Distribution, population dynamics, and life history of a mass-occurring jellyfish (Lychnorhiza lucerna) in a large temperate estuary (Río de la Plata): ecological and economic implications

Abstract

Scyphozoan medusae are critical components of marine ecosystems; however, our knowledge on their population dynamics and life history needed to understand their role on ecosystem functioning is relatively scarce. We used data from fish-stock assessment cruises (1993–2013), artisanal fisheries and stranding events (2006–2007), to assess spatio-temporal variation in biomass, growth and reproduction, of a large and abundant scyphomedusae (Lychnorhiza lucerna) in a productive estuarine ecosystem (Río de la Plata Estuary, RLPE) (35°S-57°W) from the Southwestern Atlantic Ocean. Medusae consisted of sexually mature individuals only, occurring consistently during austral summer. Medusae biomass displayed a patchy distribution, concentrating mainly in two geographically different hot-spots associated to a frontal feature (turbidity front) of the RLPE. Individual size, relative fecundity, and degree of gonad development varied significantly between hot-spots. Biomass varied greatly among years. Bell diameter, wet weight, and percentage of fully developed oocytes increased during the first half of the summer but decreased during the second half of it. Our results suggest high predictability of the period of occurrence and the distribution of L. lucerna in the RLPE. Physical mechanisms of medusa aggregation, potential effects of medusae on zooplankton dynamics, fisheries production, and conservation of sea turtles, as well as their potential for the development of a local jellyfish fishery, are here discussed. This work provides novel information on patterns of distribution, growth and development of L. lucerna medusae, which can help to enhance our understanding of the role of large medusae on ecosystem functioning of marine ecosystems worldwide.