Population dynamics of Limnoperna fortunei, an invasive fouling mollusc, in the lower Parana river (Argentina)

Settling and growth of the Asian freshwater mussel Limnoperna fortunei on experimental PVC frames in the Parana de las Palmas river, ca 130 km north of Buenos Aires was monitored at monthly intervals in 1998. Frames were deployed in January. In February and March colonization reached 38000-44000 mussels m(-2) with early juveniles (< 2 mm) accounting for over 98% of the population. in April through August the total densities decreased to 9000-2000 individuals m(-2), the populations being dominated by older (> 2 mm) mussels. In September through December densities grew steadily again, with early juveniles (< 2 mm) accounting for over 95% of the mussels recorded. During their first month, animals born in January grew to ca 3-4 mm in length; in March they reached 7-8 mm, and by mid April 11-12 mm. In late April through July the growth rate decreased to < 2 mm per month, and in August it stopped almost completely, resuming again in late September. During the first year animals born in January reached 20 mm in length; by the end of the second year the estimated length was 30 mm, with a maximum theoretical length of 35 mm being reached after 3 years. The data agree with the reported population dynamics of L. fortunei in Hong Kong in that both populations are characterized by extended reproduction periods lasting ca 9 months, and that the spring onset of breeding is triggered by a rise in temperature above approximately 16-17 degrees C. On the other hand, in the Parana river reproduction was found to be continuous between September and March, and the period of lowest yearly temperatures was characterized by a very strong breeding decline, whereas for the Chinese populations 2-3 yearly spatfalls and breeding pulses roughly coinciding with the lowest and highest water temperatures were described.