The linkages between structural anchoring traits of organisms (biomechanics) and patterns of disturbance are well-documented in marine and terrestrial communities. Although energy availability can influence quantity and quality of structural materials responsible for anchoring, it is not commonly linked to these traits explicitly. Bioenergetic models link resource acquisition to organism performance and traits. These models are structured with energy allocation priority rules, i.e. energy must go first towards maintaining biological materials before building new biomass. If structural traits are incorporated into bioenergetics models, their priority rules must be investigated. Sessile invertebrates must remain anchored to substrate, and must grow larger to more efficiently acquire resources. While hydrodynamic limitations of size and anchoring are well understood, trade-offs between growth and anchoring are less frequently considered. We studied mussels, which stabilize rocky shore communities and, as competitive dominants, modulate biodiversity in these habitats. Mussels anchor to rock by producing numerous “byssal threads”; anchoring strength influences the timing of disturbance events, when patches of mussels are dislodged by waves. The energy availability of two congener mussel species was perturbed in a laboratory exposure to a range of temperature and food levels. Increased thread production was hypothesized to be correlated with increased growth.
High temperature conditions initially increased thread production in M. trossulus, and prolonged exposure increased mortality regardless of food level. In contrast, high temperature and food increased growth of M. galloprovincialis but did not affect mortality and only temperature increased thread production. This work suggests energy allocation rules may be species-specific; thread production may be prioritized over growth and survival for the native M. trossulus, while food availability shifts the priority to growth in the non-native M. galloprovincialis. In conclusion, this work suggests that anchoring was generally prioritized over growth, and that conditions optimal for growth were not necessary for thread production. Further, not only temperature, but also food level influences thread production, and these factors may be important in driving temporal and spatial patterns of anchoring in mussel aquaculture and rocky shore ecosystems.