AVENI-DEFORGE, K.J.; WETHEY, D.S; Univ. of South Carolina, Columbia; Univ. of South Carolina, Columbia: Emergent properties of strength of attachment in beds of mussels

Individuals within a mussel aggregation resist the hydrodynamic forces of lift and drag by attaching byssal threads to the substrate on which they live and to their neighbors. This matrix of interconnection helps to distribute hydrodynamic forces experienced by the aggregation. The ability of an individual to resist dislodgement, herein called strength of attachment (SA) can be divided into two components: active (due to an animal’s own byssal threads attached to neighbors and substrate) and passive (due to byssal threads attached to the shell of an animal by its neighbors). A portable materials testing device was used to investigate the SA of the blue mussel Mytilus edulis on rock surfaces in Nahant, MA. We compared active and passive components by pulling living mussels (actively and passively attached), and shells of recently deceased mussels (passively attached) from the center of an aggregation. Dead animals had 80% of the SA of living animals, suggesting that passive attachment to neighbors accounts for the majority of resistance to dislodgement. A mussel actively contributes approximately 20% of its own SA, which is split between attachments to neighbors and attachments to the substrate. We conclude that the spatial packing of mussels in an aggregation plays a role in the distribution of byssal threads. Individuals rely heavily on the behavior of their neighbors for their own strength of attachment.