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Hewes, CD.  2017.  Net photosynthetic growth as controlled by dynamic light regimes. Journal of Plankton Research. 39:930-942.   10.1093/plankt/fbx052   Abstract

The photosynthetic response of the marine diatom Thalassiosira pseudonana to a matrix of dynamic light regimes is described. Ash-free dry weight and chlorophyll-a were measured as a function of dynamic irradiance having maximum intensities of 250, 500, 1000 and 2000 μmol photons m−2 s−1 with lengths of day being 6, 9, 12, 18 and 24-h periods. Incident irradiance followed a Gaussian (normal) distribution, which provided a statistical standard for the integrated quantum flux into a 20 cm water column. The matrix of conditions resulted with growth occurring in three groups (low, high and intermediate light) as a function of the amount for residual irradiance estimated at the mixing depth of 20 cm. The low light group displayed shade-limited (“linear” from self-shading), and the high light group displayed light-limited (“exponential” with no self-shading) phases of the light-controlled growth dynamic. For the same range of integrated daily incident irradiances, cultures growing under the phase of “linear” growth had higher biomass yields per quantum than cultures growing under an “exponential” phase of the growth dynamic. The difference in net quantum efficiency due to phase of the growth dynamic entails the relationship between photic zone and mixing depth, and provides a new perspective for interpreting Sverdrup's Critical Depth Model.

Hewes, CD, Hewes SO.  2016.  First steps toward standardizing dynamic light regimes for the quantitative study of light-controlled growth in shade-limiting water columns. Journal of Applied Phycology. :1-10.   10.1007/s10811-016-0901-9   Abstract

The diurnal solar cycle is the single most common influential variable for algae growing in a natural environment. In spite of its importance, relatively few laboratory studies have been directed towards photophysiological responses to dynamic irradiance regimes. Further, most of these studies have utilized optically thin cultures. However, phycological technologies utilize optically dense cultures grown in depths measured by centimeters. In this case, algae are harvested under self-shading conditions (all usable incident irradiance being absorbed), and the response of the entire water column to the dynamic irradiance regime is of interest. Thus, the area integrated under some modeled curve for a dynamic irradiance regime becomes the independent variable for the photobiological response being measured of a water column in laboratory studies, and this is important. But what curve should be used to model a dynamic irradiance regime? We suggest that a Gaussian (normal) distribution be used to model this dynamic irradiance because of its well-known statistical attributes. In this study, Thalassiosira pseudonana (marine diatom) was grown under shade-limited growth conditions in a 20-cm deep water column with a dynamic irradiance regime using our SolarStat™. A Gaussian distribution modeled this regime having an 11-h day length (standard deviation ±1.85 h) with an irradiance maximum of 1900 μmol photons m−2 s−1. The daily productivity of batch culture in the linear phase of the light-controlled growth dynamic is compared with those of semi-continuous cultures maintained at 1.0, 0.5, and 0.25 doublings day−1.

Hewes, CD.  2016.  Timing is everything: optimizing crop yield for Thalassiosira pseudonana (Bacillariophyceae) with semi-continuous culture. Journal of Applied Phycology. :1-11.   10.1007/s10811-016-0900-x   Abstract

There is relatively little choice in cultivation methods for growing algae outdoors, either in open pond systems or closed photobioreactors—as batch, continuous, or semi-continuous culture. Algal batch culture grown in a nutrient replete environment with adequate sunlight will become self-shaded with sufficient cell density and enter a stage in the growth dynamic known as the “phase of linear growth.” It is during this phase of linear growth that primary production is at maximum and that the highest biomass is harvested. The inherent problem with batch culture is that the exponential (and possibly lag) phases necessary to achieve densities required prior to the phase of linear growth consume time and waste surface area, and thereby make this an inefficient method to grow algae. Semi-continuous culture can be forced into shade-limiting conditions by reducing growth rate from maximum through dilution, whereby phases of lag and exponential growth are skipped, and culture growth is put into a state similar to a perpetual phase of linear growth with an appropriate culture harvest/dilution cycle. Importantly, semi-continuous culture can increase net growth efficiency over batch culture when compared by shade-limited growth rate. However, scientific study and theory covering shade-limited algal growth under semi-continuous culture conditions are nearly non-existent, which currently makes its application to phycological technologies impractical through “hit and miss” strategies. This laboratory study compares shade-limited growth dynamics for batch and semi-continuous cultures of Thalassiosira pseudonana (small-sized, marine diatom). Theory for optimizing production of mass algal culture with semi-continuous culture technique through cycle period and harvest volume is developed, and guidelines to practical industrial applications are provided.

