Long-term changes in phytoplankton phenology and community structure in the Bahía Blanca Estuary, Argentina

Abstract

The phytoplankton of the Bahía Blanca Estuary, Argentina, has been surveyed since 1978. Chlorophyll a, phytoplankton abundance, species composition and physico-chemical variables have been fortnightly recorded. From 1978 to 2002, a single winter-early spring diatom bloom has dominated the main pattern of phytoplankton interannual variability. Such pattern showed noticeable changes since 2006: the absence of the typical winter bloom and changes in phenology, together with the replacement of the dominant blooming species, i.e. Thalassiosira curviseriata, and the appearance of different blooming species, i.e. Cyclotella sp. and Thalassiosira minima. The new pattern showed relatively short-lived diatom blooms that spread throughout the year. In addition, shifts in the phytoplankton size structure toward small-sized diatoms, including the replacement of relatively large Thalassiosira spp. by small Cyclotella species and Chaetoceros species have been noticed. The changes in the phenology and composition of the phytoplankton are mainly attributed to warmer winters and the extremely dry weather conditions evidenced in recent years in the Bahía Blanca area. Changing climate has modified the hydrological features in the inner part of the estuary (i.e. higher temperatures and salinities) and potentially triggered the reorganization of the phytoplankton community. This long-term study provides evidence on species-specific and structural changes at the bottom of the pelagic food web likely related to the recent hydroclimatic conditions in a temperature estuary of the southwestern Atlantic.

Environmental modulation of the plankton community composition and size-structure along the eutrophic intertidal coast of the Río de la Plata estuary, Argentina

“…This diatom assemblage had also been recorded along the fluvial-mixohaline axis of the same study system (Gómez and Bauer, 1998;Gómez et al, 2004) and in the outer area of other estuaries worldwide (Mallin and Paerl, 1994;Muylaert and Sabbe, 1999;Domingues et al, 2005;Guinder et al, 2010). The success of these genera in competition with other taxa might be related to those diatoms' adaptive response to stressful environments.…”

Temperature effects on aggregation during a spring diatom bloom

“…One set of rolling tank samples was incubated in triplicate at the ambient temperature (6uC) and at 11uC using a 12 : 12 h light : dark cycle and an irradiance of 50 mmol m 22 s 21 at eight rotations per minute for 48 h. To another triplicate set of rolling tank samples, cells of an axenic T. rotula (CCMP 1647) culture in the stationary growth phase and grown at 11uC were added to a final concentration of 5000 cells mL 21 . This concentration is higher than the usual abundance occurring in the North Sea but is not uncommon at high nutrient concentrations in coastal ecosystems (Guinder et al 2010;Jasprica et al 2012). The rationale of this manipulation was to investigate the effects of this diatom with a high aggregation potential on the overall aggregation in the course of the phytoplankton bloom.…”

Seasonal and Inter-Annual Analysis of Chlorophyll-a and Inherent Optical Properties from Satellite Observations in the Inner and Mid-Shelves of the South of Buenos Aires Province (Argentina)

“…Phytoplankton is very sensitive to environmental changes, and shifts in cyclical behavior are reported to occur because of changes (such as ENSO events), that modify the climate and meteorological forces, at short and long time scales [74]. The decrease of rainfall in 2007-2008 (La Niña) generated a reduction in the freshwater and nutrients inputs and also an increase in the salinity, which could possibly cause deep changes in phytoplankton community composition [75,76]. This drought produced intense soil losses in the south of Buenos Aires Province, and increases of suspended sediments in the air were reported [77], as well as a strong dust advection from northern Patagonia in 2009 [78].…”