Importance of small-scale paleo-oceanographic conditions to interpret changes in size of California mussel (Mytilus californianus). Late Holocene, Santa Cruz island, California

Abstract

Abstract Several authors have highlighted the difficulties in disentangling human from natural effects when studying shellfish foraging strategies and archeo-malacogical records. In coastal settings, one of the reasons for this difficulty is the lack of understanding of small-scale oceanographic conditions and their influence on coastal and marine species used by people in the past. The present study evaluated the influence of environmental conditions on shellfish harvesting during the Late Holocene around Santa Cruz Island (Southern California) considering small-scale nearshore oceanographic variability around the Island and its effect on M. californianus (main shellfish species exploited through prehistory along the coast of California). Fluctuations in size and abundance of M. californianus shells through time and local past sea surface temperature (SST) values from oxygen isotope analysis of mussel shells are correlated throughout the stratigraphy of two shell midden sites (2200–500 cal B.P.) nearby coasts with different paleo-oceanographic characteristics. Despite the fact that human harvesting seems to have been the main force shaping length and availability of M. californianus , no clear evidence of human pressure was found on archaeological mussel assemblages. Results also show that fluctuations in regional SST records (Santa Barbara Basin marine core) do not represent local SST variations (oxygen isotope analyses on mussel shells), especially if the archaeological site is located on a coast exposed to strong and consistent upwelling activity. By re-evaluating human impact on mussel beds during the Late Holocene around Santa Cruz Island, the research presented here demonstrates the importance of considering small-scale nearshore oceanography for understanding the archaeological evidence of prehistoric human foraging on important intertidal shellfish species.