Edited by: Nina Bednarsek, Southern California Coastal Water Research Project, United States
Reviewed by: José Pinho, University of Minho, Portugal; Jun Sun, Tianjin University of Science and Technology, China
This article was submitted to Coastal Ocean Processes, a section of the journal Frontiers in Marine Science
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The interplay of coastal oceanographic processes usually results in partial pressures of CO2 (
Human activities over the last two centuries have triggered changes in the global climate system at a pace unprecedented over the past 300 Myr (Caldeira and Wickett,
Models predicting future changes in the carbonate chemistry associated to OA can be fairly accurately applied in the open ocean, where the environmental heterogeneity is rather low (Hofmann et al.,
The impact of high
In the present work, we provide insights into the natural seasonal variability of the carbonate system and the phytoplankton community structure and physiology at two contrasting coastal areas off central Chile: an estuarine ecosystem (Valdivia River estuary), and a coastal upwelling ecosystem influenced by freshwater discharges (Arauco Gulf). In addition, the response of these phytoplankton communities to elevated
In this study we investigated two coastal ecosystems off Central Chile which experience naturally high and variable
In this study, we conducted four sampling campaigns between 2014 and 2016, both during austral winter and summer; two in the Valdivia River estuary (August 2014 and January 2015) and two in the Arauco Gulf (September 2015 and January 2016). Each sampling was accomplished in 1 day and consisted in an along-shore transect of five stations (
The hydrological information on daily river flows were obtained from the Dirección General de Aguas (
Gross primary productivity (GPP) and community respiration (CR) was estimated at two stations in each study area (
Finally, two additional water samplings were carried out to perform the carbonate system manipulation experiments with phytoplankton assemblages from both coastal upwelling and estuarine ecosystems. In the Valdivia River estuary, about 70 L of surface water was collected using 10 L-Niskin bottles at the inner part of the estuary (VE2) in August 2014. Here, the CO2 manipulation experiments were conducted at the Coastal Station of Calfuco (Universidad Austral de Chile, 39° 78′ S, 73° 39′ W). In the Arauco Gulf, the sampling took place in November 2016 at the upwelling center off Lavapié Point (37° 08′ S, 73° 34′ W). A similar water volume (~70 L) was collected using a suction pump in clean plastic containers and was immediately transported to the mesocosm facilities at the Marine Biological Station of Dichato (Universidad de Concepción, 36° 33′ S, 72° 39′ W). Major physical-chemical parameters, such as temperature, salinity, nutrient concentration and CO2 system parameters (i.e., DIC and pH), as well as Chl
All the parameters were analyzed according to Riebesell et al. (
pH and DIC values (Valdivia estuary), and TA and DIC values (Arauco Gulf) were used in the software CO2SYS (Pierrot et al.,
Phytoplankton samples for microscopy were fixed with 2% acidic Lugol solution and analyzed following the Utermöhl technique (Utermöhl et al.,
Once in the laboratory, the seawater collected at each sampling site for the experiments was pre-filtered through a 200 μm mesh to eliminate large zooplankton. After acclimation to the corresponding
Pairwise comparisons were conducted applying the Student
Clear seasonal differences in the hydrographic conditions were observed at the two sampling sites. The Biobío and Valdivia rivers discharges showed a typical annual pattern during the sampling years, with maximum values in winter and minima in summer (
Hydrographic characterization of temperature, salinity, oxygen (O2), and nutrients [
Hydrographic characterization of temperature, salinity, oxygen (O2), and nutrients [
As with the hydrographic conditions, carbonate system parameters showed marked seasonal differences. The dynamics of the carbonate system in the Valdivia estuary were driven by the interplay between predominant freshwater discharges in winter and the influence of more oceanic waters in summer (
Carbonate system parameters along the transect conducted in the Valdivia river estuary in winter
In the Arauco Gulf, the highest pH
Carbonate system parameters along the transect conducted in the Arauco Gulf in winter
In general terms, the more acidic waters (low pH/ high
Seasonal differences in the Chl
Cell abundance of the phytoplankton groups (
Phytoplankton community biodiversity and species richness through the Shannon-Wiener diversity index (H′), Pielou's evenness index (J0), and Margalef's species richness (d) at both study areas.
