Complex latitudinal changes in the neritic isoscape of the south-western Atlantic shelf

SAPORITI, FABIANA; OLIVEIRA, LARISSA ROSA DE; SANTOS, ROBERTA AGUIAR DOS; TAVARES, MAURICIO; VALES, DAMIÁN GUSTAVO; GARCÍA, NÉSTOR ANÍBAL; SILVA, LAURA ALEJANDRA; CRESPO, ENRIQUE ALBERTO; CARDONA, LUIS

Brest

Conferencia; 8th ISOECOL - International Conference on Applications of Stable Isotope Techniques to Ecological Studies; 2012

&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-1610611985 1107304683 0 0 415 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-GB; mso-fareast-language:EN-US;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt;} @page WordSection1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.WordSection1 {page:WordSection1;} --&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; The use of stable isotopes analysis to study the ecology of top predators has grown exponentially during the last decade and currently is considered a standard method in marine biology. Detailed isoscapes are critical for an accurate interpretation of stable isotope ratios in top predators, but many researchers do not generate their own isoscapes and relay on previously published data sets, ignoring that general patterns observed in oceanic areas cannot be extrapolated to coastal regions. This is well illustrated by the situation in the south-western Atlantic, where modelling of data derived from oceanic sampling has been used to suggest a decrease of the δ13C values and an increase of the δ15N values of neritic species inhabiting the continental shelf of South America from latitude 35ºS to 55ºS. To test this hypothesis, we collected samples of small schooling fishes and pelagic squids from southern Brazil (26º-30ºS; 46º-50ºW), Mar del Plata (38º?S; 58ºW), northern Patagonia (43ºS; 62ºW) and southern Patagonia (49º-51ºS; 63º-69ºW) and analyzed δ13C and δ15N of the dorsal muscle of fish and mantle of squids. As the composition of the assemblage changed with latitude, we used nested ANOVA to test the hypothesis that average δ13C decreases and the average δ15N increases with latitude. Statistically significant differences were observed for the average δ15N of the assemblage (ANOVA, F16,3=102.021, p<0.001) but no latitudinal gradient was found. Instead, the lowest values were observed in southern Brazil and northern Patagonia, and the highest values in Buenos Aires and southern Patagonia. Differences in the average δ13C of the assemblage in the four areas were in the verge of statistical significance (ANOVA, F16,3=4.860, p=0.004), but patterns varied among species. For instance, the δ13C of young hake (Merluccius hubbsi ) increased southward, opposite to the expected pattern, whereas the δ13C of anchovies (Engraulis anchoita) from Brazil was higher than that of anchovies from Buenos Aires or northern Patagonia. Therefore, we conclude that the latitudinal variation of stable isotope ratios in the area is more complex than previously described on the basis of modelling of oceanographic data and that local isoscapes should always be reconstructed.