Date Published: June 19, 2019
Publisher: Public Library of Science
Author(s): María Sofía Dutto, Carlo Javier Chazarreta, Carolina Soledad Rodriguez, Agustín Schiariti, Luciana Mabel Diaz Briz, Gabriel Néstor Genzano, Maura (Gee) Geraldine Chapman.
Gelatinous organisms are crucial components of marine ecosystems and some species imply social and economic consequences. However, certain geographic areas, such as the temperate Southwestern Atlantic (SWA, 27° – 56° S), remain understudied in terms of jellyfish ecological data. We analyzed 3,727 plankton samples collected along ~6.7 million km2 over a 31-year period (1983–2014) to determine the occurrence, abundance, and diversity patterns of hydromedusae in the SWA. Analyses were made at both community and species levels. Two abundance hot spots of hydromedusae were identified, where values up to 2,480 ind. m-3 were recorded between 2003 and 2014. Liriope tetraphylla and Obelia spp. were the main responsible for recurrent peaks. Diversity indexes were in the range of those published for temperate areas worldwide, and some coastal zones showed values that can be considered moderate to high for a temperate neritic region. The community analysis yielded 10 groups following previously determined biogeographic schemes throughout the study area. This work enhances the knowledge of hydromedusae in the SWA and provides essential information about the current global warming context and the gelatinous zooplankton data necessity.
Gelatinous zooplankton (i.e., mostly medusae and ctenophores, commonly grouped as “jellyfish”) are critical components of marine ecosystems because they can shape food webs [1,2]. They are ubiquitous and voracious on a wide range of prey including fish , and they typically display events of massive occurrences over a variety of spatial and temporal scales, which might be attributable to rapid population increases or to physical forcing that aggregates individuals [3–5]. In addition to the ecological implications, aggregations of jellies can also have socioeconomic costs, such as the negative impact on fisheries, the water intake clogs in power and desalination plants, or the problems caused for public health and tourism .
This is the first study that analyzed patterns of hydromedusae on a macroscale area (~6.7 million km2) with more than 3,700 analyzed plankton samples. The long-term study of the spatial distribution of the abundance and diversity of hydromedusae over the temperate Southwestern Atlantic pointed out specific clustering and abundance hot spots that yielded relevant values and, therefore, deserve attention. In ecological terms, few hydromedusan taxa make the difference showing important abundances in few sites along this macroscale area. Both, trachymedusa L. tetraphylla and leptomedusa Obelia spp. displayed abundances which surpassed, for instance, 1,000 ind. m-3 in two estuarine and productive areas in the central part of the study region (Río de la Plata and El Rincón). Our work improves the knowledge of hydromedusae in one of the ocean regions most poorly studied in terms of jellyfish ecological data, and provides relevant data in the light of the current debate on the increasing abundance of jellyfish in the open and coastal ocean.