## 1 Introduction  
Over the last two decades, there has been growing interest in the use of microalgae as food to partially replace conventional food products (e.g., meat) or to be used as a source of high added-value compounds [1]. Marine microalgae consist of prokaryotic or eukaryotic photosynthetic microorganisms that are able to grow rapidly due to their unicellular or simple multicellular structures [2]. The main reason for the increased microalgae exploitation is due to their interesting nutritional and bioactive profiles (e.g., high protein content, healthy lipid profile and micronutrient (vitamins and minerals) composition) [3]. Moreover, microalgae is considered a sustainable biomass and can be also used to remove heavy metals from marine waters and industrial waste [4, 5]. However, the nutritional and bioactive profiles of microalgae differ according to the target species. For that reason, there is a need to explore and evaluate each microalgae species separately. _Phaeodactylum. tricornutum_ consists of a unicellular marine diatom with a high growth rate under optimal conditions. It is considered an important source of n-3 polyunsaturated fatty acids (PUFAs), particularly eicosapentaenoic acid (EPA), being an interesting alternative in the industry for EPA production [6]. Moreover, _P. tricornutum_ is a promising source of other interesting bioactive components such as fucoxanthin, a primary marine carotenoid [7]. In order to recover the different high added-value compounds from microalgae, different approaches have been taken into account. For example, traditionally, the use of liquid-liquid or solid-liquid extraction using organic solvents and high temperatures has been used. However, due to recent concerns regarding the use of toxic solvents and non-sustainable approaches, there is a growing search for green and efficient methods to avoid them [8; 9; 10]. Nowadays, innovative alternative technologies, such as supercritical fluid extraction (SFE), pressurized liquid extraction (PLE), ultrasound-assisted extraction (UAE), pulsed electric field-assisted extraction (PEF) and microwave-assisted extraction (MAE), are being studied to extract interesting compounds from microalgae [11; 12; 13; 14; 15]. These techniques produce a low environmental impact, since no organic solvents are used and there is less volume consumption. Moreover, they operate under low extraction temperatures and short extraction times, being a sustainable alternative in comparison with traditional extraction methods [16]. Among the different techniques, ultrasound has been used by different authors to ex-tract high added-value compounds from microalgae species (e.g., _Nannochloropsis_ spp., _Spir-ulina_ spp. and _Chlorella_ spp.). [PERSON] et al. [17] obtained an efficient recovery of phenolic compounds and chlorophylls from the microalgae _Nannochloropsis_ spp. after ultrasound (USN) pretreatment. [PERSON] et al. [18] reported the effective extraction of lipids from _Nannochloropsis_ _culata_ under USN treatment. On the other hand, [PERSON] et al. [11] and [PERSON] et al. [19] proposed USN technology as an effective tool for the rapid extraction of proteins from Spirulina and _Chlorella vulgaris_ microalgae, respectively. In general, all these authors obtained better results employing ultrasound than those obtained with conventional extraction. However, there is a lack of information regarding the effects of this technology on the recovery of nutrients and bioactive compounds from _Phaudoctylum tricornutum_. Ultrasound research is focused on various applications, such as food preservation, the stimulation of fermentation and enzyme reactions and the modification of food constituents or product structures, as well as the improvement of mass and heat transfer during the drying or extraction processes. This technology implies the application of ultrasound waves with a range of frequencies between 20 kHz and 100 MHz, thus leading to a constant growth of gas bubbles in the medium, resulting in the collapse and cavitation of the bubbles.