Abstract
The objective of this study was to evaluate variations in the composition and abundance of the phytoplankton community after an exceptional harmful bloom of Akashiwo sanguinea that occurred in Todos os Santos Bay (BTS) in early March, 2007. Samples were collected every ten days, between April, 2007 and March, 2008, from the estuarine gradient of the Paraguacu River to BTS. The physical and chemical variables were measured in situ using a multiparameter sensor. Water samples were collected for analysis of the dissolved inorganic nutrient concentrations and for the study of composition and abundance of the microphytoplankton. Overall, 135 taxa were identified, with a higher richness of diatoms. The total cell density ranged from 2.92 × 103 to 1.16 × 107 (5.47 × 105 ± 1.69 × 106) cells L−1, with higher values in the freshwater zone than in the marine area. Five species showed peaks of abundance throughout the study, forming small blooms. Four of these blooms occurred in the rainy season, formed by the species Guinardia striata (April, 2007), Scrippsiella cf. acuminata (August, 2007), Euglena gracilis (August, 2007), and Skeletonema cf. costatum (September, 2007), while a new bloom of the species Akashiwo sanguinea occurred during the dry season (December, 2007). The environment was typically oligotrophic, with low spatiotemporal variation in the concentrations of dissolved nutrients. Even so, we observed short-term variations in the structure and composition of the phytoplankton community, demonstrated by rapid bloom events, followed by an increase in the total abundance of microphytoplankton, especially during the rainy season. The blooms did not cause any notable changes in the water column and did not present any harmful effects on the system.
Highlights
The composition and dynamics of phytoplankton communities in estuarine systems are modulated by Submitted on: 21-August-2020 Approved on: 19-January-2021 Editor: Rubens M
The estuarine gradient was characterized by a wide variation in salinity (Figure 2), based on which, three estuarine zones were characterized, with significant variation in salinity in both pluviometric seasons (p < 0.001): (1) freshwater zone, represented by P1 site; (2) transitional zone, represented by P2 to P4 sites; and (3) marine zone represented by P5 and P6 sites (Figure 1)
The historical average rainfall in the region of Paraguaçu River Estuary - Todos os Santos Bay is 2,100 mm per year, with the highest rainfall recorded between April and September, and a dry season from October to March (Cirano and Lessa, 2007; Hatje and Andrade, 2009)
Summary
The composition and dynamics of phytoplankton communities in estuarine systems are modulated by Submitted on: 21-August-2020 Approved on: 19-January-2021 Editor: Rubens M. Algae are of significant ecological importance as indicators of ecosystem changes. Qualitative and quantitative changes in phytoplankton community and primary productivity in tropical environments are usually related to the increase in the input of dissolved nutrients in the system (Heisler et al, 2008). These changes are often related to the formation of blooms, which are usually natural events, corresponding to a significant increase in biomass in the organic production chain (Smayda, 1997). Blooms of harmful species can harm ecosystem services by compromising water quality, aesthetic characteristics, and recreational activities, for example, and such blooms appear to be increasing in frequency and magnitude in different systems (Moore et al, 2008; Hallegraeff, 2010; Affe et al, 2016)
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