input of nutrients from deep cold waters along the southern margin and higher rates of nutrient recycling along the northern front. Generalized least square models suggest that the best fit for modeling d15N values were the interaction between mean nitrate and silicates values from all along column. For d13C values best fit was find when explanatory values were the interaction of structure of temperature along the water column and silicates from the surface. Zooplankton values present clearly regionalism which respond to local variable conditions. This can be transferred to animals of higher trophic levels. Overall, baseline gradients occur over relatively small scales (200?300km) and may enable the tracking of movement and habitat use of the diverse community of top predators in this region.