DISENTANGLING ANTHROPOGENIC AND ENVIRONMENTAL EFFECTS ON THE MORPHOMETRY OF FOSSIL AND RECENT SCALLOPS FROM THE SOUTH PACIFIC

The scallop Argopecten purpuratus has been a pervasive component of benthic environments in central Chile since at least the Pleistocene. An upwelling system in Tongoy Bay (30°17'S 71°31'W) brings nutrient rich waters to the surface, supporting many benthic fisheries including the one of Argopecten. The uncontrolled extraction led this fishery to collapse in the late 80s, after which an aquaculture regime was implemented. Here, we test different predictions to understand the relationship between size and shape of fossil and recent scallops in relation to natural and anthropogenic drivers. For example, artificial selection can lead to reduced sizes if larger individuals are extracted. Alternatively, natural factors such as colder waters with lower oxygen typical of upwelling regimes can favor larger sizes. In order to determine whether anthropogenic or environmental drivers have stronger effect on morphology, left valves of Argopecten from the late Holocene (n=24), recent ones from natural populations (n=24), and recent ones from aquaculture facilities (n=24) were measured, weighed and photographed for geometric morphometry. Radiocarbon and δ¹⁸O were carried out to determine shell ages and water temperature at the time the fossils were alive. Preliminary results indicate that these populations occupy different areas of the morphometric space, and that fossil shells are significantly larger and more concave than recent ones. In addition, aquaculture shells are flatter, possibly as a result of smaller muscles due to limited mobility in the aquaculture facility. These findings suggest that anthropogenic pressure can cause dramatic changes to size and shape of scallops in less than 20 generations. In addition, outcomes from this study integrating fossil and recent individuals can provide valuable information on how environmental variables can be manipulated for a better management of this resource. Funded by FONDECYT Projects #3160342 and #1140841.