Using sea urchin remains to infer the health of kelp forest ecosystems in the past: Identification, quantification, and allometric reconstructions of harvested sea urchin (Strongylocentrotus spp.) on California’s Channel Islands

Abstract

Sea urchins, one of the few echinoids harvested for human consumption, are found in archaeological sites from coastal settings around the world spanning at least the past ∼15,000 years. Sea urchin tests and spines are commonly found in archaeological shell middens on California’s Channel Islands, sometimes forming dense “urchin lenses.” Though ubiquitous, the fragile nature of their test (outer shell) results in a high degree of fragmentation, complicating identification and quantification in archaeological assemblages. I discuss issues regarding archaeological sea urchin remains off the coast of western North America and present a method for estimating the sizes of harvested purple (Strongylocentrotus purpuratus) and red (Mesocentrotus franciscanus) sea urchins through allometry, allowing archaeologists to configure size/age estimates for harvested populations in the past. These methods are applied to two archaeological assemblages from San Nicolas and San Miguel islands, revealing evidence of a potential urchin proliferation event in the California Bight during the late Middle Holocene, and relative consistency in the primary types and sizes of harvested specimens through time. As a keystone species dominating ecological interactions in kelp forest ecosystems, sea urchin remains can provide deep historical perspective on the relative state of intertidal ecosystems.