Fecal pollution increases susceptibility to diseases in brown mussel Perna perna from cultured and wild populations

Abstract

Maricultural systems for food production have expanded worldwide since the 2000s, including the production of brown mussel Perna perna - a key aquaculture species in Venezuela, South Africa, and Brazil. Bivalves grown in sewage-polluted areas can act as sources for human diseases given their filter-feeding behavior. Moreover, sewage can affect mussels' microbiota and fitness, thereby making them more susceptible to infections and diseases, leading to mortalities. In the present study, we investigated the impacts of coastal fecal pollution on P. perna pathological conditions. Fecal indicator bacteria (FIB) were used to assess the microbiological quality in the seawater and mussels' hemolymph from four beaches located at Guanabara Bay, Rio de Janeiro, Brazil: Vermelha (VB), Icaraí (IB), and Urca (UB), where mussels are exploited for consumption and local market sale; and Jurujuba (JB) farming area where mussels are cultured. Additionally, mussels had their organs surveyed for pathological conditions and parasitic infection by histology. UB presented the highest FIB counts in seawater, followed by IB, JB and VB. Moreover, significantly lower values of total coliforms (TC) were found in mussels' hemolymph from VB and IB than JB and UB, which are probably related to differences in the hydrodynamic of these beaches; VB and IB are open beaches, while JB and UB are sheltered. Our findings suggest that mussel's hemolymph could be used as an indicator of the water quality. Mussels from VB and IB presented lower overall incidence of pathological conditions than ones from JB and UB, suggesting that higher fecal contamination increases mussel susceptibility to pathologies. Mussels from VB were associated with an elasmobranch parasite (Tylocephalum sp.) that indicate a conservative ecological dynamic. Our findings highlight that sewage inputs into coastal systems and farming areas raises the risks of parasitosis and diseases in mussels, which may compromise the quantity and quality of shellfish production and lead to economic losses. In response, public investments in urban planning and sanitary regulation close to coastal systems and farming areas are crucial to prevent future problems for the shellfish market and human safety, especially in developing countries such as Brazil.