So close, so far: differences in long-term chlorophyll a variability in three nearby estuarine-coastal stations

ABSTRACT

Three sampling stations located in the inner Patos Lagoon estuary, the lagoon’s mouth and the adjacent coastal beach were visited monthly from the end of 1992 until 2014. The stations are in close proximity, but are distributed along saline and hydrological gradients and had never previously been analysed together. Our main questions were: (1) Are the monthly, seasonal and interannual variations in chlorophyll a (Chl a) similar for the three stations? (2) Is there any type of connectivity among the sites? (3) What forces are responsible for controlling phytoplankton variability at these stations? The three stations showed distinct Chl a variability patterns, with higher concentration and variability at the beach station, where the seasonal variation presented higher values between May and October, seemingly out of phase with the estuarine station, where higher values occurred between September and January. The lagoon's mouth station acted as a transit region and incorporated the variability of the estuarine and coastal regions, and all three stations showed a lasting long-term influence from the remote and large-scale phenomenon El Niño Southern Oscillation, El Niño and La Niña periods being characterized by an increase in rainfall and drought conditions, respectively, in the region. The three stations showed no clear connectivity since the cross correlation analysis did not indicate subsequent (more than one month) influence of any station on the others with regard to Chl a. However, a large transfer of the surf-zone diatom, Asterionellopsis guyunusae, from the coast towards the estuary was observed in an apparent ‘inverted outwelling’ process. Chl a variability did not show a straight relationship with most of the measured abiotic variables, indicating that other forces such as residence time may be of greater importance.

RESPONSIBLE EDITOR:

• Dan Franklin

KEYWORDS:

• Phytoplankton biomass
• variability
• estuary
• coast

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was funded by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (grant no. CNPq Proc. No. 403805/2012-0).