We assembled a dataset of 14C-based productivity measurements to understand the critical variables required for accurate assessment of daily depth-integrated phytoplankton carbon fixation (PP(PPeu)u) from measurements of sea surface pigment concentrations (Csat)(Csat). From this dataset, we developed a light-dependent, depth-resolved model for carbon fixation (VGPM) that partitions environmental factors affecting primary production into those that influence the relative vertical distribution of primary production (Pz)z) and those that control the optimal assimilation efficiency of the productivity profile (P(PBopt). The VGPM accounted for 79% of the observed variability in Pz and 86% of the variability in PPeu by using measured values of PBopt. Our results indicate that the accuracy of productivity algorithms in estimating PPeu is dependent primarily upon the ability to accurately represent variability in Pbopt. We developed a temperature-dependent Pbopt model that was used in conjunction with monthly climatological images of Csat sea surface temperature, and cloud-corrected estimates of surface irradiance to calculate a global annual phytoplankton carbon fixation (PPannu) rate of 43.5 Pg C yr‒1. The geographical distribution of PPannu was distinctly different than results from previous models. Our results illustrate the importance of focusing Pbopt model development on temporal and spatial, rather than the vertical, variability.

https://aslopubs.onlinelibrary.wiley.com/doi/epdf/10.4319/lo.1997.42.1.0001

Photosynthetic rates derived from satellite‐based chlorophyll concentration

http://www.jlakes.org/news/hal-200812-sdarticle.pdf

Eutrophication and harmful algal blooms: A scientific consensus

Microbial activity is a fundamental component of oceanic nutrient cycles. Photosynthetic microbes, collectively termed phytoplankton, are responsible for the vast majority of primary production in marine waters. The availability of nutrients in the upper ocean frequently limits the activity and abundance of these organisms. Experimental data have revealed two broad regimes of phytoplankton nutrient limitation in the modern upper ocean. Nitrogen availability tends to limit productivity throughout much of the surface low-latitude ocean, where the supply of nutrients from the subsurface is relatively slow. In contrast, iron often limits productivity where subsurface nutrient supply is enhanced, including within the main oceanic upwelling regions of the Southern Ocean and the eastern equatorial Pacific. Phosphorus, vitamins and micronutrients other than iron may also (co-)limit marine phytoplankton. The spatial patterns and importance of co-limitation, however, remain unclear. Variability in the stoichiometries of nutrient supply and biological demand are key determinants of oceanic nutrient limitation. Deciphering the mechanisms that underpin this variability, and the consequences for marine microbes, will be a challenge. But such knowledge will be crucial for accurately predicting the consequences of ongoing anthropogenic perturbations to oceanic nutrient biogeochemistry.

https://escholarship.org/content/qt21r294gk/qt21r294gk.pdf

Processes and patterns of oceanic nutrient limitation

CONTENTS INTRODUCTION ..... .... .... .... .... .... .... .... .... .... .... ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . .... .... .... 633 MECHANISMS ..... .... .... .... .... .... .... .... .... .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... .... ........ ........ .... 636 Photosystem Il Inacti vaJion, Damage and Recovery: The DI Story 637 A voidance of PSll Damage: The Xanthophyll Cycle Story .... 640 Damage rmd A voidance: A Blurring of the Division . . . . . . ...... . . . . . . . . . . . . . . . . . . 643 PHOTOINHIBITION IN THE FIELD AND OPEN OCEAN . . . .. ... .. . .. .... .... . . . . . . . . .... 644 Terrestrial VegetaJion .. .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... .... . . . . . . . . .... .... .... . . . . . . . . . . . . . . . . . . . . . . . . 644 Phytoplankton 646 SIGNIFICANCE TO PRODUCTION: A MODELING APPROACH 648 OBSERVED CHANGES IN PRODUCTION ....... . . . .... ........ 653 PHOTO INHIBITION AND PLANT DISTRIBUTIONS .... .... .... .... .... .... . . . . . . . . . . . . . . . . . . . . 654 CONCLUSIONS .... .... .... .... .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........ .... .... .... .... ........ .... ........ 655

