## 1 Introduction  
The formation and adhesion of microbial films on marine vessels and equipment surfaces by various aquatic organisms is known as biofouling, which imposes economic and environmental costs on various industrial activities, such as ship operations and offshore structures [1]. Subsequently, using antifouling paints represents a significant strategy for protecting marine structures from biological fouling. Previously, tributytlin (TBT) was a prevalent agent, but it was globally prohibited in 2008 due to concerns regarding its significant adverse impacts on marine organisms [2]. Therefore, copper compounds and irgard-based alternatives have become predominant in antifouling paints [1]. However, the release of biocides from antifouling paints into the marine environment has been observed to result in the induction of harmful damage to a diverse range of non-target species. Irgard is an organic compound in the triazine family that can form metabolites upon release in water, which may contribute to its long-term antifouling effect [3, 4]. Irgard is considered a photosystem II inhibitor, which inhibits photosynthesis and blocks the conversion of photosystem II-derived energy into chemical energy [5]. Based on this evidence, it can be posited that the biological toxicity of rigarol is manifested through direct toxic effects on primary producers, such as algae. An investigation conducted by [PERSON] et al. [6] observed that marine algae, including Chlorella salina, exhibited toxicological effects upon exposure to rigarol, manifesting as a reduction in growth and essential metabolite content. Irgarol has also been observed to inhibit the growth and photosynthesis of marine algae, including cyanobacteria, diatoms, and macroalgae, with concentration-dependent damage observed even at low exposures [7]. Moreover, rigarol has been detected in concentrations in various environments in the ocean, with a particularly wide distribution in estuarine ecosystems [8; 9]. Therefore, it is important to monitor the health of organisms living in estuarine environments; however, while previous studies have predominantly focused on assessing the toxicity of rigarol in algae or fish, research targeting crustaceans and other estuarine benthic organisms remains limited [10]. _Macrophthalmus japonicus_, a tidal flat-dwelling benthic marine organism, is widely distributed in the Indo-Pacific region and exhibits a wide range of life history characteristics depending on environmental conditions [10]. _M. japonicus_ has high economic value in estuarine fisheries and contributes to biodiversity conservation as a key tidal mudflat food chain member. The feeding activity of _M. japonicus_ is found to be significantly correlated with the availability of oxygen and the levels of organic carbon and nitrogen present in estuarine sediments [11]. In addition, the production and biomass of _M. japonicus_ are directly affected by the biomass of the microphytobenthos it consumes as a food source [12]. Given its high dominance and extensive distribution in tidal flats, this species has been employed as an indicator for environmental monitoring. Moreover, it has been demonstrated in Korea that alterations to the chitinase gene can contribute to the concentration of heavy metals and the abundance of crustaceans in estuarine sediments [13]. Furthermore, alterations in several _M. japonicus_ physiological marker genes were noted in response to varying salinity gradients [14]. Pollutants from a variety of sources released into rivers are transported into estuarine environments with flow and readily accumulate due to the physical properties of sediment particles [15; 16]. Thus, the ongoing increase in pollutant sources has increased the importance of monitoring estuarine biological health. Arginine kinase (_AK_) plays a significant role in energy metabolism in many marine organisms, including crustaceans, mollusks, and echinoderms [17; 18].