PRELIMIRARY ASSESMENT ON THE SEDIMENTATION RATE OF THE ARMAÇÃO DE ITAPOCOROY BIGHT MUSSEL CULTURE SITE - SC.

Abstract

The mussel culture along the Santa Catarina State has increased during the last few years, and nowadays represents an important activity in complement to fishing. Although this occupation represents a new income source for the fishermen communities, it brings together several environ¬mental problems. The increase of the potential sedimentation rate is one of these problems.The Armação de Itapocoroy Bight is sheltered from the frontal attack of waves from the south, and tidal currents are usually lower than 0.3 m.s-1.During a 51 hours period from August 30 to September 1, 1995, a sediment trap system was deployed under a mussel culture long line, in a region 4 m deep on average. The system was placed 1 m over the bottom, and consisted of a floatation frame with four PVC tubes (the traps). The traps have the relation length/diameter about 5, and its deployment and retrieve were made with the help of scuba divers. We added in two traps 100 ml of a 50 %. NaCI solution, and in the other traps it was added the same solution plus 5% formaldehyde. The material trapped was filtered throughout fiber glass filters (pore = 0.45 pm), and had the salt washed out. From the material retained on the filters, we analyzed (1) the total mass, (2) zooplanktonic organisms, (3) organic carbon using standard methods titration, and (4) total organic matter by combustion. The potential sedimentation rate was estimated by the relation retained mass / (deployment time . mouth trap area). The results showed a mean sedinnentation rate of 118 ± 65 g.m-2.dia1 (dry weight). The trapped material consisted of 17 % of total organic matter, being 24 % of organic carbon, which represented 4 % of the total mass. In the traps with formaldehyde solution it was found a greater abundance of zooplankters. The estimated potential sedimentation rate for the Armação do Itapocoroy Bight,118 ± 65 g.rn-2.dia-1, was greater than the values found for other mussel cultures around the world, but must be considered as an initial approach only.