Photoinhibition of Photosynthesis in Nature

This review provides an integrated synthesis with timelines and evaluations of ecological responses to eutrophi- cation in Chesapeake Bay, the largest estuary in the USA. Analyses of dated sediment cores reveal initial evidence of organic enrichment in ~200 yr old strata, while signs of increased phytoplankton and decreased water clarity first appeared ~100 yr ago. Severe, recurring deep-water hypoxia and loss of diverse submersed vascular plants were first evident in the 1950s and 1960s, respectively. The degradation of these benthic habitats has contributed to declines in benthic macro- infauna in deep mesohaline regions of the Bay and blue crabs in shallow polyhaline areas. In contrast, copepods, which are heavily consumed in pelagic food chains, are relatively un- affected by nutrient-induced changes in phytoplankton. Intense mortality associated with fisheries and disease have caused a dramatic decline in eastern oyster stocks and associated Bay water filtration, which may have exacerbated eutrophication effects on phytoplankton and water clarity. Extensive tidal marshes, which have served as effective nutrient buffers along the Bay margins, are now being lost with rising sea level. Although the Bay's overall fisheries production has probably not been affected by eutrophication, decreases in the relative contribution of demersal fish and in the efficiency with which primary production is transferred to harvest suggest funda- mental shifts in trophic and habitat structures. Bay ecosystem responses to changes in nutrient loading are complicated by non-linear feedback mechanisms, including particle trapping and binding by benthic plants that increase water clarity, and by oxygen effects on benthic nutrient recycling efficiency. Observations in Bay tributaries undergoing recent reductions in nutrient input indicate relatively rapid recovery of some ecosystem functions but lags in the response of others.

/pdf/eutrophication-of-chesapeake-bay-historical-trends-and-1k0ro6bolk.pdf

Eutrophication of Chesapeake Bay: historical trends and ecological interactions

The microphytobenthos consists of unicellular eukaryotic algae and cyanobacteria that grow within the upper several millimeters of illuminated sediments, typically appearing only as a subtle brownish or greenish shading. The surficial layer of the sediment is a zone of intense microbial and geochemical activity and of considerable physical reworking. In many shallow ecosystems, the biomass of benthic microalgae often exceeds that of the phytoplankton in the overlying waters. Direct comparison of the abundance of benthic and suspended microalgae is complicated by the means used to measure biomass and by the vertical and horizontal distribution of the microphytobenthos in the sediment. Where biomass has been estimated as chlorophyll a, there may be negligible to large (40%) error due to interference by degradation products, except where chlorophyll is measured by high-performance liquid chromatography. The vertical distribution of microphytobenthos, aside from mat-forming species, is determined by the opposing effects of their vertical migration, which tends to concentrate them near the surface, and physical mixing by overlying currents, which tends to cause an even vertical distribution through the mixed layer of sediment. Uncertainties in vertical distribution are compounded by frequently patchy horizontal distribution. Under-sampling on small (<1 m) scales can lead to errors in the estimate that are comparable to the ranges of seasonal and geographic variation. These uncertainties are compounded by biases in the techniques used to estimate production by the microphytobenthos. In most environments studied, biomass (as chlorophyll a) and light availability appear to be the principal determinants of benthic primary production. The effect of variable light intensities on integral production can be described by a functional response curve. When normalized to the chlorophyll content of the surficial sediment, the residual variation in the data described by the functional response curve is due to changes in the chlorophyll-specific response to irradiance. Production by the benthos is often a significant fraction of production in the water column and microphytobenthos may contribute directly to water column production when they are resuspended. Thus on both the basis of biomass and biogeochemical reactivity, benthic microalgae play significant roles in system productivity and trophic dynamics, as well as such habitat characteristics as sediment stability. *** DIRECT SUPPORT *** A01BY074 00003

https://www.jstor.org/stable/info/1352224

Microphytobenthos: The ecological role of the “secret garden” of unvegetated, shallow-water marine habitats. I. Distribution, abundance and primary production

The photosynthesis-irradiance response (PE) curve, in which mass-specific photosynthetic rates are plotted versus irradiance, is commonly used to characterize photoacclimation. The interpretation of PE curves depends critically on the currency in which mass is expressed. Normalizing the light-limited rate to chl a yields the chl a-specific initial slope (α c h l ). This is proportional to the light absorption coefficient (a c h l ), the proportionality factor being the photon efficiency of photosynthesis (Φ m ). Thus, α c h l is the product of a c h l and Φ m . In microalgae α c h l typically shows little (<20%) phenotypic variability because declines of Φ m under conditions of high-light stress are accompanied by increases of a c h l , The variation of α c h l among species is dominated by changes in a c h l due to differences in pigment complement and pigment packaging. In contrast to the microalgae, α c h l declines as irradiance increases in the cyanobacteria where phycobiliproteins dominate light absorption because of plasticity in the phycobiliprotein:chl a ratio. By definition, light-saturated photosynthesis (P m ) is limited by a factor other than the rate of light absorption. Normalizing P m to organic carbon concentration to obtain P m C allows a direct comparison with growth rates. Within species, P m C is independent of growth irradiance. Among species, P m C covaries with the resource-saturated growth rate. The chl a:C ratio is a key physiological variable because the appropriate currencies for normalizing light-limited and light-saturated photosynthetic rates are, respectively, chl a and carbon. Typically, chl a:C is reduced to about 40% of its maximum value at an irradiance that supports 50% of the species-specific maximum growth rate and light-harvesting accessory pigments show similar or greater declines. In the steady state, this down-regulation of pigment content prevents microalgae and cyanobacteria from maximizing photosynthetic rates throughout the light-limited region for growth. The reason for down-regulation of light harvesting, and therefore loss of potential photosynthetic gain at moderately limiting irradiances, is unknown. However, it is clear that maximizing the rate of photosynthetic carbon assimilation is not the only criterion governing photoacclimation.

