## 5 Case Studies, Including Impact on the Ecosystem  
### Marine Ecosystems  
The influence of artificial ecosystems can be analyzed using several platforms, including positive aspects, such as increasing biodiversity, protection against erosion, and changes in the behavior of fish and other organisms, as well as potential challenges, including hazards related to the use of inappropriate materials or technologies. The use of printing techniques allows for increased structural complexity and biodiversity by precisely adapting the structure to the needs of local ecosystems [68; 83]. Artificial reefs created in this way provide additional space for organisms to settle and grow, which contributes to increasing local biodiversity and stimulating ecosystems [68; 84]. It also plays an important role with fish populations by offering complex habitat structures [9; 85]. 3D printing technology also allows for more effective environmental restoration compared to traditional solutions such as simple-shaped concrete structures [86]. Exemplary research was provided in the framework of the Interreg Atlantic project 3 DPARE [87]. The activities in this project were connected with designing and testing different types of 3D-printed concrete reefs. The differences among the particular units were connected by the sizes of holes, tunnels, and overhangs. A total of eight solutions have been tested in the UK, France, Spain, and Portugal. The obtained results show clear differences recorded between the habitat features [87; 88]. It confirms the necessity of the \"personalization\" of solutions, depending on local biodiversity. [PERSON] and [PERSON] [63] investigated the efficacy of using 3D-printed artificial reefs in comparison to natural coral reefs as habitats for blue-green chromis (_Chromis viridis_) and larval mustard hill coral (_Porites astroeides_) [63]. The provided behavior shows that both species did not discriminate or display modified behaviors between 3D-printed and natural coral skeletons. Moreover, larval mustard hill coral displayed a significantly higher settlement when provided with the artificial 3D-printed surfaces; meanwhile, the growth and mortality of the investigated species did not significantly differ [63]. Thisconfirms that this kind of artificial structure can be a valuable ecological tool for ecosystem restoration [63]. The other area of application for additive manufacturing is connected with the restoration of oyster reefs [59]. In this case, the advantage of 3D printing is connected with the possibility of designing irregular and intricate shapes of artificial structures resembling natural oyster reefs [21; 69]. This kind of complex shape can ensure optimal substrates for oyster colonization and growth [59]. Another advantage of using additive manufacturing is the possibility to perform tailored structures according to specific environmental conditions, such as water flow and sediment composition in a short time [59; 69]. The elements can be optimized for oyster survival and faster growth in a particular local ecosystem [22]. Also, it is important to monitor the efficiency of the artificial reefs and ecological succession [19; 89]. The investigation provided by [PERSON] et al. [19] confirms the efficacy of a 3D-printed terracotta artificial reef for the recruitment and settlement of fish, corals, and other marine organisms--Figure 5 [19]. The previous research confirms the usefulness of artificial reefs for the restoration of ecosystems; however, is worth noticing that there is a lack of standardization in this kind of  
Figure 5: The ecological process of artificial reef colonization. (**A**) The first artificial reef structure a week after deployment (4 July 2019). (**B**) The artificial reef structures 6 months after unification (23 November 2020). (**C**) The top of the first deployed structure after 3.5 years (1 February 2023), completely covered with _Octocorellahix Rhytsima fulum_ and _Xentiidae_ sp. with two _Stylophora pistillata_ colonies.