Morphology-based functional groups as the best tool to characterize shallow lake-dwelling phytoplankton on an Amazonian floodplain

Abstract

River floodplains are subject to different inundation scenarios, mainly related to the flood pulse. Moreover, the ecology of floodplain lakes is modulated by exchanges of water with the main stream. On Amazonian floodplains, the water level fluctuates seasonally, with four distinct stages during the year: rising, high, falling, and low water. This study evaluated how/which three functional approaches to phytoplankton (FG, functional groups; MFG, morphofunctional groups; and MBFG, morphology-based functional groups) showed the largest relation to the environmental variations in response to rising and falling water periods, using data of the seven lakes sampled during rising and falling water periods, on the Curuaí Floodplain system, Pará state, Brazil. We used a Principal Coordinates Analysis to check for differences in phytoplankton species composition between the rising and falling water periods and a Redundancy Analysis to evaluate the relationship between functional approaches and environmental. Electrical conductivity, silica, and pH were the most important environmental variables to structuring the phytoplankton. The biological dissimilarity was computed using Bray-Curtis index for species biovolume and indicated greater similarity among the species compositions in the lakes during the falling water period. During rising water species is adapted in almost all lentic ecosystems (FG Y) and autotrophic organisms typical from the meroplanktonic that can be found in phytoplankton samples of the shallow lakes (FG MP); cryptomonads (MFG 2d), large centrics (MFG 6a), and large pennates (MFG 6b); and nonflagellated organisms with siliceous exoskeletons (MBFG VI) and unicellular flagellates of medium to large size (MBFG V) were predominant. During falling water, species that tolerate eutrophic to hypertrophic environments with low nitrogen content predominated all shallow lakes (FGs H1 and M; MFGs 5e and 5b; and MBFGs III and VII) and Dolichospermum spp. formed blooms. Morphology-based functional groups were the larger relation with the environmental variations than did functional groups and morphofunctional groups. MBFGs provides a relatively simple and objective classification and were the best in characterizing phytoplankton dynamics on the Curuaí floodplain. Therefore, we recommend using these groups to study phytoplankton ecology in shallow floodplain lakes.

Phytoplankton Functional Groups Driven by Alternative States in a Tropical Floodplain Lake (Pantanal, Brazil)

“…the Coqueiro lake, the variability in phytoplankton composition and biomass was mainly related to seasonal changes in the water level, with greatest biomass and highest species richness at the low water period and lowest at the high water period, after establishing connectivity with the main river and raised water in the lake. The inverse relationship between phytoplanktonic biomass and water level elevation has been widely documented for floodplain lakes of the Paraná (Bortolini et al 2014), Amazon (Lobo et al 2018), Paraguay (Oliveira & Calheiros 2000) and temperate regions (Kasten 2003, Schemel et al 2004.…”

“…Importantly is the establishment of connectivity with the river, increasing the contribution of flagellated algae in the limnetic sites. These groups are favored in high water periods (Oliveira & Calheiros 2000, Alves 2011, Lobo et al 2018, since nanoplankton flagellates due to their rapid growth are able to maintain their populations. The nanoplanktonic organisms of functional group X 3 (chrysophyceans, Chromulinales) considered as typical of oligotrophic lakes with mixed layers, together with W 1 (euglenoids) and Y (Cryptomonas spp., Cryptomonadales, Cryptomonadaceae) were favored by the river-lake connectivity and indicate the tolerance of these functional groups to water flows (Domitrovic 2003).…”

“…Studies have analyzed phytoplankton in shallow lakes governed by natural mechanisms driving regime alternation (O'Farrell et al 2011, Izaguirre et al 2012, Tezanos-Pinto & O'Farrell 2014, Bertani et al 2016, Gamito et al 2019 and applied the approach of functional groups in systems with alternative states (Loverde- Oliveira 2005, Tezanos-Pinto et al 2015. The studies using the functional groups to analyze the phytoplankton variation and the driving factors have been efficient in several floodplain lakes for example in the Paraná River (Devercelli 2006, Devercelli et al 2014, Bortolini et al 2016, Pantanal (Loverde- Oliveira & Huszar 2007), Araguaia River (Nabout et al 2006, Nabout & Nogueira 2007 and Amazonian basin (Alves 2011, Lobo et al 2018.…”

Trophic state index validation based on the phytoplankton functional group approach in Amazon floodplain lakes

“…Phytoplankton diversity was high with 189 and 198 identified taxa during the rising and flushing periods, respectively (Lobo et al 2018). The median biomass obtained from the sampling units was 1.0 (SD 0.7) and 4.0 (SD 5.3) mg L −1 during the rising and flushing periods, respectively (Supplemental Material 2).…”

“…For example, Padisák et al (2009) consolidated the Reynolds classification and included new groups, and Kruk et al (2010) proposed a classification based on species morphology. Recently, the latter classification was shown to be most suitable for floodplain environment (Lobo et al 2018). Padisák et al (2006) developed the index Q, relating phytoplankton assemblage and water quality to lake ecological status.…”