Research papersStudy of photosynthetic productivity in the Northern Gulf of Mexico: Importance of diel cycles and light penetration
Introduction
Phytoplankton dynamics are the outcome of nutrient availability, light conditions and physical mixing. The influence of light in diel rhythms on phytoplankton is observed in many aspects such as cell divisions, photosynthesis, chl a fluorescence and gene expression (Suzuki and Johnson, 2001, Ohi et al., 2005, John et al., 2012). Both laboratory and field studies have found that diel rhythms are predictable (Vaulot and Marie, 1999, Litaker et al., 2002, Bruyant et al., 2005, Brunet et al., 2008, Quigg et al., 2012, McInnes et al., 2014). Phytoplankton carbon fixation rates usually exhibit peak values early in the morning or around noon (Harding et al., 1981, Prézelin, 1992); without consideration of this variability errors in the calculation of total integrated primary production occur (Harding et al., 1981, Harding et al., 1982). For light reactions, chl a fluorescence parameters such as minimum fluorescence (F0) and the maximum quantum yield of photosystem (PS) II (Fv/Fm) show quenching in the daytime caused by photoinhibition under excess light stress and recovery at night (Falkowski and Raven, 2007). Photoprotection involves an enzymatic-controlled epoxidation and de-epoxidation of pigment conversion, in order to dissipate extra energy as nonphotochemical quenching (NPQ) before the damage of light reaction centers (Falkowski and LaRoche, 1991). This process of pigment conversion was named the xanthophyll cycle (XC) (Long et al., 1994). In chromophyte algae, XC involves the transformation from diadinoxanthin (Dd) to diatoxanthin (Dt) (Lavaud et al., 2004, Falkowski and Raven, 2007). In cyanobacteria, photoprotection involves zeaxanthin and decoupling of phycobilisomes (Falkowski and Raven, 2007).
The diel “bio-clock” in phytoplankton shows variability in terms of frequencies and amplitudes in field studies. Physical mixing causes vertical movement of phytoplankton cells, which changes the irradiance experienced at different depths. Claustre et al. (1994) indicated the effect of mixing could diminish the difference in the proportion of Dt between day and night. At a 50 m deep coastal site with day–night alternations of thermal induced stratification and mixing, Brunet et al. (2008) found the sinusoidal diel patterns and exponential vertical patterns of Dt/ chl a, Dt/(Dt+Dd) (DES) and ∆F/F′m (effective quantum yield of fluorescence). Doblin et al. (2011) found homogenous chl a fluorescence and photoprotective pigments within the mixed layer, but a lack of diel rhythm with carbon fixation rates in the Sub-Antarctic and Polar Front Zones.
As the largest river in the North America, the Mississippi River drains 40% of the area of the United States (Dagg et al., 2007). With the influence of riverine nutrients, the Northern Gulf of Mexico (NGOM) fuels high phytoplankton biomass and primary productivity, contributing to organic matter export and the complex food web. In the NGOM, the role of nutrients is frequently investigated, particularly along the Louisiana shelf (e.g., Quigg et al., 2011; Laurent et al., 2012; Turner and Rabalais, 2013), but the importance of light is less often examined (e.g., Lohrenz et al., 1994; Lehrter et al., 2009; Nunnally et al., 2014). John et al. (2012) found diel patterns of Rubisco (rbcL) mRNA and the chl a-specific light-saturated photosynthetic rate () in four different size classes of phytoplankton in the Mississippi and Orinoco River plumes, but did not consider the influence of hydrographic factors like mixing and depth on the amplitudes of the diel patterns.
Here, we examined diel patterns of primary productivity and photosynthetic physiology at a range of depths above and below the pycnocline, across the shelf at three stations, and during two very different time periods (April and August, 2012). Multiple techniques were used in our study, such as the 14C method, Fluorescence Induction and Relaxation (FIRe) System and High Performance Liquid Chromatography (HPLC) pigments analysis, which were also common for the investigations in other field studies (Qian et al., 2003, Suggett et al., 2009a, Sylvan et al., 2011). Collectively this study provides information on the magnitude of productivity across a range of spatial and temporal scales.
