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First published online February 15, 2006
Journal of Experimental Biology 209, 881-890 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02050

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Seasonal influence of wave action on thread production in Mytilus edulis

Gretchen M. Moeser^*, Heather Leba and Emily Carrington^*

Department of Biological Sciences, University of Rhode Island, Kingston, RI 02881, USA

View larger version (24K): [in a new window]   Fig. 1. Schematic of the aquarium set-up for the laboratory experiments. (A) Top view of replicate tank. Six racks were attached to an aluminum semi-circle connected to a central pneumatic piston. A single flow level, high or low, was established in each tank by circulating the water with a trawling motor. Each rack was placed on the periphery of the tank to minimize flow gradients. (B) Side view of pneumatics. Drawer-slides were used as guides to maintain a linear displacement of the aluminum rack support and the individual racks. These slides were attached both to the rack support and the pneumatic support crossbeam. The pneumatic piston was attached to the aluminum rack support and displaced ±2.5 mm. The piston was forced to change directions when an upper or lower pneumatic button was activated. Air lines connected the buttons to the pistons and back to the regulator. (C) Side view of a single rack. Each rack supported four mussels, each with a different combination of acceleration and byssal loading. The inner support was attached to the aluminum semi-circle and vertically displaced ±2.5 mm. The outer support was attached to the bottom of the tank and held fixed throughout the experiment. The order of each treatment was randomized between racks. Accel, acceleration; Load, byssal load.

View larger version (83K): [in a new window]   Fig. 2. One valve of each mussel was fixed to a vertical nylon rod using cyanoacrylate glue, which was then suspended 6.5 mm above an acrylic plate. During each experiment, mussels gradually tethered themselves to the acrylic plate by producing byssal threads.

View larger version (16K): [in a new window]   Fig. 3. Average number of threads produced over a 48 h period in the three factor experiments. Bars represent the least square mean (± s.e.m.) of threads produced for each treatment. The temperature at which each experiment was performed is indicated in parentheses. (A) August. (B) October. (C) February. Accel, acceleration.

View larger version (19K): [in a new window]   Fig. 4. Number of threads produced over a 48 h period for mussels experiencing each of eight combinations of flow, acceleration (Accel) and byssal loading (Load). Data is pooled for the three factor experiments (August, October and February). Bars represent the least square mean (± s.e.m.) of threads produced over 48 h (N=131). High flow and byssal loading significantly reduce thread production.

View larger version (23K): [in a new window]   Fig. 5. Number of threads produced over a 48 h period for each combination of acceleration (Accel) and byssal loading (Load). Flow was kept constant at 8 cm s–1 (low flow treatment). Symbols represent the least square mean (± s.e.m.) of threads produced for each experiment. Each experiment was performed in the laboratory within 4–8°C of water temperature in the field.

View larger version (25K): [in a new window]   Fig. 6. Summary of mussel condition (gonad index, GI, and condition index, CI), water temperature and thread production for all low flow experiments. Water temperature is shown as both tank temperature and mean (± s.e.m.) bottom temperature at Bass Rock (year 2003–2004). Values for GI, CI and threads produced are means (± s.e.m.) of pooled experimental mussels (N=30–60).

View larger version (13K): [in a new window]   Fig. 7. Mean thread production over 24 h as a function of water velocity in a circulating flume. Values are means ± s.e.m. (N=10 mussels); symbols (circles, triangles) distinguish the two groups of ten mussels used. The equation is a second order polynomial fit to the data (solid line).

View larger version (12K): [in a new window]   Fig. 8. Mussel tenacity vs thread production. Thread production values are the least square means (± s.e.m.) of pooled data from each simulated wave action experiment. Tenacity in the corresponding months was estimated as mean (± s.e.m.) of 6 years of measurements at Bass Rock (see text for details). A linear regression of the data was not significant (P=0.18, r2=0.24; y=–0.17x+8.89).