Dynamical assessment of the accretionary record in the shell of the mussel Semimytilus algosus from a rocky shore in Chile.

Patterns of tidal microgrowth bands present in acetate peels of shell sections of the Chilean mussel Semimytilus algosus from three tidal levels on a wave-exposed shore were analyzed for the presence of recurring periodicities using numerical tools derived from signal nonlinear analysis. Both chaotic and coherent structure were found within the microgrowth pattern record, with mussels from the middle and lower tidal zones displaying a coherent structure to the patterns, whilst those from the upper tidal level displayed a chaotic banding pattern with a strong tidal component. It is suggested that because mussels in the upper tidal zone are subject to a wider suite of environmental conditions they are influenced by the spring-neap lunar tidal cycle to a greater extent than those growing in the mid to low tidal zone and display deterministic chaotic growth. This allows the mussels to grow continuously in the highly variable conditions that prevail in the upper tidal zone without continuous interruptions to shell deposition.