INTRODUCTION

‘Without turbulence, there would be no life on earth’ (Lugt, 1983). The full impact of this particular perspective is nowhere more evident than in the high-energy intertidal zone where mussels and other sessile organisms thrive amidst aeration, nutrient cycling, and waste removal ad libitum. The benefits of a turbulent habitat are considerable, but there are also costs. A major cost for mussels is the production of a robust holdfast or byssus. The byssus provides mussels with the necessary tenacity to survive incessant buffeting by waves. In exchange, a mussel is committed to invest 10% or more of its energy and assimilated nitrogen for making and maintaining a byssus (Jordan and Valiela, 1982).

Mussel byssus consists of a bundle of short threads that resemble tiny tendons (Figure 10.1). It is constructed entirely of extraorganismic, extracellular connective tissue. In the Mytilus species (M. edulis and M. galloprovincialis), each new thread has dimensions of a few centimetres in length and less than 0.1 mm in diameter and is made in about 5 minutes in the ventral groove of the foot by a process akin to injection moulding (Waite, 1992). Like tendons, the threads originate from the byssal retractor muscles by way of a rooted stem; unlike tendons, byssal threads do not ‘insert’ onto foreign objects as tendons do to bone (Currey, 1984). Instead, byssal adhesive plaques bond only to the surface of exogenous substrata, such as stone (Tamarin et al., 1976).