###### Abstract  
Halohyptes are salt-tolerant plants that can be used to extract dissolved inorganic nutrients from saline aquaculture effluents under a production framework commonly known as Integrated Multi-Trophic Aquaculture (IMTA). _Halimione portulacoides_ (L.[PERSON] (common name: sea purslane) is an edible saltmarsh halophyte traditionally consumed by humans living near coastal wetlands and is considered a promising extractive species for IMTA. To better understand its potential for IMTA applications, the present study investigates how artificial lighting and plant density affect its productivity and capacity to extract nitrogen and phosphorous in hydroponic conditions that mimic aquaculture effluents. Plant growth was unaffected by the type of artificial lighting employed--white fluorescent lights vs. blue-white LEDs--but LED systems were more energy-efficient, with a 17% reduction in light energy costs. Considering planting density, high-density units of 220 plants m\({}^{-2}\) produced more biomass per unit of area (54.0-56.6 g m\({}^{-2}\) day\({}^{-1}\)) than did low-density units (110 plants m\({}^{-2}\); 34.4-37.1 g m\({}^{-2}\) day\({}^{-1}\)) and extracted more dissolved inorganic nitrogen and phosphorus. Overall, _H. portulacoides_ can be easily cultivated hydroponically using nutrient-rich saline effluents, where LEDs can be employed as an alternative to fluorescent lighting and high-density planting can promote higher yields and extraction efficiencies. sea purslane; hydroponics; aquaponics; light-emitting diodes; sustainable aquaculture; nature-based solutions; saline farming +
Footnote †: journal: Applied Sciences  
002122 May 2021  
low-sodium content makes them a suitable alternative that can reduce sodium intake for populations at risk [13; 14]. Given their potential socioeconomic and nutritional benefits, continued investigation into the horticultural production of halophytes within integrated aquaculture frameworks is necessary. This paper focuses on the species _Halimione portulacoides_ (L.) [PERSON] (a.k.a. sea purslane), an edible halophyte relatively widespread throughout European and Mediterranean saltmarashes with traditional human uses [15] whose aquaculture and nutritional potential has only recently been scientifically explored [16; 17; 18; 19; 20; 21]. These first studies showed that _H. portulacoides_ has one of the highest productivity rates among studied halophytes in saline hydroponic conditions and can contribute to the substantial removal of dissolved inorganic N and P, up to a rate of approximately 4.0 mg N g\({}^{-1}\) and 0.4 mg P g\({}^{-1}\)[16]. For an effective introduction of halophytes in integrated aquaculture systems, it is first important to understand the conditions that benefit their production and estimate key variables (e.g., growth rates, nutrient extraction rates) that can help adjust those conditions for cost-efficient solutions. In the present study, the focus lays on two key variables that influence horticultural production: light and planting density [22; 23; 24; 25; 26]. Providing optimal and energy-efficient lighting conditions is paramount for commercial plant production [27], and solid-state LED lighting is nowadays considered the most flexible and cost-efficient technology for indoor hydroponics because it provides better control over different light parameters (e.g., spectrum, irradiance, photosynthetically active radiation) [28]. Different light spectra produced by LEDs, particularly red and blue, have been shown to influence the productivity of conventional leafy-green crops, and results suggest a general improvement in performance relative to other types of artificial lighting (e.g., fluorescence) and natural lighting [29; 30; 31; 32; 33; 34]. Yet, the influence of different light spectra in the development of halophyte crops is still relatively understudied [35; 36; 37].