Not surprisingly, studies have demonstrated this biocide's high toxicity to non-target organisms [12; 16]. Recently, DCOIT was classified as \"very toxic to aquatic life, with long-lasting effects\" by the European Chemicals Agency [17]. Because environmental regulations have become increasingly restrictive on national and international bases, new AF strategies need to attend some aspects such as environmental safety, AF efficacy and coating's lifetime. In this sense, promising AF alternatives to regular state-of-the-art biocides have gained space, such as the encapsulation and immobilization of the biocides in low toxic nanocontainers [18; 19; 20; 21; 22]. Novel AF nanomaterials have been recently developed using silica mesoporous nanocapsules (SiNC) to encapsulate DCOIT [23]. SiNC have an empty core and shell with gradual mesoporous which confers significant loading capacity and allows prolonged and stimuli-triggered release of the biocide, such as pH or chloride concentration [24], providing a safe environmental loading of the biocide together with specific targeting [23]. When used as coating additive, the biocide's lifetime is increased and the percentage content of the main active ingredient in the coating is also greatly reduced. This feature has been triggering the core business of the company Smallmatek, Lda, which develops and produces functionalized engineered nanomaterials, including SiNC-DCOIT, to be added in protective coatings for maritime applications. A recent study comparing the antifouling efficacy and toxicity of DCOIT in both free and encapsulated forms (DCOIT vs. SiNC-DCOIT) indicated that the novel AF nanostructured additive is much less toxic (up to 214-fold) towards non-target species from temperate regions [12]. However, there is no knowledge on the toxicity and efficacy of this AF nanomaterial on species from different climatic regions, a critical requirement on environmental risk assessment at global scale. Furthermore, the effects of SiNC-DCOIT on different life stages of a given species are also unknown so far. The brown mussel _Perna perna_ occurs on rocky reefs, forming dense colonies at the low-tidal and intertidal levels in the tropical and subtropical zones. This bivalve species is regarded as a socio-economically relevant species with a very-broad natural distribution along Africa and the Arabic Peninsula, being an invasive species in the Gulf of Mexico and, more recently, in Portugal [25]. This bivalve species is economically important in Brazilian southern and southeastern coastal areas and represents a relevant food resource for coastal populations [26]. Therefore, due to its socio-economic importance, _P. perna_ is a non-target fouling organism at adult life stages; however, it can be considered a target organism at the larval stage since it is prone to settle and become part of the undesirable fouling in human-made structures. Accordingly, this research aimed to evaluate and compare the effect of two DCOIT forms (free DCOIT vs. its nanostructured form SiNC-DCOIT) and the unloaded nanocarriers (SiNC) on different life stages of the bivalve _P. perna_, namely, on gametes (fertilization success), fertilized eggs (embryo-larval development), and juveniles mussels (byssus threads production and air survival capacity).