Abstract: Arsenic is a toxic element that is widely distributed in natural environments, posing significant risks to ecosystems and human health through trophic transfer along food chains. Arsenic pollution has emerged as a critical environmental concern in estuarine and nearshore areas. This review provides an overview of the bioaccumulation and transformation patterns of arsenic across various marine organisms, including phytoplankton, zooplankton, polychaetes, shellfish, shrimp, crabs, and marine fish. Marine organisms can accumulate high concentrations of arsenic, predominantly in the forms of arsenobetaine and arsenosugars, reflecting unique bioaccumulation and transformation mechanisms. Through biotransformation processes, marine organisms can convert highly toxic inorganic arsenic into less toxic organic arsenic compounds. Organic arsenic exhibits greater bioavailability compared to inorganic arsenic, thereby contributing to higher concentrations of arsenic in marine organisms. Additionally, both endogenous and exogenous factors influencing arsenic accumulation and transformation in these organisms. Given the complexity and specificity of arsenic enrichment in marine systems, future research should prioritize investigate the molecular mechanisms of arsenic bioaccumulation and transformation across diverse marine species.