Section snippets
Sample collections and hydrographic conditions
Two research cruises were conducted in April and August 2012 on the R/V Pelican. In each cruise, three 24 h stations along the 20 m isobath in the NGOM were studied (Fig. 1). Station A (29.07 °N, 89.93 °W) was in the Mississippi River plume while the other two stations were located further west on the Louisiana shelf area (B: 28.60 °N, 90.53 °W and C: 29.00 °N, 92.00 °W). A CTD rosette with 12 Niskin bottles and shipboard calibrated sensors was deployed overboard every 2 h to measure vertical
Hydrographic conditions
We summarized the major hydrographic parameters measured and calculated for the water column at the three stations in Table 2. Station A, located in the Mississippi River plume, showed the lowest surface salinity (25.8±0.38) in August, and the highest phytoplankton biomass (measured as chl a; 3.41±0.4 µg l−1), the highest light attenuation coefficient (kd=0.29) but the shallowest euphotic zone (Zeu, 15.75 m) in April. Stations B and C were less influenced by the Mississippi River with higher
Discussion
While it is well known that primary productivity varies with diel cycles of light, and consequently, with depth, these two factors are rarely examined simultaneously in field situations. This may be partly due to the logistics and expense of such a sampling scheme, but it is also in part due to the challenges associated with interpreting the findings given the range of abiotic and biotic factors which influence the outcomes. As part of determining the mechanisms controlling hypoxia, we were
Conclusions
Our study supported the findings of Lehrter et al. (2009) and others who identified light penetration to the bottom of the euphotic zone as an important driver of primary productivity on the Louisiana shelf along with nutrients and mixing (Lohrenz et al., 1997, Lohrenz et al., 1999, Fennel et al., 2011, Quigg et al., 2011, Laurent et al., 2012, Turner and Rabalais, 2013, Nunnally et al., 2014), and emphasized the importance of sub-pcynocline primary production. Mostly important, we provided
Acknowledgments
We thank the scientific parties from the project ‘Mechanisms Controlling Hypoxia' (especially Steve DiMarco – Lead PI; Texas A&M University, College Station), two technicians (Paul Clark and Eric Quinoz) from the Geochemical and Environmental Research Group, and the crew of the R/V Pelican for all their help. We thank Allison McInnes and Tyra Booe for help with the shipboard measurements, and Bo Li for the calculations of hydrographic parameters. This work was supported by the National Oceanic
References (54)
- et al.
Interactions between freshwater input, light, and phytoplankton dynamics on the Louisiana continental shelf
Cont. Shelf Res.
(2009) - et al.
Diel variation of phytoplankton functional groups in a subtropical reservoir in southern Brazil during an autumnal stratification period
Aquat. Ecol.
(2009) - et al.
Phytoplankton diel and vertical variability in photobiological responses at a coastal station in the Mediterranean Sea
J. Plankton Res.
(2008) - et al.
Diel variations in the photosynthetic parameters of Prochlorococcus strain PCC 9511: combined effects of light and cell cycle
Limnol. Oceanogr.
(2005) - et al.
Phytoplankton photoadaptation related to some frontal physical processes
J. Mar. Syst.
(1994) - et al.
The aquatic laser fluorescence analyzer: field evaluation in the northern Gulf of Mexico
Opt. Express
(2014) - et al.
The blank can make a big difference in oceanographic measurements
Limnol. Oceanogr. Bull.
(2003) - et al.
A review of water column processes influencing hypoxia in the northern Gulf of Mexico
Estuaries Coasts
(2007) - et al.
Rapid light-induced changes in cell fluorescence and in xantophyll-cycle pigments of Alexandrium excavatum (Dinophyceae) and Thalassiosira pseudonana (Bacillariophyceae): a photo-protection mechanism
Mar. Ecol. Prog. Ser.
(1991) - et al.