Photoacclimation of photosynthesis irradiance response curves and photosynthetic pigments in microalgae and cyanobacteria1

Acclimation of the photosynthetic apparatus to changes of irradiance, temperature and nutrient availability, involving regulation of the chlorophyll a:carbon ratio (g), is a universal feature of all phytoplankton studied to date. We derive a dynamic regulatory model that predicts the dependencies of 8 and growth rate ( U ) on irradiance, daylength, temperature and nutrient availdbilitv. Thc model requires specification of 4 parameters to describe the light-dependencies of 8 and g under nutr~ent-saturating conditions at constant temperature. These are the maximum value of 8 (B,,), the in~tial slope of the chl a-specific photosynthesis-light response curve (aCh'), the mdximum carbon-spcclfic photosynthes~s rate (P:;) and the cost of biosynthesis (C). The influences of temperature and nutnent availability are accommodated through their effects on P:. The temperature dependence is described by the slope of an Arrhenius plot and the nutrient dependence IS described through the half saturation constant (K,) of the Monod equation. Fidelity of the model results to empirical studies suggests that microalgal cells adjust 0 in response to an imbalance between the rate of light absorption and the energy demands for photosynthesis and biosynthesis.

https://www.int-res.com/articles/meps/148/m148p187.pdf

Dynamic model of phytoplankton growth and acclimation: responses of the balanced growth rate and the chlorophyll a:carbon ratio to light, nutrient-limitation and temperature

The microphytobenthos form an important component of all shallow-water ecosystems where enough light reaches the sediment surface to support appreciable primary production. Although less conspicuous than macro algae or vascular plants, the microphytobenthos can contribute significantly to primary production and can modify habitat char- acteristics. The microphytobenthos alter sediment properties (e.g., erodibility) both directly, in the extreme forming a mat or scum on the sediment surface, and indirectly by modifying the activities of benthic in fauna (e.g., pelletization, burrowing, tube building, and sediment tracking). Carbon dioxide fixed by the microphytobenthos supports higher, grazing trophic levels. These include deposit-feeding and suspension-feeding macrofauna as well as meiofauna and microfauna. Quantitative relations between the feeding and growth rates of macrofauna and the abundance of micro- phytobenthos and suspended organic matter (i.e., functional responses) are reviewed. Given the current state of knowl- edge of the direct and indirect interactions involving trophic dynamics, sediment properties, and benthic micrbalgae, we argue for reductionist studies of particular interactions as distinct entities. This is a prerequisite for the emergence of a comprehensive picture of unvegetated ecosystems and the ability to predict their responses to man's activities.

Marine Habitats. II. Role in Sediment Stability and Shallow-Water Food Webs

We present a new dynamic model that uses a small number of prescribed parameters to predict the chlorophyll a:carbon ratio and growth rate of phytoplankton in both constant and varying irradiance. The model provides a self-contained description of energy and mass fluxes and regulation of partitioning of photosynthate during phytoplankton adaptation to irradiance. The kinetics and steady-state outcomes of photoadaptation are described in terms of changes in the rates of synthesis of three intracellular carbon pools. These pools account for the distribution of cell material between light-harvesting components, the biosynthetic apparatus, and energy storage compounds. Regulation of the flow of recent photosynthate to these pools is controlled by the ratio of realized to potential photosynthetic electron flow at a given instant. The responses of growth rate and Chl a:C to static and dynamic irradiance regimes can be adequately described by specifying four parameters: the initial slope of the photosynthesis-irradiance curve, the maximum growth rate, the maximum Chl a:C observed under light limitation, and the maintenance metabolic rate. The model predictions compared favorably with observations of the diatoms Thalassiosira pseudonana and Phaedactylum tricornutum.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1996.41.1.0001

Hugh L. MacIntyre

Papers

Microphytobenthos: The ecological role of the “secret garden” of unvegetated, shallow-water marine habitats. I. Distribution, abundance and primary production

Photoacclimation of photosynthesis irradiance response curves and photosynthetic pigments in microalgae and cyanobacteria1

Dynamic model of phytoplankton growth and acclimation: responses of the balanced growth rate and the chlorophyll a:carbon ratio to light, nutrient-limitation and temperature

Marine Habitats. II. Role in Sediment Stability and Shallow-Water Food Webs

A dynamic model of photoadaptation in phytoplankton