Oceanografía acústica del plancton en áreas frontales del Mar Argentino
Zooplankton plays a key role in aquatic ecosystems and the global biogeochemical cycles, critically influencing the recruitment of commercial populations. However, the distribution of these organisms is far from homogeneous, showing a high degree of aggregation, dynamically occupying specific strata of the water column. Species interact in complex spatio-temporal patterns with each other and with the physical environment, where such physical-biological coupling changes in cyclic and episodic ways. The study of these communities therefore has represented a challenge that drove over time the development of various techniques such as the use of acoustics. In this thesis, the use of acoustics allowed the detection of aggregations of macro-zooplankton organisms, belonging to the most conspicuous and frequent species over extensive areas associated with productive sectors of the Argentine Sea (Southwest Atlantic), where they were particularly abundant. From the characterization of the acoustic response of the organisms and morphodynamic aspects of their aggregations, different groups were clearly distinguished in the echograms. The gelatinous plankton and crustaceans showed opposing acoustic responses, depending on the frequency employed. The presence of a swim bladder in fish larvae and some siphonophores colonies generated the highest acoustic responses of all groups studied, given the acoustic resonance effect. Acoustic techniques differ from conventional zooplankton sampling methods in that practically the entire water column is sampled at high speed continuously along the vessels path. The interpretation of echograms with the characterization of the species mentioned, allowed studying the structure and behavioral patterns of their aggregations with high horizontal and vertical resolution. The generation of quasi-synoptic maps of the horizontal distribution of the relative abundances of the species studied, allowed to analyze them in the context of the prevailing physical gradients. For example, as demonstrated in the case of larvae of Merluccius hubbsi, the study of spatial and temporal aspects, both at local and daily scales mediated by individual behavior, and at regional and annual scales at population level, allowed us to infer about the adaptive mechanisms of a species according to the physical dynamics of the environment.