The study of phosphorus (P) speciation has a relevant importance due to the different forms that this element can assume along its biogeochemical processes. In coastal environments where mariculture activities are developed, the physicochemical interactions between the water column and the sedimentary layer are intensified, promoting an intense influence on the P cycle. Here, we aim to evaluate the different P species in the surface sedimentary layer of an important mariculture area, Armação do Itapocoroy Bay, located in southern Brazil. Thirty-four samples of surface sediments were collected along the bay and sequential extractions were performed to determine five P species using the SEDEX method. The mean concentrations of the five P species observed in the collected samples were 28.62 ±8.08μg g−1 for exchangeable or loosely adsorbed P (Ads-P); 1.59 ±0.71μg g−1 for Fe-bound P (Fe-P); 208.0 ±19.29μg g−1 for authigenic apatite/biogenic apatite CaCO 3-bound P (Ca-P); 1.17 ±0.64μg g−1 for detrital P (Det-P); and 1.82 ±1.19μg g−1 for organic P (Org-P). The spatial distribution showed the impact of the shellfish farming on the composition of the different fractions of P, mainly in Ca-P, Ads-P, Fe-P and Org-P, while Det-P content showed to be more related to continental sources.