Shell growth of Limnoperna fortunei in two localities under different climate in the Plata basin (Argentina). An experimental field work.

GUSTAVO DARRIGRAN; NICOLÁS BONEL

Montreal, Quebec, Canadá

Congreso; 16th Internacional Conference on Aquatic Invasive Species; 2009

Limnoperna fortunei (Dunker, 1857) commonly called the golden mussel, is a freshwater mytilid native of South East Asia. It is considered a freshwater invasive pest. In 1991 it reached the Americas. It entered the Plata Basin in South America, brought in the ballast water of transoceanic ships. L. fortunei is presently found in five countries in South America. It advances at a speed of 240 km per year. The information about the longevity of the golden mussel shows a great variability. Its life span in the natural environment of Bagliardi Beach, Argentina, is 3.2 years. The longevity of 2 years was estimated in the Uji River, Japan, and from 4 to 5 years in Korea and over 10 years in Central China. There are at least two alternatives to contrast the shell growth hypothesis set by models: (1) analyzing the periodicity of growth line formation; or (2) following the growth of each cohort. The last alternative was applied in this research. Three net-bags were used in the experimental field work. A known number of specimens were placed within the net-bags, all of the same size (one cohort). The size of these specimens was followed, and their growth was tested. Two experiments were carried on simultaneously, since March 2007: one in the Río de la Plata river (34°51´S-57°53´W) (temperate locality) and other in Paraná River (31°41´S- 60°44´W) (subtropical locality). Individuals were removed from the net-bags monthly and the shell length measured with a digital caliper. For each sample a size-frequency distribution table was generated, with 1 mm class intervals. Water temperature, pH, oxygen concentration, conductivity, total solids and water transparency were measured. This kind of experimental work reduces the problems to establish the cohorts. Through a variation of the growth coefficient (k), the results show a difference between both experiments. The k value is greater in the subtropical locality, and a relationship mean temperature and bivalve growth rate was recognized.