Size-dependent changes in toxicity of Perna viridis mussels exposed to natural populations of Pyrodinium bahamense var. compressum

•We showed the growth of mussels in Sorsogon Bay, Philippines by its shell length.•Mussel growth and its total equivalent saxitoxin content were correlated.•Toxicity in mussels increases with size at high Pbc cell density.•Younger mussels are more toxic than older mussels at low Pbc cell density.

The mussel Perna viridisis used in the Philippine saxitoxin monitoring program as an indicator organism for the presence of saxitoxin in shellfish in an effort to assess concentration beyond a level considered safe for public consumption. Saxitoxin bioaccumulates in mussels through ingestion of saxitoxin-producing algae Pyrodinium bahamense var. compressum(Pbc). This study focuses on the relationship between mussel length and mussel toxicity in mussels exposed to a natural bloom of Pbc. Mussel toxicity was assessed weekly in a 134-day sampling period using Receptor Binding Assay (RBA). Smaller mussels are more toxic than larger mussels at low Pbc cell density (≈102 cells/L) and the reverse is true at higher Pbc cell density (≈5×103 cells/L). These results can be useful in developing strategies for the collection of mussel samples in a toxic algal bloom monitoring program.