## 1 Introduction  
Spain produced about 7 in every 10 tons of the EU's farmed Mediterranean mussels (_Mytilus galloprovincialis_) in 2022, largely due to its rafts in the estuaries of northern Spain using the 'off bottom' method [1]. The Mediterranean mussel (_Mytilus galloprovincialis_) is the most common species in the EU and represents 61% of the total community mussel production in the EU-28. This species is cultivated in Mediterranean countries (Italy, Greece, France, Spain, Bulgaria, Croatia, Slovenia), as well as in Galicia (Atlantic coast of Spain) [1]. Spain produces more than 250,000 tons per year (except in 2013, when red tide or algae blooms caused a drop in production) [2]. It is the largest producer in the EU (with 41% of Community production), followed by Italy, France, the Netherlands, Denmark, and Germany, with 8-12% of Community [1]. The supply of mussel seed is critical for the development of industrial mussel cultivation [3]. Mussel farming in Galicia (NW Spain) requires 9000 Tm of mussel seed per year to support the current mussel production rate [4]. A total of 66% of mussel seed used in mussel cultivation is obtained by scraping directly from intertidal exposed rocky shores where mussel seed is attached, although gathering of mussel seed from artificial collector ropes has increased in recent years [4], principally due to its higher growth rate when cultivated on the raft [5]. Since Galicia legislature restricts the number of ropes per raft (maximum 600 ropes of 12 m length during the larval settlement season), it is crucial to increase the seed yield obtained on artificial collectors by the development of new designs [6]. To improve knowledge about the presence and behavior of larvae in the sea, the Spanish administration has a sample collection program underway at seven points distributed in five Galician estuaries. Through this program, the presence of 3 larval stages can be identified: an earlier one (D-shaped larvae, 3 to 4 days old, with an average size of 40 \(\upmu\)m), a more advanced stage, close to metamorphosis and subsequent fixation (umbonate larvae, aged between 25 and 30 days and with an average size of 180 \(\upmu\)m), and an intermediate one (100 \(\upmu\)m). This information is of great interest to the sector since it warns of the optimal moments for the placement of the collector ropes. Manual counting of small species is presented as a task that requires the intervention of specialized personnel in addition to requiring a large amount of time. The effectiveness of the study, in terms of accuracy and reliability, is directly linked to the operator's experience and skills, as well as their level of fatigue. For example, when working with a sample plate with a diameter of 5 cm, it is necessary, either with a magnifying glass or a microscope, to zoom in on the sample in order to visualize the individuals present in it; Figure 1 displays mussel individuals in their early stage:  
Counting all the individuals in Figure 1 may require three/five minutes from a qualified person; even more, the visible area in the figure represents a small percentage of the entire plate area (Figure 2). Consequently, the time to manually detect, classify, and count the individuals present in a small sample is incremented exponentially. Computer vision is a part of artificial intelligence that aims to replicate the human capability to understand visual information. To achieve this, all that is needed is a computer  
Figure 1: Mussel larvae at their 40-micrometer size, under microscope. Figure 2: Laboratory test sample (a 2.5 cm radius circular plate). When observed through a microscope, 1.6 \(\times\) 1.6 square millimeters is an area that allows manual inspection. that can analyze the images and differentiate features in them that allow it to \"understand\" the objects present in them through algorithms that combine statistics, signal processing, and machine learning [7]. In this way, artificial vision can be considered an interesting tool to tackle tasks of this nature, to say the least.