Hewes, CD.  2016.  The color of mass culture: spectral characteristics of a shallow water column through shade-limited algal growth dynamics. Journal of Phycology.   10.1111/jpy.12393   Abstract

It is envisioned that mass algal cultivation for commercial biofuels production will entail the use of large raceway pond systems, which typically have shade-limited photosynthetic growth within depths of 20-30 cm. The attenuation of light and spectral qualities of red, green, and blue wavelengths in a 20 cm water column as a function of chlorophyll-a (Chl-a) concentration during exponential and linear phases of growth dynamics for the marine diatom Thalassiosira pseudonana was examined under laboratory conditions. While photosynthetically available radiation (PAR) was in excess throughout the water column during the phase of exponential growth, PAR became rate limiting differently for red, green, and blue wavelengths during the phase of linear growth. The transition from exponential to linear growth occurred at 1-2 mg Chl-a L−1, whereby a scalar ~5 μmol photons · m−2 · s−1 at 20 cm depth was found to occur as would be anticipated having the compensation point for where rates of photosynthesis and respiration are equal. During the phase of linear growth, red wavelengths became increasingly dominant at depth as Chl-a concentrations increased, being contrary to the optical conditions for those natural bodies of water that forced the evolution of phytoplankton photosynthesis. It is hypothesized this dramatic difference in water column optics between natural and synthetic environments could influence a variety of biological reactions, importantly non-photochemical quenching capacities, which could negatively impact crop yield. This article is protected by copyright. All rights reserved.

Hewes, CD.  2015.  Not all culture is created equal: A comparative study in search of the most productive cultivation methodology. Algal Research.   10.1016/j.algal.2015.06.010   Abstract

Considerable investment through public/private consortia has been towards increasing the productivity from mass algal cultivation for making the industries involved more economically viable. Although high-tech solutions have been popular in recent years, I questioned whether low-tech answers through the method that algae are cultivated could shed light on increasing productivity in mass cultivation systems. Shade-limited growth was studied for Thalassiosira pseudonana (marine diatom) cultures exposed to 85 Ein m− 2 d− 1 under continuous light, and mixed through a 20 cm water column (a standard depth for open pond cultivation), to compare ash-free dry weight (AFDW) and chlorophyll-a (Chl-a) concentrations, net primary productivity (P) and specific growth rates (μ) obtained by batch culture, continuous culture, and semi-continuous culture. Under shade-limiting conditions, both AFDW and Chl-a concentrations varied inversely with μ for the three cultivation methods. During the linear growth phase of batch culture, P did not vary in relation to μ or biomass (B), therefore μ = P / B, and growth rate varied as a power for biomass. For continuous culture methods, B is a function of μ (as dilution rate), therefore B = P μm, and m = − 1 if linear growth is modeled. Net primary production did vary in relation to μ for both continuous and semi-continuous cultures, and m > − 1. Therefore continuous and semi-continuous culture methods did not reproduce a linear growth phase as found for shade-limited growth. For growth rate > 0.5 doubling d− 1, semi-continuous culture had highest, and continuous culture had lowest P for the three methods compared. These results provide evidence that the method of cultivation introduces large variability to net primary productivity under shade-limiting conditions, and needs consideration in the design of cultivation systems and microbiological experiments.

Hewes, CD.  2015.  Transitional-state growth kinetics of Thalassiosira pseudonana (Bacillariophyceae) during self-shading in batch culture under light-limiting, nutrient-replete conditions: Improving biomass for productivity (culture quality). Algal Research.   10.1016/j.algal.2015.06.016   Abstract

Batch culture is the most common method for microbial cultivation, of which its growth dynamics is classified into distinct phases. Importantly is the phase of declining growth (but known as the “linear growth phase” during shade-limited growth for algae) that follows exponential growth and precedes the stationary growth phases. During this phase, under nutrient-replete and light (shade)-limiting conditions, an increasing algal biomass occurs concurrent with a decreasing growth rate (culture quality) that is historically thought to generate a peak of maximum productivity. Dense batch cultures (to > 2 g dry weight l− 1) of the marine diatom Thalassiosira pseudonana were grown under a range of incident scalar irradiances (2–26 Ein m− 2 d− 1) using both continuous light and 12-h day length in an integrated light environment. Under these conditions, a light-limiting, transition-state dynamic phase between exponential and stationary growth was examined. Growth rate varied to the power of biomass during the phase of linear growth. As a consequence, maximum productivity was provided a broad plateau, not a peak, throughout this phase as a function of incident irradiance, during which culture quality changed, and needs consideration in the engineering, design, and operation of mass algal cultivation systems.

Andersson, AJ, Mackenzie FT.  2011.  Technical comment on Kroeker et al. (2010) Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms. Ecology Letters, 13, 1419–1434. Ecology Letters. 14:E1–E2.: Blackwell Publishing Ltd   10.1111/j.1461-0248.2011.01646.x   AbstractWebsite

Ecology Letters (2011) 14: E1–E2AbstractMeta-analysis of experimental results has been interpreted to imply that the calcification response of organisms depositing high Mg-calcite is more resilient to ocean acidification than organisms depositing aragonite/calcite. This conclusion might be biased by inadequate recognition and categorisation of high Mg-calcite according to mineral solubility.