## 3 Results and Discussion
### Growth and Biomass Production
The authors of the above study recorded high biomass productivities during the warm season when sunlight was abundant and the cultures were supplied by 1500-2000 umol/(m\({}^{2}\cdot\)s) (i.e., equal to 2000 umE/(m\({}^{2}\cdot\)s)). Association with the season of cultivation was recorded for another _P. celeri_ strain as well [37]. On the other hand, when a _Picochlorum_ sp. was cultivated in a 1 L Duran bottle and an ORWP having the available light intensity of 600 \(\upmu\)E/(m\({}^{2}\cdot\)s) and 2256 \(\upmu\)E/(m\({}^{2}\cdot\)s), respectively, the former culture produced significantly higher amounts of biomass [38]. The authors of the aforementioned investigation attributed these observations to the small optical path and the more efficient mixing in the Duran bottle. As regards _M. gaditana_ VON5.3, the strain used in the current paper noted similar or higher productivity rates when compared with other _Microchloropsis_ (i.e., _Microchloropsis gaditana_ and _Microchloropsis salina_) and _Nunnochloropsis_ strains. For example, when _Microchloropsis salina_ (formerly known as _Nannochloropsis salina_) CCMP 1776 was cultivated in F/2 medium in a conventional raceway pond, \(p_{x}\) = 0.0013 g/(L\(\cdot\)d) was recorded even though the culture was exposed to up to 2000 \(\upmu\)E/(m\({}^{2}\cdot\)s) during clear and sunny days [39]. Biomass production of _M. gaditana_ VON5.3 was similar to the _Nannochloropsis culdata_ used by [PERSON] and [PERSON] (2017) [6] during a short time during the winter season and during spring. In contrast, _Nannochloropsis_ sp. growing in a medium enriched, or not, with a combination of vitamin supplements gained biomass in the range of 0.9 g/L, although microalgal growth seemed to be unaffected by the presence of vitamins in the growth medium [38]. Additionally, in a recent study, water-submerged LEDs were placed at the bottom of an ORWP, as artificial lighting poses as one of the major growth-controlling factors in microalgae cultures in an ORWP and is also a promising solution to limit dark zones and enhance microalgal productivity for the culture of _Nannochloropsis oceanica_. However, the extra lighting affected biomass production only to a limited extent and under low sunlight irradiances [5]. Lastly, to our knowledge, strains that belong to _Nephroselmis_ have not been cultured in ORWP. However, _N. pyriformis_ PAT2.7 presented similar or even higher yields regarding biomass production in comparison to various lab-scale investigations. For instance, _Nephroselmis_ sp. produced biomass that ranged from 0.09 to 0.13 g/L when was cultured under different values of illumination, salinity, and nitrogen content in the growth medium [40]. Similar biomass production (i.e., x = 0.45 g/L) was obtained when _Nephroselmis_ sp. KGE2 was cultivated on livestock wastewater effluent (LWE) and was slightly higher under growth medium supplementation with acid mine drainage in 5% and 10% (i.e., x = 0.59 g/L and x = 0.58 g/L, respectively) [41]. In contrast, when _Nephroselmis_ sp. KGE1 was cultivated in 500 mL Erlenmeyer flasks on BBM growth medium under white fluorescent light illumination at 100 uE/(m2-s) and 27 degC for 3 weeks, it gained more than 1 g/L of biomass [42]. Figure 2: Growth curves of the four microalgal strains for cultivation in an open raceway pond photobioreactor (ORWP) (V\({}_{\mathrm{w}}\) = 40 L). The name of the microalgae strain is indicated in the footnote of the individual graphs per case. Culture conditions: modified artificial seawater (mASW), pH: 8.5, temperature: 23 \(\pm\) 1 degC, photoperiod: 24.0, light intensity: 27–34 uE/(m2-s), agitation: 35 rpm by using a double four-bladed paddlewheel.