Tintinnid diversity trends in the southwestern Atlantic Ocean (29 to 60°S)

Abstract

A latitudinal profile of tintinnid specific richness and diversity in the southwestern Atlantic Ocean during spring was evaluated in relation to environmental parameters obtained during 4 oceanographic cruises (TABIA series). The area surveyed included different biogeographic zones and comprised waters of the Brazil-Malvinas Confluence zone, the Argentine shelf-slope, the Malvinas Current and the Antarctic Circumpolar Current. Parameters of tintinnid diversity decreased as latitude of the oceanic cruises increased (TABIA I to III). Latitude explained 53 to 60 and 28 to 60% of specific richness and diversity variation, respectively. Comparisons between cruises indicated that the rate of change in diversity parameters was constant with latitude, but diversity parameters did not change with latitude during TABIA V cruise over the shelf-break front. To explain this difference, environmental (physical and biological) factors that could affect and determine diversity parameters in the Confluence and Subantarctic Zones were analyzed. The conclusion drawn is that the determination and maintenance of tintinnid diversity were mainly caused by various biological factors (available food, predators, 'coocurrence', resilience of dominant tintinnid species) and by particular physical and hydrological characteristics of each biogeographic zone (ingress and egress of water masses in the Confluence, oscillations in the flow of the Malvinas and Brazil Currents, and the presence of a large spatial and temporal scale event: the shelf-break front).