Reconsidering evidence of human impacts: Implications of within-site variation of growth rates in Mytilus californianus along tidal gradients

Disentangling the complex web of human and natural effects that structure archaeological shellfish assemblages remains a challenging process that requires careful consideration of interdisciplinary datasets. The ecological data presented in this paper demonstrate highly variable growth rates within intertidal patches of Mytilus californianus. These results fill a spatial and conceptual gap in our understanding of small-scale variability in mussel growth rates and terminal shell size, and have significant implications for understanding ancient human foraging behavior, as well as how we interpret archaeological signatures of anthropogenic impact on mussel populations. We evaluate how small-scale variation along tidal gradients structures the size of resources available to coastal foragers throughout the lunar cycle. This ecological study leads us to propose that increased exploitation of smaller mussels available at higher shore levels during less favorable tides could result in archaeological assemblages that mimic the expected correlates for resource depression, thus, confounding interpretation of human impacts.