VE1 | 5.30–46.08 | 275.40–11462.68 | 2.75–2.14 | 0.74–0.69 | 3.19–1.29 |
VE2 | 8.36–65.51 | 304.59–9944.58 | 1.94–2.30 | 0.60–0.70 | 1.90–1.61 |
VE3 | 5.40–44.61 | 207.86–4110.04 | 2.29–2.04 | 0.68–0.62 | 2.29–1.70 |
VE4 | 6.50–16.29 | 226.32–1018.41 | 2.66–1.81 | 0.81–0.61 | 2.11–1.30 |
VE5 | 8.39–19.25 | 180.05–623.50 | 2.28–1.61 | 0.79–0.57 | 1.40–1.20 |
GA1 | 54.10–131.81 | 552.57–77002.21 | 0.83–0.24 | 0.40–0.10 | 0.53–0.50 |
GA2 | 57.81–197.65 | 2595.14–88513.84 | 0.57–0.70 | 0.25–0.30 | 0.61–0.49 |
GA3 | 32.93–151.63 | 1139.98–22736.50 | 2.09–0.56 | 0.79–0.27 | 0.93–0.41 |
GA4 | 74.77–118.82 | 992.66–2801.09 | 0.82–0.49 | 0.46–0.30 | 0.36–0.27 |
GA5 | 35.81–54.04 | 1295.29–14165.36 | 1.14–0.37 | 0.59–0.17 | 0.43–0.49 |
In the Arauco Gulf the seasonal patterns of Chl
Cell abundance of the phytoplankton groups (
As expected, the largest gross primary production rates (GPP) were recorded during summer campaigns at both study sites (
Integrated gross primary productivity (GPP), community respiration (CR), net community production (NCP), and the GPP/CR ratio at two station of the Valdivia estuary and the Arauco Gulf during winter and summer.
VE2 | Winter | 11.89 ± 2.32 | 118.15 ± 23.43 | −106.26 ± 17.34 | 0.10 ± 0.06 |
Summer | 469.37 ± 52.15 | 62.62 ± 9.98 | 406.75 ± 43.56 | 7.50 ± 2.31 | |
VE5 | Winte | 19.62 ± 3.32 | 6.66 ± 1.84 | 12.97 ± 2.43 | 2.95 ± 0.47 |
Summer | 295.84 ± 25.22 | 16.89 ± 1.89 | 278.95 ± 32.21 | 17.52 ± 2.99 | |
GA1 | Winter | 231.22 ± 34.68 | 236.97 ± 30.81 | −5.75 ± 0.75 | 0.98 ± 0.13 |
Summer | 4699.09 ± 704.86 | 1222.82 ± 158.97 | 3476.27 ± 521.44 | 3.84 ± 0.50 | |
GA3 | Winter | 140.34 ± 28.07 | 154.41 ± 23.16 | −14.07 ± 1.83 | 0.91 ± 0.14 |
Summer | 2311.12 ± 346.67 | 718.31 ± 143.66 | 1592.81 ± 318.56 | 3.22 ± 0.42 |
Several significant correlations were obtained between the structure and physiological rates of phytoplankton communities and the abiotic factors, such as the hydrographic properties and the carbonate system parameters.
Relationship between biological variables (
Chl |
Ω |
0.14* | 1.87 | >0.05 | 0.14 |
Diatoms | Salinity | 0.12* | −2.28 × 103 | >0.05 | 0.01 |
0.21** | 74.17 × 103 | >0.05 | |||
Dinoflagellates | Salinity | 0.36*** | 2.03 × 103 | >0.05 | 0.31** |
0.17* | −19.75 × 103 | <0.01 | |||
0.47*** | 80.04 × 103 | >0.01 | |||
Chlorophytes | Temperature | 0.12* | 5.03 × 103 | >0.05 | 0.03 |
pH | 0.11* | −282.49 × 103 | >0.05 | ||
0.13* | −0.31 × 103 | >0.05 | |||
0.17* | 5.63 × 103 | >0.05 | |||
Si(OH)4 | 0.12* | 0.39 × 103 | >0.05 | ||
Euglenophytes | Ω |
0.40*** | 2.20 × 103 | <0.05 | 0.08* |
Cilliates | 0.14* | 2.66 × 103 | >0.05 | 0.04 |
|
Ω |
0.23** | 9.86 × 103 | >0.05 | ||
Flagellates | Si(OH)4 | 0.12* | −6.35 | >0.05 | 0.01 |
Silicoflagellates | pH | 0.31*** | 2.52 × 103 | >0.05 | 0.02 |
0.24** | −0.38 | >0.05 | |||
Si(OH)4 | 0.13* | 18.57 | >0.05 | ||
Ω |
0.25** | −16.78 | >0.05 | ||
GPP | Si(OH)4 | 0.62* | 0.67 | >0.05 | 0.14 |
Diversity | Salinity | 0.67* | 0.01 | >0.05 | 0.69* |
0.45* | −0.02 | >0.05 | |||
0.45* | −0.13 | >0.05 | |||
Sp. richness | Salinity | 0.67* | −0.04 | >0.05 | 0.55 |
0.63** | 0.01 | >0.05 | |||
0.63** | −0.07 | >0.05 |
Relationship between biological variables (
Chl |
Temperature | 0.84*** | 0.82 | >0.05 | 0.71*** |
0.68*** | −0.23 | <0.01 | |||
0.33*** | −0.32 | >0.05 | |||
Si(OH)4 | 0.39*** | −0.03 | >0.05 | ||
Diatoms | Temperature | 0.78*** | 485.50 × 103 | >0.05 | 0.44*** |
0.60*** | −66.91 × 103 | >0.05 | |||
0.22** | 215.53 × 103 | >0.05 | |||
Si(OH)4 | 0.30** | −15.60 × 103 | >0.05 | ||
Dinoflagellates | Temperature | 0.63*** | 5.38 × 103 | <0.01 | 0.53*** |
0.61*** | −105.80 | >0.05 | |||
0.18* | 612.94 | >0.05 | |||
Si(OH)4 | 0.39*** | −5.43 | >0.05 | ||
GPP | Temperature | 0.58** | 271.98 | <0.05 | 0.65** |
0.71** | 12.48 | >0.05 | |||
DCR | Temperature | 0.50* | 26.26 | >0.05 | 0.66* |
Salinity | 0.40* | 7.38 | >0.05 | ||
0.68** | −0.49 | >0.05 | |||
Si(OH)4 | 0.35* | 1.10 | >0.05 | ||
Diversity | Temperature | 0.47* | 1.01 | >0.05 | 0.65 |
