Blue Mussel Stable Isotope Analysis on Islands of the Virginia Coast

Blue Mussel Stable Isotope Analysis on Islands of the Virginia Coast As climate change causes ocean temperatures to rise, some intertidal organisms, like blue mussels (Mytilus edulis), are retreating northward. Species that consume blue mussels, like the federally-threatened red knot (Calidris canutus rufa), may be negatively affected by this range contraction. We investigated the variation in blue mussel abundance from 2010 - 2018 on Virginia's barrier islands, where migrating red knots eat recently settled blue mussels, and compared the oxygen isotopic composition of blue mussel shell calcite (delta^18Oc; n = 74) to delta^18Oc, which is calculated to be in equilibrium with regional ocean water, to predict their origins. During peak red knot migration (May 14 - 27), between 34 - 538 blue mussels were available/core sample, with blue mussel abundance decreasing over time. Stable isotope analyses indicated that shell umbo delta^18Oc (mean = -0.23o/oo, SE = 0.12) was more ^18O enriched than shell edge delta^18Oc (mean = -0.53 o/oo, SE = 0.10). Blue mussel umbo delta^18Oc was not different than the range of delta^18Oc calculated in equilibrium with regional ocean water off the Virginia and Delaware coasts. Umbo delta^18Oc was more ^18O enriched than the expected estuarine signature at the Delaware Bay's mouth, precluding an estuarine origin, and more ^16O enriched than the expected delta^18Oc off New Hampshire's coast, likely precluding an origin that far north. We concluded that Virginia's juvenile blue mussels likely originated in the regional ocean between the Delaware Bay and Virginia. Continued increases in regional sea surface temperature may further affect the availability of blue mussels to foraging red knots in Virginia.