Photoprotection and other response of plants to high light stress
Annu. Rev. Plant Physiol. Plant Mol. Biol.
(1992)
Diel variation of chlorophyll-a fluorescence, phytoplankton pigments and productivity in the Sub-Antarctic and Polar Front Zones south of Tasmania, Australia
Deep Sea Res. II
Diel variations in photosynthetic activity of summer phytoplankton in Lindåspollene, western Norway
Mar. Ecol. Prog. Ser.
Acclimation to spectral irradiance in algae
J. Phycol.
Aquatic Photosynthesis
A coupled physical-biological model of the Northern Gulf of Mexico shelf: model description, validation and analysis of phytoplankton variability
Biogeosci. Discuss.
Size dependence of growth and photosynthesis in diatoms: a synthesis
Mar. Ecol. Prog. Ser.
Diel periodicity of photosynthesis in marine phytoplankton
Mar. Biol.
Primary production as influenced by diel periodicity of phytoplankton photosynthesis
Mar. Biol.
A day in the life in the dynamics marine environment: how nutrients shape diel patterns of phytoplankton photosynthesis and carbon fixation gene expression in the Mississippi and Orinoco River plumes
Hydrobiologia
Diel periodicity in the photosynthetic capacity of coastal and offshore phytoplankton assemblages
Mar. Ecol. Prog. Ser.
Measurements of variable chlorophyll fluorescence using fast repetition rate techniques: defining methodology and experimental protocols
Biochim. Biophys. Acta
The use of variable fluorescence measurements in aquatic ecosystems: differences between multiple and single turnover measuring protocols and suggested terminology
Eur. J. Phycol.
Simulating the effects of phosphorus limitation in the Mississippi and Atchafalaya River plumes
Biogeosciences
General features of photoprotection by energy dissipation in planktonic diatoms (Bacillariophyceae)
J. Phycol.
Diurnal hysteresis in coral photosynthesis
Mar. Ecol. Prog. Ser.
A small volume, short-incubation-time method for measurement of photosynthesis as a function of incident irradiance
Mar. Ecol. Prog. Ser.
Effect of diel and interday variations in light on the cell division pattern and in situ growth rates of the bloom-forming dinoflagellate Heterocapsa triquetra
Mar. Ecol. Prog. Ser.
Cited by (7)
Long-term study of desert dust deposition effects on phytoplankton biomass in the Persian Gulf using Google Earth Engine
2023, Marine Pollution BulletinCharacterization of common phytoplankton on the Louisiana shelf
2021, Marine Pollution BulletinCitation Excerpt :Similarly, Liu et al. (2021) found that microphytoplankton (>20 μm) dominated estuarine and nearshore waters whereas picoplankton (<2 μm) dominated offshore. Temporally, Zhao and Quigg (2015) observed that diatoms dominated in April and cyanobacteria dominated in August. Temperature and nutrient availability were thought to be the factors driving this difference.
Patterns in phytoplankton and benthic production on the shallow continental shelf in the northeastern Gulf of Mexico
2019, Continental Shelf ResearchCitation Excerpt :Our estimates of phytoplankton productivity ranged from 0.6 to 4.6 g C m−2 d−1 and were consistent with other studies performed in shallow coastal environments (Table 3). For example, phytoplankton productivity on the Louisiana shelf ranged from 0.23 to 3.8 g C m−2 d−1 (Lohrenz et al., 1994, 1997; Lehrter et al., 2009; Zhao and Quigg, 2015). The highest rates observed in this study were also similar to other nutrient rich environments such as the Amazon River Plume (Smith and Demaster, 1996) and Hong Kong waters during summer when nutrient inputs, chlorophyll a and temperature were high (Ho et al., 2010).
In situ estimates of net primary production in the open-ocean Gulf of Mexico
2022, Limnology And Oceanography LettersPhotophysiological and light absorption properties of phytoplankton communities in the river-dominated margin of the northern Gulf of Mexico
2017, Journal of Geophysical Research: Oceans