Salinity | 0.47* | −0.35 | >0.05 | ||
0.56* | 0.12 | >0.05 | |||
Si(OH)4 | 0.69** | 0.04 | >0.05 |
In the Arauco Gulf, the variability of the Chl
Seawater parameters during field collection (i.e.,
Temporal development of the pH,
Temporal development of the pH,
In the Arauco Gulf, the
A frequent research gap in OA studies is the lack of information about the natural variability of the seawater chemistry at the locations where the organisms are collected. However, it is increasingly more evident that this knowledge is critical to correctly interpret the outcome of these investigations (e.g., Boyd et al.,
The seasonal variability in the hydrographic conditions and the phytoplankton community in the Valdivia river estuary and the adjacent coastal area were mostly associated to changes in the extent of the river plume along the transect, which was primarily linked to seasonal changes in the freshwater discharges, as previously described for this area (Vargas et al.,
The hydrographic features in the Arauco Gulf follow a seasonal pattern, with higher upwelling events during austral spring/summer (Valle-Levinson et al.,
Carbonate chemistry dynamics at both sampling sites were likewise associated to the major local oceanographic forcing's dominating the water column. In Valdivia, the more corrosive conditions were observed at the inner estuarine section in winter, associated with the larger river freshwater discharges (
Previous studies have thus reported the dynamics of the hydrography, carbonate chemistry and phytoplankton community structure separately at the two study sites. However, to our knowledge, this is the first time that the relationship between abiotic factors including the carbonate system parameters and the phytoplankton is investigated along the Chilean coast. We observed significant negative correlations between carbonate system parameters and cell abundances only in certain phytoplankton taxa at the estuarine community (
A principal aim of the present study was to investigate how phytoplankton communities that experience high carbonate system variability and naturally acidified conditions respond to increases in the
Prior to evaluating the effect of increased
Owing to the key role of phytoplankton in aquatic food webs as major primary producers, the impact of high
Although there was no significant impact on total phytoplankton biomass, there were some possible effects on particular phytoplankton functional groups or even specific taxa within functional groups, particularly in the estuarine community. For example, the total numerical abundances of flagellates, diatoms, and dinoflagellates, was about 25–50% lower under the high
The mechanisms underlying differences in the response of distinct phytoplankton to elevated
The response of the phytoplankton community from the coastal-upwelling ecosystem in the Arauco Gulf showed no significant effect of short-term exposure to increased
Our results have shown that changes in the carbonate chemistry in the coastal water may have distinct implications for the phytoplankton communities inhabiting an estuarine and a coastal upwelling systems. Increases of
The datasets generated for this study are available on request to the corresponding author.
CV and BJ contributed the concept and design of the study. LL-M, BJ, and PC collected the samples during field samplings, conducted the experiments, and analyzed the samples. NO, PC, and CV organized the database and analyzed the datasets. NO drafted the manuscript with contributions from CV and PD. All authors contributed to the manuscript revision, read, and approved the submitted version.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The authors also acknowledge support from the Millennium Science Initiative from Chile's Ministry of Economy, Development, and Tourism, through both the Millennium Nucleus MUSELS MINECON NC120086 and the Millennium Institute of Oceanography (IMO), MINECON IC120019.
The Supplementary Material for this article can be found online at: