Mussels are farmed in suspended net socks , to which they are attached by byssus. This is a natural fiber with a particular composition and structure, affected by the changing of chemical/physical sea water parameters, like the temperature. In the present study, byssus production and resistance to traction were evaluated in mussels (M. galloprovincialis ) after a prolonged exposure to high temperature.
For 30 days, f armed mussels were divided in two groups: the control one at temperature of 20 ± 0,5°C and the high temperature exposed group at 28° ± 0,5°C. They were placed on square of polypropylene (PP) film in order to simulate the attach to PP socks used in farming. A portion of the basal foot tissues was collected at 3, 5, 10 and 30 days after high temperature exposure to evaluate t he expression of the three precursors genes of the byssus structural collagen, preCOL -D, preCOL-P and preCOL-NG. At the final time point, all the mussels attached on PP squares were removed from the supports, cutting the byssus, for the traction resistance test.
A collapse was found for the expression of preCOL-P , preCOL-D and preCOL-NG at 30 days of exposure (Fig.1). About the mechanical resistance to the traction, the exposed thread s are less resistant and deformable, and support half of the maximum force of control group. For the plaque adhesion resistance, no difference emerged between the groups.
The prolongation of the thermal stress affected the capacity of the basal gland of the foot to express preCOLs genes. The cost for byssus production depends on the available animal energy budget, high temperatures reduce it , consequently mussels do not have enough energy to spend for byssal collagen synthesis, which is then reflected in the reduced byssogenesis and in the lower tensile strength. Moreover, the heat stress creates an interference in collagen polymerization leading to a decrease in byssal thread resistance. Lower tensile strength represents a serious risk for the production quantity and sector economy: the more lasting the warming of sea water, the more mussels might break away from the farming socks.