Almirante Álvaro Alberto Nuclear Complex (CNAAA) uses seawater in the cooling system of its nuclear power plants. This water returns to the environment with a 2 °C to 8 °C temperature increase. To understand the effects of this thermal effluent, there is a large environmental monitoring program that analyses physicochemical and biological parameters, including a survey of brown algae at sampling site 32B, the nearest to the thermal discharge. This work compares monthly and seasonal variations of the specific composition of brown algae to evaluate the feasibility of changing the sampling frequency of the CNAAA monitoring program. The evaluation is performed by following two approaches: a species accumulation curve and comparisons between species richness values obtained from monthly and seasonal sampling. Species accumulation curve structure indicates that brown algae diversity at site 32B is well covered. Species richness measurements indicate that there are no significant differences between monthly and seasonal samples. These results suggest that it is possible to reduce brown algae sampling frequency for the CNAAA monitoring program without significant data loss. Furthermore, it would allow the company to cut costs, thus improving the distribution of resources within its environmental monitoring program.