Population structure and spatial distribution of Loripes lacteus (Linnaeus, 1758) in Varano lagoon, SE Italy.

In Varano lagoon (Puglia, Italy) the bivalve Loripes lacteus (Linnaeus, 1758) constitutes the most abundant species among the organisms of the benthic macrofauna. This work presents the results of five years (from 2001 at 2006) of observations on the abundance, size/age population structure and spatial distribution of this species within the basin (6500 ha). L. lacteus is one of the most common and frequent bivalve species in Mediterranean lagoons. It typically occurs in reduced sediments where it is able to live at low oxygen concentration due to a particular respiratory pigment haemoglobin. Lucinid bivalves house symbiotic, sulphur-oxydizing chemoautotrophic bacterias in their gills, which contribute substantially to their nutrition. The design was to perform two sampling campaignes on yearly basis during the intermediate seasons (Spring and Autumn), when possible. Each sampling was realized collecting 53 sampling units taken from 53 stations distributed regularly over the lagoon surface. Each sampling unit consisted in all the individuals contained in a solid 15 x 15 x 20 cm of sediment and held on 1 mm mesh. Growth patterns were determined with the Bhattacharya method which uses modal progression analysis from size frequency distribution. The results showed a spatial distribution of L. lacteus which occurred in patches and changed among samples. The population analysis showed two modal classes for each sampling time. L. lacteus is an "r" strategy species with small size, brief life cycle, with great capacity of recovery after environmental crises.