Potential invasion of the Atlantic coast of South America by Semimytilus algosus (Gould, 1850)

The mytilid Semimytilus algosus (Gould, 1850) was collected from a fishing vessel after an in-water hull cleaning operation at Nuevo Gulf, north Patagonia, Argentina. This species is native to the Pacific coast of South America and had not been detected on the Atlantic coast of this continent. Histological slides from male and female portions of gonads of a subsample of specimens showed spawning activity. The gonad stages observed were: developing stage, ready to spawn, spawning, or had already spawned, suggesting the possibility of establishment of a breeding population in the area. The water temperatures, its seasonal range, and the habitats occupied by S. algosus in its native area are very similar to those present in Nuevo Gulf. The plasticity of this species, and its rapid invasion in other regions of the world, suggest that it could become a new invasive species in the Southwestern Atlantic in the near future. Targeted monitoring of the rocky shores of Nuevo Gulf is recommended to determine whether this non-native species is at an early stage of becoming established.