Dynamical assessment of the accretionary record in the shell of the musselSemimytilus algosus from a rocky shore in Chile

Patterns of tidal microgrowth bands present in acetate peels of shell secti ons of the Chilean mussel Semimytilus algosus from three tidal levels on a wave-exposed shore were analyzed for the presence of recurring periodicitie s using numerical tools derived from signal nonlinear analysis. Both chaoti c and coherent structure were found within the microgrowth pattern record, with mussels from the middle and lower tidal zones displaying a coherent st ructure to the patterns, whilst those from the upper tidal level displayed a chaotic banding pattern with a strong tidal component. It is suggested th at 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 c ontinuously in the highly variable conditions that prevail in the upper tid al zone without continuous interruptions to shell deposition. (C) 2000 Else vier Science Ireland Ltd. All rights reserved.